Allow analyzer to fallback to getter documentation for setters

The analyzer server firsts looks for the setter's dartdoc, then the first parent setter's dartdoc, then the closest getter's dartdoc.

Fixes #38963

Bug: https://github.com/dart-lang/sdk/issues/38963
Change-Id: I09f7ae0e5aa49d2536ebefd44dcfd3d6101bb0a6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/148566
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Lasse R.H. Nielsen <lrn@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

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

@@ -155,24 +155,46 @@ class DartUnitHoverComputer {
       // parameter for a field that does not exist.
       return null;
     }
-    // The documentation of the element itself.
-    if (element.documentationComment != null) {
-      return dartdocInfo.processDartdoc(element.documentationComment);
-    }
-    // Look for documentation comments of overridden members.
+
+    Element documentedElement;
+    Element documentedGetter;
+
+    // Look for documentation comments of overridden members
     var overridden = findOverriddenElements(element);
-    for (var superElement in [
+    for (var candidate in [
+      element,
       ...overridden.superElements,
       ...overridden.interfaceElements
     ]) {
-      var rawDoc = superElement.documentationComment;
-      if (rawDoc != null) {
-        var interfaceClass = superElement.enclosingElement;
-        return dartdocInfo.processDartdoc(rawDoc) +
-            '\n\nCopied from `${interfaceClass.displayName}`.';
+      if (candidate.documentationComment != null) {
+        documentedElement = candidate;
+        break;
+      }
+      if (documentedGetter == null &&
+          candidate is PropertyAccessorElement &&
+          candidate.isSetter) {
+        var getter = candidate.correspondingGetter;
+        if (getter != null && getter.documentationComment != null) {
+          documentedGetter = getter;
+        }
       }
     }
-    return null;
+
+    // Use documentation of a corresponding getter if setters don't have it
+    documentedElement ??= documentedGetter;
+    if (documentedElement == null) {
+      return null;
+    }
+
+    var rawDoc = documentedElement.documentationComment;
+    var result = dartdocInfo.processDartdoc(rawDoc);
+
+    var documentedElementClass = documentedElement.enclosingElement;
+    if (documentedElementClass != element.enclosingElement) {
+      result += '\n\nCopied from `${documentedElementClass.displayName}`.';
+    }
+
+    return result;
   }
 
   static DartType _getTypeOfDeclarationOrReference(Expression node) {

pkg/analysis_server/test/analysis/get_hover_test.dart

@@ -723,4 +723,108 @@ main() {
     expect(hover.elementKind, 'parameter');
     expect(hover.staticType, 'int');
   }
+
+  Future<void> test_setter_hasDocumentation() async {
+    addTestFile('''
+class A {
+  /// getting
+  int get foo => 42;
+  /// setting
+  set foo(int x) {}
+}
+main(A a) {
+  a.foo = 123;
+}
+''');
+    var hover = await prepareHover('foo = ');
+    expect(hover.containingClassDescription, 'A');
+    expect(hover.dartdoc, '''setting''');
+    expect(hover.elementDescription, 'void set foo(int x)');
+    expect(hover.elementKind, 'setter');
+  }
+
+  Future<void> test_setter_noDocumentation() async {
+    addTestFile('''
+class A {
+  /// getting
+  int get foo => 42;
+  set foo(int x) {}
+}
+main(A a) {
+  a.foo = 123;
+}
+''');
+    var hover = await prepareHover('foo = ');
+    expect(hover.containingClassDescription, 'A');
+    expect(hover.dartdoc, '''getting''');
+    expect(hover.elementDescription, 'void set foo(int x)');
+    expect(hover.elementKind, 'setter');
+  }
+
+  Future<void> test_setter_super_hasDocumentation() async {
+    addTestFile('''
+class A {
+  /// pgetting
+  int get foo => 42;
+  /// psetting
+  set foo(int x) {}
+}
+class B extends A {
+  /// getting
+  int get foo => 42;
+  set foo(int x) {}
+}
+main(B b) {
+  b.foo = 123;
+}
+''');
+    var hover = await prepareHover('foo = ');
+    expect(hover.containingClassDescription, 'B');
+    expect(hover.dartdoc, '''psetting\n\nCopied from `A`.''');
+    expect(hover.elementDescription, 'void set foo(int x)');
+    expect(hover.elementKind, 'setter');
+  }
+
+  Future<void> test_setter_super_noDocumentation() async {
+    addTestFile('''
+class A {
+  /// pgetting
+  int get foo => 42;
+  set foo(int x) {}
+}
+class B extends A {
+  int get foo => 42;
+  set foo(int x) {}
+}
+main(B b) {
+  b.foo = 123;
+}
+''');
+    var hover = await prepareHover('foo = ');
+    expect(hover.containingClassDescription, 'B');
+    expect(hover.dartdoc, '''pgetting\n\nCopied from `A`.''');
+    expect(hover.elementDescription, 'void set foo(int x)');
+    expect(hover.elementKind, 'setter');
+  }
+
+  @failingTest
+  Future<void> test_setter_super_noSetter() async {
+    addTestFile('''
+class A {
+  /// pgetting
+  int get foo => 42;
+}
+class B extends A {
+  set foo(int x) {}
+}
+main(B b) {
+  b.foo = 123;
+}
+''');
+    var hover = await prepareHover('foo = ');
+    expect(hover.containingClassDescription, 'B');
+    expect(hover.dartdoc, '''pgetting''');
+    expect(hover.elementDescription, 'void set foo(int x)');
+    expect(hover.elementKind, 'setter');
+  }
 }