[clang] [Clang][Sema] Fix Wswitch-default bad warning in template (PR #76007)

[via cfe-commits]

https://github.com/hstk30-hw created https://github.com/llvm/llvm-project/pull/76007

Fix https://github.com/llvm/llvm-project/issues/75943

>From c3d5ac42726c49fd7036972042eb70d3e5dc01a6 Mon Sep 17 00:00:00 2001
From: hstk-hw <hanwei62 at huawei.com>
Date: Wed, 20 Dec 2023 12:26:15 +0800
Subject: [PATCH] fix: fix Wswitch-default bad warning in template

---
 clang/lib/Sema/SemaStmt.cpp                 |  4 +--
 clang/test/Sema/switch-default-template.cpp | 27 +++++++++++++++++++++
 2 files changed, 28 insertions(+), 3 deletions(-)
 create mode 100644 clang/test/Sema/switch-default-template.cpp

diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index 63348d27a8c94a..adc2055ec4e659 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -1327,9 +1327,6 @@ Sema::ActOnFinishSwitchStmt(SourceLocation SwitchLoc, Stmt *Switch,
     }
   }
 
-  if (!TheDefaultStmt)
-    Diag(SwitchLoc, diag::warn_switch_default);
-
   if (!HasDependentValue) {
     // If we don't have a default statement, check whether the
     // condition is constant.
@@ -1344,6 +1341,7 @@ Sema::ActOnFinishSwitchStmt(SourceLocation SwitchLoc, Stmt *Switch,
       assert(!HasConstantCond ||
              (ConstantCondValue.getBitWidth() == CondWidth &&
               ConstantCondValue.isSigned() == CondIsSigned));
+      Diag(SwitchLoc, diag::warn_switch_default);
     }
     bool ShouldCheckConstantCond = HasConstantCond;
 
diff --git a/clang/test/Sema/switch-default-template.cpp b/clang/test/Sema/switch-default-template.cpp
new file mode 100644
index 00000000000000..c671164bd785b0
--- /dev/null
+++ b/clang/test/Sema/switch-default-template.cpp
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 -Wswitch-default %s
+
+template<typename Index>
+int f1(Index i)
+{
+  switch (i) {              // expected-warning {{'switch' missing 'default' label}}
+    case 0: return 0;
+    case 1: return 1;
+  }
+  return 0;
+}
+
+template<typename Index>
+int f2(Index i)
+{
+  switch (i) {            // no-warning
+    case 0: return 0;
+    case 1: return 1;
+    default: return 2;
+  }
+  return 0;
+}
+
+int main() {
+  return f1(1);       // expected-note {{in instantiation of function template specialization 'f1<int>' requested here}}
+}
+