Removed implicit borrowing of literals, calls, and more (fixes #404)

6 files changed, 109 insertions, 59 deletions

diff --git a/askama_shared/src/filters/json.rs b/askama_shared/src/filters/json.rs
index ba7e61b..c0df707 100644
--- a/askama_shared/src/filters/json.rs
+++ b/askama_shared/src/filters/json.rs
@@ -8,8 +8,8 @@ use serde::Serialize;
 ///
 /// This will panic if `S`'s implementation of `Serialize` decides to fail,
 /// or if `T` contains a map with non-string keys.
-pub fn json<E: Escaper, S: Serialize>(e: E, s: &S) -> Result<MarkupDisplay<E, String>> {
-    match serde_json::to_string_pretty(s) {
+pub fn json<E: Escaper, S: Serialize>(e: E, s: S) -> Result<MarkupDisplay<E, String>> {
+    match serde_json::to_string_pretty(&s) {
         Ok(s) => Ok(MarkupDisplay::new_safe(s, e)),
         Err(e) => Err(Error::from(e)),
     }
@@ -22,6 +22,8 @@ mod tests {
 
     #[test]
     fn test_json() {
+        assert_eq!(json(Html, true).unwrap().to_string(), "true");
+        assert_eq!(json(Html, "foo").unwrap().to_string(), r#""foo""#);
         assert_eq!(json(Html, &true).unwrap().to_string(), "true");
         assert_eq!(json(Html, &"foo").unwrap().to_string(), r#""foo""#);
         assert_eq!(
diff --git a/askama_shared/src/filters/mod.rs b/askama_shared/src/filters/mod.rs
index 35989ca..6838d57 100644
--- a/askama_shared/src/filters/mod.rs
+++ b/askama_shared/src/filters/mod.rs
@@ -141,7 +141,7 @@ pub fn filesizeformat<B: FileSize>(b: &B) -> Result<String> {
 /// To encode `/` as well, see [`urlencode_strict`](./fn.urlencode_strict.html).
 ///
 /// [`urlencode_strict`]: ./fn.urlencode_strict.html
-pub fn urlencode(s: &dyn fmt::Display) -> Result<String> {
+pub fn urlencode<T: fmt::Display>(s: T) -> Result<String> {
     let s = s.to_string();
     Ok(utf8_percent_encode(&s, URLENCODE_SET).to_string())
 }
@@ -161,7 +161,7 @@ pub fn urlencode(s: &dyn fmt::Display) -> Result<String> {
 /// ```
 ///
 /// If you want to preserve `/`, see [`urlencode`](./fn.urlencode.html).
-pub fn urlencode_strict(s: &dyn fmt::Display) -> Result<String> {
+pub fn urlencode_strict<T: fmt::Display>(s: T) -> Result<String> {
     let s = s.to_string();
     Ok(utf8_percent_encode(&s, URLENCODE_STRICT_SET).to_string())
 }
@@ -199,7 +199,7 @@ pub fn format() {}
 ///
 /// A single newline becomes an HTML line break `<br>` and a new line
 /// followed by a blank line becomes a paragraph break `<p>`.
-pub fn linebreaks(s: &dyn fmt::Display) -> Result<String> {
+pub fn linebreaks<T: fmt::Display>(s: T) -> Result<String> {
     let s = s.to_string();
     let linebroken = s.replace("\n\n", "</p><p>").replace("\n", "<br/>");
 
@@ -207,46 +207,46 @@ pub fn linebreaks(s: &dyn fmt::Display) -> Result<String> {
 }
 
 /// Converts all newlines in a piece of plain text to HTML line breaks
-pub fn linebreaksbr(s: &dyn fmt::Display) -> Result<String> {
+pub fn linebreaksbr<T: fmt::Display>(s: T) -> Result<String> {
     let s = s.to_string();
     Ok(s.replace("\n", "<br/>"))
 }
 
 /// Converts to lowercase
-pub fn lower(s: &dyn fmt::Display) -> Result<String> {
+pub fn lower<T: fmt::Display>(s: T) -> Result<String> {
     let s = s.to_string();
     Ok(s.to_lowercase())
 }
 
