analyzer: separate unused_element_parameter from unused_element

Fixes #49025

This allows users to blanket ignore unused_element_parameter without
ignoring unused_element. They are reported in distinct situations so it
is valid to separate them.

Tested: Presubmit CI
Cq-Include-Trybots: luci.dart.try:flutter-analyze-try,analyzer-win-release-try,pkg-win-release-try
Change-Id: I4844a6a0e0a67cd5e37ed8735b1526e174deb950
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/378500
Reviewed-by: Brian Wilkerson <[email protected]>
Reviewed-by: Phil Quitslund <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>
Reviewed-by: Ryan Macnak <[email protected]>

Author: srawlins

pkg/analysis_server/test/src/services/correction/assist/convert_class_to_enum_test.dart

@@ -348,7 +348,7 @@ base class E {
 class _E {
   static const _E c = _E();
 
-  // ignore: unused_element, recursive_constant_constructor
+  // ignore: unused_element_parameter, recursive_constant_constructor
   const _E({_E e = const _E()});
 }
 ''');

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

@@ -7585,11 +7585,9 @@ class WarningCode extends AnalyzerErrorCode {
   ///  Parameters:
   ///  0: the name of the parameter that is declared but not used
   static const WarningCode UNUSED_ELEMENT_PARAMETER = WarningCode(
-    'UNUSED_ELEMENT',
+    'UNUSED_ELEMENT_PARAMETER',
     "A value for optional parameter '{0}' isn't ever given.",
     correctionMessage: "Try removing the unused parameter.",
-    hasPublishedDocs: true,
-    uniqueName: 'UNUSED_ELEMENT_PARAMETER',
   );
 
   ///  Parameters:

pkg/analyzer/messages.yaml

@@ -27308,8 +27308,6 @@ WarningCode:
       kinds of declarations are analyzed:
       - Private top-level declarations and all of their members
       - Private members of public declarations
-      - Optional parameters of private functions for which a value is never
-        passed
 
       Not all references to an element will mark it as "used":
       - Assigning a value to a top-level variable (with a standard `=`
@@ -27329,6 +27327,26 @@ WarningCode:
       class [!_C!] {}
       ```
 
+      #### Common fixes
+
+      If the declaration isn't needed, then remove it.
+
+      If the declaration is intended to be used, then add the code to use it.
+  UNUSED_ELEMENT_PARAMETER:
+    problemMessage: "A value for optional parameter '{0}' isn't ever given."
+    correctionMessage: Try removing the unused parameter.
+    hasPublishedDocs: false
+    comment: |-
+      Parameters:
+      0: the name of the parameter that is declared but not used
+    documentation: |-
+      #### Description
+
+      The analyzer produces this diagnostic when a value is never passed for an
+      optional parameter declared within a private declaration.
+
+      #### Example
+
       Assuming that no code in the library passes a value for `y` in any
       invocation of `_m`, the following code produces this diagnostic:
 
@@ -27353,14 +27371,6 @@ WarningCode:
       ```
 
       If the declaration is intended to be used, then add the code to use it.
-  UNUSED_ELEMENT_PARAMETER:
-    sharedName: UNUSED_ELEMENT
-    problemMessage: "A value for optional parameter '{0}' isn't ever given."
-    correctionMessage: Try removing the unused parameter.
-    hasPublishedDocs: true
-    comment: |-
-      Parameters:
-      0: the name of the parameter that is declared but not used
   UNUSED_FIELD:
     problemMessage: "The value of the field '{0}' isn't used."
     correctionMessage: Try removing the field, or using it.

pkg/analyzer/tool/diagnostics/diagnostics.md

@@ -23183,8 +23183,6 @@ void f() {
 
 ### unused_element
 
-_A value for optional parameter '{0}' isn't ever given._
-
 _The declaration '{0}' isn't referenced._
 
 #### Description
@@ -23194,8 +23192,6 @@ referenced in the library that contains the declaration. The following
 kinds of declarations are analyzed:
 - Private top-level declarations and all of their members
 - Private members of public declarations
-- Optional parameters of private functions for which a value is never
-  passed
 
 Not all references to an element will mark it as "used":
 - Assigning a value to a top-level variable (with a standard `=`
@@ -23215,6 +23211,23 @@ produces this diagnostic:
 class [!_C!] {}
 ```
 
+#### Common fixes
+
+If the declaration isn't needed, then remove it.
+
+If the declaration is intended to be used, then add the code to use it.
+
+### unused_element_parameter
+
+_A value for optional parameter '{0}' isn't ever given._
+
+#### Description
+
+The analyzer produces this diagnostic when a value is never passed for an
+optional parameter declared within a private declaration.
+
+#### Example
+
 Assuming that no code in the library passes a value for `y` in any
 invocation of `_m`, the following code produces this diagnostic:
 

runtime/observatory/lib/src/elements/debugger.dart

@@ -2942,7 +2942,7 @@ class DebuggerConsoleElement extends CustomElement implements Renderable {
   DebuggerConsoleElement.created() : super.created('debugger-console');
 
   /// Is [container] scrolled to the within [threshold] pixels of the bottom?
-  // ignore: unused_element
+  // ignore: unused_element_parameter
   static bool _isScrolledToBottom(DivElement? container, [int threshold = 2]) {
     if (container == null) {
       return false;