feat(repository): add CREATE_DEFAULT_BRANCH flag to create default branch instead of renaming

README.md

@@ -859,6 +859,10 @@ You can pass environment variables; the easiest way to do it is via a `.env` fil
   ```
   BLOCK_REPO_RENAME_BY_HUMAN=true
   ```
+1. Create the configured `default_branch` instead of renaming the current one using `CREATE_DEFAULT_BRANCH` (default is `false`). By default, when `repository.default_branch` is configured and differs from the repo's current default branch, `safe-settings` renames the current default branch to the configured name. When `CREATE_DEFAULT_BRANCH=true`, if the configured `default_branch` does not exist, `safe-settings` instead creates a new branch off the current default branch and sets it as the default, leaving the existing default branch untouched (no rename). If the configured branch already exists, it is simply set as the default. For e.g.
+  ```
+  CREATE_DEFAULT_BRANCH=true
+  ```
 
 
 ### Runtime Settings

docs/github-settings/1. repository-settings.md

@@ -226,7 +226,7 @@ repository:
 </td></tr>
 <tr><td>
 <p><code>default_branch</code><span style="color:gray;">&emsp;<i>boolean</i>&emsp;</span></p>
-<p>Updates the default branch for this repository.</p>
+<p>Updates the default branch for this repository. By default, if the configured branch differs from the current default branch, safe-settings renames the current default branch. Set the <code>CREATE_DEFAULT_BRANCH=true</code> environment variable to instead create the configured branch (off the current default) and promote it, without renaming the existing default branch.</p>
 </td><td style="vertical-align:top">
 
 ```yaml

lib/env.js

@@ -6,5 +6,6 @@ module.exports = {
   CREATE_PR_COMMENT: process.env.CREATE_PR_COMMENT || 'true',
   CREATE_ERROR_ISSUE: process.env.CREATE_ERROR_ISSUE || 'true',
   BLOCK_REPO_RENAME_BY_HUMAN: process.env.BLOCK_REPO_RENAME_BY_HUMAN || 'false',
+  CREATE_DEFAULT_BRANCH: process.env.CREATE_DEFAULT_BRANCH === 'true',
   FULL_SYNC_NOP: process.env.FULL_SYNC_NOP === 'true'
 }

lib/plugins/repository.js

@@ -3,6 +3,7 @@
 const ErrorStash = require('./errorStash')
 const NopCommand = require('../nopcommand')
 const MergeDeep = require('../mergeDeep')
+const env = require('../env')
 const ignorableFields = [
   'id',
   'node_id',
@@ -179,7 +180,7 @@ module.exports = class Repository extends ErrorStash {
       // If the old branch was renamed github will find the branch with the oldname the branch but the ref doesn't exist
       // So we'd have to rename it back to the oldname
       if (res.data.name !== newname) {
-        return this.renameBranch(oldname, newname, resArray)
+        return this.createOrRenameBranch(oldname, newname, resArray)
       } else {
         const parms = {
           owner: this.settings.owner,
@@ -195,13 +196,58 @@ module.exports = class Repository extends ErrorStash {
       }
     }).catch(e => {
       if (e.status === 404) {
-        return this.renameBranch(oldname, newname, resArray)
+        return this.createOrRenameBranch(oldname, newname, resArray)
       } else {
         this.logError(`Error ${JSON.stringify(e)}`)
       }
     })
   }
 
+  // Decide how to reconcile a missing default branch based on the
+  // CREATE_DEFAULT_BRANCH feature flag. When enabled, a new branch is created
+  // off the current default branch and promoted to default, leaving the existing
+  // default branch untouched. When disabled (default), the current default branch
+  // is renamed (the historical behavior).
+  createOrRenameBranch (oldname, newname, resArray) {
+    if (env.CREATE_DEFAULT_BRANCH) {
+      return this.createDefaultBranch(oldname, newname, resArray)
+    }
+    return this.renameBranch(oldname, newname, resArray)
+  }
+
+  createDefaultBranch (oldname, newname, resArray) {
+    this.log.debug(`Branch ${newname} does not exist. Creating it from the current default branch ${oldname} and making it the default`)
+    return this.github.repos.getBranch({
+      owner: this.settings.owner,
+      repo: this.settings.repo,
+      branch: oldname
+    }).then((res) => {
+      const sha = res.data.commit.sha
+      const createRefParms = {
+        owner: this.settings.owner,
+        repo: this.settings.repo,
+        ref: `refs/heads/${newname}`,
+        sha
+      }
+      const updateParms = {
+        owner: this.settings.owner,
+        repo: this.settings.repo,
+        default_branch: newname
+      }
+      if (this.nop) {
+        resArray.push(new NopCommand(this.constructor.name, this.repo, this.github.git.createRef.endpoint(createRefParms), `Create default branch ${newname} from ${oldname}`))
