[IDE] Fix SyntaxModel to corretly walk sequence expression correctly

* Handle sequence expression at call argument position
* Set the sequence expression as the parent when walking into its sub
  expressions.
* Correctly call walkToExprPost() to the sequence expression.

rdar://problem/47603866 / https://bugs.swift.org/browse/SR-9776
(cherry picked from commit e7700dc)

Author: rintaro

lib/IDE/SyntaxModel.cpp

@@ -425,18 +425,6 @@ std::pair<bool, Expr *> ModelASTWalker::walkToExprPre(Expr *E) {
   if (isVisitedBeforeInIfConfig(E))
     return {false, E};
 
-  // In SequenceExpr, explicit cast expressions (e.g. 'as', 'is') appear twice.
-  // Skip pointers we've already seen.
-  if (auto SE = dyn_cast<SequenceExpr>(E)) {
-    SmallPtrSet<Expr *, 5> seenExpr;
-    for (auto subExpr : SE->getElements()) {
-      if (!seenExpr.insert(subExpr).second)
-        continue;
-      subExpr->walk(*this);
-    }
-    return { false, SE };
-  }
-
   auto addCallArgExpr = [&](Expr *Elem, TupleExpr *ParentTupleExpr) {
     if (isCurrentCallArgExpr(ParentTupleExpr)) {
       CharSourceRange NR = parameterNameRangeOfCallArg(ParentTupleExpr, Elem);
@@ -558,6 +546,18 @@ std::pair<bool, Expr *> ModelASTWalker::walkToExprPre(Expr *E) {
                           Closure->getExplicitResultTypeLoc().getSourceRange());
 
     pushStructureNode(SN, Closure);
+  } else if (auto SE = dyn_cast<SequenceExpr>(E)) {
+    // In SequenceExpr, explicit cast expressions (e.g. 'as', 'is') appear
+    // twice. Skip pointers we've already seen.
+    SmallPtrSet<Expr *, 5> seenExpr;
+    for (auto subExpr : SE->getElements()) {
+      if (!seenExpr.insert(subExpr).second) {
+        continue;
+      }
+      llvm::SaveAndRestore<ASTWalker::ParentTy> SetParent(Parent, E);
+      subExpr->walk(*this);
+    }
+    return { false, walkToExprPost(SE) };
   }
 
   return { true, E };

test/IDE/structure.swift

@@ -282,3 +282,8 @@ completion(a: 1) { (x: Any, y: Int) -> Int in
 // CHECK: <call><name>completion</name>(<arg><name>a</name>: 1</arg>) <arg><closure>{ (<param>x: <type>Any</type></param>, <param>y: <type>Int</type></param>) -> <type>Int</type> in
 // CHECK:    return x as! Int + y
 // CHECK: }</closure></arg></call>
+
+myFunc(foo: 0,
+       bar: baz == 0)
+// CHECK: <call><name>myFunc</name>(<arg><name>foo</name>: 0</arg>,
+// CHECK:        <arg><name>bar</name>: baz == 0</arg>)</call>