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

[via cfe-commits]

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

>From d6c5cfe089b283b35660a48c5d056f44c65e2be4 Mon Sep 17 00:00:00 2001
From: hstk30-hw <hanwei62 at huawei.com>
Date: Wed, 20 Dec 2023 12:26:15 +0800
Subject: [PATCH] [Clang][Sema] Fix Wswitch-default bad warning in template

[#73077] added Wswitch-default diagnostic but it produced false
positives in templates. This PR address it.
---
 clang/lib/Sema/SemaStmt.cpp        |  6 ++--
 clang/test/Sema/switch-default.c   | 28 ----------------
 clang/test/Sema/switch-default.cpp | 53 ++++++++++++++++++++++++++++++
 3 files changed, 56 insertions(+), 31 deletions(-)
 delete mode 100644 clang/test/Sema/switch-default.c
 create mode 100644 clang/test/Sema/switch-default.cpp

diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index 63348d27a8c94a..f12a0af7744c1d 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -1271,6 +1271,8 @@ Sema::ActOnFinishSwitchStmt(SourceLocation SwitchLoc, Stmt *Switch,
 
   bool CaseListIsErroneous = false;
 
+  // FIXME: We'd better diagnose missing or duplicate default labels even
+  // in the dependent case. Because default labels themselves are never dependent.
   for (SwitchCase *SC = SS->getSwitchCaseList(); SC && !HasDependentValue;
        SC = SC->getNextSwitchCase()) {
 
@@ -1327,9 +1329,6 @@ 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 +1343,7 @@ 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.c b/clang/test/Sema/switch-default.c
deleted file mode 100644
index 342a97ee68b1e2..00000000000000
--- a/clang/test/Sema/switch-default.c
+++ /dev/null
@@ -1,28 +0,0 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -Wswitch-default %s
-
-int f1(int a) {
-  switch (a) {                // expected-warning {{'switch' missing 'default' label}}
-    case 1: a++; break;
-    case 2: a += 2; break;
-  }
-  return a;
-}
-
-int f2(int a) {
-  switch (a) {                // no-warning
-    default:
-      ;
-  }
-  return a;
-}
-
-// Warn even completely covered Enum cases(GCC compatibility).
-enum E { A, B };
-enum E check_enum(enum E e) {
-  switch (e) {                // expected-warning {{'switch' missing 'default' label}}
-    case A: break;
-    case B: break;
-  }
-  return e;
-}
-
diff --git a/clang/test/Sema/switch-default.cpp b/clang/test/Sema/switch-default.cpp
new file mode 100644
index 00000000000000..32d03dae882733
--- /dev/null
+++ b/clang/test/Sema/switch-default.cpp
@@ -0,0 +1,53 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 -Wswitch-default %s
+
+int f1(int a) {
+  switch (a) {                // expected-warning {{'switch' missing 'default' label}}
+    case 1: a++; break;
+    case 2: a += 2; break;
+  }
+  return a;
+}
+
+int f2(int a) {
+  switch (a) {                // no-warning
+    default:
+      ;
+  }
+  return a;
+}
+
+// Warn even completely covered Enum cases(GCC compatibility).
+enum E { A, B };
+enum E check_enum(enum E e) {
+  switch (e) {                // expected-warning {{'switch' missing 'default' label}}
+    case A: break;
+    case B: break;
+  }
+  return e;
+}
+
+template<typename Index>
+int t1(Index i)
+{
+  switch (i) {              // expected-warning {{'switch' missing 'default' label}}
+    case 0: return 0;
+    case 1: return 1;
+  }
+  return 0;
+}
+
+template<typename Index>
+int t2(Index i)
+{
+  switch (i) {            // no-warning
+    case 0: return 0;
+    case 1: return 1;
+    default: return 2;
+  }
+  return 0;
+}
+
+int main() {
+  return t1(1);       // expected-note {{in instantiation of function template specialization 't1<int>' requested here}}
+}
+