Document unreachable_from_main for instance members

Change-Id: I37ea317ad0e1fc18d509e706a3cbc355f04005be
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/330380
Auto-Submit: Samuel Rawlins <[email protected]>
Reviewed-by: Phil Quitslund <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: srawlins

pkg/linter/lib/src/rules/unreachable_from_main.dart

@@ -16,20 +16,13 @@ import '../analyzer.dart';
 const _desc = 'Unreachable top-level members in executable libraries.';
 
 const _details = r'''
-Top-level members and static members in an executable library should be used
-'''
-// TODO(srawlins): Lasse
-// [suggests](https://github.com/dart-lang/linter/issues/3625#issuecomment-1735355630)
-// changing this to use "statically resolved" members, which I love. But it
-// will mean reporting additionally on extension instance members and extension
-// type instance members, so land carefully.
-    '''
-directly inside this library.  An executable library is a library that contains
-a `main` top-level function or that contains a top-level function annotated with
+Any member declared in an executable library should be used directly inside that
+library.  An executable library is a library that contains a `main` top-level
+function or that contains a top-level function annotated with
 `@pragma('vm:entry-point')`).  Executable libraries are not usually imported
 and it's better to avoid defining unused members.
 
-This rule assumes that an executable library isn't imported by other files
+This rule assumes that an executable library isn't imported by other libraries
 except to execute its `main` function.
 
 **BAD:**

pkg/linter/test/rules/unreachable_from_main_test.dart

@@ -1020,6 +1020,35 @@ extension type E(int it) {}
 ''');
   }
 
+  test_instanceFieldOnExtension_unreachable() async {
+    await assertDiagnostics(r'''
+void main() {
+  E.f;
+}
+
+extension E on int {
+  static int f = 1;
+  void m() {}
+}
+''', [
+      lint(72, 1),
+    ]);
+  }
+
+  test_instanceMethod_unreachable_inExtensionType() async {
+    await assertDiagnostics(r'''
+void main() {
+  E(7);
+}
+
+extension type E(int it) {
+  void m() {}
+}
+''', [
+      lint(59, 1),
+    ]);
+  }
+
   test_mixin_reachable_implemented() async {
     await assertNoDiagnostics(r'''
 void main() {

pkg/linter/tool/machine/rules.json

@@ -384,11 +384,7 @@
     "group": "errors",
     "state": "stable",
     "incompatible": [],
-    "sets": [
-      "core",
-      "recommended",
-      "flutter"
-    ],
+    "sets": [],
     "fixStatus": "needsEvaluation",
     "details": "**DON'T** use wildcard parameters or variables.\n\nWildcard parameters and local variables\n(e.g. underscore-only names like `_`, `__`, `___`, etc.) will\nbecome non-binding in a future version of the Dart language.\nAny existing code that uses wildcard parameters or variables will\nbreak. In anticipation of this change, and to make adoption easier,\nthis lint disallows wildcard and variable parameter uses.\n\n\n**BAD:**\n```dart\nvar _ = 1;\nprint(_); // LINT\n```\n\n```dart\nvoid f(int __) {\n  print(__); // LINT multiple underscores too\n}\n```\n\n**GOOD:**\n```dart\nfor (var _ in [1, 2, 3]) count++;\n```\n\n```dart\nvar [a, _, b, _] = [1, 2, 3, 4];\n```\n",
     "sinceDartSdk": "3.1.0"
@@ -2646,7 +2642,7 @@
     "incompatible": [],
     "sets": [],
     "fixStatus": "hasFix",
-    "details": "Top-level members and static members in an executable library should be used\ndirectly inside this library.  An executable library is a library that contains\na `main` top-level function or that contains a top-level function annotated with\n`@pragma('vm:entry-point')`).  Executable libraries are not usually imported\nand it's better to avoid defining unused members.\n\nThis rule assumes that an executable library isn't imported by other files\nexcept to execute its `main` function.\n\n**BAD:**\n\n```dart\nmain() {}\nvoid f() {}\n```\n\n**GOOD:**\n\n```dart\nmain() {\n  f();\n}\nvoid f() {}\n```\n\n",
+    "details": "Any member declared in an executable library should be used directly inside that\nlibrary.  An executable library is a library that contains a `main` top-level\nfunction or that contains a top-level function annotated with\n`@pragma('vm:entry-point')`).  Executable libraries are not usually imported\nand it's better to avoid defining unused members.\n\nThis rule assumes that an executable library isn't imported by other libraries\nexcept to execute its `main` function.\n\n**BAD:**\n\n```dart\nmain() {}\nvoid f() {}\n```\n\n**GOOD:**\n\n```dart\nmain() {\n  f();\n}\nvoid f() {}\n```\n\n",
     "sinceDartSdk": "2.19.0"
   },
   {