 /// Alias for the `lower()` filter
-pub fn lowercase(s: &dyn fmt::Display) -> Result<String> {
+pub fn lowercase<T: fmt::Display>(s: T) -> Result<String> {
     lower(s)
 }
 
 /// Converts to uppercase
-pub fn upper(s: &dyn fmt::Display) -> Result<String> {
+pub fn upper<T: fmt::Display>(s: T) -> Result<String> {
     let s = s.to_string();
     Ok(s.to_uppercase())
 }
 
 /// Alias for the `upper()` filter
-pub fn uppercase(s: &dyn fmt::Display) -> Result<String> {
+pub fn uppercase<T: fmt::Display>(s: T) -> Result<String> {
     upper(s)
 }
 
 /// Strip leading and trailing whitespace
-pub fn trim(s: &dyn fmt::Display) -> Result<String> {
+pub fn trim<T: fmt::Display>(s: T) -> Result<String> {
     let s = s.to_string();
     Ok(s.trim().to_owned())
 }
 
 /// Limit string length, appends '...' if truncated
-pub fn truncate(s: &dyn fmt::Display, len: &usize) -> Result<String> {
+pub fn truncate<T: fmt::Display>(s: T, len: usize) -> Result<String> {
     let mut s = s.to_string();
-    if s.len() <= *len {
+    if s.len() <= len {
         Ok(s)
     } else {
-        let mut real_len = *len;
+        let mut real_len = len;
         while !s.is_char_boundary(real_len) {
             real_len += 1;
         }
@@ -257,7 +257,7 @@ pub fn truncate(s: &dyn fmt::Display, len: &usize) -> Result<String> {
 }
 
 /// Indent lines with `width` spaces
-pub fn indent(s: &dyn fmt::Display, width: &usize) -> Result<String> {
+pub fn indent<T: fmt::Display>(s: T, width: usize) -> Result<String> {
     let s = s.to_string();
 
     let mut indented = String::new();
@@ -266,7 +266,7 @@ pub fn indent(s: &dyn fmt::Display, width: &usize) -> Result<String> {
         indented.push(c);
 
         if c == '\n' && i < s.len() - 1 {
-            for _ in 0..*width {
+            for _ in 0..width {
                 indented.push(' ');
             }
         }
@@ -277,7 +277,7 @@ pub fn indent(s: &dyn fmt::Display, width: &usize) -> Result<String> {
 
 #[cfg(feature = "num-traits")]
 /// Casts number to f64
-pub fn into_f64<T>(number: &T) -> Result<f64>
+pub fn into_f64<T>(number: T) -> Result<f64>
 where
     T: NumCast,
 {
@@ -286,7 +286,7 @@ where
 
 #[cfg(feature = "num-traits")]
 /// Casts number to isize
-pub fn into_isize<T>(number: &T) -> Result<isize>
+pub fn into_isize<T>(number: T) -> Result<isize>
 where
     T: NumCast,
 {
@@ -325,7 +325,7 @@ where
 }
 
 /// Capitalize a value. The first character will be uppercase, all others lowercase.
-pub fn capitalize(s: &dyn fmt::Display) -> Result<String> {
+pub fn capitalize<T: fmt::Display>(s: T) -> Result<String> {
     let mut s = s.to_string();
 
     match s.get_mut(0..1).map(|s| {
@@ -371,7 +371,7 @@ pub fn center(src: &dyn fmt::Display, dst_len: usize) -> Result<String> {
 }
 
 /// Count the words in that string
-pub fn wordcount(s: &dyn fmt::Display) -> Result<usize> {
+pub fn wordcount<T: fmt::Display>(s: T) -> Result<usize> {
     let s = s.to_string();
 
