Move code generation into askama_derive

1 files changed, 2141 insertions, 0 deletions

diff --git a/askama_derive/src/generator.rs b/askama_derive/src/generator.rs
new file mode 100644
index 0000000..39a5380
--- /dev/null
+++ b/askama_derive/src/generator.rs
@@ -0,0 +1,2141 @@
+use crate::config::{get_template_source, read_config_file, Config, WhitespaceHandling};
+use crate::heritage::{Context, Heritage};
+use crate::input::{Print, Source, TemplateInput};
+use crate::parser::{parse, Cond, CondTest, Expr, Loop, Node, Target, When, Whitespace, Ws};
+use crate::CompileError;
+
+use proc_macro::TokenStream;
+use quote::{quote, ToTokens};
+
+use std::collections::HashMap;
+use std::path::{Path, PathBuf};
+use std::{cmp, hash, mem, str};
+
+/// The actual implementation for askama_derive::Template
+pub(crate) fn derive_template(input: TokenStream) -> TokenStream {
+    let ast: syn::DeriveInput = syn::parse(input).unwrap();
+    match build_template(&ast) {
+        Ok(source) => source.parse().unwrap(),
+        Err(e) => e.into_compile_error(),
+    }
+}
+
+/// Takes a `syn::DeriveInput` and generates source code for it
+///
+/// Reads the metadata from the `template()` attribute to get the template
+/// metadata, then fetches the source from the filesystem. The source is
+/// parsed, and the parse tree is fed to the code generator. Will print
+/// the parse tree and/or generated source according to the `print` key's
+/// value as passed to the `template()` attribute.
+fn build_template(ast: &syn::DeriveInput) -> Result<String, CompileError> {
+    let template_args = TemplateArgs::new(ast)?;
+    let config_toml = read_config_file(&template_args.config_path)?;
+    let config = Config::new(&config_toml)?;
+    let input = TemplateInput::new(ast, &config, template_args)?;
+    let source: String = match input.source {
+        Source::Source(ref s) => s.clone(),
+        Source::Path(_) => get_template_source(&input.path)?,
+    };
+
+    let mut sources = HashMap::new();
+    find_used_templates(&input, &mut sources, source)?;
+
+    let mut parsed = HashMap::new();
+    for (path, src) in &sources {
+        parsed.insert(path.as_path(), parse(src, input.syntax)?);
+    }
+
+    let mut contexts = HashMap::new();
+    for (path, nodes) in &parsed {
+        contexts.insert(*path, Context::new(input.config, path, nodes)?);
+    }
+
+    let ctx = &contexts[input.path.as_path()];
+    let heritage = if !ctx.blocks.is_empty() || ctx.extends.is_some() {
+        Some(Heritage::new(ctx, &contexts))
+    } else {
+        None
+    };
+
+    if input.print == Print::Ast || input.print == Print::All {
+        eprintln!("{:?}", parsed[input.path.as_path()]);
+    }
+
+    let code = Generator::new(
+        &input,
+        &contexts,
+        heritage.as_ref(),
+        MapChain::new(),
+        config.whitespace,
+    )
+    .build(&contexts[input.path.as_path()])?;
+    if input.print == Print::Code || input.print == Print::All {
+        eprintln!("{}", code);
+    }
+    Ok(code)
+}
+
+#[derive(Default)]
+pub(crate) struct TemplateArgs {
+    pub(crate) source: Option<Source>,
+    pub(crate) print: Print,
+    pub(crate) escaping: Option<String>,
+    pub(crate) ext: Option<String>,
+    pub(crate) syntax: Option<String>,
+    pub(crate) config_path: Option<String>,
+}
+
+impl TemplateArgs {
+    fn new(ast: &'_ syn::DeriveInput) -> Result<Self, CompileError> {
+        // Check that an attribute called `template()` exists once and that it is
+        // the proper type (list).
+        let mut template_args = None;
+        for attr in &ast.attrs {
+            let ident = match attr.path.get_ident() {
+                Some(ident) => ident,
+                None => continue,
+            };
+
+            if ident == "template" {
+                if template_args.is_some() {
+                    return Err("duplicated 'template' attribute".into());
+                }
+
+                match attr.parse_meta() {
+                    Ok(syn::Meta::List(syn::MetaList { nested, .. })) => {
+                        template_args = Some(nested);
+                    }
+                    Ok(_) => return Err("'template' attribute must be a list".into()),
+                    Err(e) => return Err(format!("unable to parse attribute: {}", e).into()),
+                }
+            }
+        }
+        let template_args =
+            template_args.ok_or_else(|| CompileError::from("no attribute 'template' found"))?;
+
+        let mut args = Self::default();
+        // Loop over the meta attributes and find everything that we
+        // understand. Return a CompileError if something is not right.
+        // `source` contains an enum that can represent `path` or `source`.
+        for item in template_args {
+            let pair = match item {
+                syn::NestedMeta::Meta(syn::Meta::NameValue(ref pair)) => pair,
+                _ => {
+                    return Err(format!(
+                        "unsupported attribute argument {:?}",
+                        item.to_token_stream()
+                    )
+                    .into())
+                }
+            };
+            let ident = match pair.path.get_ident() {
+                Some(ident) => ident,
+                None => unreachable!("not possible in syn::Meta::NameValue(…)"),
+            };
+
+            if ident == "path" {
+                if let syn::Lit::Str(ref s) = pair.lit {
+                    if args.source.is_some() {
+                        return Err("must specify 'source' or 'path', not both".into());
+                    }
+                    args.source = Some(Source::Path(s.value()));
+                } else {
+                    return Err("template path must be string literal".into());
+                }
+            } else if ident == "source" {
+                if let syn::Lit::Str(ref s) = pair.lit {
+                    if args.source.is_some() {
+                        return Err("must specify 'source' or 'path', not both".into());
+                    }
+                    args.source = Some(Source::Source(s.value()));
+                } else {
+                    return Err("template source must be string literal".into());
+                }
+            } else if ident == "print" {
+                if let syn::Lit::Str(ref s) = pair.lit {
+                    args.print = s.value().parse()?;
+                } else {
+                    return Err("print value must be string literal".into());
+                }
+            } else if ident == "escape" {
+                if let syn::Lit::Str(ref s) = pair.lit {
+                    args.escaping = Some(s.value());
+                } else {
+                    return Err("escape value must be string literal".into());
+                }
+            } else if ident == "ext" {
+                if let syn::Lit::Str(ref s) = pair.lit {
+                    args.ext = Some(s.value());
+                } else {
+                    return Err("ext value must be string literal".into());
+                }
+            } else if ident == "syntax" {
+                if let syn::Lit::Str(ref s) = pair.lit {
+                    args.syntax = Some(s.value())
+                } else {
+                    return Err("syntax value must be string literal".into());
+                }
+            } else if ident == "config" {
+                if let syn::Lit::Str(ref s) = pair.lit {
+                    args.config_path = Some(s.value())
+                } else {
+                    return Err("config value must be string literal".into());
+                }
+            } else {
+                return Err(format!("unsupported attribute key {:?} found", ident).into());
+            }
+        }
+
+        Ok(args)
+    }
+}
+
+fn find_used_templates(
+    input: &TemplateInput<'_>,
+    map: &mut HashMap<PathBuf, String>,
+    source: String,
+) -> Result<(), CompileError> {
+    let mut dependency_graph = Vec::new();
+    let mut check = vec![(input.path.clone(), source)];
+    while let Some((path, source)) = check.pop() {
+        for n in parse(&source, input.syntax)? {
+            match n {
+                Node::Extends(Expr::StrLit(extends)) => {
+                    let extends = input.config.find_template(extends, Some(&path))?;
+                    let dependency_path = (path.clone(), extends.clone());
+                    if dependency_graph.contains(&dependency_path) {
+                        return Err(format!(
+                            "cyclic dependecy in graph {:#?}",
+                            dependency_graph
+                                .iter()
+                                .map(|e| format!("{:#?} --> {:#?}", e.0, e.1))
+                                .collect::<Vec<String>>()
+                        )
+                        .into());
+                    }
+                    dependency_graph.push(dependency_path);
+                    let source = get_template_source(&extends)?;
+                    check.push((extends, source));
+                }
+                Node::Import(_, import, _) => {
+                    let import = input.config.find_template(import, Some(&path))?;
+                    let source = get_template_source(&import)?;
+                    check.push((import, source));
+                }
+                _ => {}
+            }
+        }
+        map.insert(path, source);
+    }
+    Ok(())
+}
+struct Generator<'a, S: std::hash::BuildHasher> {
+    // The template input state: original struct AST and attributes
+    input: &'a TemplateInput<'a>,
+    // All contexts, keyed by the package-relative template path
+    contexts: &'a HashMap<&'a Path, Context<'a>, S>,
+    // The heritage contains references to blocks and their ancestry
+    heritage: Option<&'a Heritage<'a>>,
+    // Variables accessible directly from the current scope (not redirected to context)
+    locals: MapChain<'a, &'a str, LocalMeta>,
+    // Suffix whitespace from the previous literal. Will be flushed to the
+    // output buffer unless suppressed by whitespace suppression on the next
+    // non-literal.
+    next_ws: Option<&'a str>,
+    // Whitespace suppression from the previous non-literal. Will be used to
+    // determine whether to flush prefix whitespace from the next literal.
