From 27d44c8d1042e5705853b272fc340c76c4d02785 Mon Sep 17 00:00:00 2001
From: Josh Matthews <josh@joshmatthews.net>
Date: Tue, 6 Sep 2016 19:58:26 -0400
Subject: [PATCH] Add a simple API to reject promises with DOM error values.

---
 components/script/dom/bindings/error.rs          | 12 ++++++++++++
 components/script/dom/promise.rs                 | 11 ++++++++++-
 components/script/dom/testbinding.rs             |  6 +++++-
 components/script/dom/webidls/TestBinding.webidl |  1 +
 tests/wpt/mozilla/tests/mozilla/promise.html     |  7 +++++++
 5 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/components/script/dom/bindings/error.rs b/components/script/dom/bindings/error.rs
index c9cbeb09f21..1c0d49c4976 100644
--- a/components/script/dom/bindings/error.rs
+++ b/components/script/dom/bindings/error.rs
@@ -19,6 +19,7 @@ use js::jsapi::JS_ErrorFromException;
 use js::jsapi::JS_GetPendingException;
 use js::jsapi::JS_IsExceptionPending;
 use js::jsapi::JS_SetPendingException;
+use js::jsapi::MutableHandleValue;
 use js::jsval::UndefinedValue;
 use libc::c_uint;
 use std::slice::from_raw_parts;
@@ -266,3 +267,14 @@ pub unsafe fn throw_invalid_this(cx: *mut JSContext, proto_id: u16) {
                         proto_id_to_name(proto_id));
     throw_type_error(cx, &error);
 }
+
+impl Error {
+    /// Convert this error value to a JS value, consuming it in the process.
+    pub unsafe fn to_jsval(self, cx: *mut JSContext, global: GlobalRef, rval: MutableHandleValue) {
+        assert!(!JS_IsExceptionPending(cx));
+        throw_dom_exception(cx, global, self);
+        assert!(JS_IsExceptionPending(cx));
+        assert!(JS_GetPendingException(cx, rval));
+        JS_ClearPendingException(cx);
+    }
+}
diff --git a/components/script/dom/promise.rs b/components/script/dom/promise.rs
index 6dd45d05219..f167d95bfd2 100644
--- a/components/script/dom/promise.rs
+++ b/components/script/dom/promise.rs
@@ -14,7 +14,7 @@
 use dom::bindings::callback::CallbackContainer;
 use dom::bindings::codegen::Bindings::PromiseBinding::AnyCallback;
 use dom::bindings::conversions::root_from_object;
-use dom::bindings::error::Fallible;
+use dom::bindings::error::{Error, Fallible};
 use dom::bindings::global::GlobalRef;
 use dom::bindings::js::MutHeapJSVal;
 use dom::bindings::reflector::{Reflectable, MutReflectable, Reflector};
@@ -156,6 +156,15 @@ impl Promise {
         self.maybe_reject(cx, v.handle());
     }
 
+    #[allow(unsafe_code)]
+    pub fn maybe_reject_error(&self, cx: *mut JSContext, error: Error) {
+        rooted!(in(cx) let mut v = UndefinedValue());
+        unsafe {
+            error.maybe_to_jsval(cx, self.global().r(), v.handle_mut());
+        }
+        self.maybe_reject(cx, v.handle());
+    }
+
     #[allow(unrooted_must_root, unsafe_code)]
     pub fn maybe_reject(&self,
                         cx: *mut JSContext,
diff --git a/components/script/dom/testbinding.rs b/components/script/dom/testbinding.rs
index c318badc1ba..a9df0a3a9d2 100644
--- a/components/script/dom/testbinding.rs
+++ b/components/script/dom/testbinding.rs
@@ -20,7 +20,7 @@ use dom::bindings::codegen::UnionTypes::{EventOrUSVString, HTMLElementOrLong, Lo
 use dom::bindings::codegen::UnionTypes::{HTMLElementOrUnsignedLongOrStringOrBoolean, LongSequenceOrBoolean};
 use dom::bindings::codegen::UnionTypes::{StringOrLongSequence, StringOrStringSequence, StringSequenceOrUnsignedLong};
 use dom::bindings::codegen::UnionTypes::{StringOrUnsignedLong, StringOrBoolean, UnsignedLongOrBoolean};
-use dom::bindings::error::Fallible;
+use dom::bindings::error::{Error, Fallible};
 use dom::bindings::global::{GlobalRef, global_root_from_context};
 use dom::bindings::js::Root;
 use dom::bindings::mozmap::MozMap;
@@ -668,6 +668,10 @@ impl TestBindingMethods for TestBinding {
         p.maybe_reject(cx, v);
     }
 
+    fn PromiseRejectWithTypeError(&self, p: &Promise, s: USVString) {
+        p.maybe_reject_error(self.global().r().get_cx(), Error::Type(s.0));
+    }
+
     #[allow(unrooted_must_root)]
     fn PromiseNativeHandler(&self,
                             resolve: Option<Rc<SimpleCallback>>,
diff --git a/components/script/dom/webidls/TestBinding.webidl b/components/script/dom/webidls/TestBinding.webidl
index 65c68514895..54e54f27c77 100644
--- a/components/script/dom/webidls/TestBinding.webidl
+++ b/components/script/dom/webidls/TestBinding.webidl
@@ -518,6 +518,7 @@ interface TestBinding {
   Promise<any> promiseNativeHandler(SimpleCallback? resolve, SimpleCallback? reject);
   void promiseResolveNative(Promise<any> p, any value);
   void promiseRejectNative(Promise<any> p, any value);
+  void promiseRejectWithTypeError(Promise<any> p, USVString message);
 
   void panic();
 };
diff --git a/tests/wpt/mozilla/tests/mozilla/promise.html b/tests/wpt/mozilla/tests/mozilla/promise.html
index 9e5175ec57a..79a0a5578a9 100644
--- a/tests/wpt/mozilla/tests/mozilla/promise.html
+++ b/tests/wpt/mozilla/tests/mozilla/promise.html
@@ -21,6 +21,13 @@
           });
   }, 'Reject callback gets argument');
 
+  promise_test(function(test) {
+      var t = new TestBinding;
+      var p = new Promise(function() {});
+      t.promiseRejectWithTypeError(p, "success");
+      return promise_rejects(test, new TypeError("success"), p, "TypeError should be instantiated");
+  }, 'Native code rejects with exception');
+
   promise_test(function(test) {
       var t = new TestBinding;
       var resolved;