[clang] Fix assert() crash when checking undeduced arg alignment

There already was a check for undeduced and incomplete types, but it
failed to trigger when outer type (SubstTemplateTypeParm in test) looked
fine, but inner type was not.

Differential Revision: https://reviews.llvm.org/D100667

clang/lib/Sema/SemaChecking.cpp

@@ -4540,8 +4540,7 @@ void Sema::CheckArgAlignment(SourceLocation Loc, NamedDecl *FDecl,
 
   // Find expected alignment, and the actual alignment of the passed object.
   // getTypeAlignInChars requires complete types
-  if (ParamTy->isIncompleteType() || ArgTy->isIncompleteType() ||
-      ParamTy->isUndeducedType() || ArgTy->isUndeducedType())
+  if (ParamTy->isIncompleteType() || ArgTy->isIncompleteType())
     return;
 
   CharUnits ParamAlign = Context.getTypeAlignInChars(ParamTy);

clang/lib/Sema/SemaExpr.cpp

@@ -19662,8 +19662,10 @@ ExprResult Sema::CreateRecoveryExpr(SourceLocation Begin, SourceLocation End,
   if (isSFINAEContext())
     return ExprError();
 
-  if (T.isNull() || !Context.getLangOpts().RecoveryASTType)
+  if (T.isNull() || T->isUndeducedType() ||
+      !Context.getLangOpts().RecoveryASTType)
     // We don't know the concrete type, fallback to dependent type.
     T = Context.DependentTy;
+
   return RecoveryExpr::Create(Context, T, Begin, End, SubExprs);
 }

clang/test/SemaCXX/recovery-expr-type.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple=x86_64-unknown-unknown -frecovery-ast -frecovery-ast-type -o - %s -fsyntax-only -verify
+// RUN: %clang_cc1 -triple=x86_64-unknown-unknown -frecovery-ast -frecovery-ast-type -o - %s -std=gnu++17 -fsyntax-only -verify
 
 namespace test0 {
 struct Indestructible {
@@ -26,7 +26,7 @@ namespace test2 {
 void foo(); // expected-note 3{{requires 0 arguments}}
 void func() {
   // verify that "field has incomplete type" diagnostic is suppressed.
-  typeof(foo(42)) var; // expected-error {{no matching function}}
+  typeof(foo(42)) var; // expected-error {{no matching function}} \
 
   // FIXME: suppress the "cannot initialize a variable" diagnostic.
   int a = foo(1); // expected-error {{no matching function}} \
@@ -116,3 +116,23 @@ int f(); // expected-note {{candidate}}
 template<typename T> const int k = f(T()); // expected-error {{no matching function}}
 static_assert(k<int> == 1, ""); // expected-note {{instantiation of}}
 }
+
+namespace test11 {
+// Verify we do not assert()-fail here.
+template <class T> void foo(T &t);
+template <typename T>
+void bar(T t) {
+  foo(t);
+}
+
+template <typename T = void *>
+struct S { // expected-note {{candidate}}
+  S(T t);  // expected-note {{candidate}}
+  ~S();
+};
+template <typename T> S(T t) -> S<void *>;
+
+void baz() {
+  bar(S(123)); // expected-error {{no matching conversion}}
+}
+} // namespace test11