+    skip_ws: WhitespaceHandling,
+    // If currently in a block, this will contain the name of a potential parent block
+    super_block: Option<(&'a str, usize)>,
+    // buffer for writable
+    buf_writable: Vec<Writable<'a>>,
+    // Counter for write! hash named arguments
+    named: usize,
+    // If set to `suppress`, the whitespace characters will be removed by default unless `+` is
+    // used.
+    whitespace: WhitespaceHandling,
+}
+
+impl<'a, S: std::hash::BuildHasher> Generator<'a, S> {
+    fn new<'n>(
+        input: &'n TemplateInput<'_>,
+        contexts: &'n HashMap<&'n Path, Context<'n>, S>,
+        heritage: Option<&'n Heritage<'_>>,
+        locals: MapChain<'n, &'n str, LocalMeta>,
+        whitespace: WhitespaceHandling,
+    ) -> Generator<'n, S> {
+        Generator {
+            input,
+            contexts,
+            heritage,
+            locals,
+            next_ws: None,
+            skip_ws: WhitespaceHandling::Preserve,
+            super_block: None,
+            buf_writable: vec![],
+            named: 0,
+            whitespace,
+        }
+    }
+
+    fn child(&mut self) -> Generator<'_, S> {
+        let locals = MapChain::with_parent(&self.locals);
+        Self::new(
+            self.input,
+            self.contexts,
+            self.heritage,
+            locals,
+            self.whitespace,
+        )
+    }
+
+    // Takes a Context and generates the relevant implementations.
+    fn build(mut self, ctx: &'a Context<'_>) -> Result<String, CompileError> {
+        let mut buf = Buffer::new(0);
+        if !ctx.blocks.is_empty() {
+            if let Some(parent) = self.input.parent {
+                self.deref_to_parent(&mut buf, parent)?;
+            }
+        };
+
+        self.impl_template(ctx, &mut buf)?;
+        self.impl_display(&mut buf)?;
+
+        #[cfg(feature = "with-actix-web")]
+        self.impl_actix_web_responder(&mut buf)?;
+        #[cfg(feature = "with-axum")]
+        self.impl_axum_into_response(&mut buf)?;
+        #[cfg(feature = "with-gotham")]
+        self.impl_gotham_into_response(&mut buf)?;
+        #[cfg(feature = "with-mendes")]
+        self.impl_mendes_responder(&mut buf)?;
+        #[cfg(feature = "with-rocket")]
+        self.impl_rocket_responder(&mut buf)?;
+        #[cfg(feature = "with-tide")]
+        self.impl_tide_integrations(&mut buf)?;
+        #[cfg(feature = "with-warp")]
+        self.impl_warp_reply(&mut buf)?;
+
+        Ok(buf.buf)
+    }
+
+    // Implement `Template` for the given context struct.
+    fn impl_template(
+        &mut self,
+        ctx: &'a Context<'_>,
+        buf: &mut Buffer,
+    ) -> Result<(), CompileError> {
+        self.write_header(buf, "::askama::Template", None)?;
+        buf.writeln(
+            "fn render_into(&self, writer: &mut (impl ::std::fmt::Write + ?Sized)) -> \
+             ::askama::Result<()> {",
+        )?;
+
+        // Make sure the compiler understands that the generated code depends on the template files.
+        for path in self.contexts.keys() {
+            // Skip the fake path of templates defined in rust source.
+            let path_is_valid = match self.input.source {
+                Source::Path(_) => true,
+                Source::Source(_) => path != &self.input.path,
+            };
+            if path_is_valid {
+                let path = path.to_str().unwrap();
+                buf.writeln(
+                    &quote! {
+                        include_bytes!(#path);
+                    }
+                    .to_string(),
+                )?;
+            }
+        }
+
+        let size_hint = if let Some(heritage) = self.heritage {
+            self.handle(heritage.root, heritage.root.nodes, buf, AstLevel::Top)
+        } else {
+            self.handle(ctx, ctx.nodes, buf, AstLevel::Top)
+        }?;
+
+        self.flush_ws(Ws(None, None));
+        buf.writeln("::askama::Result::Ok(())")?;
+        buf.writeln("}")?;
+
+        buf.writeln("const EXTENSION: ::std::option::Option<&'static ::std::primitive::str> = ")?;
+        buf.writeln(&format!("{:?}", self.input.extension()))?;
+        buf.writeln(";")?;
+
+        buf.writeln("const SIZE_HINT: ::std::primitive::usize = ")?;
+        buf.writeln(&format!("{}", size_hint))?;
+        buf.writeln(";")?;
+
+        buf.writeln("const MIME_TYPE: &'static ::std::primitive::str = ")?;
+        buf.writeln(&format!("{:?}", &self.input.mime_type))?;
+        buf.writeln(";")?;
+
+        buf.writeln("}")?;
+        Ok(())
+    }
+
+    // Implement `Deref<Parent>` for an inheriting context struct.
+    fn deref_to_parent(
+        &mut self,
+        buf: &mut Buffer,
+        parent_type: &syn::Type,
+    ) -> Result<(), CompileError> {
+        self.write_header(buf, "::std::ops::Deref", None)?;
+        buf.writeln(&format!(
+            "type Target = {};",
+            parent_type.into_token_stream()
+        ))?;
+        buf.writeln("#[inline]")?;
+        buf.writeln("fn deref(&self) -> &Self::Target {")?;
+        buf.writeln("&self._parent")?;
+        buf.writeln("}")?;
+        buf.writeln("}")
+    }
+
+    // Implement `Display` for the given context struct.
+    fn impl_display(&mut self, buf: &mut Buffer) -> Result<(), CompileError> {
+        self.write_header(buf, "::std::fmt::Display", None)?;
+        buf.writeln("#[inline]")?;
+        buf.writeln("fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {")?;
+        buf.writeln("::askama::Template::render_into(self, f).map_err(|_| ::std::fmt::Error {})")?;
+        buf.writeln("}")?;
+        buf.writeln("}")
+    }
+
+    // Implement Actix-web's `Responder`.
+    #[cfg(feature = "with-actix-web")]
+    fn impl_actix_web_responder(&mut self, buf: &mut Buffer) -> Result<(), CompileError> {
+        self.write_header(buf, "::askama_actix::actix_web::Responder", None)?;
+        buf.writeln("type Body = ::askama_actix::actix_web::body::BoxBody;")?;
+        buf.writeln("#[inline]")?;
+        buf.writeln(
+            "fn respond_to(self, _req: &::askama_actix::actix_web::HttpRequest) \
+             -> ::askama_actix::actix_web::HttpResponse<Self::Body> {",
+        )?;
+        buf.writeln("<Self as ::askama_actix::TemplateToResponse>::to_response(&self)")?;
+        buf.writeln("}")?;
+        buf.writeln("}")
+    }
+
+    // Implement Axum's `IntoResponse`.
+    #[cfg(feature = "with-axum")]
+    fn impl_axum_into_response(&mut self, buf: &mut Buffer) -> Result<(), CompileError> {
+        self.write_header(buf, "::askama_axum::IntoResponse", None)?;
+        buf.writeln("#[inline]")?;
+        buf.writeln(
+            "fn into_response(self)\
+             -> ::askama_axum::Response {",
+        )?;
+        let ext = self.input.extension().unwrap_or("txt");
+        buf.writeln(&format!("::askama_axum::into_response(&self, {:?})", ext))?;
+        buf.writeln("}")?;
+        buf.writeln("}")
+    }
+
+    // Implement gotham's `IntoResponse`.
+    #[cfg(feature = "with-gotham")]
+    fn impl_gotham_into_response(&mut self, buf: &mut Buffer) -> Result<(), CompileError> {
+        self.write_header(buf, "::askama_gotham::IntoResponse", None)?;
+        buf.writeln("#[inline]")?;
+        buf.writeln(
+            "fn into_response(self, _state: &::askama_gotham::State)\
+             -> ::askama_gotham::Response<::askama_gotham::Body> {",
+        )?;
+        let ext = self.input.extension().unwrap_or("txt");
+        buf.writeln(&format!("::askama_gotham::respond(&self, {:?})", ext))?;
+        buf.writeln("}")?;
+        buf.writeln("}")
+    }
+
+    // Implement mendes' `Responder`.
+    #[cfg(feature = "with-mendes")]
+    fn impl_mendes_responder(&mut self, buf: &mut Buffer) -> Result<(), CompileError> {
+        let param = syn::parse_str("A: ::mendes::Application").unwrap();
+
+        let mut generics = self.input.ast.generics.clone();
+        generics.params.push(param);
+        let (_, orig_ty_generics, _) = self.input.ast.generics.split_for_impl();
+        let (impl_generics, _, where_clause) = generics.split_for_impl();
+
+        let mut where_clause = match where_clause {
+            Some(clause) => clause.clone(),
+            None => syn::WhereClause {
+                where_token: syn::Token![where](proc_macro2::Span::call_site()),
+                predicates: syn::punctuated::Punctuated::new(),
+            },
+        };
+
+        where_clause
+            .predicates
+            .push(syn::parse_str("A::ResponseBody: From<String>").unwrap());
+        where_clause
+            .predicates
+            .push(syn::parse_str("A::Error: From<::askama_mendes::Error>").unwrap());
+
+        buf.writeln(
+            format!(
+                "{} {} for {} {} {{",
+                quote!(impl#impl_generics),
+                "::mendes::application::IntoResponse<A>",
+                self.input.ast.ident,
+                quote!(#orig_ty_generics #where_clause),
+            )
+            .as_ref(),
+        )?;
+
+        buf.writeln(
+            "fn into_response(self, app: &A, req: &::mendes::http::request::Parts) \
+             -> ::mendes::http::Response<A::ResponseBody> {",
+        )?;
+
+        buf.writeln(&format!(
+            "::askama_mendes::into_response(app, req, &self, {:?})",
+            self.input.extension()
+        ))?;
+        buf.writeln("}")?;
+        buf.writeln("}")?;
+        Ok(())
+    }
+
+    // Implement Rocket's `Responder`.
