[clang][Sema] Preserve the initializer of invalid VarDecls (#88645)

Fixes clangd/clangd#1821

Author: HighCommander4

clang/lib/Sema/JumpDiagnostics.cpp

@@ -180,7 +180,8 @@ static ScopePair GetDiagForGotoScopeDecl(Sema &S, const Decl *D) {
     }
 
     const Expr *Init = VD->getInit();
-    if (S.Context.getLangOpts().CPlusPlus && VD->hasLocalStorage() && Init) {
+    if (S.Context.getLangOpts().CPlusPlus && VD->hasLocalStorage() && Init &&
+        !Init->containsErrors()) {
       // C++11 [stmt.dcl]p3:
       //   A program that jumps from a point where a variable with automatic
       //   storage duration is not in scope to a point where it is in scope

clang/lib/Sema/SemaDecl.cpp

@@ -13502,16 +13502,18 @@ void Sema::checkNonTrivialCUnion(QualType QT, SourceLocation Loc,
 void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
   // If there is no declaration, there was an error parsing it.  Just ignore
   // the initializer.
-  if (!RealDecl || RealDecl->isInvalidDecl()) {
+  if (!RealDecl) {
     CorrectDelayedTyposInExpr(Init, dyn_cast_or_null<VarDecl>(RealDecl));
     return;
   }
 
-  if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(RealDecl)) {
-    // Pure-specifiers are handled in ActOnPureSpecifier.
-    Diag(Method->getLocation(), diag::err_member_function_initialization)
-      << Method->getDeclName() << Init->getSourceRange();
-    Method->setInvalidDecl();
+  if (auto *Method = dyn_cast<CXXMethodDecl>(RealDecl)) {
+    if (!Method->isInvalidDecl()) {
+      // Pure-specifiers are handled in ActOnPureSpecifier.
+      Diag(Method->getLocation(), diag::err_member_function_initialization)
+          << Method->getDeclName() << Init->getSourceRange();
+      Method->setInvalidDecl();
+    }
     return;
   }
 
@@ -13523,6 +13525,15 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
     return;
   }
 
+  if (VDecl->isInvalidDecl()) {
+    CorrectDelayedTyposInExpr(Init, VDecl);
+    ExprResult Recovery =
+        CreateRecoveryExpr(Init->getBeginLoc(), Init->getEndLoc(), {Init});
+    if (Expr *E = Recovery.get())
+      VDecl->setInit(E);
+    return;
+  }
+
   // WebAssembly tables can't be used to initialise a variable.
   if (Init && !Init->getType().isNull() &&
       Init->getType()->isWebAssemblyTableType()) {

clang/test/AST/ast-dump-recovery.cpp

@@ -413,6 +413,14 @@ void RecoveryExprForInvalidDecls(Unknown InvalidDecl) {
   // CHECK-NEXT: `-RecoveryExpr {{.*}} '<dependent type>'
 }
 
+void InitializerOfInvalidDecl() {
+  int ValidDecl;
+  Unkown InvalidDecl = ValidDecl;
+  // CHECK:      VarDecl {{.*}} invalid InvalidDecl
+  // CHECK-NEXT: `-RecoveryExpr {{.*}} '<dependent type>' contains-errors
+  // CHECK-NEXT:   `-DeclRefExpr {{.*}} 'int' lvalue Var {{.*}} 'ValidDecl'
+}
+
 void RecoverToAnInvalidDecl() {
   Unknown* foo; // invalid decl
   goo; // the typo was correct to the invalid foo.