[ASTMatcher] Add isStaticDataMember matcher for varDecl.

[aaron.ballman]

include/clang/ASTMatchers/ASTMatchers.h

3005

How does this differ from the existing matcher hasStaticStorageDuration() over a fieldDecl()?

[hokein]

include/clang/ASTMatchers/ASTMatchers.h

3005

fieldDecl document says that fieldDecl is "an instance of this class is created by Sema::ActOnField to
represent a member of a struct/union/class.". So for static class members, they should not belong to fieldDecl as they are not bound to class instances.

Technically, we can't apply hasStaticStorageDuration() and isStaticStorageClass over a fieldDecl.

[aaron.ballman]

include/clang/ASTMatchers/ASTMatchers.h

3005

That's a really good point, but the question still remains: since we have hasStaticStorageDuration() already, can we find a way to use that same matcher rather than introduce a new matcher under a new name that does the same thing?

This time I tested a matcher, and found that you get the correct behavior from varDecl(hasStaticStorageDuration(), hasParent(recordDecl())).

I think this is especially important to try to do because we have hasStaticStorageDuration() and isStaticStorageClass(), so adding isStaticDataMember() adds a third option to possibly confuse users.

[hokein]

include/clang/ASTMatchers/ASTMatchers.h

3005

Thanks for the explanations, I think it makes sense.

Previously I thought isStaticDataMember is an more obvious ast matcher.
varDecl(hasStaticStorageDuration(), hasParent(cxxRecordDecl())) and varDecl(hasStaticStorageDuration(), hasDeclContext(cxxRecordDecl()), isDefinition()) can do the same thing.

docs/LibASTMatchersReference.html

Given:
   extern "C" void f() {}
   extern "C" { void g() {} }
   void h() {}
 functionDecl(isExternC())
   matches the declaration of f and g, but not the declaration h
 </pre></td></tr>
 
 
+<tr><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1VarDecl.html">VarDecl</a>&gt;</td><td class="name" onclick="toggle('isStaticDataMember0')"><a name="isStaticDataMember0Anchor">isStaticDataMember</a></td><td></td></tr>
+<tr><td colspan="4" class="doc" id="isStaticDataMember0"><pre>Matches a variable declaration that is a static data member.
+
+Example matches x (matcher = varDecl(isStaticDataMember())
+class A {
+ static int x;
+ int y;
+};
+</pre></td></tr>
+
+
 <tr><td>Matcher&lt;<a href="http://clang.llvm.org/doxygen/classclang_1_1VarDecl.html">VarDecl</a>&gt;</td><td class="name" onclick="toggle('isStaticStorageClass1')"><a name="isStaticStorageClass1Anchor">isStaticStorageClass</a></td><td></td></tr>
 <tr><td colspan="4" class="doc" id="isStaticStorageClass1"><pre>Matches variablefunction declarations that have "static" storage
 class specifier ("static" keyword) written in the source.
 
 Given:
   static void f() {}
   static int i = 0;
   extern int j;

include/clang/ASTMatchers/ASTMatchers.h

 ///   } catch (int x) {
 ///   }
 /// }
 /// \endcode
 AST_MATCHER(VarDecl, isExceptionVariable) {
   return Node.isExceptionVariable();
 }
 
+/// \brief Matches a variable declaration that is a static data member.
+///
+/// Example matches x (matcher = varDecl(isStaticDataMember())
+/// \code
+/// class A {
+///  static int x;
+///  int y;
+/// };
+/// \endcode
+AST_MATCHER(VarDecl, isStaticDataMember) {
+  return Node.isStaticDataMember();
+}
+
 /// \brief Checks that a call expression or a constructor call expression has
 /// a specific number of arguments (including absent default arguments).
 ///
 /// Example matches f(0, 0) (matcher = callExpr(argumentCountIs(2)))
 /// \code
 ///   void f(int x, int y);
 ///   f(0, 0);
 /// \endcode

unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp

TEST(Matcher, VarDecl_StorageDuration) {
   // targets support TLS, which causes this to be an error depending on what
   // platform the test is being run on. We do not have access to the TargetInfo
   // object to be able to test whether the platform supports TLS or not.
   EXPECT_TRUE(notMatches(T, varDecl(hasName("x"), hasThreadStorageDuration())));
   EXPECT_TRUE(notMatches(T, varDecl(hasName("y"), hasThreadStorageDuration())));
   EXPECT_TRUE(notMatches(T, varDecl(hasName("a"), hasThreadStorageDuration())));
 }
 
+TEST(Matcher, VarDecl_StaticDataMember) {
+  EXPECT_TRUE(matches(
+    "class A {static int x; int y;};",
+    varDecl(hasName("x"), isStaticDataMember())));
+  EXPECT_TRUE(notMatches(
+    "class A {int x;};",
+    varDecl(isStaticDataMember())));
+}
+
 TEST(Matcher, FindsVarDeclInFunctionParameter) {
   EXPECT_TRUE(matches(
     "void f(int i) {}",
     varDecl(hasName("i"))));
 }
 
 TEST(UnaryExpressionOrTypeTraitExpression, MatchesCorrectType) {
   EXPECT_TRUE(matches("void x() { int a = sizeof(a); }", sizeOfExpr(