[Sema] Allow warnStackExhausted to show more info

[Mordante]

Summary

This allows the caller of the function to add a note about how to fix the stack exhaustion. This can be useful to aid the user. For example it can be used to show a help message for https://bugs.llvm.org/show_bug.cgi?id=14030

[xbolva00]

Exact use case? Test?

[Mordante]

The use case and its test are in D69479. Is that sufficient?

[xbolva00]

Yes, thanks!

[aaron.ballman]

I sort of feel like we don't want to go this route because we want to avoid calling runWithSufficientStackSpace whenever possible, but I am not strongly opposed to this patch. It should be combined with the usage of the new functionality, however, so that it gets adequate test coverage.

[Mordante]

@rsmith also doesn't like the approach runWithSufficientStackSpace in D69479. So I'll try to use a different approach. If that succeeds I have no use case for this patch and will probably abandon it.

clang/include/clang/Sema/Sema.h

public:
   ///
   ///\param[in] E - A non-null external sema source.
   ///
   void addExternalSource(ExternalSemaSource *E);
 
   void PrintStats() const;
 
   /// Warn that the stack is nearly exhausted.
-  void warnStackExhausted(SourceLocation Loc);
+  /// \param NoteDiagID Extra information of the user how to resolve the issue.
+  void warnStackExhausted(SourceLocation Loc, unsigned NoteDiagID = 0);
 
   /// Run some code with "sufficient" stack space. (Currently, at least 256K is
   /// guaranteed). Produces a warning if we're low on stack space and allocates
   /// more in that case. Use this in code that may recurse deeply (for example,
   /// in template instantiation) to avoid stack overflow.
+  /// \param NoteDiagID Extra information of the user how to resolve the issue.
   void runWithSufficientStackSpace(SourceLocation Loc,
-                                   llvm::function_ref<void()> Fn);
+                                   llvm::function_ref<void()> Fn,
+                                   unsigned NoteDiagID = 0);
 
   /// Helper class that creates diagnostics with optional
   /// template instantiation stacks.
   ///
   /// This class provides a wrapper around the basic DiagnosticBuilder
   /// class that emits diagnostics. SemaDiagnosticBuilder is
   /// responsible for emitting the diagnostic (as DiagnosticBuilder
   /// does) and, if the diagnostic comes from inside a template

clang/lib/Sema/Sema.cpp

Sema::~Sema() {
   // Destroys data sharing attributes stack for OpenMP
   DestroyDataSharingAttributesStack();
 
   // Detach from the PP callback handler which outlives Sema since it's owned
   // by the preprocessor.
   SemaPPCallbackHandler->reset();
 }
 
-void Sema::warnStackExhausted(SourceLocation Loc) {
+void Sema::warnStackExhausted(SourceLocation Loc, unsigned NoteDiagID) {
   // Only warn about this once.
   if (!WarnedStackExhausted) {
     Diag(Loc, diag::warn_stack_exhausted);
+    if (NoteDiagID)
+      Diag(Loc, NoteDiagID);
     WarnedStackExhausted = true;
   }
 }
 
 void Sema::runWithSufficientStackSpace(SourceLocation Loc,
-                                       llvm::function_ref<void()> Fn) {
-  clang::runWithSufficientStackSpace([&] { warnStackExhausted(Loc); }, Fn);
+                                       llvm::function_ref<void()> Fn,
+                                       unsigned NoteDiagID) {
+  clang::runWithSufficientStackSpace(
+      [&] { warnStackExhausted(Loc, NoteDiagID); }, Fn);
 }
 
 /// makeUnavailableInSystemHeader - There is an error in the current
 /// context.  If we're still in a system header, and we can plausibly
 /// make the relevant declaration unavailable instead of erroring, do
 /// so and return true.
 bool Sema::makeUnavailableInSystemHeader(SourceLocation loc,
                                       UnavailableAttr::ImplicitReason reason) {