DO NOT MERGE : This POC shows what a new GraphQLEngine might look like

src/main/java/graphql/engine/EngineParameters.java

@@ -0,0 +1,184 @@
+package graphql.engine;
+
+import graphql.Assert;
+import graphql.Internal;
+import graphql.PublicApi;
+import graphql.execution.ExecutionStepInfo;
+import graphql.execution.MergedField;
+import graphql.execution.MergedSelectionSet;
+import graphql.execution.NonNullableFieldValidator;
+import graphql.execution.ResultPath;
+import graphql.language.OperationDefinition;
+
+import java.util.function.Consumer;
+
+import static graphql.Assert.assertNotNull;
+
+/**
+ * The parameters that are passed to {@link GraphQLEngine}s
+ */
+@PublicApi
+public class EngineParameters {
+    private final ExecutionStepInfo executionStepInfo;
+    private final Object source;
+    private final Object localContext;
+    private final MergedSelectionSet fields;
+    private final NonNullableFieldValidator nonNullableFieldValidator;
+    private final ResultPath path;
+    private final MergedField currentField;
+    private final OperationDefinition.Operation operation;
+
+    private EngineParameters(Builder builder) {
+
+        this.executionStepInfo = assertNotNull(builder.executionStepInfo, () -> "executionStepInfo is null");
+        this.localContext = builder.localContext;
+        this.fields = assertNotNull(builder.fields, () -> "fields is null");
+        this.source = builder.source;
+        this.nonNullableFieldValidator = builder.nonNullableFieldValidator;
+        this.path = builder.path;
+        this.currentField = builder.currentField;
+        this.operation = builder.operation;
+    }
+
+    public NonNullableFieldValidator getNonNullableFieldValidator() {
+        return nonNullableFieldValidator;
+    }
+
+    public OperationDefinition.Operation getOperation() {
+        return operation;
+    }
+
+    public ExecutionStepInfo getExecutionStepInfo() {
+        return executionStepInfo;
+    }
+
+    public Object getSource() {
+        return source;
+    }
+
+    public MergedSelectionSet getFields() {
+        return fields;
+    }
+
+    public NonNullableFieldValidator getNonNullFieldValidator() {
+        return nonNullableFieldValidator;
+    }
+
+    public ResultPath getPath() {
+        return path;
+    }
+
+    public Object getLocalContext() {
+        return localContext;
+    }
+
+    /**
+     * This returns the current field in its query representations.
+     *
+     * @return the current merged fields
+     */
+    public MergedField getField() {
+        return currentField;
+    }
+
+    public EngineParameters transform(Consumer<Builder> builderConsumer) {
+        Builder builder = newParameters(this);
+        builderConsumer.accept(builder);
+        return builder.build();
+    }
+
+    @Override
+    public String toString() {
+        return String.format("EngineParameters { path=%s, executionStepInfo=%s, source=%s, fields=%s }",
+                path, executionStepInfo, source, fields);
+    }
+
+    public static Builder newParameters() {
+        return new Builder();
+    }
+
+    public static Builder newParameters(EngineParameters oldParameters) {
+        return new Builder(oldParameters);
+    }
+
+    @Internal
+    public static class Builder {
+        ExecutionStepInfo executionStepInfo;
+        Object source;
+        Object localContext;
+        MergedSelectionSet fields;
+        NonNullableFieldValidator nonNullableFieldValidator;
+        ResultPath path = ResultPath.rootPath();
+        MergedField currentField;
+        OperationDefinition.Operation operation;
+
+        /**
+         * @see EngineParameters#newParameters()
+         */
+        private Builder() {
+        }
+
+        /**
+         * @see EngineParameters#newParameters(EngineParameters)
+         */
+        private Builder(EngineParameters oldParameters) {
+            this.executionStepInfo = oldParameters.executionStepInfo;
+            this.source = oldParameters.source;
+            this.localContext = oldParameters.localContext;
+            this.fields = oldParameters.fields;
+            this.nonNullableFieldValidator = oldParameters.nonNullableFieldValidator;
+            this.currentField = oldParameters.currentField;
+            this.path = oldParameters.path;
+            this.operation = oldParameters.operation;
+        }
+
+        public Builder executionStepInfo(ExecutionStepInfo executionStepInfo) {
+            this.executionStepInfo = executionStepInfo;
+            return this;
+        }
+
+        public Builder executionStepInfo(ExecutionStepInfo.Builder executionStepInfoBuilder) {
+            this.executionStepInfo = executionStepInfoBuilder.build();
+            return this;
+        }
+
+        public Builder fields(MergedSelectionSet fields) {
+            this.fields = fields;
+            return this;
+        }
+
+        public Builder field(MergedField currentField) {
+            this.currentField = currentField;
+            return this;
+        }
+
+        public Builder source(Object source) {
+            this.source = source;
+            return this;
+        }
+
+        public Builder localContext(Object localContext) {
+            this.localContext = localContext;
+            return this;
+        }
+
+        public Builder nonNullFieldValidator(NonNullableFieldValidator nonNullableFieldValidator) {
+            this.nonNullableFieldValidator = Assert.assertNotNull(nonNullableFieldValidator, () -> "requires a NonNullValidator");
+            return this;
+        }
+
+        public Builder path(ResultPath path) {
+            this.path = path;
+            return this;
+        }
+
+        public Builder operation(OperationDefinition.Operation operation) {
+            this.operation = operation;
+            return this;
+        }
+
+        public EngineParameters build() {
+            return new EngineParameters(this);
+        }
+    }
+}

src/main/java/graphql/engine/GraphQLEngine.java

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+package graphql.engine;
+
+import graphql.ExecutionResult;
+import graphql.execution.ExecutionContext;
+import graphql.execution.NonNullableFieldWasNullException;
+import graphql.execution.instrumentation.Instrumentation;
+
+import java.util.concurrent.CompletableFuture;
+
+public interface GraphQLEngine {
+
+    Instrumentation getInstrumentation();
+
+    CompletableFuture<ExecutionResult> execute(ExecutionContext executionContext, EngineParameters parameters) throws NonNullableFieldWasNullException;
+}