rustdoc: Catch fatal errors when syntax highlighting

For some errors the lexer will unwind so we need to handle that in addition to handling `token::Unknown`.

src/librustdoc/html/highlight.rs

@@ -41,7 +41,7 @@ pub fn render_with_highlighting(
     let fm = sess
         .source_map()
         .new_source_file(FileName::Custom(String::from("rustdoc-highlighting")), src.to_owned());
-    let highlight_result = {
+    let highlight_result = rustc_driver::catch_fatal_errors(|| {
         let lexer = lexer::StringReader::new(&sess, fm, None);
         let mut classifier = Classifier::new(lexer, sess.source_map());
 
@@ -51,7 +51,8 @@ pub fn render_with_highlighting(
         } else {
             Ok(String::from_utf8_lossy(&highlighted_source).into_owned())
         }
-    };
+    })
+    .unwrap_or(Err(()));
 
     match highlight_result {
         Ok(highlighted_source) => {

src/librustdoc/passes/check_code_block_syntax.rs

@@ -40,7 +40,7 @@ impl<'a, 'tcx> SyntaxChecker<'a, 'tcx> {
             dox[code_block.code].to_owned(),
         );
 
-        let validation_status = {
+        let validation_status = rustc_driver::catch_fatal_errors(|| {
             let mut has_syntax_errors = false;
             let mut only_whitespace = true;
             // even if there is a syntax error, we need to run the lexer over the whole file
@@ -61,7 +61,8 @@ impl<'a, 'tcx> SyntaxChecker<'a, 'tcx> {
             } else {
                 None
             }
-        };
+        })
+        .unwrap_or(Some(CodeBlockInvalid::SyntaxError));
 
         if let Some(code_block_invalid) = validation_status {
             let mut diag = if let Some(sp) =

src/test/rustdoc-ui/invalid-syntax.rs

@@ -93,3 +93,9 @@ pub fn empty_rust_with_whitespace() {}
 ///
 pub fn indent_after_fenced() {}
 //~^^^ WARNING could not parse code block as Rust code
+
+/// ```
+/// "invalid
+/// ```
+pub fn invalid() {}
+//~^^^^ WARNING could not parse code block as Rust code

src/test/rustdoc-ui/invalid-syntax.stderr

@@ -132,3 +132,18 @@ LL | ///     \____/
    |
    = note: error from rustc: unknown start of token: \
 
+warning: could not parse code block as Rust code
+  --> $DIR/invalid-syntax.rs:97:5
+   |
+LL |   /// ```
+   |  _____^
+LL | | /// "invalid
+LL | | /// ```
+   | |_______^
+   |
+   = note: error from rustc: unterminated double quote string
+help: mark blocks that do not contain Rust code as text
+   |
+LL | /// ```text
+   |     ^^^^^^^
+

src/test/rustdoc/bad-codeblock-syntax.rs

@@ -33,3 +33,10 @@ pub fn ok() {}
 /// <script>alert("not valid Rust");</script>
 /// ```
 pub fn escape() {}
+
+// @has bad_codeblock_syntax/fn.unterminated.html
+// @has - '//*[@class="docblock"]/pre/code' '"unterminated'
+/// ```
+/// "unterminated
+/// ```
+pub fn unterminated() {}