Merge pull request #584 from GuillaumeGomez/extends-first

Emit an error if an extends block doesn't come first in a template

askama_derive/src/tests.rs

@@ -44,7 +44,9 @@ fn compare_ex(
 ) {
     let generated = jinja_to_rust(jinja, fields, prefix);
 
-    let expected: TokenStream = expected.parse().unwrap();
+    let expected: TokenStream = expected
+        .parse()
+        .expect("`TokenStream` failed to parse input");
     let expected: syn::File = syn::parse_quote! {
         #[automatically_derived]
         impl askama::Template for Foo {
@@ -159,7 +161,10 @@ struct Foo {{ {} }}"##,
             .join(","),
     );
 
-    let generated = build_template(&syn::parse_str::<syn::DeriveInput>(&jinja).unwrap()).unwrap();
+    let generated = build_template(
+        &syn::parse_str::<syn::DeriveInput>(&jinja).expect("`syn` failed to parse code"),
+    )
+    .expect("`build_template` failed");
     match syn::parse2(generated.clone()) {
         Ok(generated) => generated,
         Err(err) => panic!(
@@ -1150,11 +1155,11 @@ fn test_concat() {
 fn extends_with_whitespace_control() {
     const CONTROL: &[&str] = &["", "\t", "-", "+", "~"];
 
-    let expected = jinja_to_rust(r#"front {% extends "a.html" %} back"#, &[], "");
+    let expected = jinja_to_rust(r#"{% extends "a.html" %} back"#, &[], "");
     let expected = unparse(&expected);
     for front in CONTROL {
         for back in CONTROL {
-            let src = format!(r#"front {{%{front} extends "a.html" {back}%}} back"#);
+            let src = format!(r#"{{%{front} extends "a.html" {back}%}} back"#);
             let actual = jinja_to_rust(&src, &[], "");
             let actual = unparse(&actual);
             assert_eq!(expected, actual, "source: {src:?}");

askama_parser/src/node.rs

@@ -38,8 +38,27 @@ pub enum Node<'a> {
 
 impl<'a: 'l, 'l> Node<'a> {
     pub(super) fn parse_template(i: &mut InputStream<'a, 'l>) -> ParseResult<'a, Vec<Box<Self>>> {
-        let mut p = parse_with_unexpected_fallback(Self::many, unexpected_tag);
-        let nodes = p.parse_next(i)?;
+        let mut nodes = vec![];
+        let mut allow_extends = true;
+        while let Some(node) = parse_with_unexpected_fallback(
+            opt(move |i: &mut _| Self::one(i, allow_extends)),
+            unexpected_tag,
+        )
+        .parse_next(i)?
+        {
+            if allow_extends {
+                match &*node {
+                    // Since comments don't impact generated code, we allow them before `extends`.
+                    Node::Comment(_) => {}
+                    // If it only contains whitespace characters, it's fine too.
+                    Node::Lit(lit) if lit.val.is_empty() => {}
+                    // Everything else must not come before an `extends` block.
+                    _ => allow_extends = false,
+                }
+            }
+            nodes.push(node);
+        }
+
         if !i.is_empty() {
             opt(unexpected_tag).parse_next(i)?;
             return cut_error!(
@@ -53,12 +72,15 @@ impl<'a: 'l, 'l> Node<'a> {
     }
 
     fn many(i: &mut InputStream<'a, 'l>) -> ParseResult<'a, Vec<Box<Self>>> {
-        repeat(
-            0..,
-            alt((Lit::parse, Comment::parse, Self::expr, Self::parse)),
-        )
-        .map(|v: Vec<_>| v)
-        .parse_next(i)
+        repeat(0.., |i: &mut _| Self::one(i, false)).parse_next(i)
+    }
+
+    fn one(i: &mut InputStream<'a, 'l>, allow_extends: bool) -> ParseResult<'a, Box<Self>> {
+        let node = alt((Lit::parse, Comment::parse, Self::expr, Self::parse)).parse_next(i)?;
+        if !allow_extends && let Node::Extends(node) = &*node {
+            return cut_error!("`extends` block must come first in a template", node.span());
+        }
+        Ok(node)
     }
 
     fn parse(i: &mut InputStream<'a, 'l>) -> ParseResult<'a, Box<Self>> {

askama_parser/src/tests.rs

@@ -1160,10 +1160,10 @@ fn extends_with_whitespace_control() {
     const CONTROL: &[&str] = &["", "\t", "-", "+", "~"];
 
     let syntax = Syntax::default();
-    let expected = Ast::from_str(r#"front {% extends "nothing" %} back"#, None, &syntax).unwrap();
+    let expected = Ast::from_str(r#"{% extends "nothing" %} back"#, None, &syntax).unwrap();
     for front in CONTROL {
         for back in CONTROL {
-            let src = format!(r#"front {{%{front} extends "nothing" {back}%}} back"#);
+            let src = format!(r#"{{%{front} extends "nothing" {back}%}} back"#);
             let actual = Ast::from_str(&src, None, &syntax).unwrap();
             assert_eq!(expected.nodes(), actual.nodes(), "source: {src:?}");
         }

testing/tests/extend.rs

@@ -25,3 +25,17 @@ fn test_macro_in_block_inheritance() {
 
     assert_eq!(A.render().unwrap(), "\n\n1 1\n2 2\n--> 3");
 }
+
+// This test ensures that comments are allowed before `extends` block.
+#[test]
+fn test_comment_before_extend() {
+    #[derive(Template)]
+    #[template(
+        source = r##"{# comment #}{% extends "base.html" %}"##,
+        ext = "txt",
+        print = "ast"
+    )]
+    pub struct X {
+        title: &'static str,
+    }
+}

testing/tests/ui/blocks_below_top_level.stderr

@@ -1,5 +1,5 @@
-error: `extends` blocks are not allowed below top level
- --> MyTemplate1.txt:3:2
+error: `extends` block must come first in a template
+ --> <source attribute>:3:2
        " extends \"bla.txt\" %}\n{% endblock %}\n"
  --> tests/ui/blocks_below_top_level.rs:4:21
   |

testing/tests/ui/extend.rs

@@ -0,0 +1,13 @@
+use askama::Template;
+
+#[derive(Template)]
+#[template(
+    source = r##"bla
+{% extends "base.html" %}
+"##,
+    ext = "txt",
+    print = "ast"
+)]
+pub struct X;
+
+fn main() {}

testing/tests/ui/extend.stderr

@@ -0,0 +1,10 @@
+error: `extends` block must come first in a template
+ --> <source attribute>:2:2
+       " extends \"base.html\" %}\n"
+ --> tests/ui/extend.rs:5:14
+  |
+5 |       source = r##"bla
+  |  ______________^
+6 | | {% extends "base.html" %}
+7 | | "##,
+  | |___^

testing/tests/ui/multiple_extends.stderr

@@ -1,5 +1,5 @@
-error: multiple extend blocks found
- --> MyTemplate4.txt:3:2
+error: `extends` block must come first in a template
+ --> <source attribute>:3:2
        " extends \"foo.html\" %}\n"
  --> tests/ui/multiple_extends.rs:4:21
   |