buffer lexer errors in rustdoc syntax checking

src/librustdoc/passes/check_code_block_syntax.rs

@@ -1,6 +1,7 @@
-use errors::Applicability;
+use errors::{emitter::Emitter, Applicability, Diagnostic, Handler};
+use rustc_data_structures::sync::{Lock, Lrc};
 use rustc_parse::lexer::StringReader as Lexer;
-use rustc_span::source_map::FilePathMapping;
+use rustc_span::source_map::{FilePathMapping, SourceMap};
 use rustc_span::{FileName, InnerSpan};
 use syntax::sess::ParseSess;
 use syntax::token;
@@ -27,7 +28,13 @@ struct SyntaxChecker<'a, 'tcx> {
 
 impl<'a, 'tcx> SyntaxChecker<'a, 'tcx> {
     fn check_rust_syntax(&self, item: &clean::Item, dox: &str, code_block: RustCodeBlock) {
-        let sess = ParseSess::new(FilePathMapping::empty());
+        let buffered_messages = Lrc::new(Lock::new(vec![]));
+
+        let emitter = BufferEmitter { messages: Lrc::clone(&buffered_messages) };
+
+        let cm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let handler = Handler::with_emitter(false, None, Box::new(emitter));
+        let sess = ParseSess::with_span_handler(handler, cm);
         let source_file = sess.source_map().new_source_file(
             FileName::Custom(String::from("doctest")),
             dox[code_block.code].to_owned(),
@@ -93,6 +100,11 @@ impl<'a, 'tcx> SyntaxChecker<'a, 'tcx> {
                 diag
             };
 
+            // FIXME(#67563): Provide more context for these errors by displaying the spans inline.
+            for message in buffered_messages.borrow().iter() {
+                diag.note(&message);
+            }
+
             diag.emit();
         }
     }
@@ -110,6 +122,20 @@ impl<'a, 'tcx> DocFolder for SyntaxChecker<'a, 'tcx> {
     }
 }
 
+struct BufferEmitter {
+    messages: Lrc<Lock<Vec<String>>>,
+}
+
+impl Emitter for BufferEmitter {
+    fn emit_diagnostic(&mut self, diag: &Diagnostic) {
+        self.messages.borrow_mut().push(format!("error from rustc: {}", diag.message[0].0));
+    }
+
+    fn source_map(&self) -> Option<&Lrc<SourceMap>> {
+        None
+    }
+}
+
 enum CodeBlockInvalid {
     SyntaxError,
     Empty,