+    #[cfg(feature = "with-rocket")]
+    fn impl_rocket_responder(&mut self, buf: &mut Buffer) -> Result<(), CompileError> {
+        let lifetime = syn::Lifetime::new("'askama", proc_macro2::Span::call_site());
+        let param = syn::GenericParam::Lifetime(syn::LifetimeDef::new(lifetime));
+        self.write_header(
+            buf,
+            "::askama_rocket::Responder<'askama>",
+            Some(vec![param]),
+        )?;
+
+        buf.writeln("#[inline]")?;
+        buf.writeln(
+            "fn respond_to(self, _: &::askama_rocket::Request) \
+             -> ::askama_rocket::Result<'askama> {",
+        )?;
+        let ext = self.input.extension().unwrap_or("txt");
+        buf.writeln(&format!("::askama_rocket::respond(&self, {:?})", ext))?;
+
+        buf.writeln("}")?;
+        buf.writeln("}")?;
+        Ok(())
+    }
+
+    #[cfg(feature = "with-tide")]
+    fn impl_tide_integrations(&mut self, buf: &mut Buffer) -> Result<(), CompileError> {
+        let ext = self.input.extension().unwrap_or("txt");
+
+        self.write_header(
+            buf,
+            "::std::convert::TryInto<::askama_tide::tide::Body>",
+            None,
+        )?;
+        buf.writeln(
+            "type Error = ::askama_tide::askama::Error;\n\
+            #[inline]\n\
+            fn try_into(self) -> ::askama_tide::askama::Result<::askama_tide::tide::Body> {",
+        )?;
+        buf.writeln(&format!("::askama_tide::try_into_body(&self, {:?})", &ext))?;
+        buf.writeln("}")?;
+        buf.writeln("}")?;
+
+        buf.writeln("#[allow(clippy::from_over_into)]")?;
+        self.write_header(buf, "Into<::askama_tide::tide::Response>", None)?;
+        buf.writeln("#[inline]")?;
+        buf.writeln("fn into(self) -> ::askama_tide::tide::Response {")?;
+        buf.writeln(&format!("::askama_tide::into_response(&self, {:?})", ext))?;
+        buf.writeln("}\n}")
+    }
+
+    #[cfg(feature = "with-warp")]
+    fn impl_warp_reply(&mut self, buf: &mut Buffer) -> Result<(), CompileError> {
+        self.write_header(buf, "::askama_warp::warp::reply::Reply", None)?;
+        buf.writeln("#[inline]")?;
+        buf.writeln("fn into_response(self) -> ::askama_warp::warp::reply::Response {")?;
+        let ext = self.input.extension().unwrap_or("txt");
+        buf.writeln(&format!("::askama_warp::reply(&self, {:?})", ext))?;
+        buf.writeln("}")?;
+        buf.writeln("}")
+    }
+
+    // Writes header for the `impl` for `TraitFromPathName` or `Template`
+    // for the given context struct.
+    fn write_header(
+        &mut self,
+        buf: &mut Buffer,
+        target: &str,
+        params: Option<Vec<syn::GenericParam>>,
+    ) -> Result<(), CompileError> {
+        let mut generics = self.input.ast.generics.clone();
+        if let Some(params) = params {
+            for param in params {
+                generics.params.push(param);
+            }
+        }
+        let (_, orig_ty_generics, _) = self.input.ast.generics.split_for_impl();
+        let (impl_generics, _, where_clause) = generics.split_for_impl();
+        buf.writeln(
+            format!(
+                "{} {} for {}{} {{",
+                quote!(impl#impl_generics),
+                target,
+                self.input.ast.ident,
+                quote!(#orig_ty_generics #where_clause),
+            )
+            .as_ref(),
+        )
+    }
+
+    /* Helper methods for handling node types */
+
+    fn handle(
+        &mut self,
+        ctx: &'a Context<'_>,
+        nodes: &'a [Node<'_>],
+        buf: &mut Buffer,
+        level: AstLevel,
+    ) -> Result<usize, CompileError> {
+        let mut size_hint = 0;
+        for n in nodes {
+            match *n {
+                Node::Lit(lws, val, rws) => {
+                    self.visit_lit(lws, val, rws);
+                }
+                Node::Comment(ws) => {
+                    self.write_comment(ws);
+                }
+                Node::Expr(ws, ref val) => {
+                    self.write_expr(ws, val);
+                }
+                Node::LetDecl(ws, ref var) => {
+                    self.write_let_decl(buf, ws, var)?;
+                }
+                Node::Let(ws, ref var, ref val) => {
+                    self.write_let(buf, ws, var, val)?;
+                }
+                Node::Cond(ref conds, ws) => {
+                    self.write_cond(ctx, buf, conds, ws)?;
+                }
+                Node::Match(ws1, ref expr, ref arms, ws2) => {
+                    self.write_match(ctx, buf, ws1, expr, arms, ws2)?;
+                }
+                Node::Loop(ref loop_block) => {
+                    self.write_loop(ctx, buf, loop_block)?;
+                }
+                Node::BlockDef(ws1, name, _, ws2) => {
+                    self.write_block(buf, Some(name), Ws(ws1.0, ws2.1))?;
+                }
+                Node::Include(ws, path) => {
+                    size_hint += self.handle_include(ctx, buf, ws, path)?;
+                }
+                Node::Call(ws, scope, name, ref args) => {
+                    size_hint += self.write_call(ctx, buf, ws, scope, name, args)?;
+                }
+                Node::Macro(_, ref m) => {
+                    if level != AstLevel::Top {
+                        return Err("macro blocks only allowed at the top level".into());
+                    }
+                    self.flush_ws(m.ws1);
+                    self.prepare_ws(m.ws2);
+                }
+                Node::Raw(ws1, lws, val, rws, ws2) => {
+                    self.handle_ws(ws1);
+                    self.visit_lit(lws, val, rws);
+                    self.handle_ws(ws2);
+                }
+                Node::Import(ws, _, _) => {
+                    if level != AstLevel::Top {
+                        return Err("import blocks only allowed at the top level".into());
+                    }
+                    self.handle_ws(ws);
+                }
+                Node::Extends(_) => {
+                    if level != AstLevel::Top {
+                        return Err("extend blocks only allowed at the top level".into());
+                    }
+                    // No whitespace handling: child template top-level is not used,
+                    // except for the blocks defined in it.
+                }
+                Node::Break(ws) => {
+                    self.handle_ws(ws);
+                    self.write_buf_writable(buf)?;
+                    buf.writeln("break;")?;
+                }
+                Node::Continue(ws) => {
+                    self.handle_ws(ws);
+                    self.write_buf_writable(buf)?;
+                    buf.writeln("continue;")?;
+                }
+            }
+        }
+
+        if AstLevel::Top == level {
+            size_hint += self.write_buf_writable(buf)?;
+        }
+        Ok(size_hint)
+    }
+
+    fn write_cond(
+        &mut self,
+        ctx: &'a Context<'_>,
+        buf: &mut Buffer,
+        conds: &'a [Cond<'_>],
+        ws: Ws,
+    ) -> Result<usize, CompileError> {
+        let mut flushed = 0;
+        let mut arm_sizes = Vec::new();
+        let mut has_else = false;
+        for (i, &(cws, ref cond, ref nodes)) in conds.iter().enumerate() {
+            self.handle_ws(cws);
+            flushed += self.write_buf_writable(buf)?;
+            if i > 0 {
+                self.locals.pop();
+            }
+
+            self.locals.push();
+            let mut arm_size = 0;
+            if let Some(CondTest { target, expr }) = cond {
+                if i == 0 {
+                    buf.write("if ");
+                } else {
+                    buf.dedent()?;
+                    buf.write("} else if ");
+                }
+
+                if let Some(target) = target {
+                    let mut expr_buf = Buffer::new(0);
+                    self.visit_expr(&mut expr_buf, expr)?;
+                    buf.write("let ");
+                    self.visit_target(buf, true, true, target);
+                    buf.write(" = &(");
+                    buf.write(&expr_buf.buf);
+                    buf.write(")");
+                } else {
+                    // The following syntax `*(&(...) as &bool)` is used to
+                    // trigger Rust's automatic dereferencing, to coerce
+                    // e.g. `&&&&&bool` to `bool`. First `&(...) as &bool`
+                    // coerces e.g. `&&&bool` to `&bool`. Then `*(&bool)`
+                    // finally dereferences it to `bool`.
