[clang] [Clang][Sema] Fix crash when type used in return statement contains errors (PR #79788)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik created https://github.com/llvm/llvm-project/pull/79788

In Sema in `BuildReturnStmt(...)` when we try to determine is the type is move eligable or copy elidable we don't currently check of the init of the `VarDecl` contain errors or not. This can lead to a crash since we may send a type that is not complete into `getTypeInfo(...)` which does not allow this.

This fixes: https://github.com/llvm/llvm-project/issues/63244
https://github.com/llvm/llvm-project/issues/79745

>From 82d2561488a13edd9527737fbcc2391bb30a78e8 Mon Sep 17 00:00:00 2001
From: Shafik Yaghmour <shafik.yaghmour at intel.com>
Date: Sun, 28 Jan 2024 22:42:53 -0800
Subject: [PATCH] [Clang][Sema] Fix crash when type used in return statement
 contains errors

In Sema in `BuildReturnStmt(...)` when we try to determine is the type is move
eligable or copy elidable we don't currently check of the init of the `VarDecl`
contain errors or not. This can lead to a crash since we may send a type that
is not complete into `getTypeInfo(...)` which does not allow this.

This fixes: https://github.com/llvm/llvm-project/issues/63244
https://github.com/llvm/llvm-project/issues/79745
---
 clang/lib/Sema/SemaStmt.cpp                      | 2 ++
 clang/test/SemaCXX/deduced-return-type-cxx14.cpp | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index 9e7c8c7e4e8c12c..5d5a29b825ae7d7 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -3391,6 +3391,8 @@ Sema::NamedReturnInfo Sema::getNamedReturnInfo(Expr *&E,
   const auto *VD = dyn_cast<VarDecl>(DR->getDecl());
   if (!VD)
     return NamedReturnInfo();
+  if (VD->getInit() && VD->getInit()->containsErrors())
+    return NamedReturnInfo();
   NamedReturnInfo Res = getNamedReturnInfo(VD);
   if (Res.Candidate && !E->isXValue() &&
       (Mode == SimplerImplicitMoveMode::ForceOn ||
diff --git a/clang/test/SemaCXX/deduced-return-type-cxx14.cpp b/clang/test/SemaCXX/deduced-return-type-cxx14.cpp
index c0d43911b8c7174..415bbbf1a0bc509 100644
--- a/clang/test/SemaCXX/deduced-return-type-cxx14.cpp
+++ b/clang/test/SemaCXX/deduced-return-type-cxx14.cpp
@@ -724,3 +724,12 @@ struct DeducedTargetTypeOfConversionFunction {
   // since-cxx20-error at -1 {{'decltype(auto)' not allowed in declaration of conversion function template}}
 #endif
 };
+
+namespace GH79745 {
+template <typename = int> struct a; // expected-note {{template is declared here}}
+auto f() {
+  a c; // cxx20_23-error {{implicit instantiation of undefined template}} \
+       // cxx14-error {{use of class template 'a' requires template arguments}}
+  return c;
+}
+}