feat(visitor-plugin-common): support object form for the codegenScalarType extension

.changeset/codegenscalartype-input-output.md

@@ -0,0 +1,7 @@
+---
+'@graphql-codegen/visitor-plugin-common': minor
+---
+
+Support an object form for the `codegenScalarType` scalar extension.
+
+A scalar's `extensions.codegenScalarType` can now be either a string (applied to both the `input` and `output` types, as before) or `{ input, output }` to map the two positions independently — matching what the `scalars` config option already accepts. This lets schema-first scalar libraries declare a stricter parsed/input type than the accepted resolver-return/output type directly from the schema, instead of collapsing both into one type.

packages/plugins/other/visitor-plugin-common/src/utils.ts

@@ -366,14 +366,17 @@ export function buildScalars(
             };
           }
         } else if (scalarType.extensions?.codegenScalarType) {
+          const normalizedScalar = normalizeScalarType(
+            scalarType.extensions.codegenScalarType as string | { input: string; output: string },
+          );
           result[name] = {
             input: {
               isExternal: false,
-              type: scalarType.extensions.codegenScalarType as string,
+              type: normalizedScalar.input,
             },
             output: {
               isExternal: false,
-              type: scalarType.extensions.codegenScalarType as string,
+              type: normalizedScalar.output,
             },
           };
         } else if (!defaultScalarsMapping[name]) {

packages/plugins/typescript/typescript/tests/typescript.spec.ts

@@ -1,4 +1,11 @@
-import { buildSchema, GraphQLEnumType, GraphQLObjectType, GraphQLSchema, parse } from 'graphql';
+import {
+  buildSchema,
+  GraphQLEnumType,
+  GraphQLObjectType,
+  GraphQLScalarType,
+  GraphQLSchema,
+  parse,
+} from 'graphql';
 import { mergeOutputs, Types } from '@graphql-codegen/plugin-helpers';
 import { validateTs } from '@graphql-codegen/testing';
 import { plugin } from '../src/index.js';
@@ -12,6 +19,32 @@ describe('TypeScript', () => {
     expect(result.prepend).toBeSimilarStringTo('export type Maybe<T> =');
   });
 
+  describe('codegenScalarType extension', () => {
+    const schemaWithScalarExtension = (codegenScalarType: unknown) =>
+      new GraphQLSchema({
+        query: new GraphQLObjectType({
+          name: 'Query',
+          fields: {
+            a: {
+              type: new GraphQLScalarType({ name: 'MyScalar', extensions: { codegenScalarType } }),
+            },
+          },
+        }),
+      });
+
+    it('maps a string codegenScalarType to both input and output', async () => {
+      const schema = schemaWithScalarExtension('MyType');
+      const result = await plugin(schema, [], {}, { outputFile: '' });
+      expect(result.content).toBeSimilarStringTo(`MyScalar: { input: MyType; output: MyType; }`);
+    });
+
+    it('maps an object codegenScalarType to distinct input and output', async () => {
+      const schema = schemaWithScalarExtension({ input: 'MyInput', output: 'MyOutput' });
+      const result = await plugin(schema, [], {}, { outputFile: '' });
+      expect(result.content).toBeSimilarStringTo(`MyScalar: { input: MyInput; output: MyOutput; }`);
+    });
+  });
+
   describe('description to comment', () => {
     it('Should include a description for Scalars type', async () => {
       const schema = buildSchema(/* GraphQL */ `