fix: description decorator placement for type properties

src/Bicep.Core/CodeAction/Fixes/DecoratorCodeFixProvider.cs

@@ -24,7 +24,7 @@ public DecoratorCodeFixProvider(string decoratorName, Decorator decorator)
 
     public IEnumerable<CodeFix> GetFixes(SemanticModel semanticModel, IReadOnlyList<SyntaxBase> matchingNodes)
     {
-        if (matchingNodes.OfType<DecorableSyntax>().FirstOrDefault() is not { } decorableSyntax || decorableSyntax.Decorators.Any(IsTargetDecorator))
+        if (matchingNodes.OfType<DecorableSyntax>().LastOrDefault() is not { } decorableSyntax || decorableSyntax.Decorators.Any(IsTargetDecorator))
         {
             yield break;
         }
@@ -40,10 +40,7 @@ public IEnumerable<CodeFix> GetFixes(SemanticModel semanticModel, IReadOnlyList<
         }
 
         var decoratorSyntax = SyntaxFactory.CreateDecorator(decoratorName, GetEmptyParams());
-        var newline = semanticModel.Configuration.Formatting.Data.NewlineKind.ToEscapeSequence();
-        var decoratorText = $"{decoratorSyntax}{newline}";
-        var newSpan = new TextSpan(decorableSyntax.Span.Position, 0);
-        var codeReplacement = new CodeReplacement(newSpan, decoratorText);
+        var codeReplacement = CreateCodeReplacement(semanticModel, decorableSyntax, decoratorSyntax);
 
         yield return new CodeFix(
             $"Add @{decoratorName}",
@@ -64,21 +61,45 @@ private bool IsTargetDecorator(DecoratorSyntax decoratorSyntax)
         OutputDeclarationSyntax => FunctionFlags.OutputDecorator,
         ExtensionDeclarationSyntax => FunctionFlags.ExtensionDecorator,
         MetadataDeclarationSyntax => FunctionFlags.MetadataDecorator,
-        TypeDeclarationSyntax or ObjectTypePropertySyntax => FunctionFlags.TypeDecorator,
+        TypeDeclarationSyntax or ObjectTypePropertySyntax or ObjectTypeAdditionalPropertiesSyntax or TupleTypeItemSyntax => FunctionFlags.TypeDecorator,
         _ => FunctionFlags.AnyDecorator,
     };
 
     private TypeSymbol? GetPotentialTargetType(SemanticModel model, DecorableSyntax potentialTarget) => potentialTarget switch
     {
-        // The properties of explicitly declared object types will not be bound to a specific symbol, but the TypeManager will have cached the property's type
-        ObjectTypePropertySyntax objectTypeProperty when model.GetDeclaredType(objectTypeProperty) is { } typePropertyType => typePropertyType,
+        // Members of explicitly declared aggregate types will not be bound to a specific symbol,
+        // but the TypeManager will have cached the member's type.
+        ObjectTypePropertySyntax or ObjectTypeAdditionalPropertiesSyntax or TupleTypeItemSyntax
+            when model.GetDeclaredType(potentialTarget) is { } typeMemberType => typeMemberType,
         // Type declaration statements have a type of Type<T>, but decorators evaluate T (e.g., string, not Type<string>) to determine whether they can attach to a given type declaration
         TypeDeclarationSyntax typeDeclaration when model.GetDeclaredType(typeDeclaration) is { } declaredType => declaredType is TypeType typeType ? typeType.Unwrapped : declaredType,
         // All other statements should use their assigned type
         StatementSyntax declaration when model.GetSymbolInfo(declaration) is DeclaredSymbol symbol => symbol.Type,
         _ => null,
     };
 
