[Fusion] Added SourceSchemaPreprocessor (#7975)

Author: tobias-tengler

src/HotChocolate/Fusion-vnext/src/Fusion.Composition/Extensions/ComplexTypeDefinitionExtensions.cs

@@ -0,0 +1,16 @@
+using HotChocolate.Skimmed;
+using ArgumentNames = HotChocolate.Fusion.WellKnownArgumentNames;
+using DirectiveNames = HotChocolate.Fusion.WellKnownDirectiveNames;
+
+namespace HotChocolate.Fusion.Extensions;
+
+internal static class ComplexTypeDefinitionExtensions
+{
+    public static void ApplyKeyDirective(this ComplexTypeDefinition type, string[] fields)
+    {
+        var fieldsArgument = new ArgumentAssignment(ArgumentNames.Fields, string.Join(" ", fields));
+        var keyDirective = new Directive(new DirectiveDefinition(DirectiveNames.Key), fieldsArgument);
+
+        type.Directives.Add(keyDirective);
+    }
+}

src/HotChocolate/Fusion-vnext/src/Fusion.Composition/Extensions/ObjectFieldDefinitionExtensions.cs

@@ -0,0 +1,12 @@
+using HotChocolate.Skimmed;
+using DirectiveNames = HotChocolate.Fusion.WellKnownDirectiveNames;
+
+namespace HotChocolate.Fusion.Extensions;
+
+public static class ObjectFieldDefinitionExtensions
+{
+    public static void ApplyLookupDirective(this OutputFieldDefinition outputField)
+    {
+        outputField.Directives.Add(new Directive(new DirectiveDefinition(DirectiveNames.Lookup)));
+    }
+}

src/HotChocolate/Fusion-vnext/src/Fusion.Composition/Extensions/ObjectTypeDefinitionExtensions.cs

@@ -0,0 +1,12 @@
+using HotChocolate.Skimmed;
+using DirectiveNames = HotChocolate.Fusion.WellKnownDirectiveNames;
+
+namespace HotChocolate.Fusion.Extensions;
+
+internal static class ObjectTypeDefinitionExtensions
+{
+    public static void ApplyShareableDirective(this ObjectTypeDefinition type)
+    {
+        type.Directives.Add(new Directive(new DirectiveDefinition(DirectiveNames.Shareable)));
+    }
+}

src/HotChocolate/Fusion-vnext/src/Fusion.Composition/Options/SourceSchemaPreprocessorOptions.cs

@@ -0,0 +1,6 @@
+namespace HotChocolate.Fusion.Options;
+
+internal sealed class SourceSchemaPreprocessorOptions
+{
+    public bool ApplyShareableToAllTypes { get; set; } = true;
+}

src/HotChocolate/Fusion-vnext/src/Fusion.Composition/SourceSchemaPreprocessor.cs

@@ -0,0 +1,102 @@
+using HotChocolate.Fusion.Extensions;
+using HotChocolate.Fusion.Options;
+using HotChocolate.Skimmed;
+using HotChocolate.Types;
+
+namespace HotChocolate.Fusion;
+
+/// <summary>
+/// Applies @lookup, @key, and optionally @shareable to a source schema to make it equivalent to a Fusion v1 source schema.
+/// </summary>
+internal sealed class SourceSchemaPreprocessor(
+    SchemaDefinition schema,
+    SourceSchemaPreprocessorOptions? options = null)
+{
+    public SchemaDefinition Process()
+    {
+        var context = new SourceSchemaPreprocessorContext(schema, options ?? new());
+
+        ApplyLookups(context);
+
+        if (context.Options.ApplyShareableToAllTypes)
+        {
+            ApplyShareableToAllTypes(context);
+        }
+
+        return schema;
+    }
+
+    private static void ApplyLookups(SourceSchemaPreprocessorContext context)
+    {
+        if (context.Schema.QueryType is not { } queryType)
+        {
+            return;
+        }
+
+        foreach (var queryField in queryType.Fields)
+        {
+            if (queryField.HasLookupDirective()
+                || queryField.Type.IsListType()
+                || queryField.Type.Kind == TypeKind.NonNull
+                || queryField.Arguments.Count != 1)
+            {
+                continue;
+            }
+
+            var keyArgument = queryField.Arguments.First();
+            var @is = keyArgument.GetIsFieldSelectionMap();
+
+            var queryFieldType = queryField.Type.NamedType();
+            var keyOutputFieldName = @is ?? keyArgument.Name;
+
+            if (!context.Schema.Types.TryGetType(queryFieldType.Name, out var resultType))
+            {
+                continue;
+            }
+
+            if (resultType is ObjectTypeDefinition resultObjectType)
+            {
+                if (resultObjectType.Fields.TryGetField(keyOutputFieldName, out var keyField))
+                {
+                    queryField.ApplyLookupDirective();
+
+                    resultObjectType.ApplyKeyDirective([keyField.Name]);
+                }
+            }
+            else if (resultType is InterfaceTypeDefinition resultInterfaceType)
+            {
+                if (resultInterfaceType.Fields.TryGetField(keyOutputFieldName, out var keyField))
+                {
+                    queryField.ApplyLookupDirective();
+
+                    resultInterfaceType.ApplyKeyDirective([keyField.Name]);
+
+                    foreach (var objectType in context.Schema.Types.OfType<ObjectTypeDefinition>())
+                    {
+                        if (objectType.Implements.ContainsName(resultInterfaceType.Name))
+                        {
+                            objectType.ApplyKeyDirective([keyField.Name]);
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    private static void ApplyShareableToAllTypes(SourceSchemaPreprocessorContext context)
+    {
+        foreach (var objectType in context.Schema.Types.OfType<ObjectTypeDefinition>())
+        {
+            objectType.ApplyShareableDirective();
+        }
+    }
+}
+
+internal sealed class SourceSchemaPreprocessorContext(
+    SchemaDefinition schema,
+    SourceSchemaPreprocessorOptions options)
+{
+    public SchemaDefinition Schema => schema;
+
+    public SourceSchemaPreprocessorOptions Options => options;
+}