+                    buf.write("*(&(");
+                    let expr_code = self.visit_expr_root(expr)?;
+                    buf.write(&expr_code);
+                    buf.write(") as &bool)");
+                }
+            } else {
+                buf.dedent()?;
+                buf.write("} else");
+                has_else = true;
+            }
+
+            buf.writeln(" {")?;
+
+            arm_size += self.handle(ctx, nodes, buf, AstLevel::Nested)?;
+            arm_sizes.push(arm_size);
+        }
+        self.handle_ws(ws);
+        flushed += self.write_buf_writable(buf)?;
+        buf.writeln("}")?;
+
+        self.locals.pop();
+
+        if !has_else {
+            arm_sizes.push(0);
+        }
+        Ok(flushed + median(&mut arm_sizes))
+    }
+
+    #[allow(clippy::too_many_arguments)]
+    fn write_match(
+        &mut self,
+        ctx: &'a Context<'_>,
+        buf: &mut Buffer,
+        ws1: Ws,
+        expr: &Expr<'_>,
+        arms: &'a [When<'_>],
+        ws2: Ws,
+    ) -> Result<usize, CompileError> {
+        self.flush_ws(ws1);
+        let flushed = self.write_buf_writable(buf)?;
+        let mut arm_sizes = Vec::new();
+
+        let expr_code = self.visit_expr_root(expr)?;
+        buf.writeln(&format!("match &{} {{", expr_code))?;
+
+        let mut arm_size = 0;
+        for (i, arm) in arms.iter().enumerate() {
+            let &(ws, ref target, ref body) = arm;
+            self.handle_ws(ws);
+
+            if i > 0 {
+                arm_sizes.push(arm_size + self.write_buf_writable(buf)?);
+
+                buf.writeln("}")?;
+                self.locals.pop();
+            }
+
+            self.locals.push();
+            self.visit_target(buf, true, true, target);
+            buf.writeln(" => {")?;
+
+            arm_size = self.handle(ctx, body, buf, AstLevel::Nested)?;
+        }
+
+        self.handle_ws(ws2);
+        arm_sizes.push(arm_size + self.write_buf_writable(buf)?);
+        buf.writeln("}")?;
+        self.locals.pop();
+
+        buf.writeln("}")?;
+
+        Ok(flushed + median(&mut arm_sizes))
+    }
+
+    #[allow(clippy::too_many_arguments)]
+    fn write_loop(
+        &mut self,
+        ctx: &'a Context<'_>,
+        buf: &mut Buffer,
+        loop_block: &'a Loop<'_>,
+    ) -> Result<usize, CompileError> {
+        self.handle_ws(loop_block.ws1);
+        self.locals.push();
+
+        let expr_code = self.visit_expr_root(&loop_block.iter)?;
+
+        let flushed = self.write_buf_writable(buf)?;
+        buf.writeln("{")?;
+        buf.writeln("let mut _did_loop = false;")?;
+        match loop_block.iter {
+            Expr::Range(_, _, _) => buf.writeln(&format!("let _iter = {};", expr_code)),
+            Expr::Array(..) => buf.writeln(&format!("let _iter = {}.iter();", expr_code)),
+            // If `iter` is a call then we assume it's something that returns
+            // an iterator. If not then the user can explicitly add the needed
+            // call without issues.
+            Expr::Call(..) | Expr::Index(..) => {
+                buf.writeln(&format!("let _iter = ({}).into_iter();", expr_code))
+            }
+            // If accessing `self` then it most likely needs to be
+            // borrowed, to prevent an attempt of moving.
+            _ if expr_code.starts_with("self.") => {
+                buf.writeln(&format!("let _iter = (&{}).into_iter();", expr_code))
+            }
+            // If accessing a field then it most likely needs to be
+            // borrowed, to prevent an attempt of moving.
+            Expr::Attr(..) => buf.writeln(&format!("let _iter = (&{}).into_iter();", expr_code)),
+            // Otherwise, we borrow `iter` assuming that it implements `IntoIterator`.
+            _ => buf.writeln(&format!("let _iter = ({}).into_iter();", expr_code)),
+        }?;
+        if let Some(cond) = &loop_block.cond {
+            self.locals.push();
+            buf.write("let _iter = _iter.filter(|");
+            self.visit_target(buf, true, true, &loop_block.var);
+            buf.write("| -> bool {");
+            self.visit_expr(buf, cond)?;
+            buf.writeln("});")?;
+            self.locals.pop();
+        }
+
+        self.locals.push();
+        buf.write("for (");
+        self.visit_target(buf, true, true, &loop_block.var);
+        buf.writeln(", _loop_item) in ::askama::helpers::TemplateLoop::new(_iter) {")?;
+
+        buf.writeln("_did_loop = true;")?;
+        let mut size_hint1 = self.handle(ctx, &loop_block.body, buf, AstLevel::Nested)?;
+        self.handle_ws(loop_block.ws2);
+        size_hint1 += self.write_buf_writable(buf)?;
+        self.locals.pop();
+        buf.writeln("}")?;
+
+        buf.writeln("if !_did_loop {")?;
+        self.locals.push();
+        let mut size_hint2 = self.handle(ctx, &loop_block.else_block, buf, AstLevel::Nested)?;
+        self.handle_ws(loop_block.ws3);
+        size_hint2 += self.write_buf_writable(buf)?;
+        self.locals.pop();
+        buf.writeln("}")?;
+
+        buf.writeln("}")?;
+
+        Ok(flushed + ((size_hint1 * 3) + size_hint2) / 2)
+    }
+
+    fn write_call(
+        &mut self,
+        ctx: &'a Context<'_>,
+        buf: &mut Buffer,
+        ws: Ws,
+        scope: Option<&str>,
+        name: &str,
+        args: &[Expr<'_>],
+    ) -> Result<usize, CompileError> {
+        if name == "super" {
+            return self.write_block(buf, None, ws);
+        }
+
+        let (def, own_ctx) = match scope {
+            Some(s) => {
+                let path = ctx.imports.get(s).ok_or_else(|| {
+                    CompileError::from(format!("no import found for scope {:?}", s))
+                })?;
+                let mctx = self.contexts.get(path.as_path()).ok_or_else(|| {
+                    CompileError::from(format!("context for {:?} not found", path))
+                })?;
+                let def = mctx.macros.get(name).ok_or_else(|| {
+                    CompileError::from(format!("macro {:?} not found in scope {:?}", name, s))
+                })?;
+                (def, mctx)
+            }
+            None => {
+                let def = ctx
+                    .macros
+                    .get(name)
+                    .ok_or_else(|| CompileError::from(format!("macro {:?} not found", name)))?;
+                (def, ctx)
+            }
+        };
+
+        self.flush_ws(ws); // Cannot handle_ws() here: whitespace from macro definition comes first
+        self.locals.push();
+        self.write_buf_writable(buf)?;
+        buf.writeln("{")?;
+        self.prepare_ws(def.ws1);
+
+        let mut names = Buffer::new(0);
+        let mut values = Buffer::new(0);
+        let mut is_first_variable = true;
+        for (i, arg) in def.args.iter().enumerate() {
+            let expr = args.get(i).ok_or_else(|| {
+                CompileError::from(format!("macro {:?} takes more than {} arguments", name, i))
+            })?;
+
+            match expr {
+                // If `expr` is already a form of variable then
+                // don't reintroduce a new variable. This is
+                // to avoid moving non-copyable values.
+                Expr::Var(name) => {
+                    let var = self.locals.resolve_or_self(name);
+                    self.locals.insert(arg, LocalMeta::with_ref(var));
+                }
+                Expr::Attr(obj, attr) => {
+                    let mut attr_buf = Buffer::new(0);
+                    self.visit_attr(&mut attr_buf, obj, attr)?;
+
+                    let var = self.locals.resolve(&attr_buf.buf).unwrap_or(attr_buf.buf);
+                    self.locals.insert(arg, LocalMeta::with_ref(var));
+                }
+                // Everything else still needs to become variables,
+                // to avoid having the same logic be executed
+                // multiple times, e.g. in the case of macro
+                // parameters being used multiple times.
+                _ => {
+                    if is_first_variable {
+                        is_first_variable = false
+                    } else {
+                        names.write(", ");
+                        values.write(", ");
+                    }
+                    names.write(arg);
+
+                    values.write("(");
+                    values.write(&self.visit_expr_root(expr)?);
+                    values.write(")");
+                    self.locals.insert_with_default(arg);
+                }
+            }
+        }
+
+        debug_assert_eq!(names.buf.is_empty(), values.buf.is_empty());
+        if !names.buf.is_empty() {
+            buf.writeln(&format!("let ({}) = ({});", names.buf, values.buf))?;
+        }
+
+        let mut size_hint = self.handle(own_ctx, &def.nodes, buf, AstLevel::Nested)?;
+
+        self.flush_ws(def.ws2);
+        size_hint += self.write_buf_writable(buf)?;
+        buf.writeln("}")?;
+        self.locals.pop();
+        self.prepare_ws(ws);
+        Ok(size_hint)
+    }
+
+    fn handle_include(
+        &mut self,
+        ctx: &'a Context<'_>,
+        buf: &mut Buffer,
+        ws: Ws,
+        path: &str,
+    ) -> Result<usize, CompileError> {
+        self.flush_ws(ws);
+        self.write_buf_writable(buf)?;
+        let path = self
+            .input
+            .config
+            .find_template(path, Some(&self.input.path))?;
+        let src = get_template_source(&path)?;
+        let nodes = parse(&src, self.input.syntax)?;
+
+        // Make sure the compiler understands that the generated code depends on the template file.
+        {
+            let path = path.to_str().unwrap();
+            buf.writeln(
+                &quote! {
+                    include_bytes!(#path);
+                }
+                .to_string(),
+            )?;
+        }
+
+        let size_hint = {
+            // Since nodes must not outlive the Generator, we instantiate
+            // a nested Generator here to handle the include's nodes.
