Fix false @defer/@stream label collision in reused fragments (#9709)

Author: glen-84

src/HotChocolate/Core/src/Validation/Rules/DirectiveVisitor.cs

@@ -172,9 +172,14 @@ private static void ValidateDirectives<T>(
             }
 
             // Defer And Stream Directive Labels Are Unique
+            // The spec iterates over every directive in the document. Because the
+            // document walker descends into fragment definitions once per spread,
+            // the same lexical @defer/@stream directive may be visited multiple
+            // times. Track the processed directive nodes so each is counted once.
             if (node.Kind is Field or InlineFragment or FragmentSpread
                 && (directive.Name.Value.Equals(DirectiveNames.Defer.Name, StringComparison.Ordinal)
-                || directive.Name.Value.Equals(DirectiveNames.Stream.Name, StringComparison.Ordinal)))
+                || directive.Name.Value.Equals(DirectiveNames.Stream.Name, StringComparison.Ordinal))
+                && feature.ProcessedLabelDirectives.Add(directive))
             {
                 switch (directive.GetArgumentValue(DirectiveNames.Defer.Arguments.Label))
                 {
@@ -249,10 +254,13 @@ private sealed class DirectiveVisitorFeature : ValidatorFeature
 
         public HashSet<string> Labels { get; } = [];
 
+        public HashSet<DirectiveNode> ProcessedLabelDirectives { get; } = [];
+
         protected internal override void Reset()
         {
             DirectiveNames.Clear();
             Labels.Clear();
+            ProcessedLabelDirectives.Clear();
         }
     }
 }

src/HotChocolate/Core/test/Validation.Tests/DeferAndStreamDirectiveLabelsAreUniqueTests.cs

@@ -87,6 +87,90 @@ ... @defer(label: $a) {
                 t.Message));
     }
 
+    [Fact]
+    public void Label_Should_Be_Valid_When_Defer_Is_In_Reused_Fragment()
+    {
+        ExpectValid(
+            """
+            query {
+              ...Repeated
+              ...Repeated
+            }
+
+            fragment Repeated on Query {
+              ... @defer(label: "details") {
+                __typename
+              }
+            }
+            """);
+    }
+
+    [Fact]
+    public void Label_Should_Be_Valid_When_Stream_Is_In_Reused_Fragment()
+    {
+        ExpectValid(
+            """
+            query {
+              ...Repeated
+              ...Repeated
+            }
+
+            fragment Repeated on Query {
+              __schema {
+                _types @stream(label: "types") {
+                  name
+                }
+              }
+            }
+            """);
+    }
+
+    [Fact]
+    public void Label_Should_Be_Valid_When_Fragment_Is_Spread_Across_Operations()
+    {
+        ExpectValid(
+            """
+            query A {
+              ...Repeated
+            }
+
+            query B {
+              ...Repeated
+            }
+
+            fragment Repeated on Query {
+              ... @defer(label: "details") {
+                __typename
+              }
+            }
+            """);
+    }
+
+    [Fact]
+    public void Label_Duplicate_When_Reused_Fragment_Label_Also_Used_Outside()
+    {
+        ExpectErrors(
+            """
+            query {
+              ...Repeated
+              ...Repeated
+              ... @defer(label: "details") {
+                __typename
+              }
+            }
+
+            fragment Repeated on Query {
+              ... @defer(label: "details") {
+                __typename
+              }
+            }
+            """,
+            t => Assert.Equal(
+                "If a label is passed, it must be unique within all other @defer "
+                + "and @stream directives in the document.",
+                t.Message));
+    }
+
     [Fact]
     public void Label_Can_Be_Null_And_Is_Optional_And_Can_Be_A_Unique_Name()
     {

src/HotChocolate/Core/test/Validation.Tests/__snapshots__/DeferAndStreamDirectiveLabelsAreUniqueTests.Label_Duplicate_When_Reused_Fragment_Label_Also_Used_Outside.snap

@@ -0,0 +1,14 @@
+{
+  "message": "If a label is passed, it must be unique within all other @defer and @stream directives in the document.",
+  "locations": [
+    {
+      "line": 4,
+      "column": 3
+    }
+  ],
+  "extensions": {
+    "specifiedBy": "https://spec.graphql.org/draft/#sec-Defer-And-Stream-Directive-Labels-Are-Unique",
+    "rfc": "https://github.com/graphql/graphql-spec/pull/1110",
+    "label": "details"
+  }
+}