Add 'refersToPack' AST matcher

[hach-que]

This adds a 'refersToPack' AST matcher, which can be used to match against template arguments that are inside parameter packs. The inner matcher is evaluated against each argument in the parameter pack, such that given:

template<typename T, typename... Params> class A {};
A<int, double> a;
A<double, int> b;
A<double, int, long> c;

The matcher classTemplateSpecializationDecl(hasAnyTemplateArgument(refersToPack(refersToType(...)))) would evaluate the refersToType against:

• For a, the double template argument.
• For b, the int template argument.
• For c, the int template argument, then the long template argument.

If the inner matcher matches against any argument of the parameter pack, then refersToPack matches.

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[llvmbot]

@llvm/pr-subscribers-clang

Author: June Rhodes (hach-que)

Changes

This adds a 'refersToPack' AST matcher, which can be used to match against template arguments that are inside parameter packs. The inner matcher is evaluated against each argument in the parameter pack, such that given:

template<typename T, typename... Params> class A {};
A<int, double> a;
A<double, int> b;
A<double, int, long> c;

The matcher classTemplateSpecializationDecl(hasAnyTemplateArgument(refersToPack(refersToType(...)))) would evaluate the refersToType against:

• For a, the double template argument.
• For b, the int template argument.
• For c, the int template argument, then the long template argument.

If the inner matcher matches against any argument of the parameter pack, then refersToPack matches.

---

Full diff: https://github.com/llvm/llvm-project/pull/86228.diff

2 Files Affected:

• (modified) clang/include/clang/ASTMatchers/ASTMatchers.h (+29)
• (modified) clang/lib/ASTMatchers/Dynamic/Registry.cpp (+1)

diff --git a/clang/include/clang/ASTMatchers/ASTMatchers.h b/clang/include/clang/ASTMatchers/ASTMatchers.h
index 2f71053d030f68..df30d4c85c22c6 100644
--- a/clang/include/clang/ASTMatchers/ASTMatchers.h
+++ b/clang/include/clang/ASTMatchers/ASTMatchers.h
@@ -1151,6 +1151,35 @@ AST_MATCHER_P(TemplateArgument, refersToDeclaration,
   return false;
 }
 
+/// Matches template arguments within a pack template argument; the inner
+/// matcher is compared against each argument of the parameter pack.
+///
+/// Given
+/// \code
+///   template<typename T, typename... Params> class A {};
+///   A<int, double> a;
+///   A<double, int> b;
+/// \endcode
+///
+/// \endcode
+/// classTemplateSpecializationDecl(hasAnyTemplateArgument(
+///     refersToPack(refersToType(asString("double")))))
+///   matches the specialization \c A<int, double>
+///   but does not match the specialization \c A<double, int>
+AST_MATCHER_P(TemplateArgument, refersToPack,
+              internal::Matcher<TemplateArgument>, InnerMatcher) {
+  if (Node.getKind() == TemplateArgument::Pack) {
+    for (const TemplateArgument &Arg : Node.pack_elements()) {
+      BoundNodesTreeBuilder Result(*Builder);
+      if (InnerMatcher.matches(Arg, Finder, &Result)) {
+        *Builder = std::move(Result);
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
 /// Matches a sugar TemplateArgument that refers to a certain expression.
 ///
 /// Given
diff --git a/clang/lib/ASTMatchers/Dynamic/Registry.cpp b/clang/lib/ASTMatchers/Dynamic/Registry.cpp
index 2c75e6beb74301..732d49e850288a 100644
--- a/clang/lib/ASTMatchers/Dynamic/Registry.cpp
+++ b/clang/lib/ASTMatchers/Dynamic/Registry.cpp
@@ -551,6 +551,7 @@ RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(referenceType);
   REGISTER_MATCHER(referenceTypeLoc);
   REGISTER_MATCHER(refersToDeclaration);
+  REGISTER_MATCHER(refersToPack);
   REGISTER_MATCHER(refersToIntegralType);
   REGISTER_MATCHER(refersToTemplate);
   REGISTER_MATCHER(refersToType);