Enable 'wildcard-variables' feature flag.

This CL enables the wildcard variables feature by default in Dart 3.7.

Local variables and parameters named `_` are now non-binding and they can be declared multiple times without collisions. All wildcard variable declaration types that have this behavior are described in the
wildcard variables specification: https://github.com/dart-lang/language/blob/main/accepted/future-releases/wildcard-variables/feature-specification.md.

Top-level variables, top-level function names, type names, member names, etc.
are unchanged. They can be named `_` and used as they are today.

These are a few examples of where wildcard variables can be used:
```dart
Foo(_, this._, super._, void _()) {}

typedef T = void Function(String _, String _);

main() {
  var _ = 1;
  int _ = 2;

  list.where((_) => true);
}
```

Bug: #55673
Fixes: #55654
Change-Id: I80e904d39b364f5e54b8406b4db02ec40ecc9db0
TEST=Existing tests, language tests for wildcards.
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/381311
Reviewed-by: Mark Zhou <[email protected]>
Reviewed-by: Mayank Patke <[email protected]>
Reviewed-by: Ben Konyi <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>
Reviewed-by: Siva Annamalai <[email protected]>
Commit-Queue: Kallen Tu <[email protected]>
Reviewed-by: Phil Quitslund <[email protected]>
Reviewed-by: Bob Nystrom <[email protected]>

Author: kallentu

CHANGELOG.md

@@ -1,5 +1,36 @@
 ## 3.7.0
 
+### Language
+
+Dart 3.7 adds [wildcard variables] to the language. To use them, set your
+package's [SDK constraint][language version] lower bound to 3.7 or greater
+(`sdk: '^3.7.0'`).
+
+#### Wildcard Variables
+
+[wildcard variables]: https://github.com/dart-lang/language/issues/3712
+
+Local variables and parameters named `_` are now non-binding and they can
+be declared multiple times without collisions. You will no longer be able to use
+these variables nor access their values. All wildcard variable declaration types
+that have this behavior are described in the
+[wildcard variables specification](https://github.com/dart-lang/language/blob/main/accepted/future-releases/wildcard-variables/feature-specification.md).
+
+Top-level variables, top-level function names, type names, member names, etc.
+are unchanged. They can be named `_` and used as they are today.
+
+These are a few examples of where wildcard variables can be used:
+```dart
+Foo(_, this._, super._, void _()) {}
+
+main() {
+  var _ = 1;
+  int _ = 2;
+
+  list.where((_) => true);
+}
+```
+
 ###### Dart to Javascript Compiler (dart2js)
 
 - The dart2js compiler which is invoked when the command

pkg/_fe_analyzer_shared/lib/src/experiments/flags.dart

@@ -257,10 +257,10 @@ enum ExperimentalFlag {
 
   wildcardVariables(
       name: 'wildcard-variables',
-      isEnabledByDefault: false,
+      isEnabledByDefault: true,
       isExpired: false,
-      experimentEnabledVersion: defaultLanguageVersion,
-      experimentReleasedVersion: defaultLanguageVersion),
+      experimentEnabledVersion: const Version(3, 7),
+      experimentReleasedVersion: const Version(3, 7)),
   ;
 
   final String name;

pkg/analyzer/lib/src/dart/analysis/experiments.g.dart

@@ -536,7 +536,7 @@ class ExperimentalFeatures {
     documentation:
         'Local declarations and parameters named `_` are non-binding.',
     experimentalReleaseVersion: null,
-    releaseVersion: null,
+    releaseVersion: Version.parse('3.7.0'),
   );
 }
 
@@ -649,7 +649,7 @@ class IsEnabledByDefault {
   static const bool variance = false;
 
   /// Default state of the experiment "wildcard-variables"
-  static const bool wildcard_variables = false;
+  static const bool wildcard_variables = true;
 }
 
 /// Constant bools indicating whether each experimental flag is currently

pkg/analyzer/test/src/dart/analysis/analysis_context_collection_test.dart

@@ -418,6 +418,7 @@ analysisOptions
       triple-shift
       unnamed-libraries
       variance
+      wildcard-variables
 workspaces
   workspace_0: PackageConfigWorkspace
     root: /home/test
@@ -493,6 +494,7 @@ analysisOptions
       triple-shift
       unnamed-libraries
       variance
+      wildcard-variables
 workspaces
   workspace_0: PackageConfigWorkspace
     root: /home/test

pkg/analyzer/tool/diagnostics/diagnostics.md

@@ -26404,6 +26404,7 @@ The following code produces this diagnostic because the name of the
 parameter consists of two underscores:
 
 ```dart
+// @dart = 3.6
 void f(int __) {
   print([!__!]);
 }
@@ -26413,6 +26414,7 @@ The following code produces this diagnostic because the name of the
 local variable consists of a single underscore:
 
