[clang] [clang] Extend -Wunused-but-set-variable to static globals (PR #178342)

[Yanzuo Liu via cfe-commits]

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@@ -1212,6 +1212,16 @@ class VarDecl : public DeclaratorDecl, public Redeclarable<VarDecl> {
       && !isFileVarDecl();
   }
 
+  /// Returns true if a variable is a static file-scope variable.
+  bool isStaticFileVar() const {
+    return isFileVarDecl() && getStorageClass() == SC_Static;
+  }
+
+  /// Returns true if this is a file-scope variable with internal linkage.
+  bool hasInternalLinkageFileVar() const {
+    return isFileVarDecl() && !isExternallyVisible() && !isStaticDataMember();
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zwuis wrote:

Does `isExternallyVisible()` handle static data members expectedly? If yes, could you please try to resolve the TODO comment in this PR now?

https://github.com/llvm/llvm-project/pull/178342