[analyzer] Introduce experimental_member_use warning.

In a follow-up CL, I will add logic to report this warning if
reference is made to an element annotated with `@experimental`.

In order to do that without causing trybot failures, I will need a
preparatory CL that add some analysis_options directives to ignore the
new warning in places where it's expected.

But the analyzer contains logic to warn if an unknown diargnostic code
is referenced from an analysis_options file. So to avoid that
preparatory CL causing trybot failures, I need to first add the
warning code itself, which is what this CL does.

Change-Id: I6a6a69642c1487bf765b49f0e73c6e8468615fcc
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/451341
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Paul Berry <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

Author: stereotype441

pkg/analysis_server/lib/src/services/correction/error_fix_status.yaml

@@ -3560,6 +3560,8 @@ WarningCode.EQUAL_KEYS_IN_MAP:
   status: noFix
   notes: |-
     Fix depends on user's intent, which can't be known.
+WarningCode.EXPERIMENTAL_MEMBER_USE:
+  status: needsEvaluation
 WarningCode.INFERENCE_FAILURE_ON_COLLECTION_LITERAL:
   status: noFix
 WarningCode.INFERENCE_FAILURE_ON_FUNCTION_INVOCATION:

pkg/analyzer/lib/src/diagnostic/diagnostic_code_values.g.dart

@@ -1014,6 +1014,7 @@ const List<DiagnosticCode> diagnosticCodeValues = [
   WarningCode.duplicateShownName,
   WarningCode.equalElementsInSet,
   WarningCode.equalKeysInMap,
+  WarningCode.experimentalMemberUse,
   WarningCode.inferenceFailureOnCollectionLiteral,
   WarningCode.inferenceFailureOnFunctionInvocation,
   WarningCode.inferenceFailureOnFunctionReturnType,

pkg/analyzer/lib/src/error/codes.g.dart

@@ -11220,6 +11220,18 @@ class WarningCode extends DiagnosticCodeWithExpectedTypes {
     expectedTypes: [],
   );
 
+  /// Parameters:
+  /// String member: the name of the member
+  static const WarningTemplate<
+    LocatableDiagnostic Function({required String member})
+  >
+  experimentalMemberUse = WarningTemplate(
+    'EXPERIMENTAL_MEMBER_USE',
+    "'{0}' is experimental and could be removed or changed at any time.",
+    withArguments: _withArgumentsExperimentalMemberUse,
+    expectedTypes: [ExpectedType.string],
+  );
+
   /// When "strict-inference" is enabled, collection literal types must be
   /// inferred via the context type, or have type arguments.
   ///
@@ -13110,6 +13122,12 @@ class WarningCode extends DiagnosticCodeWithExpectedTypes {
     return LocatableDiagnosticImpl(duplicateIgnore, [p0]);
   }
 
+  static LocatableDiagnostic _withArgumentsExperimentalMemberUse({
+    required String member,
+  }) {
+    return LocatableDiagnosticImpl(experimentalMemberUse, [member]);
+  }
+
   static LocatableDiagnostic _withArgumentsInferenceFailureOnCollectionLiteral({
     required String p0,
   }) {

pkg/analyzer/messages.yaml

@@ -24790,6 +24790,11 @@ WarningCode:
       Note that literal maps preserve the order of their entries, so the choice
       of which entry to remove might affect the order in which the keys and
       values are returned by an iterator.
+  EXPERIMENTAL_MEMBER_USE:
+    parameters:
+      String member: the name of the member
+    problemMessage: "'#member' is experimental and could be removed or changed at any time."
+    hasPublishedDocs: false
   INFERENCE_FAILURE_ON_COLLECTION_LITERAL:
     parameters:
       String p0: the name of the collection