Merge PR when checks are ready (#13)

There is an issue that you can not enable `auto-merge` when a PR is
ready to merge.

For this situation, I have added a try/catch block where it evaluates if
the error contains the message `Pull request is in clean status`. If so,
it will use the
[mergePullRequest](https://docs.github.com/en/graphql/reference/mutations#mergepullrequest)
mutation to merge the PR directly.

This fixes #12

src/github/merger.ts

@@ -19,6 +19,14 @@ mutation($prId: ID!) {
     }
 }`;
 
+// https://docs.github.com/en/graphql/reference/mutations#mergepullrequest
+export const MERGE_PULL_REQUEST = `
+mutation($prId: ID!, $mergeMethod: PullRequestMergeMethod!) {
+  mergePullRequest(input: {pullRequestId: $prId, mergeMethod: $mergeMethod}) {
+      clientMutationId
+  }
+}`;
+
 export type MergeMethod = "SQUASH" | "MERGE" | "REBASE";
 
 export class Merger {
@@ -30,13 +38,34 @@ export class Merger {
   ) {}
 
   async enableAutoMerge(): Promise<void> {
-    await this.gql<{
-      enablePullRequestAutoMerge: { clientMutationId: unknown };
-    }>(ENABLE_AUTO_MERGE, {
-      prId: this.nodeId,
-      mergeMethod: this.mergeMethod,
-    });
-    this.logger.info("Succesfully enabled auto-merge");
+    try {
+      await this.gql<{
+        enablePullRequestAutoMerge: { clientMutationId: unknown };
+      }>(ENABLE_AUTO_MERGE, {
+        prId: this.nodeId,
+        mergeMethod: this.mergeMethod,
+      });
+      this.logger.info("Succesfully enabled auto-merge");
+    } catch (error) {
+      this.logger.warn(error as Error);
+      if (
+        error instanceof Error &&
+        error.message.includes("Pull request is in clean status")
+      ) {
+        this.logger.warn(
+          "Pull Request is ready to merge. Running merge command instead",
+        );
+        await this.gql<{
+          mergePullRequest: { clientMutationId: unknown };
+        }>(MERGE_PULL_REQUEST, {
+          prId: this.nodeId,
+          mergeMethod: this.mergeMethod,
+        });
+        this.logger.info("Succesfully merged PR");
+      } else {
+        throw error;
+      }
+    }
   }
 
   async disableAutoMerge(): Promise<void> {

src/test/queries.test.ts

@@ -1,6 +1,10 @@
 import { validate } from "@octokit/graphql-schema";
 
-import { DISABLE_AUTO_MERGE, ENABLE_AUTO_MERGE } from "../github/merger";
+import {
+  DISABLE_AUTO_MERGE,
+  ENABLE_AUTO_MERGE,
+  MERGE_PULL_REQUEST,
+} from "../github/merger";
 
 describe("Schemas", () => {
   test("ENABLE_AUTO_MERGE", () => {
@@ -10,4 +14,8 @@ describe("Schemas", () => {
   test("DISABLE_AUTO_MERGE", () => {
     expect(validate(DISABLE_AUTO_MERGE)).toEqual([]);
   });
+
+  test("MERGE_PULL_REQUEST", () => {
+    expect(validate(MERGE_PULL_REQUEST)).toEqual([]);
+  });
 });