From 93b8e764b555d665aa7fe0f322e614922a2f3181 Mon Sep 17 00:00:00 2001
From: Caleb Meredith <calebmeredith8@gmail.com>
Date: Wed, 25 Jul 2018 16:13:03 -0700
Subject: [PATCH] Add message to error stack (#2311)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Summary:
Because of an ordering bug messages weren’t being added to the error stacks thrown by Prepack. This made debugging runtime issues in generated Prepack code difficult.

```js
throw new Error("foo");
```

```js
(function() {
  var $$0 = {
    enumerable: false,
    configurable: true,
    writable: true,
  };

  var _$0 = this;

  var _$1 = _$0.Error;
  var _$2 = _$1.prototype;
  var _$3 = _$0.Object;
  var _$4 = _$3.defineProperty;

  var __constructor = function() {};

  var _0 = ((__constructor.prototype = _$2), new __constructor());

  ($$0.value = "Error\n    at /Users/calebmer/prepack/fb-www/input.js:4:7"), _$4(_0, "stack", $$0);
  ($$0.value = "foo"), _$4(_0, "message", $$0);
  throw _0;
}.call(this));
```

```js
(function() {
  var $$0 = {
    enumerable: false,
    configurable: true,
    writable: true,
  };

  var _$0 = this;

  var _$1 = _$0.Error;
  var _$2 = _$1.prototype;
  var _$3 = _$0.Object;
  var _$4 = _$3.defineProperty;

  var __constructor = function() {};

  var _0 = ((__constructor.prototype = _$2), new __constructor());

  ($$0.value = "foo"), _$4(_0, "message", $$0);
  ($$0.value = "Error: foo\n    at /Users/calebmer/prepack/fb-www/input.js:4:7"), _$4(_0, "stack", $$0);
  throw _0;
}.call(this));
```
Pull Request resolved: https://github.com/facebook/prepack/pull/2311

Differential Revision: D9005517

Pulled By: calebmer

fbshipit-source-id: 8567624a67a78085d4072560541785e412cd6645
---
 src/intrinsics/ecma262/Error.js | 57 +++++++++++++++++++++------------
 1 file changed, 37 insertions(+), 20 deletions(-)

diff --git a/src/intrinsics/ecma262/Error.js b/src/intrinsics/ecma262/Error.js
index 4d8afbfa8..9f2af66a8 100644
--- a/src/intrinsics/ecma262/Error.js
+++ b/src/intrinsics/ecma262/Error.js
@@ -11,10 +11,18 @@
 
 import type { Realm } from "../../realm.js";
 import type { LexicalEnvironment } from "../../environment.js";
-import { ObjectValue, FunctionValue, NativeFunctionValue, StringValue } from "../../values/index.js";
+import {
+  AbstractValue,
+  ObjectValue,
+  FunctionValue,
+  NativeFunctionValue,
+  StringValue,
+  Value,
+} from "../../values/index.js";
 import { Get } from "../../methods/index.js";
 import { Create, Properties, To } from "../../singletons.js";
 import invariant from "../../invariant.js";
+import buildExpressionTemplate from "../../utils/builder.js";
 import type { BabelNodeSourceLocation } from "@babel/types";
 
 export default function(realm: Realm): NativeFunctionValue {
@@ -76,23 +84,23 @@ export function describeLocation(
   return location;
 }
 
-function buildStack(realm: Realm, context: ObjectValue) {
+const buildStackTemplateSrc = 'A + (B ? ": " + B : "") + C';
+const buildStackTemplate = buildExpressionTemplate(buildStackTemplateSrc);
+
+function buildStack(realm: Realm, context: ObjectValue): Value {
   invariant(context.$ErrorData);
 
   let stack = context.$ErrorData.contextStack;
   if (!stack) return realm.intrinsics.undefined;
 
   let lines = [];
-  let header = "";
+  let header = To.ToStringPartial(realm, Get(realm, context, "name"));
 
-  header += To.ToStringPartial(realm, Get(realm, context, "name"));
-
-  let msg = Get(realm, context, "message");
-  if (!msg.mightBeUndefined()) {
-    msg = To.ToStringPartial(realm, msg);
-    if (msg) header += `: ${msg}`;
+  let message = Get(realm, context, "message");
+  if (!message.mightBeUndefined()) {
+    message = To.ToStringValue(realm, message);
   } else {
-    msg.throwIfNotConcrete();
+    message.throwIfNotConcrete();
   }
 
   for (let executionContext of stack.reverse()) {
@@ -106,8 +114,17 @@ function buildStack(realm: Realm, context: ObjectValue) {
     );
     if (locString !== undefined) lines.push(locString);
   }
+  let footer = `\n    ${lines.join("\n    ")}`;
 
-  return new StringValue(realm, `${header}\n    ${lines.join("\n    ")}`);
+  return message instanceof StringValue
+    ? new StringValue(realm, `${header}${message.value ? `: ${message.value}` : ""}${footer}`)
+    : AbstractValue.createFromTemplate(
+        realm,
+        buildStackTemplate,
+        StringValue,
+        [new StringValue(realm, header), message, new StringValue(realm, footer)],
+        buildStackTemplateSrc
+      );
 }
 
 export function build(name: string, realm: Realm, inheritError?: boolean = true): NativeFunctionValue {
@@ -122,15 +139,6 @@ export function build(name: string, realm: Realm, inheritError?: boolean = true)
       locationData: undefined,
     };
 
-    // Build a text description of the stack.
-    let stackDesc = {
-      value: buildStack(realm, O),
-      enumerable: false,
-      configurable: true,
-      writable: true,
-    };
-    Properties.DefinePropertyOrThrow(realm, O, "stack", stackDesc);
-
     // 3. If message is not undefined, then
     if (!message.mightBeUndefined()) {
       // a. Let msg be ? ToString(message).
@@ -150,6 +158,15 @@ export function build(name: string, realm: Realm, inheritError?: boolean = true)
       message.throwIfNotConcrete();
     }
 
+    // Build a text description of the stack.
+    let stackDesc = {
+      value: buildStack(realm, O),
+      enumerable: false,
+      configurable: true,
+      writable: true,
+    };
+    Properties.DefinePropertyOrThrow(realm, O, "stack", stackDesc);
+
     // 4. Return O.
     return O;
   });