[analysis_server] Handle callable classes and function expressions fo…

…r LSP Signature Help

Fixes Dart-Code/Dart-Code#5153.

Change-Id: I4335c2378c4e863a38d2f802ff1618b23917ba7d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/377460
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Samuel Rawlins <srawlins@google.com>

pkg/analysis_server/lib/src/computer/computer_hover.dart

@@ -293,11 +293,14 @@ class DartUnitHoverComputer {
 
     // Look for documentation comments of overridden members
     var overridden = findOverriddenElements(element);
-    for (var candidate in [
+    var candidates = [
       element,
       ...overridden.superElements,
-      ...overridden.interfaceElements
-    ]) {
+      ...overridden.interfaceElements,
+      if (element case PropertyAccessorElement(variable2: var variable?))
+        variable
+    ];
+    for (var candidate in candidates) {
       if (candidate.documentationComment != null) {
         documentedElement = candidate;
         break;

pkg/analysis_server/lib/src/computer/computer_signature.dart

@@ -7,6 +7,7 @@ import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/utilities/extensions/ast.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/ast/element_locator.dart';
 import 'package:analyzer/src/dart/ast/utilities.dart';
 import 'package:analyzer/src/dartdoc/dartdoc_directive_info.dart';
@@ -38,33 +39,53 @@ class DartUnitSignatureComputer {
       return null;
     }
     String? name;
-    ExecutableElement? execElement;
+    Element? element;
+    List<ParameterElement>? parameters;
     var parent = argumentList.parent;
     if (parent is MethodInvocation) {
       name = parent.methodName.name;
-      var element = ElementLocator.locate(parent);
-      execElement = element is ExecutableElement ? element : null;
+      element = ElementLocator.locate(parent);
+      parameters = element is FunctionTypedElement ? element.parameters : null;
     } else if (parent is InstanceCreationExpression) {
       name = parent.constructorName.type.qualifiedName;
       var constructorName = parent.constructorName.name;
       if (constructorName != null) {
         name += '.${constructorName.name}';
       }
-      execElement = ElementLocator.locate(parent) as ExecutableElement?;
+      element = ElementLocator.locate(parent);
+      parameters = element is FunctionTypedElement ? element.parameters : null;
+    } else if (parent
+        case FunctionExpressionInvocation(function: Identifier function)) {
+      name = function.name;
+
+      if (function.staticType case FunctionType functionType) {
+        // Standard function expression.
+        element = function.staticElement;
+        parameters = functionType.parameters;
+      } else if (parent.staticElement case ExecutableElement staticElement) {
+        // Callable class instance (where we'll look at the `call` method).
+        element = staticElement;
+        parameters = staticElement.parameters;
+      }
     }
 
-    if (name == null || execElement == null) {
+    if (name == null || element == null || parameters == null) {
       return null;
     }
 
     _argumentList = argumentList;
+    var convertedParameters = parameters.map((p) => _convertParam(p)).toList();
+    var dartdoc = DartUnitHoverComputer.computePreferredDocumentation(
+      _dartdocInfo,
+      element,
+      documentationPreference,
+    );
 
-    var parameters =
-        execElement.parameters.map((p) => _convertParam(p)).toList();
-
-    return AnalysisGetSignatureResult(name, parameters,
-        dartdoc: DartUnitHoverComputer.computePreferredDocumentation(
-            _dartdocInfo, execElement, documentationPreference));
+    return AnalysisGetSignatureResult(
+      name,
+      convertedParameters,
+      dartdoc: dartdoc,
+    );
   }
 
   ParameterInfo _convertParam(ParameterElement param) {

pkg/analysis_server/test/lsp/signature_help_test.dart

@@ -189,6 +189,30 @@ augment class Foo {
     );
   }
 
+  Future<void> test_callableClass() async {
+    var content = '''
+class Foo {
+  /// Does foo.
+  int call(String s, int i) {
+    var foo = Foo();
+    return foo(^);
+  }
+}
+''';
+    var expectedLabel = 'foo(String s, int i)';
+    var expectedDoc = 'Does foo.';
+
+    await _expectSignature(
+      content,
+      expectedLabel,
+      expectedDoc,
+      [
+        ParameterInformation(label: 'String s'),
+        ParameterInformation(label: 'int i'),
+      ],
+    );
+  }
+
   Future<void> test_dartDocMacro() async {
     setSignatureHelpContentFormat(null);
 
@@ -367,6 +391,50 @@ foo(String s, int i) {
     );
   }
 
+  Future<void> test_functionExpression_local() async {
+    var content = '''
+
+void f() {
+  var foo = (String s, int i) => s;
+  foo(^);
+}
+''';
+    var expectedLabel = 'foo(String s, int i)';
+
+    await _expectSignature(
+      content,
+      expectedLabel,
+      null, // expectedDoc, not dartDocs on local vars.
+      [
+        ParameterInformation(label: 'String s'),
+        ParameterInformation(label: 'int i'),
+      ],
+    );
+  }
+
+  Future<void> test_functionExpression_topLevel() async {
+    var content = '''
+/// Does foo.
+var foo = (String s, int i) => s;
+
+void f() {
+  foo(^);
+}
+''';
+    var expectedLabel = 'foo(String s, int i)';
+    var expectedDoc = 'Does foo.';
+
+    await _expectSignature(
+      content,
+      expectedLabel,
+      expectedDoc,
+      [
+        ParameterInformation(label: 'String s'),
+        ParameterInformation(label: 'int i'),
+      ],
+    );
+  }
+
   Future<void> test_manualTrigger_invalidLocation() async {
     // If the user invokes signature help, we should show it even if it's a
     // location where we wouldn't automatically trigger (for example in a string).