1 files changed, 205 insertions, 0 deletions
diff --git a/src/librustdoc/passes/check_code_block_syntax.rs b/src/librustdoc/passes/check_code_block_syntax.rs
new file mode 100644
index 000000000..0172ef570
--- /dev/null
+++ b/src/librustdoc/passes/check_code_block_syntax.rs
@@ -0,0 +1,205 @@
+//! Validates syntax inside Rust code blocks (\`\`\`rust).
+use rustc_data_structures::sync::{Lock, Lrc};
+use rustc_errors::{
+    emitter::Emitter, Applicability, Diagnostic, Handler, LazyFallbackBundle, LintDiagnosticBuilder,
+};
+use rustc_parse::parse_stream_from_source_str;
+use rustc_session::parse::ParseSess;
+use rustc_span::hygiene::{AstPass, ExpnData, ExpnKind, LocalExpnId};
+use rustc_span::source_map::{FilePathMapping, SourceMap};
+use rustc_span::{FileName, InnerSpan, DUMMY_SP};
+
+use crate::clean;
+use crate::core::DocContext;
+use crate::html::markdown::{self, RustCodeBlock};
+use crate::passes::Pass;
+use crate::visit::DocVisitor;
+
+pub(crate) const CHECK_CODE_BLOCK_SYNTAX: Pass = Pass {
+    name: "check-code-block-syntax",
+    run: check_code_block_syntax,
+    description: "validates syntax inside Rust code blocks",
+};
+
+pub(crate) fn check_code_block_syntax(
+    krate: clean::Crate,
+    cx: &mut DocContext<'_>,
+) -> clean::Crate {
+    SyntaxChecker { cx }.visit_crate(&krate);
+    krate
+}
+
+struct SyntaxChecker<'a, 'tcx> {
+    cx: &'a DocContext<'tcx>,
+}
+
+impl<'a, 'tcx> SyntaxChecker<'a, 'tcx> {
+    fn check_rust_syntax(&self, item: &clean::Item, dox: &str, code_block: RustCodeBlock) {
+        let buffer = Lrc::new(Lock::new(Buffer::default()));
+        let fallback_bundle =
+            rustc_errors::fallback_fluent_bundle(rustc_errors::DEFAULT_LOCALE_RESOURCES, false);
+        let emitter = BufferEmitter { buffer: Lrc::clone(&buffer), fallback_bundle };
+
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let handler = Handler::with_emitter(false, None, Box::new(emitter));
+        let source = dox[code_block.code].to_owned();
+        let sess = ParseSess::with_span_handler(handler, sm);
+
+        let edition = code_block.lang_string.edition.unwrap_or_else(|| self.cx.tcx.sess.edition());
+        let expn_data = ExpnData::default(
+            ExpnKind::AstPass(AstPass::TestHarness),
+            DUMMY_SP,
+            edition,
+            None,
+            None,
+        );
+        let expn_id =
+            self.cx.tcx.with_stable_hashing_context(|hcx| LocalExpnId::fresh(expn_data, hcx));
+        let span = DUMMY_SP.fresh_expansion(expn_id);
+
+        let is_empty = rustc_driver::catch_fatal_errors(|| {
+            parse_stream_from_source_str(
+                FileName::Custom(String::from("doctest")),
+                source,
+                &sess,
+                Some(span),
+            )
+            .is_empty()
+        })
+        .unwrap_or(false);
+        let buffer = buffer.borrow();
+
+        if !buffer.has_errors && !is_empty {
+            // No errors in a non-empty program.
+            return;
+        }
+
+        let Some(local_id) = item.item_id.as_def_id().and_then(|x| x.as_local())
+        else {
+            // We don't need to check the syntax for other crates so returning
+            // without doing anything should not be a problem.
+            return;
+        };
+
+        let hir_id = self.cx.tcx.hir().local_def_id_to_hir_id(local_id);
+        let empty_block = code_block.lang_string == Default::default() && code_block.is_fenced;
+        let is_ignore = code_block.lang_string.ignore != markdown::Ignore::None;
+
+        // The span and whether it is precise or not.