+        resArray.push(new NopCommand(this.constructor.name, this.repo, this.github.repos.update.endpoint(updateParms), `Set default branch to ${newname}`))
+        return Promise.resolve(resArray)
+      }
+      this.log.info(`Creating branch ${newname} from ${oldname} (${sha}) and setting it as the default branch`)
+      return this.github.git.createRef(createRefParms).then(() => {
+        return this.github.repos.update(updateParms)
+      })
+    }).catch(e => {
+      this.logError(`Error creating default branch ${newname} from ${oldname}: ${JSON.stringify(e)}`)
+    })
+  }
+
   renameBranch (oldname, newname, resArray) {
     this.log.error(`Branch ${newname} does not exist. So renaming the current default branch ${oldname} to ${newname}`)
     const parms = {

test/unit/lib/plugins/repository.test.js

@@ -1,4 +1,5 @@
 const Repository = require('../../../../lib/plugins/repository')
+const env = require('../../../../lib/env')
 
 describe('Repository', () => {
   const github = {
@@ -8,13 +9,19 @@ describe('Repository', () => {
           topics: []
         }
       }),
+      getBranch: jest.fn().mockResolvedValue({ data: { name: 'main', commit: { sha: 'abc123' } } }),
       update: jest.fn().mockResolvedValue(),
+      renameBranch: jest.fn().mockResolvedValue(),
       replaceAllTopics: jest.fn().mockResolvedValue()
+    },
+    git: {
+      createRef: jest.fn().mockResolvedValue()
     }
   }
   const log = jest.fn()
   log.debug = jest.fn()
   log.error = jest.fn()
+  log.info = jest.fn()
 
   function configure (config) {
     const nop = false
@@ -58,7 +65,7 @@ describe('Repository', () => {
       })
     })
 
-    it.only('syncs topics', () => {
+    it('syncs topics', () => {
       const plugin = configure({
         topics: ['foo', 'bar']
       })
@@ -75,4 +82,86 @@ describe('Repository', () => {
       })
     })
   })
+
+  describe('default_branch reconciliation', () => {
+    const originalFlag = env.CREATE_DEFAULT_BRANCH
+
+    beforeEach(() => {
+      jest.clearAllMocks()
+      github.repos.get.mockResolvedValue({
+        data: {
+          name: 'test',
+          default_branch: 'master',
+          topics: []
+        }
+      })
+    })
+
+    afterEach(() => {
+      env.CREATE_DEFAULT_BRANCH = originalFlag
+    })
+
+    describe('when CREATE_DEFAULT_BRANCH is disabled (default)', () => {
+      beforeEach(() => {
+        env.CREATE_DEFAULT_BRANCH = false
+      })
+
+      it('renames the current default branch when the configured branch is missing', () => {
+        github.repos.getBranch.mockRejectedValueOnce({ status: 404 })
+        const plugin = configure({ default_branch: 'main' })
+        return plugin.sync().then(() => {
+          expect(github.repos.renameBranch).toHaveBeenCalledWith({
+            owner: 'bkeepers',
+            repo: 'test',
+            branch: 'master',
+            new_name: 'main'
+          })
+          expect(github.git.createRef).not.toHaveBeenCalled()
+        })
+      })
+    })
+
+    describe('when CREATE_DEFAULT_BRANCH is enabled', () => {
+      beforeEach(() => {
+        env.CREATE_DEFAULT_BRANCH = true
+      })
+
+      it('creates the branch off the current default and promotes it without renaming', () => {
+        // First getBranch call (for the configured branch) 404s; the second
+        // (for the current default) returns its SHA.
+        github.repos.getBranch
+          .mockRejectedValueOnce({ status: 404 })
+          .mockResolvedValueOnce({ data: { name: 'master', commit: { sha: 'deadbeef' } } })
+        const plugin = configure({ default_branch: 'main' })
+        return plugin.sync().then(() => {
+          expect(github.git.createRef).toHaveBeenCalledWith({
+            owner: 'bkeepers',
+            repo: 'test',
+            ref: 'refs/heads/main',
+            sha: 'deadbeef'
+          })
+          expect(github.repos.update).toHaveBeenCalledWith({
+            owner: 'bkeepers',
+            repo: 'test',
+            default_branch: 'main'
+          })
+          expect(github.repos.renameBranch).not.toHaveBeenCalled()
+        })
+      })
+
+      it('only sets the default branch when the configured branch already exists', () => {
+        github.repos.getBranch.mockResolvedValueOnce({ data: { name: 'main', commit: { sha: 'abc123' } } })
+        const plugin = configure({ default_branch: 'main' })
+        return plugin.sync().then(() => {
+          expect(github.git.createRef).not.toHaveBeenCalled()
+          expect(github.repos.renameBranch).not.toHaveBeenCalled()
+          expect(github.repos.update).toHaveBeenCalledWith({
+            owner: 'bkeepers',
+            repo: 'test',
+            default_branch: 'main'
+          })
+        })
+      })
+    })
+  })
 })