[CodeComplete] Strip out try and optional eval expr in operator compilation

foldSequence() may hoist these expression up by mutating their sub
expression. When completing operators, this behavior ruins reusability
of operand. Since these expression doesn't affect completion, we can
strip them out.

rdar://problem/42452085

Author: rintaro

lib/IDE/CodeCompletion.cpp

@@ -3522,24 +3522,38 @@ class CompletionLookup final : public swift::VisibleDeclConsumer {
       flattenBinaryExpr(assignExpr->getSrc(), sequence);
       assignExpr->setDest(nullptr);
       assignExpr->setSrc(nullptr);
+    } else if (auto tryExpr = dyn_cast<AnyTryExpr>(expr)) {
+      // Strip out try expression. It doesn't affect completion.
+      flattenBinaryExpr(tryExpr->getSubExpr(), sequence);
+    } else if (auto optEval = dyn_cast<OptionalEvaluationExpr>(expr)){
+      // Strip out optional evaluation expression. It doesn't affect completion.
+      flattenBinaryExpr(optEval->getSubExpr(), sequence);
     } else {
       sequence.push_back(expr);
     }
   }
 
   void typeCheckLeadingSequence(SmallVectorImpl<Expr *> &sequence) {
+
+    // Strip out try and optional evaluation expr because foldSequence() mutates
+    // hierarchy of these expressions. They don't affect completion anyway.
+    for (auto &element : sequence) {
+      if (auto *tryExpr = dyn_cast<AnyTryExpr>(element))
+        element = tryExpr->getSubExpr();
+      if (auto *optEval = dyn_cast<OptionalEvaluationExpr>(element))
+        element = optEval->getSubExpr();
+    }
+
     Expr *expr =
         SequenceExpr::create(CurrDeclContext->getASTContext(), sequence);
     prepareForRetypechecking(expr);
     // Take advantage of the fact the type-checker leaves the types on the AST.
     if (!typeCheckExpression(const_cast<DeclContext *>(CurrDeclContext),
                              expr)) {
-      if (isa<BinaryExpr>(expr) || isa<AssignExpr>(expr)) {
-        // Rebuild the sequence from the type-checked version.
-        sequence.clear();
-        flattenBinaryExpr(expr, sequence);
-        return;
-      }
+      // Rebuild the sequence from the type-checked version.
+      sequence.clear();
+      flattenBinaryExpr(expr, sequence);
+      return;
     }
 
     // Fall back to just using the immediate LHS.

test/IDE/complete_crashes.swift

@@ -312,3 +312,19 @@ func test_40956846(
 // RDAR_40956846-DAG: Decl[LocalVar]/Local:               arg_40956846_3[#(() -> Int)!#]; name=arg_40956846_3
 // RDAR_40956846-DAG: Decl[LocalVar]/Local:               arg_40956846_4[#inout ((Int) -> Int)!#]; name=arg_40956846_4
 // RDAR_40956846: End completions
+
+// rdar://problem/42452085
+// RUN: %target-swift-ide-test -code-completion -code-completion-token=RDAR_42452085_1 -source-filename=%s | %FileCheck %s -check-prefix=RDAR_42452085
+// RUN: %target-swift-ide-test -code-completion -code-completion-token=RDAR_42452085_2 -source-filename=%s | %FileCheck %s -check-prefix=RDAR_42452085
+// RUN: %target-swift-ide-test -code-completion -code-completion-token=RDAR_42452085_3 -source-filename=%s | %FileCheck %s -check-prefix=RDAR_42452085
+class cls_42452085 {
+  var value: Any
+  func canThrow() throws -> Int { return 1 }
+}
+func test_42452085(any: Any, obj: cls_42452085?) throws {
+  var object: Any? = nil
+  object = (any as? String) #^RDAR_42452085_1^#
+  obj?.value = any #^RDAR_42452085_2^#
+  _ = try obj?.canThrow() #^RDAR_42452085_3^#
+}
+// RDAR_42452085: found code completion token