[dart2wasm] Make dart.library.js false in conditional imports (attemp…

…t 2)

This change removes the implementation of `dart:js` for dart2wasm. The
code is no longer in use and the compiler already provides a static
error if you import `dart:js` internally.

By removing the implementation from the libraries.json spec, we also
show this as unaccessible on conditional imports. This will allow
developers to distinguish JS and Wasm backends

This adapts the original implementation in
https://dart-review.googlesource.com/c/sdk/+/368642 with a few small
changes, but keeps around the existing allowances on `package:js`. Those
can be addressed separately to reduce the disruption from this change.

Closes #55266.

Change-Id: I0d01a424f2fdb4f48879bd1a41c847a92439e74a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/380583
Reviewed-by: Ömer Ağacan <omersa@google.com>
Commit-Queue: Sigmund Cherem <sigmund@google.com>

CHANGELOG.md

@@ -56,6 +56,16 @@ number, like `.`, `x`, or the `e` in scientific notation.
 - Added `toJSCaptureThis` so `this` is passed in from JavaScript to the
   callback as the first parameter.
 
+### Tools
+
+#### Wasm compiler (dart2wasm)
+
+- The condition `dart.library.js` is now false on conditional imports in
+  dart2wasm. Note that it was already a static error to import `dart:js`
+  directly (see [#55266][]).
+
+[#55266]: https://github.com/dart-lang/sdk/issues/55266
+
 ## 3.5.0
 
 ### Language

pkg/_js_interop_checks/lib/js_interop_checks.dart

@@ -136,7 +136,6 @@ class JsInteropChecks extends RecursiveVisitor {
     'package:js/js.dart',
     'package:js/js_util.dart',
     'dart:js_util',
-    'dart:js',
     'dart:ffi',
   ];
 

pkg/dart2wasm/lib/target.dart

@@ -156,7 +156,6 @@ class WasmTarget extends Target {
         'dart:developer',
         'dart:ffi',
         'dart:io',
-        'dart:js',
         'dart:js_interop',
         'dart:js_interop_unsafe',
         'dart:js_util',
@@ -202,7 +201,7 @@ class WasmTarget extends Target {
     // Flutter's dart:ui is also package:ui (in test mode)
     if (importerString.startsWith('package:ui/')) return true;
 
-    // package:js can import dart:js* & dart:_js_*
+    // package:js can import dart:js_util & dart:_js_*
     if (importerString.startsWith('package:js/')) return true;
 
     return false;

sdk/lib/libraries.json

@@ -333,10 +333,6 @@
           "_internal/wasm/lib/isolate_patch.dart"
         ]
       },
-      "js": {
-        "uri": "js/js.dart",
-        "patches": "_internal/wasm/lib/js_patch.dart"
-      },
       "js_interop": {
         "uri": "js_interop/js_interop.dart",
         "patches": "_internal/wasm/lib/js_interop_patch.dart"

sdk/lib/libraries.yaml

@@ -271,9 +271,6 @@ wasm_common:
       uri: isolate/isolate.dart
       patches:
         - "_internal/wasm/lib/isolate_patch.dart"
-    js:
-      uri: js/js.dart
-      patches: _internal/wasm/lib/js_patch.dart
     js_interop:
       uri: js_interop/js_interop.dart
       patches: _internal/wasm/lib/js_interop_patch.dart

tests/lib/js/static_interop_test/disallowed_interop_libraries_test.dart

@@ -5,8 +5,8 @@
 // Check that dart2wasm disallows these interop libraries from being imported.
 
 /**/ import 'dart:js';
-//   ^
-// [web] JS interop library 'dart:js' can't be imported when compiling to Wasm.
+//          ^
+// [web] Dart library 'dart:js' is not available on this platform.
 
 /**/ import 'dart:js_util';
 //   ^