[clang-tidy] Improved modernize-use-using by fixing a false-negative

The check needs a parent decl to match but if the typedef is in a function,
the parent is a declStmt which is not a decl by itself.
Improved the matcher to match on either a decl or a declstmt and extract
the decl from the stmt in the latter case.

fixes #72179

Author: felix642

clang-tools-extra/clang-tidy/modernize/UseUsingCheck.cpp

@@ -24,6 +24,7 @@ static constexpr llvm::StringLiteral ExternCDeclName = "extern-c-decl";
 static constexpr llvm::StringLiteral ParentDeclName = "parent-decl";
 static constexpr llvm::StringLiteral TagDeclName = "tag-decl";
 static constexpr llvm::StringLiteral TypedefName = "typedef";
+static constexpr llvm::StringLiteral DeclStmtName = "decl-stmt";
 
 UseUsingCheck::UseUsingCheck(StringRef Name, ClangTidyContext *Context)
     : ClangTidyCheck(Name, Context),
@@ -41,7 +42,8 @@ void UseUsingCheck::registerMatchers(MatchFinder *Finder) {
           unless(isInstantiated()),
           optionally(hasAncestor(
               linkageSpecDecl(isExternCLinkage()).bind(ExternCDeclName))),
-          hasParent(decl().bind(ParentDeclName)))
+          anyOf(hasParent(decl().bind(ParentDeclName)),
+                hasParent(declStmt().bind(DeclStmtName))))
           .bind(TypedefName),
       this);
 
@@ -51,17 +53,25 @@ void UseUsingCheck::registerMatchers(MatchFinder *Finder) {
       tagDecl(
           anyOf(allOf(unless(anyOf(isImplicit(),
                                    classTemplateSpecializationDecl())),
-                      hasParent(decl().bind(ParentDeclName))),
+                      anyOf(hasParent(decl().bind(ParentDeclName)),
+                            hasParent(declStmt().bind(DeclStmtName)))),
                 // We want the parent of the ClassTemplateDecl, not the parent
                 // of the specialization.
                 classTemplateSpecializationDecl(hasAncestor(classTemplateDecl(
-                    hasParent(decl().bind(ParentDeclName)))))))
+                    anyOf(hasParent(decl().bind(ParentDeclName)),
+                          hasParent(declStmt().bind(DeclStmtName))))))))
           .bind(TagDeclName),
       this);
 }
 
 void UseUsingCheck::check(const MatchFinder::MatchResult &Result) {
   const auto *ParentDecl = Result.Nodes.getNodeAs<Decl>(ParentDeclName);
+
+  if (!ParentDecl) {
+    const auto *ParentDeclStmt = Result.Nodes.getNodeAs<DeclStmt>(DeclStmtName);
+    ParentDecl = ParentDeclStmt->getSingleDecl();
+  }
+
   if (!ParentDecl)
     return;
 

clang-tools-extra/docs/ReleaseNotes.rst

@@ -183,6 +183,9 @@ Changes in existing checks
   <clang-tidy/checks/modernize/use-override>` check to also remove any trailing
   whitespace when deleting the ``virtual`` keyword.
 
+- Improved :doc:`modernize-use-using <clang-tidy/checks/modernize/use-using>`
+  check by fixing false-negative in functions.
+
 - Improved :doc:`readability-implicit-bool-conversion
   <clang-tidy/checks/readability/implicit-bool-conversion>` check to provide
   valid fix suggestions for ``static_cast`` without a preceding space and

clang-tools-extra/test/clang-tidy/checkers/modernize/use-using.cpp

@@ -342,3 +342,21 @@ typedef int InExternCPP;
 // CHECK-FIXES: using InExternCPP = int;
 
 }
+
+namespace ISSUE_72179
+{  
+  void foo()
+  {
+    typedef int a;
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: use 'using' instead of 'typedef' [modernize-use-using]
+    // CHECK-FIXES: using a = int;
+
+  }
+
+  void foo2()
+  {
+    typedef struct { int a; union { int b; }; } c;
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: use 'using' instead of 'typedef' [modernize-use-using]
+    // CHECK-FIXES: using c = struct { int a; union { int b; }; };
+  }
+}