     Ok(s.split_whitespace().count())
@@ -480,36 +480,36 @@ mod tests {
 
     #[test]
     fn test_truncate() {
-        assert_eq!(truncate(&"hello", &2).unwrap(), "he...");
+        assert_eq!(truncate(&"hello", 2).unwrap(), "he...");
         let a = String::from("您好");
         assert_eq!(a.len(), 6);
         assert_eq!(String::from("您").len(), 3);
-        assert_eq!(truncate(&"您好", &1).unwrap(), "您...");
-        assert_eq!(truncate(&"您好", &2).unwrap(), "您...");
-        assert_eq!(truncate(&"您好", &3).unwrap(), "您...");
-        assert_eq!(truncate(&"您好", &4).unwrap(), "您好...");
-        assert_eq!(truncate(&"您好", &6).unwrap(), "您好");
-        assert_eq!(truncate(&"您好", &7).unwrap(), "您好");
+        assert_eq!(truncate(&"您好", 1).unwrap(), "您...");
+        assert_eq!(truncate(&"您好", 2).unwrap(), "您...");
+        assert_eq!(truncate(&"您好", 3).unwrap(), "您...");
+        assert_eq!(truncate(&"您好", 4).unwrap(), "您好...");
+        assert_eq!(truncate(&"您好", 6).unwrap(), "您好");
+        assert_eq!(truncate(&"您好", 7).unwrap(), "您好");
         let s = String::from("🤚a🤚");
         assert_eq!(s.len(), 9);
         assert_eq!(String::from("🤚").len(), 4);
-        assert_eq!(truncate(&"🤚a🤚", &1).unwrap(), "🤚...");
-        assert_eq!(truncate(&"🤚a🤚", &2).unwrap(), "🤚...");
-        assert_eq!(truncate(&"🤚a🤚", &3).unwrap(), "🤚...");
-        assert_eq!(truncate(&"🤚a🤚", &4).unwrap(), "🤚...");
-        assert_eq!(truncate(&"🤚a🤚", &5).unwrap(), "🤚a...");
-        assert_eq!(truncate(&"🤚a🤚", &6).unwrap(), "🤚a🤚...");
-        assert_eq!(truncate(&"🤚a🤚", &9).unwrap(), "🤚a🤚");
-        assert_eq!(truncate(&"🤚a🤚", &10).unwrap(), "🤚a🤚");
+        assert_eq!(truncate(&"🤚a🤚", 1).unwrap(), "🤚...");
+        assert_eq!(truncate(&"🤚a🤚", 2).unwrap(), "🤚...");
+        assert_eq!(truncate(&"🤚a🤚", 3).unwrap(), "🤚...");
+        assert_eq!(truncate(&"🤚a🤚", 4).unwrap(), "🤚...");
+        assert_eq!(truncate(&"🤚a🤚", 5).unwrap(), "🤚a...");
+        assert_eq!(truncate(&"🤚a🤚", 6).unwrap(), "🤚a🤚...");
+        assert_eq!(truncate(&"🤚a🤚", 9).unwrap(), "🤚a🤚");
+        assert_eq!(truncate(&"🤚a🤚", 10).unwrap(), "🤚a🤚");
     }
 
     #[test]
     fn test_indent() {
-        assert_eq!(indent(&"hello", &2).unwrap(), "hello");
-        assert_eq!(indent(&"hello\n", &2).unwrap(), "hello\n");
-        assert_eq!(indent(&"hello\nfoo", &2).unwrap(), "hello\n  foo");
+        assert_eq!(indent(&"hello", 2).unwrap(), "hello");
+        assert_eq!(indent(&"hello\n", 2).unwrap(), "hello\n");
+        assert_eq!(indent(&"hello\nfoo", 2).unwrap(), "hello\n  foo");
         assert_eq!(
-            indent(&"hello\nfoo\n bar", &4).unwrap(),
+            indent(&"hello\nfoo\n bar", 4).unwrap(),
             "hello\n    foo\n     bar"
         );
     }
@@ -518,22 +518,22 @@ mod tests {
     #[test]
     #[allow(clippy::float_cmp)]
     fn test_into_f64() {
-        assert_eq!(into_f64(&1).unwrap(), 1.0_f64);
-        assert_eq!(into_f64(&1.9).unwrap(), 1.9_f64);
-        assert_eq!(into_f64(&-1.9).unwrap(), -1.9_f64);
-        assert_eq!(into_f64(&(INFINITY as f32)).unwrap(), INFINITY);
-        assert_eq!(into_f64(&(-INFINITY as f32)).unwrap(), -INFINITY);
+        assert_eq!(into_f64(1).unwrap(), 1.0_f64);
+        assert_eq!(into_f64(1.9).unwrap(), 1.9_f64);
+        assert_eq!(into_f64(-1.9).unwrap(), -1.9_f64);
+        assert_eq!(into_f64(INFINITY as f32).unwrap(), INFINITY);
+        assert_eq!(into_f64(-INFINITY as f32).unwrap(), -INFINITY);
     }
 