+            let mut gen = self.child();
+            let mut size_hint = gen.handle(ctx, &nodes, buf, AstLevel::Nested)?;
+            size_hint += gen.write_buf_writable(buf)?;
+            size_hint
+        };
+        self.prepare_ws(ws);
+        Ok(size_hint)
+    }
+
+    fn write_let_decl(
+        &mut self,
+        buf: &mut Buffer,
+        ws: Ws,
+        var: &'a Target<'_>,
+    ) -> Result<(), CompileError> {
+        self.handle_ws(ws);
+        self.write_buf_writable(buf)?;
+        buf.write("let ");
+        self.visit_target(buf, false, true, var);
+        buf.writeln(";")
+    }
+
+    fn is_shadowing_variable(&self, var: &Target<'a>) -> Result<bool, CompileError> {
+        match var {
+            Target::Name(name) => {
+                let name = normalize_identifier(name);
+                match self.locals.get(&name) {
+                    // declares a new variable
+                    None => Ok(false),
+                    // an initialized variable gets shadowed
+                    Some(meta) if meta.initialized => Ok(true),
+                    // initializes a variable that was introduced in a LetDecl before
+                    _ => Ok(false),
+                }
+            }
+            Target::Tuple(_, targets) => {
+                for target in targets {
+                    match self.is_shadowing_variable(target) {
+                        Ok(false) => continue,
+                        outcome => return outcome,
+                    }
+                }
+                Ok(false)
+            }
+            Target::Struct(_, named_targets) => {
+                for (_, target) in named_targets {
+                    match self.is_shadowing_variable(target) {
+                        Ok(false) => continue,
+                        outcome => return outcome,
+                    }
+                }
+                Ok(false)
+            }
+            _ => Err("literals are not allowed on the left-hand side of an assignment".into()),
+        }
+    }
+
+    fn write_let(
+        &mut self,
+        buf: &mut Buffer,
+        ws: Ws,
+        var: &'a Target<'_>,
+        val: &Expr<'_>,
+    ) -> Result<(), CompileError> {
+        self.handle_ws(ws);
+        let mut expr_buf = Buffer::new(0);
+        self.visit_expr(&mut expr_buf, val)?;
+
+        let shadowed = self.is_shadowing_variable(var)?;
+        if shadowed {
+            // Need to flush the buffer if the variable is being shadowed,
+            // to ensure the old variable is used.
+            self.write_buf_writable(buf)?;
+        }
+        if shadowed
+            || !matches!(var, &Target::Name(_))
+            || matches!(var, Target::Name(name) if self.locals.get(name).is_none())
+        {
+            buf.write("let ");
+        }
+
+        self.visit_target(buf, true, true, var);
+        buf.writeln(&format!(" = {};", &expr_buf.buf))
+    }
+
+    // If `name` is `Some`, this is a call to a block definition, and we have to find
+    // the first block for that name from the ancestry chain. If name is `None`, this
+    // is from a `super()` call, and we can get the name from `self.super_block`.
+    fn write_block(
+        &mut self,
+        buf: &mut Buffer,
+        name: Option<&'a str>,
+        outer: Ws,
+    ) -> Result<usize, CompileError> {
+        // Flush preceding whitespace according to the outer WS spec
+        self.flush_ws(outer);
+
+        let prev_block = self.super_block;
+        let cur = match (name, prev_block) {
+            // The top-level context contains a block definition
+            (Some(cur_name), None) => (cur_name, 0),
+            // A block definition contains a block definition of the same name
+            (Some(cur_name), Some((prev_name, _))) if cur_name == prev_name => {
+                return Err(format!("cannot define recursive blocks ({})", cur_name).into());
+            }
+            // A block definition contains a definition of another block
+            (Some(cur_name), Some((_, _))) => (cur_name, 0),
+            // `super()` was called inside a block
+            (None, Some((prev_name, gen))) => (prev_name, gen + 1),
+            // `super()` is called from outside a block
+            (None, None) => return Err("cannot call 'super()' outside block".into()),
+        };
+        self.super_block = Some(cur);
+
+        // Get the block definition from the heritage chain
+        let heritage = self
+            .heritage
+            .as_ref()
+            .ok_or_else(|| CompileError::from("no block ancestors available"))?;
+        let (ctx, def) = heritage.blocks[cur.0].get(cur.1).ok_or_else(|| {
+            CompileError::from(match name {
+                None => format!("no super() block found for block '{}'", cur.0),
+                Some(name) => format!("no block found for name '{}'", name),
+            })
+        })?;
+
+        // Get the nodes and whitespace suppression data from the block definition
+        let (ws1, nodes, ws2) = if let Node::BlockDef(ws1, _, nodes, ws2) = def {
+            (ws1, nodes, ws2)
+        } else {
+            unreachable!()
+        };
+
+        // Handle inner whitespace suppression spec and process block nodes
+        self.prepare_ws(*ws1);
+        self.locals.push();
+        let size_hint = self.handle(ctx, nodes, buf, AstLevel::Block)?;
+
+        if !self.locals.is_current_empty() {
+            // Need to flush the buffer before popping the variable stack
+            self.write_buf_writable(buf)?;
+        }
+
+        self.locals.pop();
+        self.flush_ws(*ws2);
+
+        // Restore original block context and set whitespace suppression for
+        // succeeding whitespace according to the outer WS spec
+        self.super_block = prev_block;
+        self.prepare_ws(outer);
+        Ok(size_hint)
+    }
+
+    fn write_expr(&mut self, ws: Ws, s: &'a Expr<'a>) {
+        self.handle_ws(ws);
+        self.buf_writable.push(Writable::Expr(s));
+    }
+
+    // Write expression buffer and empty
+    fn write_buf_writable(&mut self, buf: &mut Buffer) -> Result<usize, CompileError> {
+        if self.buf_writable.is_empty() {
+            return Ok(0);
+        }
+
+        if self
+            .buf_writable
+            .iter()
+            .all(|w| matches!(w, Writable::Lit(_)))
+        {
+            let mut buf_lit = Buffer::new(0);
+            for s in mem::take(&mut self.buf_writable) {
+                if let Writable::Lit(s) = s {
+                    buf_lit.write(s);
+                };
+            }
+            buf.writeln(&format!("writer.write_str({:#?})?;", &buf_lit.buf))?;
+            return Ok(buf_lit.buf.len());
+        }
+
+        let mut size_hint = 0;
+        let mut buf_format = Buffer::new(0);
+        let mut buf_expr = Buffer::new(buf.indent + 1);
+        let mut expr_cache = HashMap::with_capacity(self.buf_writable.len());
+        for s in mem::take(&mut self.buf_writable) {
+            match s {
+                Writable::Lit(s) => {
+                    buf_format.write(&s.replace('{', "{{").replace('}', "}}"));
+                    size_hint += s.len();
+                }
+                Writable::Expr(s) => {
+                    use self::DisplayWrap::*;
+                    let mut expr_buf = Buffer::new(0);
+                    let wrapped = self.visit_expr(&mut expr_buf, s)?;
+                    let expression = match wrapped {
+                        Wrapped => expr_buf.buf,
+                        Unwrapped => format!(
+                            "::askama::MarkupDisplay::new_unsafe(&({}), {})",
+                            expr_buf.buf, self.input.escaper
+                        ),
+                    };
+
+                    use std::collections::hash_map::Entry;
+                    let id = match expr_cache.entry(expression.clone()) {
+                        Entry::Occupied(e) => *e.get(),
+                        Entry::Vacant(e) => {
+                            let id = self.named;
+                            self.named += 1;
+
+                            buf_expr.write(&format!("expr{} = ", id));
+                            buf_expr.write("&");
+                            buf_expr.write(&expression);
+                            buf_expr.writeln(",")?;
+
+                            e.insert(id);
+                            id
+                        }
+                    };
+
+                    buf_format.write(&format!("{{expr{}}}", id));
+                    size_hint += 3;
+                }
+            }
+        }
+
+        buf.writeln("::std::write!(")?;
+        buf.indent();
+        buf.writeln("writer,")?;
+        buf.writeln(&format!("{:#?},", &buf_format.buf))?;
+        buf.writeln(buf_expr.buf.trim())?;
+        buf.dedent()?;
+        buf.writeln(")?;")?;
+        Ok(size_hint)
+    }
+
+    fn visit_lit(&mut self, lws: &'a str, val: &'a str, rws: &'a str) {
