Shared pattern logic: clean up nomenclature around guards.

Change-Id: I596362dab53ac2efc68cb45dbb29feab80c6240a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/259463
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

pkg/_fe_analyzer_shared/lib/src/type_inference/type_analyzer.dart

@@ -19,11 +19,11 @@ class CaseHeadInfo<Node extends Object, Expression extends Node> {
   /// For a `case` clause, the case pattern.  For a `default` clause, `null`.
   final Node? pattern;
 
-  /// For a `case` clause that has a `when` part, the expression following
+  /// For a `case` clause that has a guard clause, the expression following
   /// `when`.  Otherwise `null`.
-  final Expression? when;
+  final Expression? guard;
 
-  CaseHeadInfo({required this.node, required this.pattern, this.when});
+  CaseHeadInfo({required this.node, required this.pattern, this.guard});
 }
 
 /// Information supplied by the client to [TypeAnalyzer.analyzeSwitchExpression]
@@ -38,7 +38,7 @@ class ExpressionCaseInfo<Node extends Object, Expression extends Node>
   ExpressionCaseInfo(
       {required super.node,
       required super.pattern,
-      super.when,
+      super.guard,
       required this.body});
 }
 
@@ -334,7 +334,7 @@ mixin TypeAnalyzer<Node extends Object, Statement extends Node,
                 switchScrutinee: scrutinee,
                 topPattern: pattern));
         // Stack: (Expression, i * ExpressionCase, Pattern)
-        Expression? guard = caseInfo.when;
+        Expression? guard = caseInfo.guard;
         bool hasGuard = guard != null;
         if (hasGuard) {
           _checkGuardType(guard, analyzeExpression(guard, boolType));
@@ -410,7 +410,7 @@ mixin TypeAnalyzer<Node extends Object, Statement extends Node,
                     topPattern: pattern));
             // Stack: (Expression, numExecutionPaths * StatementCase,
             //         numHeads * CaseHead, Pattern),
-            Expression? guard = head.when;
+            Expression? guard = head.guard;
             bool hasGuard = guard != null;
             if (hasGuard) {
               _checkGuardType(guard, analyzeExpression(guard, boolType));
@@ -582,7 +582,7 @@ mixin TypeAnalyzer<Node extends Object, Statement extends Node,
   void handleCase_afterCaseHeads(Statement node, int caseIndex, int numHeads);
 
   /// Called after visiting a single `case` clause, consisting of a pattern and
-  /// a `when` condition.
+  /// an optional guard.
   ///
   /// [node] is the enclosing switch statement or switch expression and
   /// [caseIndex] is the index of the `case` clause.
@@ -607,8 +607,8 @@ mixin TypeAnalyzer<Node extends Object, Statement extends Node,
   /// Stack effect: pushes (CaseHead).
   void handleDefault(Node node, int caseIndex);
 
-  /// Called when visiting a `case` that lacks a `when` clause.  Since the lack
-  /// of a `when` clause is semantically equivalent to `when true`, this method
+  /// Called when visiting a `case` that lacks a guard clause.  Since the lack
+  /// of a guard clause is semantically equivalent to `when true`, this method
   /// should behave similarly to visiting the boolean literal `true`.
   ///
   /// [node] is the enclosing switch statement, switch expression, or `if`, and

pkg/_fe_analyzer_shared/test/mini_ast.dart

@@ -404,12 +404,12 @@ class ExpressionCase extends Node
   final Pattern? pattern;
 
   @override
-  final Expression? when;
+  final Expression? guard;
 
   @override
   final Expression body;
 
-  ExpressionCase._(this.pattern, this.when, this.body,
+  ExpressionCase._(this.pattern, this.guard, this.body,
       {required super.location})
       : super._();
 
@@ -418,7 +418,7 @@ class ExpressionCase extends Node
 
   String toString() => [
         pattern == null ? 'default' : 'case $pattern',
-        if (when != null) ' when $when',
+        if (guard != null) ' when $guard',
         ': $body'
       ].join('');
 
@@ -906,8 +906,8 @@ abstract class Pattern extends Node with CaseHead, CaseHeads {
 
   PatternDispatchResult<Node, Expression, Var, Type> visit(Harness h);
 
-  CaseHead when(Expression whenExpression) =>
-      _When(this, whenExpression, location: location);
+  CaseHead when(Expression guard) =>
+      _GuardedCaseHead(this, guard, location: location);
 
   String _debugString({required bool needsKeywordOrType});
 }
@@ -1741,6 +1741,17 @@ class _ForEach extends Statement {
   }
 }
 
+class _GuardedCaseHead extends Node with CaseHead, CaseHeads {
+  @override
+  final Pattern _pattern;
+
+  @override
+  final Expression _guard;
+
+  _GuardedCaseHead(this._pattern, this._guard, {required super.location})
+      : super._();
+}
+
 class _If extends _IfBase {
   final Expression condition;
 
@@ -2447,7 +2458,7 @@ class _MiniAstTypeAnalyzer
     return StatementCaseInfo([
       for (var caseHead in case_._caseHeads._caseHeads)
         CaseHeadInfo(
-            node: caseHead, pattern: caseHead._pattern, when: caseHead._guard)
+            node: caseHead, pattern: caseHead._pattern, guard: caseHead._guard)
     ], case_._body.statements, labels: case_._caseHeads._labels);
   }
 
@@ -3103,16 +3114,6 @@ class _VariableReference extends LValue {
   }
 }
 
-class _When extends Node with CaseHead, CaseHeads {
-  @override
-  final Pattern _pattern;
-
-  @override
-  final Expression _guard;
-
-  _When(this._pattern, this._guard, {required super.location}) : super._();
-}
-
 class _While extends Statement {
   final Expression condition;
   final Statement body;