     #[cfg(feature = "num-traits")]
     #[test]
     fn test_into_isize() {
-        assert_eq!(into_isize(&1).unwrap(), 1_isize);
-        assert_eq!(into_isize(&1.9).unwrap(), 1_isize);
-        assert_eq!(into_isize(&-1.9).unwrap(), -1_isize);
-        assert_eq!(into_isize(&(1.5_f64)).unwrap(), 1_isize);
-        assert_eq!(into_isize(&(-1.5_f64)).unwrap(), -1_isize);
-        match into_isize(&INFINITY) {
+        assert_eq!(into_isize(1).unwrap(), 1_isize);
+        assert_eq!(into_isize(1.9).unwrap(), 1_isize);
+        assert_eq!(into_isize(-1.9).unwrap(), -1_isize);
+        assert_eq!(into_isize(1.5_f64).unwrap(), 1_isize);
+        assert_eq!(into_isize(-1.5_f64).unwrap(), -1_isize);
+        match into_isize(INFINITY) {
             Err(Fmt(fmt::Error)) => {}
             _ => panic!("Should return error of type Err(Fmt(fmt::Error))"),
         };
diff --git a/askama_shared/src/filters/yaml.rs b/askama_shared/src/filters/yaml.rs
index fdd03f6..a6059b7 100644
--- a/askama_shared/src/filters/yaml.rs
+++ b/askama_shared/src/filters/yaml.rs
@@ -8,8 +8,8 @@ use serde::Serialize;
 ///
 /// This will panic if `S`'s implementation of `Serialize` decides to fail,
 /// or if `T` contains a map with non-string keys.
-pub fn yaml<E: Escaper, S: Serialize>(e: E, s: &S) -> Result<MarkupDisplay<E, String>> {
-    match serde_yaml::to_string(s) {
+pub fn yaml<E: Escaper, S: Serialize>(e: E, s: S) -> Result<MarkupDisplay<E, String>> {
+    match serde_yaml::to_string(&s) {
         Ok(s) => Ok(MarkupDisplay::new_safe(s, e)),
         Err(e) => Err(Error::from(e)),
     }
@@ -22,6 +22,8 @@ mod tests {
 
     #[test]
     fn test_yaml() {
+        assert_eq!(yaml(Html, true).unwrap().to_string(), "---\ntrue");
+        assert_eq!(yaml(Html, "foo").unwrap().to_string(), "---\nfoo");
         assert_eq!(yaml(Html, &true).unwrap().to_string(), "---\ntrue");
         assert_eq!(yaml(Html, &"foo").unwrap().to_string(), "---\nfoo");
         assert_eq!(
diff --git a/askama_shared/src/generator.rs b/askama_shared/src/generator.rs
index cde0ead..801db37 100644
--- a/askama_shared/src/generator.rs
+++ b/askama_shared/src/generator.rs
@@ -1275,9 +1275,12 @@ impl<'a, S: std::hash::BuildHasher> Generator<'a, S> {
 
         for (i, arg) in args.iter().enumerate() {
             if i > 0 {
-                buf.write(", &");
-            } else {
-                buf.write("&");
+                buf.write(", ");
+            }
+
+            let borrow = !arg.is_copyable();
+            if borrow {
+                buf.write("&(");
             }
 
