[Clang][Sema] Fix Wswitch-default bad warning in template

[hstk30-hw]

#73077 added -Wswitch-default diagnostic but it produced false positives in templates. This PR will address that. #75943

[llvmbot]

@llvm/pr-subscribers-clang

Author: None (hstk30-hw)

Changes

Fix #75943

---

Full diff: https://github.com/llvm/llvm-project/pull/76007.diff

2 Files Affected:

• (modified) clang/lib/Sema/SemaStmt.cpp (+1-3)
• (added) clang/test/Sema/switch-default-template.cpp (+27)

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}}
+}
+

[shafik]

Can you add more details to you summary e.g. "#73077 added -Wswitch-default diagnostic but it produced false positives in templates. This PR will address that issue"

[dongjianqiang2]

thanks for correcting this.

[cor3ntin]

LGTM, thanks

[aaronpuchert]

For now I guess this is Ok, although I think the better fix would be to diagnose missing or duplicate default labels even in the dependent case. Because default labels themselves are never dependent.

[shafik]

For now I guess this is Ok, although I think the better fix would be to diagnose missing or duplicate default labels even in the dependent case. Because default labels themselves are never dependent.

We should probably add a FIXME for this.

[dongjianqiang2]

LGTM, thanks

[github-actions]

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