 ```dart
+// @dart = 3.6
 void f() {
   int _ = 0;
   print([!_!]);

pkg/analyzer_utilities/lib/test/experiments/experiments.dart

@@ -19,5 +19,4 @@ List<String> experimentsForTests = [
   Feature.enhanced_parts.enableString,
   Feature.macros.enableString,
   Feature.null_aware_elements.enableString,
-  Feature.wildcard_variables.enableString,
 ];

pkg/compiler/test/dump_info/data/deferred/main.dart

@@ -2,7 +2,125 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/*library: 
+/*spec.library: 
+ constant=[
+  {
+  "id": "constant/B.C_Deferred = A.lib__funky$closure();\n",
+  "kind": "constant",
+  "name": "",
+  "size": 39,
+  "outputUnit": "outputUnit/1",
+  "code": "B.C_Deferred = A.lib__funky$closure();\n"
+},
+  {
+  "id": "constant/B.C_JS_CONST = function getTagFallback(o) {\n  var s = Object.prototype.toString.call(o);\n  return s.substring(8, s.length - 1);\n};\n",
+  "kind": "constant",
+  "name": "",
+  "size": 131,
+  "outputUnit": "outputUnit/main",
+  "code": "B.C_JS_CONST = function getTagFallback(o) {\n  var s = Object.prototype.toString.call(o);\n  return s.substring(8, s.length - 1);\n};\n"
+},
+  {
+  "id": "constant/B.C__RootZone = new A._RootZone();\n",
+  "kind": "constant",
+  "name": "",
+  "size": 35,
+  "outputUnit": "outputUnit/main",
+  "code": "B.C__RootZone = new A._RootZone();\n"
+},
+  {
+  "id": "constant/B.C__StringStackTrace = new A._StringStackTrace();\n",
+  "kind": "constant",
+  "name": "",
+  "size": 51,
+  "outputUnit": "outputUnit/main",
+  "code": "B.C__StringStackTrace = new A._StringStackTrace();\n"
+},
+  {
+  "id": "constant/B.Interceptor_methods = J.Interceptor.prototype;\n",
+  "kind": "constant",
+  "name": "",
+  "size": 49,
+  "outputUnit": "outputUnit/main",
+  "code": "B.Interceptor_methods = J.Interceptor.prototype;\n"
+},
+  {
+  "id": "constant/B.JSArray_methods = J.JSArray.prototype;\n",
+  "kind": "constant",
+  "name": "",
+  "size": 41,
+  "outputUnit": "outputUnit/main",
+  "code": "B.JSArray_methods = J.JSArray.prototype;\n"
+},
+  {
+  "id": "constant/B.JSInt_methods = J.JSInt.prototype;\n",
+  "kind": "constant",
+  "name": "",
+  "size": 37,
+  "outputUnit": "outputUnit/main",
+  "code": "B.JSInt_methods = J.JSInt.prototype;\n"
+},
+  {
+  "id": "constant/B.JSString_methods = J.JSString.prototype;\n",
+  "kind": "constant",
+  "name": "",
+  "size": 43,
+  "outputUnit": "outputUnit/main",
+  "code": "B.JSString_methods = J.JSString.prototype;\n"
+},
+  {
+  "id": "constant/B.JavaScriptObject_methods = J.JavaScriptObject.prototype;\n",
+  "kind": "constant",
+  "name": "",
+  "size": 59,
+  "outputUnit": "outputUnit/main",
+  "code": "B.JavaScriptObject_methods = J.JavaScriptObject.prototype;\n"
+}],
+ deferredFiles=[{
+  "main.dart": {
+    "name": "<unnamed>",
+    "imports": {
+      "lib": [
+        "out_1.part.js"
+      ]
+    },
+    "importPrefixToLoadId": {
+      "lib": "lib"
+    }
+  }
+}],
+ dependencies=[{}],
+ library=[{
+  "id": "library/memory:sdk/tests/web/native/main.dart::",
+  "kind": "library",
+  "name": "<unnamed>",
+  "size": 316,
+  "children": [
+    "function/memory:sdk/tests/web/native/main.dart::main"
+  ],
+  "canonicalUri": "memory:sdk/tests/web/native/main.dart"
+}],
+ outputUnits=[
+  {
+  "id": "outputUnit/1",
+  "kind": "outputUnit",
+  "name": "1",
+  "size": 1204,
+  "filename": "out_1.part.js",
+  "imports": [
+    "lib"
+  ]
+},
+  {
+  "id": "outputUnit/main",
+  "kind": "outputUnit",
+  "name": "main",
+  "filename": "out",
+  "imports": []
+}]
+*/
+
+/*kernel.library: 
  constant=[
   {
   "id": "constant/B.C_Deferred = A.lib__funky$closure();\n",
@@ -122,7 +240,80 @@
 
 import 'lib.dart' deferred as lib;
 
