[Fusion] Fail Query Plan generation early (#7989)

Author: tobias-tengler

src/HotChocolate/Fusion/src/Core/Planning/Pipeline/ExecutionStepDiscoveryMiddleware.cs

@@ -797,9 +797,9 @@ private bool EnsureStepCanBeResolvedFromRoot(
 
         while (current is not null)
         {
-            var typeMetadata = _config.GetType<ObjectTypeMetadata>(path.Selection.DeclaringType.Name);
+            var typeMetadata = _config.GetType<ObjectTypeMetadata>(current.Selection.DeclaringType.Name);
 
-            if (!typeMetadata.Fields[path.Selection.Field.Name].Bindings.ContainsSubgraph(subgraphName))
+            if (!typeMetadata.Fields[current.Selection.Field.Name].Bindings.ContainsSubgraph(subgraphName))
             {
                 return false;
             }

src/HotChocolate/Fusion/src/Core/Planning/Steps/SelectionExecutionStep.cs

@@ -22,7 +22,7 @@ internal sealed class SelectionExecutionStep : ExecutionStep
     /// <param name="subgraphName">
     /// The name of the subgraph from which this execution step will fetch data.
     /// </param>
-    /// <param name="selectionSet">
+    /// <param name="selectionSetType">
     /// The selection set that is part of this execution step.
     /// </param>
     /// <param name="selectionSetTypeMetadata">
@@ -31,9 +31,9 @@ internal sealed class SelectionExecutionStep : ExecutionStep
     public SelectionExecutionStep(
         int id,
         string subgraphName,
-        IObjectType selectionSet,
+        IObjectType selectionSetType,
         ObjectTypeMetadata selectionSetTypeMetadata)
-        : this(id, subgraphName, null, null, selectionSet, selectionSetTypeMetadata)
+        : this(id, subgraphName, null, null, selectionSetType, selectionSetTypeMetadata)
     {
     }
 
@@ -52,7 +52,7 @@ public SelectionExecutionStep(
     /// <param name="parentSelectionPath">
     /// The selection path from which this execution step was spawned.
     /// </param>
-    /// <param name="selectionSet">
+    /// <param name="selectionSetType">
     /// The selection set that is part of this execution step.
     /// </param>
     /// <param name="selectionSetTypeMetadata">
@@ -63,9 +63,9 @@ public SelectionExecutionStep(
         string subgraphName,
         ISelection? parentSelection,
         SelectionPath? parentSelectionPath,
-        IObjectType selectionSet,
+        IObjectType selectionSetType,
         ObjectTypeMetadata selectionSetTypeMetadata)
-        : base(id, parentSelection, selectionSet, selectionSetTypeMetadata)
+        : base(id, parentSelection, selectionSetType, selectionSetTypeMetadata)
     {
         SubgraphName = subgraphName;
         ParentSelectionPath = parentSelectionPath;

src/HotChocolate/Fusion/src/Core/Planning/Steps/SelectionPath.cs

@@ -35,8 +35,8 @@ public override string ToString()
 
         while (current is not null)
         {
-            sb.Append('/');
-            sb.Append(Selection.ResponseName);
+            sb.Insert(0, '/');
+            sb.Insert(1, current.Selection.ResponseName);
             current = current.Parent;
         }
 

src/HotChocolate/Fusion/test/Core.Tests/RequestPlannerTests.cs

@@ -2650,6 +2650,80 @@ query Requires {
         await snapshot.MatchMarkdownAsync();
     }
 
+    [Fact]
+    public async Task Throw_Instead_Of_Creating_Faulty_QueryPlan()
+    {
+        // arrange
+        var subgraphA = await TestSubgraph.CreateAsync(
+            """
+            type Query {
+              node(id: ID!): Node
+              productById(id: ID!): Product
+            }
+
+            interface Node {
+              id: ID!
+            }
+
+            type Product implements Node {
+              id: ID!
+              review: Review
+            }
+
+            type Review implements Node {
+              id: ID!
+              ratings: Ratings
+            }
+
+            type Ratings {
+              upvotes: Int!
+            }
+            """);
+
+        var subgraphB = await TestSubgraph.CreateAsync(
+            """
+            type Query {
+              node(id: ID!): Node
+            }
+
+            interface Node {
+              id: ID!
+            }
+
+            type Review implements Node {
+              id: ID!
+              ratings: Ratings
+            }
+
+            type Ratings {
+              downvotes: Int!
+            }
+            """);
+
+        using var subgraphs = new TestSubgraphCollection(output, [subgraphA, subgraphB]);
+        var fusionGraph = await subgraphs.GetFusionGraphAsync();
+
+        // act
+        var act = () => CreateQueryPlanAsync(
+            fusionGraph,
+            """
+            query {
+              productById(id: "1") {
+                review {
+                  ratings {
+                    upvotes
+                    downvotes
+                  }
+                }
+              }
+            }
+            """);
+
+        // assert
+        var exception = await Assert.ThrowsAsync<InvalidOperationException>(act);
+        Assert.Equal(FusionResources.ThrowHelper_NoResolverInContext, exception.Message);
+    }
+
     private static async Task<(DocumentNode UserRequest, Execution.Nodes.QueryPlan QueryPlan)> CreateQueryPlanAsync(
         Skimmed.SchemaDefinition fusionGraph,
         [StringSyntax("graphql")] string query)