[clang] [clang-tools-extra] [llvm] [clang] WIP: Improved Context Declaration tracking (PR #107942)

[Matheus Izvekov via llvm-commits]

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@@ -17658,8 +17662,49 @@ HandleImmediateInvocations(Sema &SemaRef,
   }
 }
 
+static void setContextDecl(Sema &S, Decl *Base, Decl *ContextDecl) {
+  switch (Base->getKind()) {
+  case Decl::CXXRecord: {
+    auto *RD = cast<CXXRecordDecl>(Base);
+    RD->setLambdaContextDecl(ContextDecl);
+    S.handleLambdaNumbering(RD, RD->getLambdaCallOperator(),
+                            /*NumberingOverride=*/std::nullopt,
+                            /*InSignature=*/true);
+  } break;
+  case Decl::RequiresExprBody:
+    cast<RequiresExprBodyDecl>(Base)->setContextDecl(ContextDecl);
+    break;
+  default:
+    llvm_unreachable("Undexpected Decl Kind");
+  }
+}
+
+void Sema::UpdateCurrentContextDecl(Decl *ContextDecl) {
+  assert(ContextDecl);
+  ExpressionEvaluationContextRecord &Rec = ExprEvalContexts.back();
+  assert(!Rec.ContextDecl.hasValue());
+  assert(Rec.LazyContextDeclPos <= PendingLazyContextDecls.size());
+  Rec.ContextDecl = ContextDecl;
+  while (PendingLazyContextDecls.size() > Rec.LazyContextDeclPos)
+    setContextDecl(*this, PendingLazyContextDecls.pop_back_val(), ContextDecl);
+}
+
 void Sema::PopExpressionEvaluationContext() {
   ExpressionEvaluationContextRecord& Rec = ExprEvalContexts.back();
+  assert(Rec.LazyContextDeclPos <= PendingLazyContextDecls.size());
+  if (!Rec.HasReusedDeclContext) {
+    if (Rec.ContextDecl.hasValue()) {
+      assert(Rec.LazyContextDeclPos == PendingLazyContextDecls.size());
+    } else {
+      while (PendingLazyContextDecls.size() > Rec.LazyContextDeclPos) {
+        Decl *D = PendingLazyContextDecls.pop_back_val();
+        setContextDecl(*this, D, nullptr);
----------------
mizvekov wrote:

This is the error path. Basically we had a bunch of declarations waiting for their parents to be created, but for some reason we bailed out and we are never going to create their parents anymore.

Before this patch, these declarations would have stayed parented to their parent's parent.

These declarations would never make it to codegen, so don't matter much except for analysis.
The upside is that by staying as lazycontext entities, we don't lose track of their template depth.

https://github.com/llvm/llvm-project/pull/107942