+        assert!(self.next_ws.is_none());
+        if !lws.is_empty() {
+            match self.skip_ws {
+                WhitespaceHandling::Suppress => {
+                    self.skip_ws = WhitespaceHandling::Preserve;
+                }
+                _ if val.is_empty() => {
+                    assert!(rws.is_empty());
+                    self.next_ws = Some(lws);
+                }
+                WhitespaceHandling::Preserve => self.buf_writable.push(Writable::Lit(lws)),
+                WhitespaceHandling::Minimize => {
+                    self.buf_writable
+                        .push(Writable::Lit(match lws.contains('\n') {
+                            true => "\n",
+                            false => " ",
+                        }))
+                }
+            }
+        }
+
+        if !val.is_empty() {
+            self.buf_writable.push(Writable::Lit(val));
+        }
+
+        if !rws.is_empty() {
+            self.next_ws = Some(rws);
+        }
+    }
+
+    fn write_comment(&mut self, ws: Ws) {
+        self.handle_ws(ws);
+    }
+
+    /* Visitor methods for expression types */
+
+    fn visit_expr_root(&mut self, expr: &Expr<'_>) -> Result<String, CompileError> {
+        let mut buf = Buffer::new(0);
+        self.visit_expr(&mut buf, expr)?;
+        Ok(buf.buf)
+    }
+
+    fn visit_expr(
+        &mut self,
+        buf: &mut Buffer,
+        expr: &Expr<'_>,
+    ) -> Result<DisplayWrap, CompileError> {
+        Ok(match *expr {
+            Expr::BoolLit(s) => self.visit_bool_lit(buf, s),
+            Expr::NumLit(s) => self.visit_num_lit(buf, s),
+            Expr::StrLit(s) => self.visit_str_lit(buf, s),
+            Expr::CharLit(s) => self.visit_char_lit(buf, s),
+            Expr::Var(s) => self.visit_var(buf, s),
+            Expr::Path(ref path) => self.visit_path(buf, path),
+            Expr::Array(ref elements) => self.visit_array(buf, elements)?,
+            Expr::Attr(ref obj, name) => self.visit_attr(buf, obj, name)?,
+            Expr::Index(ref obj, ref key) => self.visit_index(buf, obj, key)?,
+            Expr::Filter(name, ref args) => self.visit_filter(buf, name, args)?,
+            Expr::Unary(op, ref inner) => self.visit_unary(buf, op, inner)?,
+            Expr::BinOp(op, ref left, ref right) => self.visit_binop(buf, op, left, right)?,
+            Expr::Range(op, ref left, ref right) => self.visit_range(buf, op, left, right)?,
+            Expr::Group(ref inner) => self.visit_group(buf, inner)?,
+            Expr::Call(ref obj, ref args) => self.visit_call(buf, obj, args)?,
+            Expr::RustMacro(name, args) => self.visit_rust_macro(buf, name, args),
+            Expr::Try(ref expr) => self.visit_try(buf, expr.as_ref())?,
+            Expr::Tuple(ref exprs) => self.visit_tuple(buf, exprs)?,
+        })
+    }
+
+    fn visit_try(
+        &mut self,
+        buf: &mut Buffer,
+        expr: &Expr<'_>,
+    ) -> Result<DisplayWrap, CompileError> {
+        buf.write("::core::result::Result::map_err(");
+        self.visit_expr(buf, expr)?;
+        buf.write(", |err| ::askama::shared::Error::Custom(::core::convert::Into::into(err)))?");
+        Ok(DisplayWrap::Unwrapped)
+    }
+
+    fn visit_rust_macro(&mut self, buf: &mut Buffer, name: &str, args: &str) -> DisplayWrap {
+        buf.write(name);
+        buf.write("!(");
+        buf.write(args);
+        buf.write(")");
+
+        DisplayWrap::Unwrapped
+    }
+
+    #[cfg(not(feature = "markdown"))]
+    fn _visit_markdown_filter(
+        &mut self,
+        _buf: &mut Buffer,
+        _args: &[Expr<'_>],
+    ) -> Result<DisplayWrap, CompileError> {
+        Err("the `markdown` filter requires the `markdown` feature to be enabled".into())
+    }
+
+    #[cfg(feature = "markdown")]
+    fn _visit_markdown_filter(
+        &mut self,
+        buf: &mut Buffer,
+        args: &[Expr<'_>],
+    ) -> Result<DisplayWrap, CompileError> {
+        let (md, options) = match args {
+            [md] => (md, None),
+            [md, options] => (md, Some(options)),
+            _ => return Err("markdown filter expects no more than one option argument".into()),
+        };
+
+        buf.write(&format!(
+            "::askama::filters::markdown({}, ",
+            self.input.escaper
+        ));
+        self.visit_expr(buf, md)?;
+        match options {
+            Some(options) => {
+                buf.write(", ::core::option::Option::Some(");
+                self.visit_expr(buf, options)?;
+                buf.write(")");
+            }
+            None => buf.write(", ::core::option::Option::None"),
+        }
+        buf.write(")?");
+
+        Ok(DisplayWrap::Wrapped)
+    }
+
+    fn visit_filter(
+        &mut self,
+        buf: &mut Buffer,
+        mut name: &str,
+        args: &[Expr<'_>],
+    ) -> Result<DisplayWrap, CompileError> {
+        if matches!(name, "escape" | "e") {
+            self._visit_escape_filter(buf, args)?;
+            return Ok(DisplayWrap::Wrapped);
+        } else if name == "format" {
+            self._visit_format_filter(buf, args)?;
+            return Ok(DisplayWrap::Unwrapped);
+        } else if name == "fmt" {
+            self._visit_fmt_filter(buf, args)?;
+            return Ok(DisplayWrap::Unwrapped);
+        } else if name == "join" {
+            self._visit_join_filter(buf, args)?;
+            return Ok(DisplayWrap::Unwrapped);
+        } else if name == "markdown" {
+            return self._visit_markdown_filter(buf, args);
+        }
+
+        if name == "tojson" {
+            name = "json";
+        }
+
+        #[cfg(not(feature = "serde-json"))]
+        if name == "json" {
+            return Err("the `json` filter requires the `serde-json` feature to be enabled".into());
+        }
+        #[cfg(not(feature = "serde-yaml"))]
+        if name == "yaml" {
+            return Err("the `yaml` filter requires the `serde-yaml` feature to be enabled".into());
+        }
+
+        const FILTERS: [&str; 2] = ["safe", "yaml"];
+        if FILTERS.contains(&name) {
+            buf.write(&format!(
+                "::askama::filters::{}({}, ",
+                name, self.input.escaper
+            ));
+        } else if crate::BUILT_IN_FILTERS.contains(&name) {
+            buf.write(&format!("::askama::filters::{}(", name));
+        } else {
+            buf.write(&format!("filters::{}(", name));
+        }
+
+        self._visit_args(buf, args)?;
+        buf.write(")?");
+        Ok(match FILTERS.contains(&name) {
+            true => DisplayWrap::Wrapped,
+            false => DisplayWrap::Unwrapped,
+        })
+    }
+
+    fn _visit_escape_filter(
+        &mut self,
+        buf: &mut Buffer,
+        args: &[Expr<'_>],
+    ) -> Result<(), CompileError> {
+        if args.len() > 2 {
+            return Err("only two arguments allowed to escape filter".into());
+        }
+        let opt_escaper = match args.get(1) {
+            Some(Expr::StrLit(name)) => Some(*name),
+            Some(_) => return Err("invalid escaper type for escape filter".into()),
+            None => None,
+        };
+        let escaper = match opt_escaper {
+            Some(name) => self
+                .input
+                .config
+                .escapers
+                .iter()
+                .find_map(|(escapers, escaper)| escapers.contains(name).then(|| escaper))
+                .ok_or_else(|| CompileError::from("invalid escaper for escape filter"))?,
+            None => self.input.escaper,
+        };
+        buf.write("::askama::filters::escape(");
+        buf.write(escaper);
+        buf.write(", ");
+        self._visit_args(buf, &args[..1])?;
+        buf.write(")?");
+        Ok(())
+    }
+
+    fn _visit_format_filter(
+        &mut self,
+        buf: &mut Buffer,
+        args: &[Expr<'_>],
+    ) -> Result<(), CompileError> {
+        buf.write("format!(");
+        if let Some(Expr::StrLit(v)) = args.first() {
+            self.visit_str_lit(buf, v);
+            if args.len() > 1 {
+                buf.write(", ");
+            }
+        } else {
+            return Err("invalid expression type for format filter".into());
+        }
+        self._visit_args(buf, &args[1..])?;
+        buf.write(")");
+        Ok(())
+    }
+
+    fn _visit_fmt_filter(
+        &mut self,
+        buf: &mut Buffer,
+        args: &[Expr<'_>],
+    ) -> Result<(), CompileError> {
+        buf.write("format!(");
+        if let Some(Expr::StrLit(v)) = args.get(1) {
+            self.visit_str_lit(buf, v);
+            buf.write(", ");
+        } else {
+            return Err("invalid expression type for fmt filter".into());
+        }
+        self._visit_args(buf, &args[0..1])?;
+        if args.len() > 2 {
+            return Err("only two arguments allowed to fmt filter".into());
+        }
+        buf.write(")");
+        Ok(())
+    }
+
+    // Force type coercion on first argument to `join` filter (see #39).