             let scoped = matches!(arg,
@@ -1293,6 +1296,10 @@ impl<'a, S: std::hash::BuildHasher> Generator<'a, S> {
             } else {
                 self.visit_expr(buf, arg)?;
             }
+
+            if borrow {
+                buf.write(")");
+            }
         }
         Ok(())
     }
diff --git a/askama_shared/src/parser.rs b/askama_shared/src/parser.rs
index 43377a6..3b3d4f4 100644
--- a/askama_shared/src/parser.rs
+++ b/askama_shared/src/parser.rs
@@ -51,6 +51,45 @@ pub enum Expr<'a> {
     RustMacro(&'a str, &'a str),
 }
 
+impl Expr<'_> {
+    /// Returns `true` if enough assumptions can be made,
+    /// to determine that `self` is copyable.
+    pub fn is_copyable(&self) -> bool {
+        self.is_copyable_within_op(false)
+    }
+
+    fn is_copyable_within_op(&self, within_op: bool) -> bool {
+        use Expr::*;
+        match self {
+            BoolLit(_) | NumLit(_) | StrLit(_) | CharLit(_) => true,
+            Unary(.., expr) => expr.is_copyable_within_op(true),
+            BinOp(_, lhs, rhs) => {
+                lhs.is_copyable_within_op(true) && rhs.is_copyable_within_op(true)
+            }
+            // The result of a call likely doesn't need to be borrowed,
+            // as in that case the call is more likely to return a
+            // reference in the first place then.
+            VarCall(..) | PathCall(..) | MethodCall(..) => true,
+            // If the `expr` is within a `Unary` or `BinOp` then
+            // an assumption can be made that the operand is copy.
+            // If not, then the value is moved and adding `.clone()`
+            // will solve that issue. However, if the operand is
+            // implicitly borrowed, then it's likely not even possible
+            // to get the template to compile.
+            _ => within_op && self.is_attr_self(),
+        }
+    }
+
+    /// Returns `true` if this is an `Attr` where the `obj` is `"self"`.
+    pub fn is_attr_self(&self) -> bool {
+        match self {
+            Expr::Attr(obj, _) if matches!(obj.as_ref(), Expr::Var("self")) => true,
+            Expr::Attr(obj, _) if matches!(obj.as_ref(), Expr::Attr(..)) => obj.is_attr_self(),
+            _ => false,
+        }
+    }
+}
+
 pub type When<'a> = (
     WS,
     Option<MatchVariant<'a>>,
diff --git a/testing/tests/simple.rs b/testing/tests/simple.rs
index 5ef03b1..0c6b17e 100644
--- a/testing/tests/simple.rs
+++ b/testing/tests/simple.rs
@@ -265,7 +265,7 @@ fn test_slice_literal() {
 #[derive(Template)]
 #[template(source = "Hello, {{ world(\"123\", 4) }}!", ext = "txt")]
 struct FunctionRefTemplate {
-    world: fn(s: &str, v: &u8) -> String,
+    world: fn(s: &str, v: u8) -> String,
 }
 
 #[test]
@@ -277,7 +277,7 @@ fn test_func_ref_call() {
 }
 
 #[allow(clippy::trivially_copy_pass_by_ref)]
-fn world2(s: &str, v: &u8) -> String {
+fn world2(s: &str, v: u8) -> String {
     format!("world{}{}", v, s)
 }
 
@@ -291,7 +291,7 @@ fn test_path_func_call() {
 }
 
 #[derive(Template)]
-#[template(source = "{{ ::std::string::ToString::to_string(123) }}", ext = "txt")]
+#[template(source = "{{ ::std::string::String::from(\"123\") }}", ext = "txt")]
 struct RootPathFunctionTemplate;
 
 #[test]
@@ -305,7 +305,7 @@ struct FunctionTemplate;
 
 impl FunctionTemplate {
     #[allow(clippy::trivially_copy_pass_by_ref)]
-    fn world3(&self, s: &str, v: &u8) -> String {
+    fn world3(&self, s: &str, v: u8) -> String {
         format!("world{}{}", s, v)
     }
 }