Simplify implementation of FindNode.singleX getters.

Change-Id: I434cf2371dee4269747b21413d6d15cbd4fa4e3c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/287672
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

pkg/analyzer/lib/src/test_utilities/find_node.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/ast/utilities.dart';
 import 'package:analyzer/src/test_utilities/function_ast_visitor.dart';
@@ -13,11 +14,6 @@ class FindNode {
 
   FindNode(this.content, this.unit);
 
-  LibraryDirective get libraryDirective {
-    return unit.directives.singleWhere((d) => d is LibraryDirective)
-        as LibraryDirective;
-  }
-
   List<MethodInvocation> get methodInvocations {
     var result = <MethodInvocation>[];
     unit.accept(
@@ -28,143 +24,30 @@ class FindNode {
     return result;
   }
 
-  /// Returns the [Block], there must be only one.
+  Block get singleBlock => _single();
-  Block get singleBlock {
-    var nodes = <Block>[];
-    unit.accept(
-      FunctionAstVisitor(
-        block: (node) {
-          nodes.add(node);
-        },
-      ),
-    );
-    return nodes.single;
-  }
 
-  /// Returns the [ForElement], there must be only one.
+  ForElement get singleForElement => _single();
-  ForElement get singleForElement {
-    var nodes = <ForElement>[];
-    unit.accept(
-      FunctionAstVisitor(
-        forElement: (node) {
-          nodes.add(node);
-        },
-      ),
-    );
-    return nodes.single;
-  }
 
-  /// Returns the [ForStatement], there must be only one.
+  ForStatement get singleForStatement => _single();
-  ForStatement get singleForStatement {
-    var nodes = <ForStatement>[];
-    unit.accept(
-      FunctionAstVisitor(
-        forStatement: (node) {
-          nodes.add(node);
-        },
-      ),
-    );
-    return nodes.single;
-  }
 
-  /// Returns the [GuardedPattern], there must be only one.
+  GuardedPattern get singleGuardedPattern => _single();
-  GuardedPattern get singleGuardedPattern {
-    var nodes = <GuardedPattern>[];
-    unit.accept(
-      FunctionAstVisitor(
-        guardedPattern: (node) {
-          nodes.add(node);
-        },
-      ),
-    );
-    return nodes.single;
-  }
 
-  /// Returns the [IfElement], there must be only one.
+  IfElement get singleIfElement => _single();
-  IfElement get singleIfElement {
-    var nodes = <IfElement>[];
-    unit.accept(
-      FunctionAstVisitor(
-        ifElement: (node) {
-          nodes.add(node);
-        },
-      ),
-    );
-    return nodes.single;
-  }
 
-  /// Returns the [IfStatement], there must be only one.
+  IfStatement get singleIfStatement => _single();
-  IfStatement get singleIfStatement {
-    var nodes = <IfStatement>[];
-    unit.accept(
-      FunctionAstVisitor(
-        ifStatement: (node) {
-          nodes.add(node);
-        },
-      ),
-    );
-    return nodes.single;
-  }
 
-  /// Returns the [PatternAssignment], there must be only one.
+  LibraryDirective get singleLibraryDirective => _single();
-  PatternAssignment get singlePatternAssignment {
-    var nodes = <PatternAssignment>[];
-    unit.accept(
-      FunctionAstVisitor(
-        patternAssignment: nodes.add,
-      ),
-    );
-    return nodes.single;
-  }
 
-  /// Returns the [PatternVariableDeclaration], there must be only one.
+  PatternAssignment get singlePatternAssignment => _single();
-  PatternVariableDeclaration get singlePatternVariableDeclaration {
+
-    var nodes = <PatternVariableDeclaration>[];
+  PatternVariableDeclaration get singlePatternVariableDeclaration => _single();
-    unit.accept(
-      FunctionAstVisitor(
-        patternVariableDeclaration: nodes.add,
-      ),
-    );
-    return nodes.single;
-  }
 
-  /// Returns the [PatternVariableDeclarationStatement], there must be only one.
   PatternVariableDeclarationStatement
-      get singlePatternVariableDeclarationStatement {
+      get singlePatternVariableDeclarationStatement => _single();
-    var nodes = <PatternVariableDeclarationStatement>[];
-    unit.accept(
-      FunctionAstVisitor(
-        patternVariableDeclarationStatement: nodes.add,
-      ),
-    );
-    return nodes.single;
-  }
 
-  /// Returns the [SwitchExpression], there must be only one.
+  SwitchExpression get singleSwitchExpression => _single();
-  SwitchExpression get singleSwitchExpression {
-    var nodes = <SwitchExpression>[];
-    unit.accept(
-      FunctionAstVisitor(
-        switchExpression: (node) {
-          nodes.add(node);
-        },
-      ),
-    );
-    return nodes.single;
-  }
 
-  /// Returns the [SwitchPatternCase], there must be only one.
+  SwitchPatternCase get singleSwitchPatternCase => _single();
-  SwitchPatternCase get singleSwitchPatternCase {
-    var nodes = <SwitchPatternCase>[];
-    unit.accept(
-      FunctionAstVisitor(
-        switchPatternCase: (node) {
-          nodes.add(node);
-        },
-      ),
-    );
-    return nodes.single;
-  }
 
   AdjacentStrings adjacentStrings(String search) {
     return _node(search, (n) => n is AdjacentStrings);
@@ -889,4 +772,25 @@ class FindNode {
     }
     return result as T;
   }
+
+  /// If [unit] has exactly one node of type [T], returns it.
+  /// Otherwise, throws.
+  T _single<T extends AstNode>() {
+    final visitor = _TypedNodeVisitor<T>();
+    unit.accept(visitor);
+    return visitor.nodes.single;
+  }
+}
+
+class _TypedNodeVisitor<T extends AstNode>
+    extends GeneralizingAstVisitor<void> {
+  final List<T> nodes = [];
+
+  @override
+  void visitNode(AstNode node) {
+    if (node is T) {
+      nodes.add(node);
+    }
+    super.visitNode(node);
+  }
 }

pkg/analyzer/test/generated/utilities_test.dart

@@ -1266,7 +1266,7 @@ void f() {
 @myA2
 library foo;
 ''');
-    var node = findNode.libraryDirective;
+    var node = findNode.singleLibraryDirective;
     _assertAnnotatedNode(node);
     _assertReplacementForChildren<LibraryDirective>(
       destination: node,

pkg/analyzer/test/src/dart/analysis/driver_resolution_test.dart

@@ -230,7 +230,7 @@ const a = 1;
 ''');
     await resolveTestFile();
 
-    var directive = findNode.libraryDirective;
+    var directive = findNode.singleLibraryDirective;
 
     expect(directive.metadata, hasLength(1));
     Annotation annotation = directive.metadata[0];