-/*member: main:
+/*spec.member: main:
+ closure=[{
+  "id": "closure/memory:sdk/tests/web/native/main.dart::main.main_closure",
+  "kind": "closure",
+  "name": "main_closure",
+  "size": 212,
+  "outputUnit": "outputUnit/main",
+  "parent": "function/memory:sdk/tests/web/native/main.dart::main",
+  "function": "function/memory:sdk/tests/web/native/main.dart::main.main_closure.call"
+}],
+ function=[
+  {
+  "id": "function/memory:sdk/tests/web/native/main.dart::main",
+  "kind": "function",
+  "name": "main",
+  "size": 316,
+  "outputUnit": "outputUnit/main",
+  "parent": "library/memory:sdk/tests/web/native/main.dart::",
+  "children": [
+    "closure/memory:sdk/tests/web/native/main.dart::main.main_closure"
+  ],
+  "modifiers": {
+    "static": false,
+    "const": false,
+    "factory": false,
+    "external": false
+  },
+  "returnType": "dynamic",
+  "inferredReturnType": "[exact=_Future]",
+  "parameters": [],
+  "sideEffects": "SideEffects(reads anything; writes anything)",
+  "inlinedCount": 0,
+  "code": "main() {\n      return A.loadDeferredLibrary(\"lib\", \"\").then$1$1(new A.main_closure(), type$.Null);\n    }",
+  "type": "dynamic Function()",
+  "functionKind": 0
+},
+  {
+  "id": "function/memory:sdk/tests/web/native/main.dart::main.main_closure.call",
+  "kind": "function",
+  "name": "call",
+  "size": 95,
+  "outputUnit": "outputUnit/main",
+  "parent": "closure/memory:sdk/tests/web/native/main.dart::main.main_closure",
+  "children": [],
+  "modifiers": {
+    "static": false,
+    "const": false,
+    "factory": false,
+    "external": false
+  },
+  "returnType": "Null",
+  "inferredReturnType": "[null]",
+  "parameters": [
+    {
+      "name": "_#wc0#formal",
+      "type": "[null|subclass=Object]",
+      "declaredType": "dynamic"
+    }
+  ],
+  "sideEffects": "SideEffects(reads anything; writes anything)",
+  "inlinedCount": 0,
+  "code": "call$1(__wc0_formal) {\n      A.checkDeferredIsLoaded(\"lib\");\n      C.C_Deferred.call$0();\n    }",
+  "type": "Null Function(dynamic)",
+  "functionKind": 2
+}],
+ holding=[
+  {"id":"function/dart:_js_helper::loadDeferredLibrary"},
+  {"id":"function/dart:_rti::_setArrayType"},
+  {"id":"function/dart:_rti::findType"},
+  {"id":"function/dart:async::_Future.then","mask":"[exact=_Future]"},
+  {"id":"function/memory:sdk/tests/web/native/main.dart::main.main_closure.call"},
+  {"id":"function/memory:sdk/tests/web/native/main.dart::main.main_closure.call"}]
+*/
+/*kernel.member: main:
  closure=[{
   "id": "closure/memory:sdk/tests/web/native/main.dart::main.main_closure",
   "kind": "closure",

pkg/front_end/lib/src/api_prototype/experimental_flags_generated.dart

@@ -341,11 +341,11 @@ class ExperimentalFlag {
 
   static const ExperimentalFlag wildcardVariables = const ExperimentalFlag(
       name: 'wildcard-variables',
-      isEnabledByDefault: false,
+      isEnabledByDefault: true,
       isExpired: false,
-      enabledVersion: defaultLanguageVersion,
-      experimentEnabledVersion: defaultLanguageVersion,
-      experimentReleasedVersion: defaultLanguageVersion);
+      enabledVersion: const Version(3, 7),
+      experimentEnabledVersion: const Version(3, 7),
+      experimentReleasedVersion: const Version(3, 7));
 }
 
 /// Interface for accessing the global state of experimental features.