[clang-tidy] Fix bugprone-incorrect-enable-if inserting duplicate typename

[localspook]

This PR resolves one of our FIXME's. Pre-C++20, this check turns

typename std::enable_if<...>

into

typename typename std::enable_if<...>::type

instead of

typename std::enable_if<...>::type

https://godbolt.org/z/4s4ozPsM3

[llvmbot]

@llvm/pr-subscribers-clang-tidy

@llvm/pr-subscribers-clang-tools-extra

Author: Victor Chernyakin (localspook)

Changes

This PR resolves one of our FIXME's. Pre-C++20, this check turns

typename std::enable_if<...>

into

typename typename std::enable_if<...>::type

instead of

typename std::enable_if<...>::type

---

Full diff: https://github.com/llvm/llvm-project/pull/190899.diff

3 Files Affected:

• (modified) clang-tools-extra/clang-tidy/bugprone/IncorrectEnableIfCheck.cpp (+4-5)
• (modified) clang-tools-extra/docs/ReleaseNotes.rst (+6)
• (modified) clang-tools-extra/test/clang-tidy/checkers/bugprone/incorrect-enable-if.cpp (+6)

diff --git a/clang-tools-extra/clang-tidy/bugprone/IncorrectEnableIfCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/IncorrectEnableIfCheck.cpp
index 6181ac84f36e3..5a592e10a599e 100644
--- a/clang-tools-extra/clang-tidy/bugprone/IncorrectEnableIfCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/IncorrectEnableIfCheck.cpp
@@ -47,8 +47,8 @@ void IncorrectEnableIfCheck::check(const MatchFinder::MatchResult &Result) {
       Result.Nodes.getNodeAs<TemplateSpecializationTypeLoc>(
           "enable_if_specialization");
 
-  if (!EnableIf || !EnableIfSpecializationLoc)
-    return;
+  assert(EnableIf);
+  assert(EnableIfSpecializationLoc);
 
   const SourceManager &SM = *Result.SourceManager;
   const SourceLocation RAngleLoc =
@@ -57,9 +57,8 @@ void IncorrectEnableIfCheck::check(const MatchFinder::MatchResult &Result) {
   auto Diag = diag(EnableIf->getBeginLoc(),
                    "incorrect std::enable_if usage detected; use "
                    "'typename std::enable_if<...>::type'");
-  // FIXME: This should handle the enable_if specialization already having an
-  // elaborated keyword.
-  if (!getLangOpts().CPlusPlus20) {
+  if (!getLangOpts().CPlusPlus20 &&
+      EnableIfSpecializationLoc->getElaboratedKeywordLoc().isInvalid()) {
     Diag << FixItHint::CreateInsertion(EnableIfSpecializationLoc->getBeginLoc(),
                                        "typename ");
   }
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index eb735e6e62ee4..4f5a219747bae 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -219,6 +219,12 @@ Changes in existing checks
   loss in overloads with transparent standard functors (e.g. ``std::plus<>``)
   for ``std::accumulate``, ``std::reduce``, and ``std::inner_product``.
 
+- Improved :doc:`bugprone-incorrect-enable-if
+  <clang-tidy/checks/bugprone/incorrect-enable-if>` check to not
+  insert an extraneous ``typename`` on code like
+  ``typename std::enable_if<...>``, where there's already a
+  ``typename`` and only the ``::type`` at the end is missing.
+
 - Improved :doc:`bugprone-inc-dec-in-conditions
   <clang-tidy/checks/bugprone/inc-dec-in-conditions>` check by fixing a false
   positive when increment/decrement operators appear inside lambda bodies that
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/incorrect-enable-if.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/incorrect-enable-if.cpp
index 0c418efe1420b..81612a50e5bbd 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/incorrect-enable-if.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/incorrect-enable-if.cpp
@@ -42,6 +42,12 @@ void invalid_multiple() {}
 // CHECK-FIXES: template <typename T, typename = typename std::enable_if<T::some_value>::type, typename = typename std::enable_if<T::other_value>::type>
 // CHECK-FIXES-CXX20: template <typename T, typename = std::enable_if<T::some_value>::type, typename = std::enable_if<T::other_value>::type>
 
+template <typename T, typename = typename std::enable_if<T::some_value>>
+void invalid_typename_keyword() {}
+// CHECK-MESSAGES: [[@LINE-2]]:23: warning: incorrect std::enable_if usage detected; use 'typename std::enable_if<...>::type' [bugprone-incorrect-enable-if]
+// CHECK-FIXES: template <typename T, typename = typename std::enable_if<T::some_value>::type>
+// CHECK-FIXES-CXX20: template <typename T, typename = typename std::enable_if<T::some_value>::type>
+
 template <typename T, typename = std::enable_if<T::some_value>>
 struct InvalidClass {};
 // CHECK-MESSAGES: [[@LINE-2]]:23: warning: incorrect std::enable_if usage detected; use 'typename std::enable_if<...>::type' [bugprone-incorrect-enable-if]

[vbvictor]

LGTM