[Serialization] Check for stack exhaustion when reading declarations (#79875)

Particular example that lead to this is a very long chain of
`UsingShadowDecl`s that we hit in our codebase in generated code.

To avoid that, check for stack exhaustion when deserializing the
declaration. At that point, we can point to source location of a
particular declaration that is being deserialized.

Author: ilya-biryukov

clang/include/clang/Serialization/ASTReader.h

@@ -429,6 +429,9 @@ class ASTReader
   FileManager &FileMgr;
   const PCHContainerReader &PCHContainerRdr;
   DiagnosticsEngine &Diags;
+  // Sema has duplicate logic, but SemaObj can sometimes be null so ASTReader
+  // has its own version.
+  bool WarnedStackExhausted = false;
 
   /// The semantic analysis object that will be processing the
   /// AST files and the translation unit that uses it.
@@ -2135,6 +2138,8 @@ class ASTReader
   /// Report a diagnostic.
   DiagnosticBuilder Diag(SourceLocation Loc, unsigned DiagID) const;
 
+  void warnStackExhausted(SourceLocation Loc);
+
   IdentifierInfo *DecodeIdentifierInfo(serialization::IdentifierID ID);
 
   IdentifierInfo *readIdentifier(ModuleFile &M, const RecordData &Record,

clang/lib/Serialization/ASTReader.cpp

@@ -44,6 +44,7 @@
 #include "clang/Basic/CommentOptions.h"
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Basic/DiagnosticError.h"
+#include "clang/Basic/DiagnosticIDs.h"
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/DiagnosticSema.h"
 #include "clang/Basic/ExceptionSpecificationType.h"
@@ -9404,6 +9405,20 @@ DiagnosticBuilder ASTReader::Diag(SourceLocation Loc, unsigned DiagID) const {
   return Diags.Report(Loc, DiagID);
 }
 
+void ASTReader::warnStackExhausted(SourceLocation Loc) {
+  // When Sema is available, avoid duplicate errors.
+  if (SemaObj) {
+    SemaObj->warnStackExhausted(Loc);
+    return;
+  }
+
+  if (WarnedStackExhausted)
+    return;
+  WarnedStackExhausted = true;
+
+  Diag(Loc, diag::warn_stack_exhausted);
+}
+
 /// Retrieve the identifier table associated with the
 /// preprocessor.
 IdentifierTable &ASTReader::getIdentifierTable() {

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -49,6 +49,7 @@
 #include "clang/Basic/PragmaKinds.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/Specifiers.h"
+#include "clang/Basic/Stack.h"
 #include "clang/Sema/IdentifierResolver.h"
 #include "clang/Serialization/ASTBitCodes.h"
 #include "clang/Serialization/ASTRecordReader.h"
@@ -4127,7 +4128,10 @@ Decl *ASTReader::ReadDeclRecord(GlobalDeclID ID) {
   // calls to Decl::getASTContext() by Decl's methods will find the
   // TranslationUnitDecl without crashing.
   D->setDeclContext(Context.getTranslationUnitDecl());
-  Reader.Visit(D);
+
+  // Reading some declarations can result in deep recursion.
+  clang::runWithSufficientStackSpace([&] { warnStackExhausted(DeclLoc); },
+                                     [&] { Reader.Visit(D); });
 
   // If this declaration is also a declaration context, get the
   // offsets for its tables of lexical and visible declarations.