Bugfix getArgumentValues: DefaultValue not used

When no argument was provided, the defaultValue should be used as argument value

Author: andimarek

src/executor/__tests__/variables.js

@@ -51,6 +51,11 @@ var TestType = new GraphQLObjectType({
       args: { input: { type: new GraphQLNonNull(GraphQLString) } },
       resolve: (_, { input }) => input && JSON.stringify(input)
     },
+    fieldWithDefaultArgumentValue: {
+      type: GraphQLString,
+      args: { input: { type: GraphQLString, defaultValue: 'Hello World' } },
+      resolve: (_, { input }) => input && JSON.stringify(input)
+    },
     list: {
       type: GraphQLString,
       args: { input: { type: new GraphQLList(GraphQLString) } },
@@ -720,4 +725,45 @@ describe('Execute: Handles inputs', () => {
     });
 
   });
+
+  describe('Execute: Uses argument default values', () => {
+
+    it('when no argument provided', async () => {
+      var ast = parse(`{
+        fieldWithDefaultArgumentValue
+      }`);
+
+      return expect(await execute(schema, ast)).to.deep.equal({
+        data: {
+          fieldWithDefaultArgumentValue: '"Hello World"'
+        }
+      });
+    });
+
+    it('when nullable variable provided', async () => {
+      var ast = parse(`query optionalVariable($optional: String) {
+        fieldWithDefaultArgumentValue(input: $optional)
+      }`);
+
+      return expect(await execute(schema, ast)).to.deep.equal({
+        data: {
+          fieldWithDefaultArgumentValue: '"Hello World"'
+        }
+      });
+    });
+
+    it('when argument provided cannot be coerced', async () => {
+      var ast = parse(`{
+        fieldWithDefaultArgumentValue(input: WRONG_TYPE)
+      }`);
+
+      return expect(await execute(schema, ast)).to.deep.equal({
+        data: {
+          fieldWithDefaultArgumentValue: '"Hello World"'
+        }
+      });
+    });
+
+  });
+
 });

src/executor/values.js

@@ -64,8 +64,12 @@ export function getArgumentValues(
   var argASTMap = argASTs ? keyMap(argASTs, arg => arg.name.value) : {};
   return argDefs.reduce((result, argDef) => {
     var name = argDef.name;
-    var valueAST = argASTMap[name] && argASTMap[name].value;
-    result[name] = coerceValueAST(argDef.type, valueAST, variables);
+    var valueAST = argASTMap[name] ? argASTMap[name].value : null;
+    var value = coerceValueAST(argDef.type, valueAST, variables);
+    if (isNullish(value) && !isNullish(argDef.defaultValue)) {
+      value = argDef.defaultValue;
+    }
+    result[name] = value;
     return result;
   }, {});
 }