[Typechain] Investigate how to support the attach method

.changeset/small-buckets-ring.md

@@ -0,0 +1,5 @@
+---
+"@nomicfoundation/hardhat-typechain": patch
+---
+
+Added support for the `attach` method in `hardhat-typechain`.

v-next/hardhat-typechain/src/internal/generate-types.ts

@@ -110,6 +110,8 @@ function addCompiledFilesTransformerIfAbsent(
       'declare module "@nomicfoundation/hardhat-ethers/types"',
     );
 
+    modifiedContent = addSupportForAttachMethod(modifiedContent);
+
     return modifiedContent;
   };
 
@@ -140,3 +142,45 @@ export function addJsExtensionsIfNeeded(content: string): string {
       `import ${imports} from ${quote}${path}/index.js${quote};`,
   );
 }
+
+// We expect the structure of the factory files to be:
+// /* eslint-disable */
+// ...
+// export class [contractName]__factory extends ContractFactory {
+//   ...
+//   static connect(
+//   ...
+// }
+function addSupportForAttachMethod(modifiedContent: string): string {
+  const pattern = /class\s+(\w+)__factory/; // Pattern to find the contract name in factory files
+  const match = modifiedContent.match(pattern);
+
+  if (match === null) {
+    // File is not a factory file, so there is no need to modify it
+    return modifiedContent;
+  }
+
+  const contractName = match[1];
+
+  // Insert the "attach" snippet right before the "connect" method
+  const insertPoint = modifiedContent.lastIndexOf("static connect(");
+
+  const attachMethod = `
+    override attach(address: string | Addressable): ${contractName} {
+      return super.attach(address) as ${contractName};
+    }
+  `;
+
+  modifiedContent =
+    modifiedContent.slice(0, insertPoint) +
+    attachMethod +
+    modifiedContent.slice(insertPoint);
+
+  // Import the "Addressable" type as it is required by the "attach" method
+  modifiedContent = modifiedContent.replace(
+    "/* eslint-disable */",
+    '/* eslint-disable */\nimport type { Addressable } from "ethers";',
+  );
+
+  return modifiedContent;
+}

v-next/hardhat-typechain/test/index.ts

@@ -18,11 +18,6 @@ describe("hardhat-typechain", () => {
 
     before(async () => {
       await remove(`${process.cwd()}/types`);
-    });
-
-    it("should generate the types", async () => {
-      // Check that the types are generated with the expected addition of the "/index.js" extensions
-      // and the v3 modules
 
       const hardhatConfig = await import(
         // eslint-disable-next-line import/no-relative-packages -- allow for fixture projects
@@ -36,6 +31,11 @@ describe("hardhat-typechain", () => {
       await hre.tasks.getTask("clean").run();
 
       await hre.tasks.getTask("compile").run();
+    });
+
+    it("should generate the types for the `hardhat.d.ts` file", async () => {
+      // Check that the types are generated with the expected addition of the "/index.js" extensions
+      // and the v3 modules
 
       const content = await readUtf8File(
         path.join(process.cwd(), "types", "ethers-contracts", "hardhat.d.ts"),
@@ -63,12 +63,28 @@ describe("hardhat-typechain", () => {
 
       // The import from a npm package should have ".js" extensions
       assert.equal(content.includes(`import { ethers } from 'ethers'`), true);
+    });
 
-      // Check that the types for the contract are generated
-      assert.equal(
-        await exists(
-          `${process.cwd()}/types/ethers-contracts/factories/A__factory.ts`,
+    it("should generated types for the contracts and add the support for the `attach` method", async () => {
+      const content = await readUtf8File(
+        path.join(
+          process.cwd(),
+          "types",
+          "ethers-contracts",
+          "factories",
+          "A__factory.ts",
         ),
+      );
+
+      // The "Addressable" type should be imported
+      assert.equal(
+        content.includes(`import type { Addressable } from "ethers";`),
+        true,
+      );
+
+      // The "attach" method should be added to the factory
+      assert.equal(
+        content.includes(`override attach(address: string | Addressable): A {`),
         true,
       );
     });