[SyntaxTree] Add test coverage for `->*` operator

[eduucaldas]

Summary

This was the last binary operator that we supported but didn't have any
test coverage. The recent fix in a crash in member pointers allowed us
to add this test.

[gribozavr2]

clang/unittests/Tooling/Syntax/TreeTest.cpp

2337

Could you add pmi as a function parameter (for consistency)?

[eduucaldas]

Answer comments

clang/unittests/Tooling/Syntax/TreeTest.cpp

TEST_P(SyntaxTreeTest, UserDefinedBinaryOperator) {
   EXPECT_TRUE(treeDumpEqual(
       R"cpp(
 struct X {
   X& operator=(const X&);
   friend X operator+(X, const X&);
   friend bool operator<(const X&, const X&);
   friend X operator<<(X&, const X&);
   X operator,(X&);
-  // TODO: Fix crash on member function pointer and add a test for `->*`
-  // TODO: Unbox operators in syntax tree. 
+  X operator->*(int);
+  // TODO: Unbox operators in syntax tree.
   // Represent operators by `+` instead of `IdExpression-UnqualifiedId-+`
 };
-void test(X x, X y) {
+void test(X x, X y, X* xp, int X::* pmi) {
   x = y;
   x + y;
   x < y;
   x << y;
   x, y;
+  xp->*pmi;
 }
 )cpp",
       R"txt(
 *: TranslationUnit
 |-SimpleDeclaration
 | |-struct
 | |-X
 | |-{

 | | | `-ParametersAndQualifiers
 | | |   |-(
 | | |   |-SimpleDeclaration
 | | |   | |-X
 | | |   | `-SimpleDeclarator
 | | |   |   `-&
 | | |   `-)
 | | `-;
+| |-SimpleDeclaration
+| | |-X
+| | |-SimpleDeclarator
+| | | |-operator
+| | | |-->*
+| | | `-ParametersAndQualifiers
+| | |   |-(
+| | |   |-SimpleDeclaration
+| | |   | `-int
+| | |   `-)
+| | `-;
 | |-}
 | `-;
 `-SimpleDeclaration
   |-void
   |-SimpleDeclarator
   | |-test
   | `-ParametersAndQualifiers
   |   |-(
   |   |-SimpleDeclaration
   |   | |-X
   |   | `-SimpleDeclarator
   |   |   `-x
   |   |-,
   |   |-SimpleDeclaration
   |   | |-X
   |   | `-SimpleDeclarator
   |   |   `-y
+  |   |-,
+  |   |-SimpleDeclaration
+  |   | |-X
+  |   | `-SimpleDeclarator
+  |   |   |-*
+  |   |   `-xp
+  |   |-,
+  |   |-SimpleDeclaration
+  |   | |-int
+  |   | `-SimpleDeclarator
+  |   |   |-MemberPointer
+  |   |   | |-X
+  |   |   | |-::
+  |   |   | `-*
+  |   |   `-pmi
   |   `-)
   `-CompoundStatement
     |-{
     |-ExpressionStatement
     | |-BinaryOperatorExpression
     | | |-IdExpression
     | | | `-UnqualifiedId
     | | |   `-x
`-CompoundStatement
     | | |   `-x
     | | |-IdExpression
     | | | `-UnqualifiedId
     | | |   `-,
     | | `-IdExpression
     | |   `-UnqualifiedId
     | |     `-y
     | `-;
+    |-ExpressionStatement
+    | |-BinaryOperatorExpression
+    | | |-IdExpression
+    | | | `-UnqualifiedId
+    | | |   `-xp
+    | | |-->*
+    | | `-IdExpression
+    | |   `-UnqualifiedId
+    | |     `-pmi
+    | `-;
     `-}
 )txt"));
 }
 
 TEST_P(SyntaxTreeTest, UserDefinedUnaryPrefixOperator) {
   if (!GetParam().isCXX()) {
     return;
   }