+    fn _visit_join_filter(
+        &mut self,
+        buf: &mut Buffer,
+        args: &[Expr<'_>],
+    ) -> Result<(), CompileError> {
+        buf.write("::askama::filters::join((&");
+        for (i, arg) in args.iter().enumerate() {
+            if i > 0 {
+                buf.write(", &");
+            }
+            self.visit_expr(buf, arg)?;
+            if i == 0 {
+                buf.write(").into_iter()");
+            }
+        }
+        buf.write(")?");
+        Ok(())
+    }
+
+    fn _visit_args(&mut self, buf: &mut Buffer, args: &[Expr<'_>]) -> Result<(), CompileError> {
+        if args.is_empty() {
+            return Ok(());
+        }
+
+        for (i, arg) in args.iter().enumerate() {
+            if i > 0 {
+                buf.write(", ");
+            }
+
+            let borrow = !arg.is_copyable();
+            if borrow {
+                buf.write("&(");
+            }
+
+            match arg {
+                Expr::Call(left, _) if !matches!(left.as_ref(), Expr::Path(_)) => {
+                    buf.writeln("{")?;
+                    self.visit_expr(buf, arg)?;
+                    buf.writeln("}")?;
+                }
+                _ => {
+                    self.visit_expr(buf, arg)?;
+                }
+            }
+
+            if borrow {
+                buf.write(")");
+            }
+        }
+        Ok(())
+    }
+
+    fn visit_attr(
+        &mut self,
+        buf: &mut Buffer,
+        obj: &Expr<'_>,
+        attr: &str,
+    ) -> Result<DisplayWrap, CompileError> {
+        if let Expr::Var(name) = *obj {
+            if name == "loop" {
+                if attr == "index" {
+                    buf.write("(_loop_item.index + 1)");
+                    return Ok(DisplayWrap::Unwrapped);
+                } else if attr == "index0" {
+                    buf.write("_loop_item.index");
+                    return Ok(DisplayWrap::Unwrapped);
+                } else if attr == "first" {
+                    buf.write("_loop_item.first");
+                    return Ok(DisplayWrap::Unwrapped);
+                } else if attr == "last" {
+                    buf.write("_loop_item.last");
+                    return Ok(DisplayWrap::Unwrapped);
+                } else {
+                    return Err("unknown loop variable".into());
+                }
+            }
+        }
+        self.visit_expr(buf, obj)?;
+        buf.write(&format!(".{}", normalize_identifier(attr)));
+        Ok(DisplayWrap::Unwrapped)
+    }
+
+    fn visit_index(
+        &mut self,
+        buf: &mut Buffer,
+        obj: &Expr<'_>,
+        key: &Expr<'_>,
+    ) -> Result<DisplayWrap, CompileError> {
+        buf.write("&");
+        self.visit_expr(buf, obj)?;
+        buf.write("[");
+        self.visit_expr(buf, key)?;
+        buf.write("]");
+        Ok(DisplayWrap::Unwrapped)
+    }
+
+    fn visit_call(
+        &mut self,
+        buf: &mut Buffer,
+        left: &Expr<'_>,
+        args: &[Expr<'_>],
+    ) -> Result<DisplayWrap, CompileError> {
+        match left {
+            Expr::Attr(left, method) if **left == Expr::Var("loop") => match *method {
+                "cycle" => match args {
+                    [arg] => {
+                        if matches!(arg, Expr::Array(arr) if arr.is_empty()) {
+                            return Err("loop.cycle(…) cannot use an empty array".into());
+                        }
+                        buf.write("({");
+                        buf.write("let _cycle = &(");
+                        self.visit_expr(buf, arg)?;
+                        buf.writeln(");")?;
+                        buf.writeln("let _len = _cycle.len();")?;
+                        buf.writeln("if _len == 0 {")?;
+                        buf.writeln("return ::core::result::Result::Err(::askama::Error::Fmt(::core::fmt::Error));")?;
+                        buf.writeln("}")?;
+                        buf.writeln("_cycle[_loop_item.index % _len]")?;
+                        buf.writeln("})")?;
+                    }
+                    _ => return Err("loop.cycle(…) expects exactly one argument".into()),
+                },
+                s => return Err(format!("unknown loop method: {:?}", s).into()),
+            },
+            left => {
+                match left {
+                    Expr::Var(name) => match self.locals.resolve(name) {
+                        Some(resolved) => buf.write(&resolved),
+                        None => buf.write(&format!("(&self.{})", normalize_identifier(name))),
+                    },
+                    left => {
+                        self.visit_expr(buf, left)?;
+                    }
+                }
+
+                buf.write("(");
+                self._visit_args(buf, args)?;
+                buf.write(")");
+            }
+        }
+        Ok(DisplayWrap::Unwrapped)
+    }
+
+    fn visit_unary(
+        &mut self,
+        buf: &mut Buffer,
+        op: &str,
+        inner: &Expr<'_>,
+    ) -> Result<DisplayWrap, CompileError> {
+        buf.write(op);
+        self.visit_expr(buf, inner)?;
+        Ok(DisplayWrap::Unwrapped)
+    }
+
+    fn visit_range(
+        &mut self,
+        buf: &mut Buffer,
+        op: &str,
+        left: &Option<Box<Expr<'_>>>,
+        right: &Option<Box<Expr<'_>>>,
+    ) -> Result<DisplayWrap, CompileError> {
+        if let Some(left) = left {
+            self.visit_expr(buf, left)?;
+        }
+        buf.write(op);
+        if let Some(right) = right {
+            self.visit_expr(buf, right)?;
+        }
+        Ok(DisplayWrap::Unwrapped)
+    }
+
+    fn visit_binop(
+        &mut self,
+        buf: &mut Buffer,
+        op: &str,
+        left: &Expr<'_>,
+        right: &Expr<'_>,
+    ) -> Result<DisplayWrap, CompileError> {
+        self.visit_expr(buf, left)?;
+        buf.write(&format!(" {} ", op));
+        self.visit_expr(buf, right)?;
+        Ok(DisplayWrap::Unwrapped)
+    }
+
+    fn visit_group(
+        &mut self,
+        buf: &mut Buffer,
+        inner: &Expr<'_>,
+    ) -> Result<DisplayWrap, CompileError> {
+        buf.write("(");
+        self.visit_expr(buf, inner)?;
+        buf.write(")");
+        Ok(DisplayWrap::Unwrapped)
+    }
+
+    fn visit_tuple(
+        &mut self,
+        buf: &mut Buffer,
+        exprs: &[Expr<'_>],
+    ) -> Result<DisplayWrap, CompileError> {
+        buf.write("(");
+        for (index, expr) in exprs.iter().enumerate() {
+            if index > 0 {
+                buf.write(" ");
+            }
+            self.visit_expr(buf, expr)?;
+            buf.write(",");
+        }
+        buf.write(")");
+        Ok(DisplayWrap::Unwrapped)
+    }
+
+    fn visit_array(
+        &mut self,
+        buf: &mut Buffer,
+        elements: &[Expr<'_>],
+    ) -> Result<DisplayWrap, CompileError> {
+        buf.write("[");
+        for (i, el) in elements.iter().enumerate() {
+            if i > 0 {
+                buf.write(", ");
+            }
+            self.visit_expr(buf, el)?;
+        }
+        buf.write("]");
+        Ok(DisplayWrap::Unwrapped)
+    }
+
+    fn visit_path(&mut self, buf: &mut Buffer, path: &[&str]) -> DisplayWrap {
+        for (i, part) in path.iter().enumerate() {
+            if i > 0 {
+                buf.write("::");
+            }
+            buf.write(part);
+        }
+        DisplayWrap::Unwrapped
+    }
+
+    fn visit_var(&mut self, buf: &mut Buffer, s: &str) -> DisplayWrap {
+        if s == "self" {
+            buf.write(s);
+            return DisplayWrap::Unwrapped;
+        }
+
+        buf.write(normalize_identifier(&self.locals.resolve_or_self(s)));
+        DisplayWrap::Unwrapped
+    }
+
+    fn visit_bool_lit(&mut self, buf: &mut Buffer, s: &str) -> DisplayWrap {
+        buf.write(s);
+        DisplayWrap::Unwrapped
+    }
+
+    fn visit_str_lit(&mut self, buf: &mut Buffer, s: &str) -> DisplayWrap {
+        buf.write(&format!("\"{}\"", s));
+        DisplayWrap::Unwrapped
+    }
+
+    fn visit_char_lit(&mut self, buf: &mut Buffer, s: &str) -> DisplayWrap {
+        buf.write(&format!("'{}'", s));
+        DisplayWrap::Unwrapped
+    }
+
+    fn visit_num_lit(&mut self, buf: &mut Buffer, s: &str) -> DisplayWrap {
+        buf.write(s);
+        DisplayWrap::Unwrapped
+    }
+
+    fn visit_target(
+        &mut self,
+        buf: &mut Buffer,
+        initialized: bool,
+        first_level: bool,
+        target: &Target<'a>,
+    ) {
+        match target {
+            Target::Name("_") => {
+                buf.write("_");
+            }
+            Target::Name(name) => {
+                let name = normalize_identifier(name);
+                match initialized {
+                    true => self.locals.insert(name, LocalMeta::initialized()),
+                    false => self.locals.insert_with_default(name),
+                }
+                buf.write(name);
+            }
+            Target::Tuple(path, targets) => {
+                buf.write(&path.join("::"));
+                buf.write("(");
+                for target in targets {
+                    self.visit_target(buf, initialized, false, target);
+                    buf.write(",");
+                }
+                buf.write(")");
+            }
+            Target::Struct(path, targets) => {
+                buf.write(&path.join("::"));
+                buf.write(" { ");
+                for (name, target) in targets {
+                    buf.write(normalize_identifier(name));
+                    buf.write(": ");
+                    self.visit_target(buf, initialized, false, target);
+                    buf.write(",");
+                }
+                buf.write(" }");
+            }
+            Target::Path(path) => {
+                self.visit_path(buf, path);
+            }
+            Target::StrLit(s) => {
+                if first_level {
+                    buf.write("&");
+                }
+                self.visit_str_lit(buf, s);
+            }
+            Target::NumLit(s) => {
+                if first_level {
+                    buf.write("&");
+                }
+                self.visit_num_lit(buf, s);
+            }
+            Target::CharLit(s) => {
+                if first_level {
+                    buf.write("&");
+                }
+                self.visit_char_lit(buf, s);
+            }
+            Target::BoolLit(s) => {
+                if first_level {
+                    buf.write("&");
+                }
+                buf.write(s);
+            }
+        }
+    }
+
+    /* Helper methods for dealing with whitespace nodes */
+
+    // Combines `flush_ws()` and `prepare_ws()` to handle both trailing whitespace from the
+    // preceding literal and leading whitespace from the succeeding literal.
