[Fusion] FieldSelectionMapParser support for Path.SelectedObjectValue (#8203)

Author: glen-84

src/HotChocolate/Fusion-vnext/src/Fusion.Language/Parsers/FieldSelectionMapParser.cs

@@ -97,9 +97,17 @@ private SelectedValueEntryNode ParseSelectedValueEntry()
             case TokenKind.LeftAngleBracket: // For a <TypeName>.
                 path = ParsePath();
 
-                if (_reader.TokenKind == TokenKind.LeftSquareBracket)
+                // ReSharper disable once SwitchStatementMissingSomeEnumCasesNoDefault
+                switch (_reader.TokenKind)
                 {
-                    selectedListValue = ParseSelectedListValue();
+                    case TokenKind.Period:
+                        MoveNext(); // skip "."
+                        selectedObjectValue = ParseSelectedObjectValue();
+                        break;
+
+                    case TokenKind.LeftSquareBracket:
+                        selectedListValue = ParseSelectedListValue();
+                        break;
                 }
 
                 break;
@@ -202,7 +210,8 @@ private PathSegmentNode ParsePathSegment()
             Expect(TokenKind.Period);
             pathSegment = ParsePathSegment();
         }
-        else if (_reader.TokenKind == TokenKind.Period)
+        else if (_reader.TokenKind == TokenKind.Period
+            && _reader.GetNextTokenKind() != TokenKind.LeftBrace)
         {
             MoveNext(); // skip "."
             pathSegment = ParsePathSegment();

src/HotChocolate/Fusion-vnext/src/Fusion.Language/Readers/FieldSelectionMapReader.cs

@@ -124,6 +124,46 @@ public bool Read()
         throw new FieldSelectionMapSyntaxException(this, UnexpectedCharacter, code);
     }
 
+    public readonly TokenKind GetNextTokenKind()
+    {
+        if (Position >= _length)
+        {
+            return TokenKind.EndOfFile;
+        }
+
+        var position = Position;
+        var code = _sourceText[position];
+
+        // Skip insignificant characters.
+        while (position < _length - 1)
+        {
+            if (code
+                is CharConstants.Space
+                or CharConstants.LineFeed
+                or CharConstants.Return
+                or CharConstants.HorizontalTab
+                or CharConstants.Comma)
+            {
+                code = _sourceText[++position];
+                continue;
+            }
+
+            break;
+        }
+
+        if (code.IsPunctuator())
+        {
+            return GetPunctuatorTokenKind(code);
+        }
+
+        if (code.IsLetterOrUnderscore())
+        {
+            return TokenKind.Name;
+        }
+
+        throw new FieldSelectionMapSyntaxException(this, UnexpectedCharacter, code);
+    }
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public bool Skip(TokenKind tokenKind)
     {
@@ -219,8 +259,13 @@ private void ReadPunctuatorToken(char code)
         Start = Position;
         End = ++Position;
         Value = null;
+        TokenKind = GetPunctuatorTokenKind(code);
+    }
 
-        TokenKind = code switch
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static TokenKind GetPunctuatorTokenKind(char code)
+    {
+        return code switch
         {
             CharConstants.Colon => TokenKind.Colon,
             CharConstants.LeftAngleBracket => TokenKind.LeftAngleBracket,

src/HotChocolate/Fusion-vnext/src/Fusion.Language/SyntaxSerializers/FieldSelectionMapSyntaxSerializer.cs

@@ -146,6 +146,11 @@ protected override ISyntaxVisitorAction Enter(
         if (node.Path is not null)
         {
             Visit(node.Path, writer);
+
+            if (node.SelectedObjectValue is not null)
+            {
+                writer.Write(Period);
+            }
         }
 
         if (node.SelectedObjectValue is not null)

src/HotChocolate/Fusion-vnext/test/Fusion.Language.Tests/FieldSelectionMapParserTests.cs

@@ -187,8 +187,7 @@ public void Parse_SelectedObjectValueMultipleFieldsNoSelectedValue_MatchesSnapsh
 
     [Theory]
     // https://graphql.github.io/composite-schemas-spec/draft/#sec-SelectedObjectValue
-    // TODO: Enable this test when the parser supports it.
-    [InlineData("dimension.{ size weight }", Skip = "Not yet supported by parser")]
+    [InlineData("dimension.{ size weight }")]
     [InlineData("{ size: dimensions.size weight: dimensions.weight }")]
     public void ParseAndPrint_SelectedObjectValueValidExamples_Matches(string sourceText)
     {

src/HotChocolate/Fusion-vnext/test/Fusion.Utilities.Tests/Rewriters/SelectedValueToSelectionSetRewriterTests.cs

@@ -60,7 +60,18 @@ ... on Book {
                 }
                 """
             },
-            // TODO: Test "dimension.{ size weight }" (not yet supported by parser).
+            {
+                "Product",
+                "dimensions.{ size weight }",
+                """
+                {
+                    dimensions {
+                        size
+                        weight
+                    }
+                }
+                """
+            },
             {
                 "Product",
                 "{ size: dimensions.size weight: dimensions.weight }",