Enable tracking of the offending span of an error

2 files changed, 25 insertions, 9 deletions

diff --git a/askama_derive/src/lib.rs b/askama_derive/src/lib.rs
index 4d81433..2409ba4 100644
--- a/askama_derive/src/lib.rs
+++ b/askama_derive/src/lib.rs
@@ -9,7 +9,6 @@ use askama_shared::{
     generator, get_template_source, read_config_file, CompileError, Config, Integrations,
 };
 use proc_macro::TokenStream;
-use proc_macro2::Span;
 
 use std::collections::HashMap;
 use std::path::PathBuf;
@@ -19,9 +18,7 @@ pub 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) => syn::Error::new(Span::call_site(), e)
-            .to_compile_error()
-            .into(),
+        Err(e) => e.to_compile_error().into(),
     }
 }
 
diff --git a/askama_shared/src/lib.rs b/askama_shared/src/lib.rs
index b2bebd0..994662c 100644
--- a/askama_shared/src/lib.rs
+++ b/askama_shared/src/lib.rs
@@ -9,6 +9,7 @@ use std::convert::TryFrom;
 use std::path::{Path, PathBuf};
 use std::{env, fmt, fs};
 
+use proc_macro2::{Span, TokenStream};
 #[cfg(feature = "serde")]
 use serde::Deserialize;
 
@@ -292,27 +293,45 @@ static DEFAULT_ESCAPERS: &[(&[&str], &str)] = &[
     (&["j2", "jinja", "jinja2"], "::askama::Html"),
 ];
 
-#[derive(Debug)]
-pub struct CompileError(Cow<'static, str>);
+#[derive(Debug, Clone)]
+pub struct CompileError {
+    msg: Cow<'static, str>,
+    span: Span,
+}
+
+impl CompileError {
+    pub fn new<S: Into<Cow<'static, str>>>(s: S, span: Span) -> Self {
+        Self {
+            msg: s.into(),
+            span,
+        }
+    }
+
+    pub fn to_compile_error(self) -> TokenStream {
+        syn::Error::new(self.span, self.msg).to_compile_error()
+    }
+}
+
+impl std::error::Error for CompileError {}
 
 impl fmt::Display for CompileError {
     #[inline]
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt.write_str(&self.0)
+        fmt.write_str(&self.msg)
     }
 }
 
 impl From<&'static str> for CompileError {
     #[inline]
     fn from(s: &'static str) -> Self {
-        Self(s.into())
+        Self::new(s, Span::call_site())
     }
 }
 
 impl From<String> for CompileError {
     #[inline]
     fn from(s: String) -> Self {
-        Self(s.into())
+        Self::new(s, Span::call_site())
     }
 }