Fix crash with delayed typo correction

[AaronBallman]

Delayed typo correction does not emit a diagnostic until the end of the
TU. However, codegen is run on each top-level declaration unless an
unrecoverable error occurred. The check for the diagnostic ensures that
CodeGen does not have to handle generating code for invalid constructs.

Due to typo correction delaying unrecoverable diagnostic emission until
the end of the TU, we would try to run CodeGen on invalid AST nodes and
that broke some invariants. Now, we specify that an unrecoverable error
will be emitted when emitting the delayed typo correction so that we
skip performing code generation.

Fixes #140461

[llvmbot]

@llvm/pr-subscribers-clang-codegen

@llvm/pr-subscribers-clang

Author: Aaron Ballman (AaronBallman)

Changes

Delayed typo correction does not emit a diagnostic until the end of the
TU. However, codegen is run on each top-level declaration unless an
unrecoverable error occurred. The check for the diagnostic ensures that
CodeGen does not have to handle generating code for invalid constructs.

Due to typo correction delaying unrecoverable diagnostic emission until
the end of the TU, we would try to run CodeGen on invalid AST nodes and
that broke some invariants. Now, we specify that an unrecoverable error
will be emitted when emitting the delayed typo correction so that we
skip performing code generation.

Fixes #140461

---

Full diff: https://github.com/llvm/llvm-project/pull/140571.diff

4 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+3)
• (modified) clang/include/clang/Basic/Diagnostic.h (+12)
• (modified) clang/lib/Sema/SemaLookup.cpp (+7)
• (added) clang/test/CodeGenCXX/typo-correction-delayed.cpp (+11)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 472b70b46fcc0..faa9c95211791 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -537,6 +537,9 @@ Improvements to Clang's diagnostics
   constant expression. Prior to this, the error inaccurately implied that assert
   could not be used at all in a constant expression (#GH130458)
 
+- No longer crashing during code generation due to delayed typo correction not
+  causing an unrecoverable error until the end of the translation unit. (#GH140461)
+
 - A new off-by-default warning ``-Wms-bitfield-padding`` has been added to alert to cases where bit-field
   packing may differ under the MS struct ABI (#GH117428).
 
diff --git a/clang/include/clang/Basic/Diagnostic.h b/clang/include/clang/Basic/Diagnostic.h
index 49ef22d4e4eb6..0e540fb2db346 100644
--- a/clang/include/clang/Basic/Diagnostic.h
+++ b/clang/include/clang/Basic/Diagnostic.h
@@ -861,6 +861,18 @@ class DiagnosticsEngine : public RefCountedBase<DiagnosticsEngine> {
 
   bool hasErrorOccurred() const { return ErrorOccurred; }
 
+  /// Sometimes we know an error will be produced at the end of a translation
+  /// unit, such as a delayed typo correction. However, CodeGen is run on each
+  /// top-level decl in an incremental fashion. We don't want CodeGen to run on
+  /// a declaration if an unrecoverable error occurred, but in those cases, the
+  /// error has not yet been emitted. This helper function lets you specify
+  /// that an unrecoverable error will occur later, specifically to ensure that
+  /// CodeGen is not run on those declarations.
+  void setUnrecoverableErrorWillOccur() {
+    UnrecoverableErrorOccurred = true;
+    ErrorOccurred = true;
+  }
+
   /// Errors that actually prevent compilation, not those that are
   /// upgraded from a warning by -Werror.
   bool hasUncompilableErrorOccurred() const {
diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index 29bf274f8a39f..f263feeda17a2 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -5419,6 +5419,13 @@ TypoExpr *Sema::CorrectTypoDelayed(
     TypoDiagnosticGenerator TDG, TypoRecoveryCallback TRC, CorrectTypoKind Mode,
     DeclContext *MemberContext, bool EnteringContext,
     const ObjCObjectPointerType *OPT) {
+
+  // A typo is an unrecoverable diagnostic. However, we sometimes perform code
+  // gen incrementally rather than waiting until the end of the TU, which means
+  // we want to tell the diagnostics engine that an unrecoverable error will
+  // occur eventually.
+  getDiagnostics().setUnrecoverableErrorWillOccur();
+
   auto Consumer = makeTypoCorrectionConsumer(
       TypoName, LookupKind, S, SS, CCC, MemberContext, EnteringContext, OPT,
       Mode == CorrectTypoKind::ErrorRecovery);
diff --git a/clang/test/CodeGenCXX/typo-correction-delayed.cpp b/clang/test/CodeGenCXX/typo-correction-delayed.cpp
new file mode 100644
index 0000000000000..3000e768fd163
--- /dev/null
+++ b/clang/test/CodeGenCXX/typo-correction-delayed.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -emit-llvm %s -verify -o /dev/null
+
+// Previously, delayed typo correction would cause a crash because codegen is
+// run on each top-level declaration as we finish with it unless an
+// unrecoverable error occured. However, with delayed typo correction, the
+// error is not emit until the end of the TU, so CodeGen would be run on
+// invalid declarations.
+namespace GH140461 {
+auto s{new auto(one)}; // expected-error {{use of undeclared identifier 'one'}}
+} // namespace GH140461
+

[AaronBallman]

Linux precommit CI failure looks to be unrelated. Given that this is an interaction between Sema and CodeGen, I'd like at least one approval from John or Eli before I land.

[cor3ntin]

Did you check if that fixes any of the other delayed typo issues?

[AaronBallman]

Did you check if that fixes any of the other delayed typo issues?

I suspect it might, but I'm currently working on a PR to disable delayed typo correction entirely with intent to remove the feature. When I work on that patch, I plan to check all the delayed typo related diagnostics at that point to ensure they'll all be closed once the feature is removed. At which point, this PR may not be necessary. So I'm going to hold off on landing this PR for now.