[Syntax] No crash on OpaqueValueExpr.

[hokein]

Summary

OpaqueValueExpr doesn't correspond to the concrete syntax, it has
invalid source location, ignore them.

[kbobyrev]

LGTM, thanks!

Sorry for the delay.

clang/lib/Tooling/Syntax/BuildTree.cpp

if (auto *DS = dyn_cast_or_null<DeclStmt>(S)) {
       for (auto *D : DS->decls())
         Builder.noticeDeclWithoutSemicolon(D);
     } else if (auto *E = dyn_cast_or_null<Expr>(S)) {
       return RecursiveASTVisitor::TraverseStmt(IgnoreImplicit(E));
     }
     return RecursiveASTVisitor::TraverseStmt(S);
   }
 
+  bool TraverseOpaqueValueExpr(OpaqueValueExpr *VE) {
+    // OpaqueValue doesn't correspond to concrete syntax, ignore it.
+    return true;
+  }
+
   // Some expressions are not yet handled by syntax trees.
   bool WalkUpFromExpr(Expr *E) {
     assert(!isImplicitExpr(E) && "should be handled by TraverseStmt");
     Builder.foldNode(Builder.getExprRange(E),
                      new (allocator()) syntax::UnknownExpression, E);
     return true;
   }
 

clang/unittests/Tooling/Syntax/BuildTreeTest.cpp

`-CompoundStatement
     |   | |   `-'test'
     |   | |-'(' OpenParen
     |   | `-')' CloseParen
     |   `-';'
     `-'}' CloseParen
 )txt"));
 }
 
+TEST_P(BuildSyntaxTreeTest, ConditionalOperator) {
+  // FIXME: conditional expression is not modeled yet.
+  EXPECT_TRUE(treeDumpEqualOnAnnotations(
+      R"cpp(
+void test() {
+  [[1?:2]];
+}
+)cpp",
+      {R"txt(
+UnknownExpression Expression
+|-IntegerLiteralExpression
+| `-'1' LiteralToken
+|-'?'
+|-':'
+`-IntegerLiteralExpression
+  `-'2' LiteralToken
+)txt"}));
+}
+
 TEST_P(BuildSyntaxTreeTest, UnqualifiedId_Identifier) {
   EXPECT_TRUE(treeDumpEqualOnAnnotations(
       R"cpp(
 void test(int a) {
   [[a]];
 }
 )cpp",
       {R"txt(