+    fn handle_ws(&mut self, ws: Ws) {
+        self.flush_ws(ws);
+        self.prepare_ws(ws);
+    }
+
+    fn should_trim_ws(&self, ws: Option<Whitespace>) -> WhitespaceHandling {
+        match ws {
+            Some(Whitespace::Suppress) => WhitespaceHandling::Suppress,
+            Some(Whitespace::Preserve) => WhitespaceHandling::Preserve,
+            Some(Whitespace::Minimize) => WhitespaceHandling::Minimize,
+            None => self.whitespace,
+        }
+    }
+
+    // If the previous literal left some trailing whitespace in `next_ws` and the
+    // prefix whitespace suppressor from the given argument, flush that whitespace.
+    // In either case, `next_ws` is reset to `None` (no trailing whitespace).
+    fn flush_ws(&mut self, ws: Ws) {
+        if self.next_ws.is_none() {
+            return;
+        }
+
+        // If `whitespace` is set to `suppress`, we keep the whitespace characters only if there is
+        // a `+` character.
+        match self.should_trim_ws(ws.0) {
+            WhitespaceHandling::Preserve => {
+                let val = self.next_ws.unwrap();
+                if !val.is_empty() {
+                    self.buf_writable.push(Writable::Lit(val));
+                }
+            }
+            WhitespaceHandling::Minimize => {
+                let val = self.next_ws.unwrap();
+                if !val.is_empty() {
+                    self.buf_writable
+                        .push(Writable::Lit(match val.contains('\n') {
+                            true => "\n",
+                            false => " ",
+                        }));
+                }
+            }
+            WhitespaceHandling::Suppress => {}
+        }
+        self.next_ws = None;
+    }
+
+    // Sets `skip_ws` to match the suffix whitespace suppressor from the given
+    // argument, to determine whether to suppress leading whitespace from the
+    // next literal.
+    fn prepare_ws(&mut self, ws: Ws) {
+        self.skip_ws = self.should_trim_ws(ws.1);
+    }
+}
+
+struct Buffer {
+    // The buffer to generate the code into
+    buf: String,
+    // The current level of indentation (in spaces)
+    indent: u8,
+    // Whether the output buffer is currently at the start of a line
+    start: bool,
+}
+
+impl Buffer {
+    fn new(indent: u8) -> Self {
+        Self {
+            buf: String::new(),
+            indent,
+            start: true,
+        }
+    }
+
+    fn writeln(&mut self, s: &str) -> Result<(), CompileError> {
+        if s == "}" {
+            self.dedent()?;
+        }
+        if !s.is_empty() {
+            self.write(s);
+        }
+        self.buf.push('\n');
+        if s.ends_with('{') {
+            self.indent();
+        }
+        self.start = true;
+        Ok(())
+    }
+
+    fn write(&mut self, s: &str) {
+        if self.start {
+            for _ in 0..(self.indent * 4) {
+                self.buf.push(' ');
+            }
+            self.start = false;
+        }
+        self.buf.push_str(s);
+    }
+
+    fn indent(&mut self) {
+        self.indent += 1;
+    }
+
+    fn dedent(&mut self) -> Result<(), CompileError> {
+        if self.indent == 0 {
+            return Err("dedent() called while indentation == 0".into());
+        }
+        self.indent -= 1;
+        Ok(())
+    }
+}
+
+#[derive(Clone, Default)]
+struct LocalMeta {
+    refs: Option<String>,
+    initialized: bool,
+}
+
+impl LocalMeta {
+    fn initialized() -> Self {
+        Self {
+            refs: None,
+            initialized: true,
+        }
+    }
+
+    fn with_ref(refs: String) -> Self {
+        Self {
+            refs: Some(refs),
+            initialized: true,
+        }
+    }
+}
+
+// type SetChain<'a, T> = MapChain<'a, T, ()>;
+
+#[derive(Debug)]
+struct MapChain<'a, K, V>
+where
+    K: cmp::Eq + hash::Hash,
+{
+    parent: Option<&'a MapChain<'a, K, V>>,
+    scopes: Vec<HashMap<K, V>>,
+}
+
+impl<'a, K: 'a, V: 'a> MapChain<'a, K, V>
+where
+    K: cmp::Eq + hash::Hash,
+{
+    fn new() -> MapChain<'a, K, V> {
+        MapChain {
+            parent: None,
+            scopes: vec![HashMap::new()],
+        }
+    }
+
+    fn with_parent<'p>(parent: &'p MapChain<'_, K, V>) -> MapChain<'p, K, V> {
+        MapChain {
+            parent: Some(parent),
+            scopes: vec![HashMap::new()],
+        }
+    }
+
+    /// Iterates the scopes in reverse and returns `Some(LocalMeta)`
+    /// from the first scope where `key` exists.
+    fn get(&self, key: &K) -> Option<&V> {
+        let scopes = self.scopes.iter().rev();
+        scopes
+            .filter_map(|set| set.get(key))
+            .next()
+            .or_else(|| self.parent.and_then(|set| set.get(key)))
+    }
+
+    fn is_current_empty(&self) -> bool {
+        self.scopes.last().unwrap().is_empty()
+    }
+
+    fn insert(&mut self, key: K, val: V) {
+        self.scopes.last_mut().unwrap().insert(key, val);
+
+        // Note that if `insert` returns `Some` then it implies
+        // an identifier is reused. For e.g. `{% macro f(a, a) %}`
+        // and `{% let (a, a) = ... %}` then this results in a
+        // generated template, which when compiled fails with the
+        // compile error "identifier `a` used more than once".
+    }
+
+    fn insert_with_default(&mut self, key: K)
+    where
+        V: Default,
+    {
+        self.insert(key, V::default());
+    }
+
+    fn push(&mut self) {
+        self.scopes.push(HashMap::new());
+    }
+
+    fn pop(&mut self) {
+        self.scopes.pop().unwrap();
+        assert!(!self.scopes.is_empty());
+    }
+}
+
+impl MapChain<'_, &str, LocalMeta> {
+    fn resolve(&self, name: &str) -> Option<String> {
+        let name = normalize_identifier(name);
+        self.get(&name).map(|meta| match &meta.refs {
+            Some(expr) => expr.clone(),
+            None => name.to_string(),
+        })
+    }
+
+    fn resolve_or_self(&self, name: &str) -> String {
+        let name = normalize_identifier(name);
+        self.resolve(name)
+            .unwrap_or_else(|| format!("self.{}", name))
+    }
+}
+
+fn median(sizes: &mut [usize]) -> usize {
+    sizes.sort_unstable();
+    if sizes.len() % 2 == 1 {
+        sizes[sizes.len() / 2]
+    } else {
+        (sizes[sizes.len() / 2 - 1] + sizes[sizes.len() / 2]) / 2
+    }
+}
+
+#[derive(Clone, PartialEq)]
+enum AstLevel {
+    Top,
+    Block,
+    Nested,
+}
+
+impl Copy for AstLevel {}
+
+#[derive(Clone)]
+enum DisplayWrap {
+    Wrapped,
+    Unwrapped,
+}
+
+impl Copy for DisplayWrap {}
+
+#[derive(Debug)]
+enum Writable<'a> {
+    Lit(&'a str),
+    Expr(&'a Expr<'a>),
+}
+
+// Identifiers to be replaced with raw identifiers, so as to avoid
+// collisions between template syntax and Rust's syntax. In particular
+// [Rust keywords](https://doc.rust-lang.org/reference/keywords.html)
+// should be replaced, since they're not reserved words in Askama
+// syntax but have a high probability of causing problems in the
+// generated code.
+//
+// This list excludes the Rust keywords *self*, *Self*, and *super*
+// because they are not allowed to be raw identifiers, and *loop*
+// because it's used something like a keyword in the template
+// language.
+static USE_RAW: [(&str, &str); 47] = [
+    ("as", "r#as"),
+    ("break", "r#break"),
+    ("const", "r#const"),
+    ("continue", "r#continue"),
+    ("crate", "r#crate"),
+    ("else", "r#else"),
+    ("enum", "r#enum"),
+    ("extern", "r#extern"),
+    ("false", "r#false"),
+    ("fn", "r#fn"),
+    ("for", "r#for"),
+    ("if", "r#if"),
+    ("impl", "r#impl"),
+    ("in", "r#in"),
+    ("let", "r#let"),
+    ("match", "r#match"),
+    ("mod", "r#mod"),
+    ("move", "r#move"),
+    ("mut", "r#mut"),
+    ("pub", "r#pub"),
+    ("ref", "r#ref"),
+    ("return", "r#return"),
+    ("static", "r#static"),
+    ("struct", "r#struct"),
+    ("trait", "r#trait"),
+    ("true", "r#true"),
+    ("type", "r#type"),
+    ("unsafe", "r#unsafe"),
+    ("use", "r#use"),
+    ("where", "r#where"),
+    ("while", "r#while"),
+    ("async", "r#async"),
+    ("await", "r#await"),
+    ("dyn", "r#dyn"),
+    ("abstract", "r#abstract"),
+    ("become", "r#become"),
+    ("box", "r#box"),
+    ("do", "r#do"),
+    ("final", "r#final"),
+    ("macro", "r#macro"),
+    ("override", "r#override"),
+    ("priv", "r#priv"),
+    ("typeof", "r#typeof"),
+    ("unsized", "r#unsized"),
+    ("virtual", "r#virtual"),
+    ("yield", "r#yield"),
+    ("try", "r#try"),
+];
+
+fn normalize_identifier(ident: &str) -> &str {
+    if let Some(word) = USE_RAW.iter().find(|x| x.0 == ident) {
+        word.1
+    } else {
+        ident
+    }
+}