Auto merge of #53933 - GuillaumeGomez:codeblock-error-display, r=QuietMisdreavus

Improve error display for codeblocks in rustdoc

Part of #53919.

r? @QuietMisdreavus

1 files changed, 18 insertions, 7 deletions

diff --git a/src/librustdoc/html/highlight.rs b/src/librustdoc/html/highlight.rs
index 5df4862290e..87b4527a2a7 100644
--- a/src/librustdoc/html/highlight.rs
+++ b/src/librustdoc/html/highlight.rs
@@ -44,9 +44,21 @@ pub fn render_with_highlighting(src: &str, class: Option<&str>,
     }
     write_header(class, &mut out).unwrap();
 
-    let mut classifier = Classifier::new(lexer::StringReader::new(&sess, fm, None),
-                                         sess.source_map());
+    let lexer = match lexer::StringReader::new_without_err(&sess, fm, None, "Output from rustc:") {
+        Ok(l) => l,
+        Err(_) => {
+            let first_line = src.lines().next().unwrap_or_else(|| "");
+            let mut err = sess.span_diagnostic
+                              .struct_warn(&format!("Invalid doc comment starting with: `{}`\n\
+                                                     (Ignoring this codeblock)",
+                                                    first_line));
+            err.emit();
+            return String::new();
+        }
+    };
+    let mut classifier = Classifier::new(lexer, sess.source_map());
     if classifier.write_source(&mut out).is_err() {
+        classifier.lexer.emit_fatal_errors();
         return format!("<pre>{}</pre>", src);
     }
 
@@ -162,11 +174,10 @@ impl<'a> Classifier<'a> {
         match self.lexer.try_next_token() {
             Ok(tas) => Ok(tas),
             Err(_) => {
-                self.lexer.emit_fatal_errors();
-                self.lexer.sess.span_diagnostic
-                    .struct_warn("Backing out of syntax highlighting")
-                    .note("You probably did not intend to render this as a rust code-block")
-                    .emit();
+                let mut err = self.lexer.sess.span_diagnostic
+                                  .struct_warn("Backing out of syntax highlighting");
+                err.note("You probably did not intend to render this as a rust code-block");
+                err.emit();
                 Err(io::Error::new(io::ErrorKind::Other, ""))
             }
         }