+    private static CodeReplacement CreateCodeReplacement(SemanticModel model, DecorableSyntax syntax, DecoratorSyntax decorator)
+    {
+        var formatting = model.Configuration.Formatting.Data;
+        var newline = formatting.NewlineKind.ToEscapeSequence();
+        var position = syntax.Span.Position;
+        var (_, character) = TextCoordinateConverter.GetPosition(model.SourceFile.LineStarts, position);
+        var linePrefix = model.SourceFile.Text[(position - character)..position];
+        var indentation = linePrefix[..(linePrefix.Length - linePrefix.TrimStart(' ', '\t').Length)];
+
+        if (indentation.Length == linePrefix.Length)
+        {
+            return new(new TextSpan(position, 0), $"{decorator}{newline}{indentation}");
+        }
+
+        indentation += formatting.IndentKind == IndentKind.Tab ? "\t" : new string(' ', formatting.IndentSize);
+
+        var whitespaceLength = linePrefix.Length - linePrefix.TrimEnd(' ', '\t').Length;
+        var replacementSpan = new TextSpan(position - whitespaceLength, whitespaceLength);
+
+        return new(replacementSpan, $"{newline}{indentation}{decorator}{newline}{indentation}");
+    }
+
     private SyntaxBase[] GetEmptyParams()
     {
         if (decorator.Overload.MinimumArgumentCount == 1 &&

src/Bicep.LangServer.UnitTests/Handlers/BicepCodeActionHandlerTests.cs

@@ -128,6 +128,110 @@ public async Task Multiline_string_suggestion_skips_strings_without_newline_char
             codeActions.Should().NotContain(x => x.Title == MultilineStringCodeFixProvider.Title);
         }
 
+        [DataRow(
+            """
+            @description('Type description.')
+            type BarConfig = {
+              ty|pe: 'bar'
+              value: bool
+            }
+            """,
+            """
+            @description('Type description.')
+            type BarConfig = {
+              @description('')
+              type: 'bar'
+              value: bool
+            }
+            """)]
+        [DataRow(
+            """
+            type config = {
+              nested: {
+                val|ue: string
+              }
+            }
+            """,
+            """
+            type config = {
+              nested: {
+                @description('')
+                value: string
+              }
+            }
+            """)]
+        [DataRow(
+            """
+            type config = {
+              |*: string
+            }
+            """,
+            """
+            type config = {
+              @description('')
+              *: string
+            }
+            """)]
+        [DataRow(
+            """
+            type config = [
+              str|ing
+            ]
+            """,
+            """
+            type config = [
+              @description('')
+              string
+            ]
+            """)]
+        [DataRow(
+            "type config = { val|ue: string }",
+            """
+            type config = {
+              @description('')
+              value: string }
+            """)]
+        [DataTestMethod]
+        public async Task Type_member_decorator_actions_target_the_innermost_decorable_syntax(string fileWithCursor, string expectedText)
+        {
+            var (contents, cursor) = ParserHelper.GetFileWithSingleCursor(fileWithCursor);
+            var bicepFile = GetBicepFile(contents);
+            var codeAction = await GetSingleCodeAction(bicepFile, cursor, "Add @description");
+
+            codeAction.Kind.Should().Be(CodeActionKind.Refactor);
+            LspRefactoringHelper.ApplyCodeAction(bicepFile, codeAction).Text.Should().Be(expectedText);
+        }
+
+        [TestMethod]
+        public async Task Type_property_description_action_is_not_suggested_when_property_already_has_description()
+        {
+            var (contents, cursor) = ParserHelper.GetFileWithSingleCursor(
+                """
+                type config = {
+                  @description('Property description.')
+                  val|ue: string
+                }
+                """);
+
+            var codeActions = await GetCodeActions(GetBicepFile(contents), cursor);
+
+            codeActions.Should().NotContain(x => x.Title == "Add @description");
+        }
+
+        [TestMethod]
+        public async Task Type_declaration_decorator_actions_still_target_the_type_declaration()
+        {
+            var (contents, cursor) = ParserHelper.GetFileWithSingleCursor("type con|fig = string");
+            var bicepFile = GetBicepFile(contents);
+            var codeAction = await GetSingleCodeAction(bicepFile, cursor, "Add @description");
+
+            LspRefactoringHelper.ApplyCodeAction(bicepFile, codeAction).Text.Should().Be(
+                """
+                @description('')
+                type config = string
+                """);
+        }
+
         private static LanguageClientFile GetBicepFile(string contents)
             => new(new Uri("file:///main.bicep"), contents);