[PATCH] D73876: [clang-tidy] Fix a false positive about C++17 deduced class template types in unused-using-decl check.

[Haojian Wu via Phabricator via cfe-commits]

hokein created this revision.
hokein added a reviewer: gribozavr2.
Herald added a subscriber: xazax.hun.
Herald added a project: clang.

Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73876

Files:
  clang-tools-extra/clang-tidy/misc/UnusedUsingDeclsCheck.cpp
  clang-tools-extra/test/clang-tidy/checkers/misc-unused-using-decls-cxx17.cpp


Index: clang-tools-extra/test/clang-tidy/checkers/misc-unused-using-decls-cxx17.cpp
===================================================================
--- /dev/null
+++ clang-tools-extra/test/clang-tidy/checkers/misc-unused-using-decls-cxx17.cpp
@@ -0,0 +1,31 @@
+// RUN: %check_clang_tidy -std=c++17-or-later %s misc-unused-using-decls %t --
+// -- -fno-delayed-template-parsing -isystem %S/Inputs/
+
+namespace ns {
+
+template <typename T> class Foo {
+public:
+  Foo(T);
+};
+// Deduction hint (CTAD)
+template <typename T> Foo(T t) -> Foo<T>;
+
+template <typename T> class Bar {
+public:
+  Bar(T);
+};
+
+template <typename T> class Unused {};
+
+} // namespace ns
+
+using ns::Bar;
+using ns::Foo;
+using ns::Unused; // Unused
+// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: using decl 'Unused' is unused
+// CHECK-FIXES: {{^}}// Unused
+
+void f() {
+  Foo(123);
+  Bar(1);
+}
Index: clang-tools-extra/clang-tidy/misc/UnusedUsingDeclsCheck.cpp
===================================================================
--- clang-tools-extra/clang-tidy/misc/UnusedUsingDeclsCheck.cpp
+++ clang-tools-extra/clang-tidy/misc/UnusedUsingDeclsCheck.cpp
@@ -38,6 +38,13 @@
   *Builder = std::move(Result);
   return Matched;
 }
+
+AST_MATCHER_P(DeducedTemplateSpecializationType, refsToTemplatedDecl,
+              clang::ast_matchers::internal::Matcher<NamedDecl>, DeclMatcher) {
+  if (const auto *TD = Node.getTemplateName().getAsTemplateDecl())
+    return DeclMatcher.matches(*TD, Finder, Builder);
+  return false;
+}
 } // namespace
 
 // A function that helps to tell whether a TargetDecl in a UsingDecl will be
@@ -56,6 +63,9 @@
   Finder->addMatcher(loc(enumType(DeclMatcher)), this);
   Finder->addMatcher(loc(recordType(DeclMatcher)), this);
   Finder->addMatcher(loc(templateSpecializationType(DeclMatcher)), this);
+  Finder->addMatcher(loc(deducedTemplateSpecializationType(
+                         refsToTemplatedDecl(namedDecl().bind("used")))),
+                     this);
   Finder->addMatcher(declRefExpr().bind("used"), this);
   Finder->addMatcher(callExpr(callee(unresolvedLookupExpr().bind("used"))),
                      this);


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