[clang-repl] Names declared in if conditions and for-init statements are local to the inner context (#84150)

Make TopLevelStmtDecl a DeclContext so that variables defined in statements
are attached to the TopLevelDeclContext. This fixes redefinition errors
from variables declared in if conditions and for-init statements. These
must be local to the inner context (C++ 3.3.2p4), but they had generated
definitions on global scope instead.

This PR makes the TopLevelStmtDecl looking more like a FunctionDecl and
that's fine because the FunctionDecl is very close in terms of semantics.

Additionally, ActOnForStmt() requires a CompoundScope when processing a
NullStmt body.

---------

Co-authored-by: Vassil Vassilev <v.g.vassilev@gmail.com>

1 files changed, 13 insertions, 3 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 6b81ee1..67e56a9 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -20519,12 +20519,22 @@ Decl *Sema::ActOnFileScopeAsmDecl(Expr *expr,
   return New;
 }
 
-Decl *Sema::ActOnTopLevelStmtDecl(Stmt *Statement) {
-  auto *New = TopLevelStmtDecl::Create(Context, Statement);
-  Context.getTranslationUnitDecl()->addDecl(New);
+TopLevelStmtDecl *Sema::ActOnStartTopLevelStmtDecl(Scope *S) {
+  auto *New = TopLevelStmtDecl::Create(Context, /*Statement=*/nullptr);
+  CurContext->addDecl(New);
+  PushDeclContext(S, New);
+  PushFunctionScope();
+  PushCompoundScope(false);
   return New;
 }
 
+void Sema::ActOnFinishTopLevelStmtDecl(TopLevelStmtDecl *D, Stmt *Statement) {
+  D->setStmt(Statement);
+  PopCompoundScope();
+  PopFunctionScopeInfo();
+  PopDeclContext();
+}
+
 void Sema::ActOnPragmaRedefineExtname(IdentifierInfo* Name,
                                       IdentifierInfo* AliasName,
                                       SourceLocation PragmaLoc,