+        let (sp, precise_span) = match super::source_span_for_markdown_range(
+            self.cx.tcx,
+            dox,
+            &code_block.range,
+            &item.attrs,
+        ) {
+            Some(sp) => (sp, true),
+            None => (item.attr_span(self.cx.tcx), false),
+        };
+
+        // lambda that will use the lint to start a new diagnostic and add
+        // a suggestion to it when needed.
+        let diag_builder = |lint: LintDiagnosticBuilder<'_, ()>| {
+            let explanation = if is_ignore {
+                "`ignore` code blocks require valid Rust code for syntax highlighting; \
+                    mark blocks that do not contain Rust code as text"
+            } else {
+                "mark blocks that do not contain Rust code as text"
+            };
+            let msg = if buffer.has_errors {
+                "could not parse code block as Rust code"
+            } else {
+                "Rust code block is empty"
+            };
+            let mut diag = lint.build(msg);
+
+            if precise_span {
+                if is_ignore {
+                    // giving an accurate suggestion is hard because `ignore` might not have come first in the list.
+                    // just give a `help` instead.
+                    diag.span_help(
+                        sp.from_inner(InnerSpan::new(0, 3)),
+                        &format!("{}: ```text", explanation),
+                    );
+                } else if empty_block {
+                    diag.span_suggestion(
+                        sp.from_inner(InnerSpan::new(0, 3)).shrink_to_hi(),
+                        explanation,
+                        "text",
+                        Applicability::MachineApplicable,
+                    );
+                }
+            } else if empty_block || is_ignore {
+                diag.help(&format!("{}: ```text", explanation));
+            }
+
+            // FIXME(#67563): Provide more context for these errors by displaying the spans inline.
+            for message in buffer.messages.iter() {
+                diag.note(message);
+            }
+
+            diag.emit();
+        };
+
+        // Finally build and emit the completed diagnostic.
+        // All points of divergence have been handled earlier so this can be
+        // done the same way whether the span is precise or not.
+        self.cx.tcx.struct_span_lint_hir(
+            crate::lint::INVALID_RUST_CODEBLOCKS,
+            hir_id,
+            sp,
+            diag_builder,
+        );
+    }
+}
+
+impl<'a, 'tcx> DocVisitor for SyntaxChecker<'a, 'tcx> {
+    fn visit_item(&mut self, item: &clean::Item) {
+        if let Some(dox) = &item.attrs.collapsed_doc_value() {
+            let sp = item.attr_span(self.cx.tcx);
+            let extra = crate::html::markdown::ExtraInfo::new_did(
+                self.cx.tcx,
+                item.item_id.expect_def_id(),
+                sp,
+            );
+            for code_block in markdown::rust_code_blocks(dox, &extra) {
+                self.check_rust_syntax(item, dox, code_block);
+            }
+        }
+
+        self.visit_item_recur(item)
+    }
+}
+
+#[derive(Default)]
+struct Buffer {
+    messages: Vec<String>,
+    has_errors: bool,
+}
+
+struct BufferEmitter {
+    buffer: Lrc<Lock<Buffer>>,
+    fallback_bundle: LazyFallbackBundle,
+}
+
+impl Emitter for BufferEmitter {
+    fn emit_diagnostic(&mut self, diag: &Diagnostic) {
+        let mut buffer = self.buffer.borrow_mut();
+        // FIXME(davidtwco): need to support translation here eventually
+        buffer.messages.push(format!("error from rustc: {}", diag.message[0].0.expect_str()));
+        if diag.is_error() {
+            buffer.has_errors = true;
+        }
+    }
+
+    fn source_map(&self) -> Option<&Lrc<SourceMap>> {
+        None
+    }
+
+    fn fluent_bundle(&self) -> Option<&Lrc<rustc_errors::FluentBundle>> {
+        None
+    }
+
+    fn fallback_fluent_bundle(&self) -> &rustc_errors::FluentBundle {
+        &**self.fallback_bundle
+    }
+}