add test and doc

Author: HerrCai0907

clang/docs/LibASTMatchersReference.html

@@ -4108,8 +4108,14 @@ <h2 id="narrowing-matchers">Narrowing Matchers</h2>
 Given
   template&lt;typename T&gt; struct C {};
   C&lt;int&gt; c;
+  template&lt;typename T&gt; void f() {}
+  void func() { f&lt;int&gt;(); };
+
 classTemplateSpecializationDecl(templateArgumentCountIs(1))
   matches C&lt;int&gt;.
+
+functionDecl(templateArgumentCountIs(1))
+  matches f&lt;int&gt;();
 </pre></td></tr>
 
 
@@ -4839,8 +4845,14 @@ <h2 id="narrowing-matchers">Narrowing Matchers</h2>
 Given
   template&lt;typename T&gt; struct C {};
   C&lt;int&gt; c;
+  template&lt;typename T&gt; void f() {}
+  void func() { f&lt;int&gt;(); };
+
 classTemplateSpecializationDecl(templateArgumentCountIs(1))
   matches C&lt;int&gt;.
+
+functionDecl(templateArgumentCountIs(1))
+  matches f&lt;int&gt;();
 </pre></td></tr>
 
 
@@ -5800,8 +5812,14 @@ <h2 id="narrowing-matchers">Narrowing Matchers</h2>
 Given
   template&lt;typename T&gt; struct C {};
   C&lt;int&gt; c;
+  template&lt;typename T&gt; void f() {}
+  void func() { f&lt;int&gt;(); };
+
 classTemplateSpecializationDecl(templateArgumentCountIs(1))
   matches C&lt;int&gt;.
+
+functionDecl(templateArgumentCountIs(1))
+  matches f&lt;int&gt;();
 </pre></td></tr>
 
 
@@ -6237,8 +6255,14 @@ <h2 id="narrowing-matchers">Narrowing Matchers</h2>
 Given
   template&lt;typename T&gt; struct C {};
   C&lt;int&gt; c;
+  template&lt;typename T&gt; void f() {}
+  void func() { f&lt;int&gt;(); };
+
 classTemplateSpecializationDecl(templateArgumentCountIs(1))
   matches C&lt;int&gt;.
+
+functionDecl(templateArgumentCountIs(1))
+  matches f&lt;int&gt;();
 </pre></td></tr>
 
 <!--END_NARROWING_MATCHERS -->

clang/docs/ReleaseNotes.rst

@@ -395,6 +395,8 @@ AST Matchers
 ------------
 
 - Ensure ``isDerivedFrom`` matches the correct base in case more than one alias exists.
+- Extend ``templateArgumentCountIs`` to support function and variable template
+  specialization.
 
 clang-format
 ------------

clang/include/clang/ASTMatchers/ASTMatchers.h

@@ -1084,9 +1084,15 @@ AST_POLYMORPHIC_MATCHER_P2(
 /// \code
 ///   template<typename T> struct C {};
 ///   C<int> c;
+///   template<typename T> void f() {}
+///   void func() { f<int>(); };
 /// \endcode
+///
 /// classTemplateSpecializationDecl(templateArgumentCountIs(1))
 ///   matches C<int>.
+///
+/// functionDecl(templateArgumentCountIs(1))
+///   matches f<int>();
 AST_POLYMORPHIC_MATCHER_P(
     templateArgumentCountIs,
     AST_POLYMORPHIC_SUPPORTED_TYPES(ClassTemplateSpecializationDecl,

clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp

@@ -2028,6 +2028,13 @@ TEST_P(ASTMatchersTest, TemplateArgumentCountIs) {
   EXPECT_TRUE(
       notMatches("template<typename T> struct C {}; C<int> c;",
                  templateSpecializationType(templateArgumentCountIs(2))));
+
+  const char *FuncTemplateCode =
+      "template<typename T> T f(); auto v = f<int>();";
+  EXPECT_TRUE(
+      matches(FuncTemplateCode, functionDecl(templateArgumentCountIs(1))));
+  EXPECT_TRUE(
+      notMatches(FuncTemplateCode, functionDecl(templateArgumentCountIs(2))));
 }
 
 TEST_P(ASTMatchersTest, IsIntegral) {