parser: add better error messages for broken closing block tags

rinja_parser/src/lib.rs

@@ -12,10 +12,10 @@ use std::{fmt, str};
 
 use winnow::Parser;
 use winnow::ascii::escaped;
-use winnow::combinator::{alt, cut_err, delimited, fail, not, opt, preceded, repeat};
+use winnow::combinator::{alt, cut_err, delimited, fail, not, opt, peek, preceded, repeat};
 use winnow::error::{ErrorKind, FromExternalError};
 use winnow::stream::AsChar;
-use winnow::token::{any, one_of, tag, take_till0, take_till1, take_while};
+use winnow::token::{any, one_of, take_till0, take_till1, take_while};
 
 pub mod expr;
 pub use expr::{Expr, Filter};
@@ -666,28 +666,42 @@ impl<'a> State<'a> {
         ret
     }
 
-    fn tag_block_start<'i>(&self, i: &'i str) -> ParseResult<'i> {
-        tag(self.syntax.block_start).parse_next(i)
+    fn tag_block_start<'i>(&self, i: &'i str) -> ParseResult<'i, ()> {
+        self.syntax.block_start.value(()).parse_next(i)
     }
 
-    fn tag_block_end<'i>(&self, i: &'i str) -> ParseResult<'i> {
-        tag(self.syntax.block_end).parse_next(i)
+    fn tag_block_end<'i>(&self, i: &'i str) -> ParseResult<'i, ()> {
+        let (i, control) = alt((
+            self.syntax.block_end.value(None),
+            peek(delimited('%', alt(('-', '~', '+')).map(Some), '}')),
+            |_| fail(i), // rollback on partial matches in the previous line
+        ))
+        .parse_next(i)?;
+        if let Some(control) = control {
+            let message = format!(
+                "unclosed block, you likely meant to apply whitespace control: {:?}",
+                format!("{control}{}", self.syntax.block_end),
+            );
+            Err(ParseErr::backtrack(ErrorContext::new(message, i).into()))
+        } else {
+            Ok((i, ()))
+        }
     }
 
-    fn tag_comment_start<'i>(&self, i: &'i str) -> ParseResult<'i> {
-        tag(self.syntax.comment_start).parse_next(i)
+    fn tag_comment_start<'i>(&self, i: &'i str) -> ParseResult<'i, ()> {
+        self.syntax.comment_start.value(()).parse_next(i)
     }
 
-    fn tag_comment_end<'i>(&self, i: &'i str) -> ParseResult<'i> {
-        tag(self.syntax.comment_end).parse_next(i)
+    fn tag_comment_end<'i>(&self, i: &'i str) -> ParseResult<'i, ()> {
+        self.syntax.comment_end.value(()).parse_next(i)
     }
 
-    fn tag_expr_start<'i>(&self, i: &'i str) -> ParseResult<'i> {
-        tag(self.syntax.expr_start).parse_next(i)
+    fn tag_expr_start<'i>(&self, i: &'i str) -> ParseResult<'i, ()> {
+        self.syntax.expr_start.value(()).parse_next(i)
     }
 
-    fn tag_expr_end<'i>(&self, i: &'i str) -> ParseResult<'i> {
-        tag(self.syntax.expr_end).parse_next(i)
+    fn tag_expr_end<'i>(&self, i: &'i str) -> ParseResult<'i, ()> {
+        self.syntax.expr_end.value(()).parse_next(i)
     }
 
     fn enter_loop(&self) {

rinja_parser/src/node.rs

@@ -117,7 +117,7 @@ impl<'a> Node<'a> {
 
         let (i, closed) = cut_node(
             None,
-            alt(((|i| s.tag_block_end(i)).value(true), ws(eof).value(false))),
+            alt((ws(eof).value(false), (|i| s.tag_block_end(i)).value(true))),
         )
         .parse_next(i)?;
         match closed {
@@ -457,7 +457,7 @@ fn check_block_start<'a>(
     s: &State<'_>,
     node: &str,
     expected: &str,
-) -> ParseResult<'a> {
+) -> ParseResult<'a, ()> {
     if i.is_empty() {
         return Err(winnow::error::ErrMode::Cut(ErrorContext::new(
             format!("expected `{expected}` to terminate `{node}` node, found nothing"),

testing/tests/ui/garbled-closing-blocks.rs

@@ -0,0 +1,39 @@
+use rinja::Template;
+
+#[derive(Template)]
+#[template(ext = "txt", source = "{% if cond %-}{% endif %}")]
+struct BlockSuppress {
+    cond: bool,
+}
+
+#[derive(Template)]
+#[template(ext = "txt", source = "{% if cond %+}{% endif %}")]
+struct BlockPreserve {
+    cond: bool,
+}
+
+#[derive(Template)]
+#[template(ext = "txt", source = "{% if cond %~}{% endif %}")]
+struct BlockFold {
+    cond: bool,
+}
+
+#[derive(Template)]
+#[template(ext = "txt", source = "{% if cond %}{% endif %-}")]
+struct BlockSuppress2 {
+    cond: bool,
+}
+
+#[derive(Template)]
+#[template(ext = "txt", source = "{% if cond %}{% endif %+}")]
+struct BlockPreserve2 {
+    cond: bool,
+}
+
+#[derive(Template)]
+#[template(ext = "txt", source = "{% if cond %}{% endif %~}")]
+struct BlockFold2 {
+    cond: bool,
+}
+
+fn main() {}

testing/tests/ui/garbled-closing-blocks.stderr

@@ -0,0 +1,47 @@
+error: unclosed block, you likely meant to apply whitespace control: "-%}"
+ --> <source attribute>:1:11
+       "%-}{% endif %}"
+ --> tests/ui/garbled-closing-blocks.rs:4:34
+  |
+4 | #[template(ext = "txt", source = "{% if cond %-}{% endif %}")]
+  |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: unclosed block, you likely meant to apply whitespace control: "+%}"
+ --> <source attribute>:1:11
+       "%+}{% endif %}"
+  --> tests/ui/garbled-closing-blocks.rs:10:34
+   |
+10 | #[template(ext = "txt", source = "{% if cond %+}{% endif %}")]
+   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: unclosed block, you likely meant to apply whitespace control: "~%}"
+ --> <source attribute>:1:11
+       "%~}{% endif %}"
+  --> tests/ui/garbled-closing-blocks.rs:16:34
+   |
+16 | #[template(ext = "txt", source = "{% if cond %~}{% endif %}")]
+   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: unclosed block, you likely meant to apply whitespace control: "-%}"
+ --> <source attribute>:1:22
+       "%-}"
+  --> tests/ui/garbled-closing-blocks.rs:22:34
+   |
+22 | #[template(ext = "txt", source = "{% if cond %}{% endif %-}")]
+   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: unclosed block, you likely meant to apply whitespace control: "+%}"
+ --> <source attribute>:1:22
+       "%+}"
+  --> tests/ui/garbled-closing-blocks.rs:28:34
+   |
+28 | #[template(ext = "txt", source = "{% if cond %}{% endif %+}")]
+   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: unclosed block, you likely meant to apply whitespace control: "~%}"
+ --> <source attribute>:1:22
+       "%~}"
+  --> tests/ui/garbled-closing-blocks.rs:34:34
+   |
+34 | #[template(ext = "txt", source = "{% if cond %}{% endif %~}")]
+   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^