Add extension name getter on Enum.

We use an extension getter instead of an instance getter because
it doesn't conflict with any potential existing or future enums
which want an element named `name`.
Keeping the namespace for enum elements open is a priority.
We currently only reserve `index` and `values`.

BUG: dart-lang/language#1511

Fixes language issue #1511, which is a long-standing request,
and should replace a number of alternative implementations
which are based on parsing the `toString()`.


This version has two fields on the shared superclass, the index
and private name, and has a separate `toString` for each `enum` class
which hard-codes that enum's class name.

An earlier version had both `"name"` and `"ClassName.name"` as fields
to be able to reuse the same `toString` method on all enum classes,
but that cost too much for JS compiled code.
Even having just `ClassName.` as a field and then combining inside
`toString` requires more code to create the enum instances.
Instead this version hardcodes the `ClassName.` string once
in the `toString` method, which means each enum class has its own
toString (which can *potentially* be tree-shaken then.)

This still tree-shakes slightly worse than the previous implementation
where every enum class had its own `index` and `_name` fields
independent of each other, which could then be tree-shaken independently.
However, the `index` was already made an interface member with the
addition of the `Enum` interface, so code which accesses `.index`
on something of the `Enum` supertype could prevent tree-shaking of
all enum classes' `index` fields.
Likewise any general access to the "name" of an enum would necessarily
do the same for the name.
This CL makes up for some of that by sharing more implementation
between enum classes.

DartVM AOT CodeSize impact: ~0.15% regression on gallery (little less on big g3 app)

TEST= New tests added to enum_test.dart

Change-Id: Id25334e6c987f470f558de3c141d0e3ff542b020
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/210480
Commit-Queue: Lasse R.H. Nielsen <[email protected]>
Reviewed-by: Stephen Adams <[email protected]>
Reviewed-by: Martin Kustermann <[email protected]>

Author: lrhn

CHANGELOG.md

@@ -31,7 +31,7 @@
     if (!iIsNull) {
       print(i + 1); // OK, because `i` is known to be non-null
     }
-  }
+  }<>
   ```
 
   Previously, the above program had a compile-time error because type promotion
@@ -82,7 +82,11 @@
 
 ### `dart:core`
 
+- Add extension `name` getter on enum values.
 - Add `Enum.compareByIndex` helper function for comparing enum values by index.
+- Add `Enum.compareByName` helper function for comparing enum values by name.
+- Add extension methods on `Iterable<T extends Enum>`, intended for
+  `SomeEnumType.values` lists, to look up values by name.
 
 ### Tools
 
@@ -130,9 +134,9 @@ Updated the Linter to `1.12.0`, which includes changes that
 - update `avoid_print` to allow `kDebugMode`-wrapped print calls.
 - fix handling of initializing formals in `prefer_final_parameters`.
 - fix `unnecessary_parenthesis` false positive with function expressions.
-- adds support for constructor tear-offs to `avoid_redundant_argument_values`, 
+- adds support for constructor tear-offs to `avoid_redundant_argument_values`,
   `unnecessary_lambdas`, and `unnecessary_parenthesis`.
-- adds a new lint: `unnecessary_constructor_name` to flag unnecessary uses of 
+- adds a new lint: `unnecessary_constructor_name` to flag unnecessary uses of
   `.new`.
 - improves regular expression parsing performance for common checks
   (`camel_case_types`, `file_names`, etc.).
@@ -180,9 +184,9 @@ Updated the Linter to `1.12.0`, which includes changes that
   [`false_secrets`](https://dart.dev/go/false-secrets) section of your
   `pubspec.yaml`.
 - Fixes unicode terminal detection windows.
-- New flag `--example` to the commands 
+- New flag `--example` to the commands
   `dart pub get/upgrade/downgrade/add/remove` that will result in the `example/`
-  folder dependencies to be updated after operating in the current directory. 
+  folder dependencies to be updated after operating in the current directory.
 
 ## 2.14.2 - 2021-09-16
 

pkg/analyzer/lib/src/test_utilities/mock_sdk.dart

@@ -531,6 +531,10 @@ abstract class Enum {
   int get index;
 }
 
+abstract class _Enum extends Enum {
+  String _name;
+}
+
 abstract class Pattern {
   Iterable<Match> allMatches(String string, [int start = 0]);
 }

pkg/compiler/lib/src/ssa/builder_kernel.dart

@@ -4499,12 +4499,16 @@ class KernelSsaGraphBuilder extends ir.Visitor<void> with ir.VisitorVoidMixin {
 
   int _extractEnumIndexFromConstantValue(
       ConstantValue constant, ClassEntity classElement) {
-    if (constant is ConstructedConstantValue) {
-      if (constant.type.element == classElement) {
-        assert(constant.fields.length == 1 || constant.fields.length == 2);
-        ConstantValue indexConstant = constant.fields.values.first;
-        if (indexConstant is IntConstantValue) {
-          return indexConstant.intValue.toInt();
+    if (constant is ConstructedConstantValue &&
+        constant.type.element == classElement) {
+      assert(constant.fields.length >= 1);
+      for (var field in constant.fields.keys) {
+        if (field.memberName.text == "index") {
+          ConstantValue indexConstant = constant.fields[field];
+          if (indexConstant is IntConstantValue) {
+            return indexConstant.intValue.toInt();
+          }
+          break;
         }
       }
     }

pkg/compiler/test/field_analysis/jdata/effectively_constant_state.dart

@@ -25,7 +25,7 @@ class Class {
   /*member: Class.state1:constant=IntConstant(1)*/
   final int state1;
 
-  /*member: Class.state2:constant=ConstructedConstant(Enum(_name=StringConstant("Enum.c"),index=IntConstant(2)))*/
+  /*member: Class.state2:constant=ConstructedConstant(Enum(_name=StringConstant("c"),index=IntConstant(2)))*/
   final Enum state2;
 
   Class({this.state1: 1, this.state2: Enum.c});

pkg/compiler/test/impact/data/classes.dart

@@ -264,8 +264,8 @@ enum Enum { A }
 
 /*member: testEnum:
  static=[
-  Enum._name=StringConstant("Enum.A"),
-  Enum.index=IntConstant(0)],
+  _Enum._name=StringConstant("A"),
+  _Enum.index=IntConstant(0)],
  type=[
   const:Enum,
   inst:JSInt,

pkg/compiler/test/inference/data/enum.dart

@@ -55,7 +55,7 @@ enum Enum4 {
   a,
 }
 
-/*member: enumToString1:Value([exact=JSString], value: "Enum4.a")*/
+/*member: enumToString1:[exact=JSString]*/
 enumToString1() {
   return Enum4.a. /*invoke: [exact=Enum4]*/ toString();
 }