[ASTMatchers] Add hasSubExpr() matcher.

[courbet]

Summary

This is needed to implement more checks in D38455.

[aaron.ballman]

I think hasSourceExpression() already does what you're looking for.

void f() {
  int i = 1.0f;
}

clang-query> match implicitCastExpr(hasSourceExpression(floatLiteral()))

Match #1:

C:\Users\aballman.GRAMMATECH\Desktop\test.c:2:11: note: "root" binds here

int i = 1.0f;
        ^~~~

1 match.

[courbet]

Thanks for the pointer. I missed the trampoline through GetSourceExpressionMatcher<T>.

docs/LibASTMatchersReference.html

 URL url = "a string";
 
 Example 2: matches 'b' (matcher =
 opaqueValueExpr(hasSourceExpression(implicitCastExpr(declRefExpr())))
 int a = b ?: 1;
 </pre></td></tr>
 
 
+<tr><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1CastExpr.html">CastExpr</a>&gt;</td><td class="name" onclick="toggle('hasSubExpr0')"><a name="hasSubExpr0Anchor">hasSubExpr</a></td><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1Expr.html">Expr</a>&gt; InnerMatcher</td></tr>
+<tr><td colspan="4" class="doc" id="hasSubExpr0"><pre>Matches casts whose subexpr matches a given matcher.
+
+Example matches the first cast
+    (matcher = implicitCastExpr(hasSubExpr(floatLiteral())))))
+  int i = 0.0;
+  int j = '0';
+</pre></td></tr>
+
+
 <tr><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1ClassTemplateSpecializationDecl.html">ClassTemplateSpecializationDecl</a>&gt;</td><td class="name" onclick="toggle('hasAnyTemplateArgument0')"><a name="hasAnyTemplateArgument0Anchor">hasAnyTemplateArgument</a></td><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1TemplateArgument.html">TemplateArgument</a>&gt; InnerMatcher</td></tr>
 <tr><td colspan="4" class="doc" id="hasAnyTemplateArgument0"><pre>Matches classTemplateSpecializations, templateSpecializationType and
 functionDecl that have at least one TemplateArgument matching the given
 InnerMatcher.
 
 Given
   template&lt;typename T&gt; class A {};
   template&lt;&gt; class A&lt;double&gt; {};

include/clang/ASTMatchers/ASTMatchers.h

 /// matcher.
 ///
 /// FIXME: Unit test this matcher
 AST_MATCHER_P(ImplicitCastExpr, hasImplicitDestinationType,
               internal::Matcher<QualType>, InnerMatcher) {
   return InnerMatcher.matches(Node.getType(), Finder, Builder);
 }
 
+/// \brief Matches casts whose subexpr matches a given matcher.
+///
+/// Example matches the first cast
+///     (matcher = implicitCastExpr(hasSubExpr(floatLiteral())))))
+///   int i = 0.0;
+///   int j = '0';
+AST_POLYMORPHIC_MATCHER_P(
+    hasSubExpr,
+    AST_POLYMORPHIC_SUPPORTED_TYPES(CastExpr),
+    internal::Matcher<Expr>, InnerMatcher) {
+  const Expr *const SubExpr = Node.getSubExpr();
+  return (SubExpr != nullptr &&
+          InnerMatcher.matches(*SubExpr, Finder, Builder));
+}
+
 /// \brief Matches RecordDecl object that are spelled with "struct."
 ///
 /// Example matches S, but not C or U.
 /// \code
 ///   struct S {};
 ///   class C {};
 ///   union U {};
 /// \endcode

unittests/ASTMatchers/ASTMatchersTraversalTest.cpp

TEST(Member, MatchesMemberAllocationFunction) {
 
   // Fails in C++11 mode
   EXPECT_TRUE(matchesConditionally(
     "namespace std { typedef typeof(sizeof(int)) size_t; }"
       "class X { void operator delete[](void*, std::size_t); };",
     cxxMethodDecl(ofClass(hasName("X"))), true, "-std=gnu++98"));
 }
 
+TEST(HasSubExpr, MatchesSimpleCase) {
+  EXPECT_TRUE(matches("int i = 0.0;",
+                      implicitCastExpr(hasSubExpr(floatLiteral()))));
+  EXPECT_TRUE(notMatches("int i = '0';",
+                      implicitCastExpr(hasSubExpr(floatLiteral()))));
+}
+
 TEST(HasDestinationType, MatchesSimpleCase) {
   EXPECT_TRUE(matches("char* p = static_cast<char*>(0);",
                       cxxStaticCastExpr(hasDestinationType(
                         pointsTo(TypeMatcher(anything()))))));
 }
 
 TEST(HasImplicitDestinationType, MatchesSimpleCase) {
   // This test creates an implicit const cast.