[ASTMatchers] Fix isDerivedFrom for recursive templates

[jkorous]

comment & test case

[NoQ]

This looks perfectly correct to me.
Added more folks, just in case.

[gribozavr2]

clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp

460

80 columns, please.

clang/lib/ASTMatchers/ASTMatchFinder.cpp

for (const auto &It : Declaration->bases()) {
 
     // FIXME: Going to the primary template here isn't really correct, but
     // unfortunately we accept a Decl matcher for the base class not a Type
     // matcher, so it's the best thing we can do with our current interface.
     CXXRecordDecl *ClassDecl = getAsCXXRecordDeclOrPrimaryTemplate(TypeNode);
     if (!ClassDecl)
       continue;
     if (ClassDecl == Declaration) {
-      // This can happen for recursive template definitions; if the
-      // current declaration did not match, we can safely return false.
-      return false;
+      // This can happen for recursive template definitions.
+      continue;
     }
     BoundNodesTreeBuilder Result(*Builder);
     if (Base.matches(*ClassDecl, this, &Result)) {
       *Builder = std::move(Result);
       return true;
     }
     if (!Directly && classIsDerivedFrom(ClassDecl, Base, Builder, Directly))
       return true;

clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp

 TEST(DeclarationMatcher, ClassIsDerived) {
   DeclarationMatcher IsDerivedFromX = cxxRecordDecl(isDerivedFrom("X"));
 
   EXPECT_TRUE(matches("class X {}; class Y : public X {};", IsDerivedFromX));
   EXPECT_TRUE(notMatches("class X {};", IsDerivedFromX));
   EXPECT_TRUE(notMatches("class X;", IsDerivedFromX));
   EXPECT_TRUE(notMatches("class Y;", IsDerivedFromX));
   EXPECT_TRUE(notMatches("", IsDerivedFromX));
+  EXPECT_TRUE(matches("class X {}; template<int N> class Y : Y<N-1>, X {};",
+    IsDerivedFromX));
+  EXPECT_TRUE(matches("class X {}; template<int N> class Y : X, Y<N-1> {};",
+    IsDerivedFromX));
+
+  DeclarationMatcher IsZDerivedFromX = cxxRecordDecl(hasName("Z"),
+    isDerivedFrom("X"));
+  EXPECT_TRUE(
+    matches(
+      "class X {};"
+      "template<int N> class Y : Y<N-1> {};"
+      "template<> class Y<0> : X {};"
+      "class Z : Y<1> {};",
+      IsZDerivedFromX));
 
   DeclarationMatcher IsDirectlyDerivedFromX =
       cxxRecordDecl(isDirectlyDerivedFrom("X"));
 
   EXPECT_TRUE(
       matches("class X {}; class Y : public X {};", IsDirectlyDerivedFromX));
   EXPECT_TRUE(notMatches("class X {};", IsDirectlyDerivedFromX));
   EXPECT_TRUE(notMatches("class X;", IsDirectlyDerivedFromX));