Replace fragment argument variables at execution time with passed-in arguments.

Author: mjmahone

src/execution/__tests__/variables-test.ts

@@ -130,6 +130,14 @@ function executeQuery(
   return executeSync({ schema, document, variableValues });
 }
 
+function executeQueryWithFragmentArguments(
+  query: string,
+  variableValues?: { [variable: string]: unknown },
+) {
+  const document = parse(query, {allowFragmentArguments: true});
+  return executeSync({ schema, document, variableValues });
+}
+
 describe('Execute: Handles inputs', () => {
   describe('Handles objects and nullability', () => {
     describe('using inline structs', () => {
@@ -1005,6 +1013,25 @@ describe('Execute: Handles inputs', () => {
     });
   });
 
+  describe('using fragment arguments', () => {
+    const result = executeQueryWithFragmentArguments(`
+      query {
+        ...a(value: "A")
+      }
+
+      fragment a($value: String!) on TestType {
+        fieldWithNonNullableStringInput(input: $value)
+      }
+    `);
+    console.log(JSON.stringify(result));
+    expect(result).to.deep.equal({
+      data: {
+        fieldWithNonNullableStringInput:
+          '"A"',
+      },
+    });
+  });
+
   describe('getVariableValues: limit maximum number of coercion errors', () => {
     const doc = parse(`
       query ($input: [String!]) {

src/execution/execute.ts

@@ -25,8 +25,12 @@ import type {
   FragmentSpreadNode,
   InlineFragmentNode,
   FragmentDefinitionNode,
+  ArgumentNode,
+  ValueNode,
+  DirectiveNode,
 } from '../language/ast';
 import { Kind } from '../language/kinds';
+import { print } from '../language/printer';
 
 import type { GraphQLSchema } from '../type/schema';
 import type {
@@ -66,6 +70,7 @@ import {
   getArgumentValues,
   getDirectiveValues,
 } from './values';
+import { visit } from '../language';
 
 /**
  * Terminology
@@ -511,10 +516,14 @@ export function collectFields(
         ) {
           continue;
         }
+        const selectionSet = selectionSetWithFragmentArgumentsApplied(
+          fragment,
+          selection.arguments,
+        );
         collectFields(
           exeContext,
           runtimeType,
-          fragment.selectionSet,
+          selectionSet,
           fields,
           visitedFragmentNames,
         );
@@ -525,6 +534,38 @@ export function collectFields(
   return fields;
 }
 
+function selectionSetWithFragmentArgumentsApplied(fragment: FragmentDefinitionNode, fragmentArguments?: ReadonlyArray<ArgumentNode>): SelectionSetNode {
+  if (fragment.variableDefinitions == null) {
+    return fragment.selectionSet;
+  }
+
+  const providedArguments: Map<string, ArgumentNode> = new Map();
+  for (const arg of fragmentArguments ?? []) {
+    providedArguments.set(arg.name.value, arg);
+  }
+  const fragmentArgumentValues: Map<string, ValueNode> = new Map();
+  for (const argDef of fragment.variableDefinitions ?? []) {
+    const argName = argDef.variable.name.value;
+    const providedArg = providedArguments.get(argName);
+    const argDefaultValue = argDef.defaultValue;
+    if (providedArg != null) {
+      fragmentArgumentValues.set(argName, providedArg.value);
+    } else if (argDefaultValue != null) {
+      fragmentArgumentValues.set(argName, argDefaultValue);
+    }
+  }
+
+  return visit(fragment.selectionSet, {
+    Variable(variable) {
+      const replacementValue = fragmentArgumentValues.get(variable.name.value);
+      if (replacementValue != null) {
+        return replacementValue;
+      }
+      return variable;
+    }
+  });
+}
+
 /**
  * Determines if a field should be included based on the @include and @skip
  * directives, where @skip has higher precedence than @include.