Auto merge of #26170 - Manishearth:enum-convertible, r=asajeffrey

Add FromJSValConvertible for enums

Fixes https://github.com/servo/servo/issues/26169

This adds FromJSValConvertible implementations for webidl enums, which allows them to be used within `sequence<>`, etc.

This also uses these implementations when converting arguments.

components/script/dom/bindings/codegen/CodegenRust.py

@@ -1004,17 +1004,16 @@ def getJSToNativeConversionInfo(type, descriptorProvider, failureCode=None,
                             "yet")
         enum = type.inner.identifier.name
         if invalidEnumValueFatal:
-            handleInvalidEnumValueCode = onFailureInvalidEnumValue(failureCode, 'search').define()
+            handleInvalidEnumValueCode = failureCode or "throw_type_error(*cx, &error); %s" % exceptionCode
         else:
             handleInvalidEnumValueCode = "return true;"
 
         template = (
-            "match find_enum_value(*cx, ${val}, %(pairs)s) {\n"
+            "match FromJSValConvertible::from_jsval(*cx, ${val}, ()) {"
             "    Err(_) => { %(exceptionCode)s },\n"
-            "    Ok((None, search)) => { %(handleInvalidEnumValueCode)s },\n"
+            "    Ok(ConversionResult::Success(v)) => v,\n"
-            "    Ok((Some(&value), _)) => value,\n"
+            "    Ok(ConversionResult::Failure(error)) => { %(handleInvalidEnumValueCode)s },\n"
-            "}" % {"pairs": enum + "Values::pairs",
+            "}" % {"exceptionCode": exceptionCode,
-                   "exceptionCode": exceptionCode,
                    "handleInvalidEnumValueCode": handleInvalidEnumValueCode})
 
         if defaultValue is not None:
@@ -2418,7 +2417,6 @@ def UnionTypes(descriptors, dictionaries, callbacks, typedefs, config):
         'crate::dom::bindings::str::DOMString',
         'crate::dom::bindings::str::USVString',
         'crate::dom::bindings::trace::RootedTraceableBox',
-        'crate::dom::bindings::utils::find_enum_value',
         'crate::dom::types::*',
         'crate::dom::windowproxy::WindowProxy',
         'crate::script_runtime::JSContext as SafeJSContext',
@@ -4347,8 +4345,12 @@ pub enum %s {
         pairs = ",\n    ".join(['("%s", super::%s::%s)' % (val, ident, getEnumValueName(val)) for val in enum.values()])
 
         inner = string.Template("""\
+use crate::dom::bindings::conversions::ConversionResult;
+use crate::dom::bindings::conversions::FromJSValConvertible;
 use crate::dom::bindings::conversions::ToJSValConvertible;
+use crate::dom::bindings::utils::find_enum_value;
 use js::jsapi::JSContext;
+use js::rust::HandleValue;
 use js::rust::MutableHandleValue;
 use js::jsval::JSVal;
 
@@ -4373,6 +4375,22 @@ impl ToJSValConvertible for super::${ident} {
         pairs[*self as usize].0.to_jsval(cx, rval);
     }
 }
+
+impl FromJSValConvertible for super::${ident} {
+    type Config = ();
+    unsafe fn from_jsval(cx: *mut JSContext, value: HandleValue, _option: ())
+                         -> Result<ConversionResult<super::${ident}>, ()> {
+        match find_enum_value(cx, value, pairs) {
+            Err(_) => Err(()),
+            Ok((None, search)) => {
+                Ok(ConversionResult::Failure(
+                    format!("'{}' is not a valid enum value for enumeration '${ident}'.", search).into()
+                ))
+            }
+            Ok((Some(&value), _)) => Ok(ConversionResult::Success(value)),
+        }
+    }
+}
     """).substitute({
             'ident': ident,
             'pairs': pairs
@@ -6138,7 +6156,6 @@ def generate_imports(config, cgthings, descriptors, callbacks=None, dictionaries
         'crate::dom::bindings::utils::ProtoOrIfaceArray',
         'crate::dom::bindings::utils::enumerate_global',
         'crate::dom::bindings::utils::finalize_global',
-        'crate::dom::bindings::utils::find_enum_value',
         'crate::dom::bindings::utils::generic_getter',
         'crate::dom::bindings::utils::generic_lenient_getter',
         'crate::dom::bindings::utils::generic_lenient_setter',