feat: when error occures save last succesfull migration version

Author: AuHau

README.md

@@ -102,6 +102,10 @@ Migrations are one of those things that can be extremely painful on users. At th
 - Tests. Migrations have to be well tested.
 - To Spec. The tools must conform to the spec.
 
+If your migration has several parts, it should be fail-proof enough that if one part of migration fails the previous changes
+are reverted before propagating the error. If possible then the outcome should be consistent repo so it migration could
+be run again. 
+
 #### Architecture of migrations
 
 All migrations are placed in the `/migrations` folder. Each folder there represents one migration that follows the migration

src/index.js

@@ -98,9 +98,14 @@ async function migrate (path, { toVersion, ignoreLock = false, repoOptions, onPr
       try {
         if (!isDryRun) await migration.migrate(path, repoOptions, isBrowser)
       } catch (e) {
+        const lastSuccessfullyMigratedVersion = migration.version - 1
+        log(`An exception was raised during execution of migration. Setting the repo\'s version to last successfully migrated version: ${lastSuccessfullyMigratedVersion}`)
+        await repoVersion.setVersion(path, lastSuccessfullyMigratedVersion)
+
         e.message = `During migration to version ${migration.version} exception was raised: ${e.message}`
         throw e
       }
+
       typeof onProgress === 'function' && onProgress(migration, counter, totalMigrations) // Reports on migration process
       log(`Migrating to version ${migration.version} finished`)
     }
@@ -187,9 +192,14 @@ async function revert (path, toVersion, { ignoreLock = false, repoOptions, onPro
       try {
         if (!isDryRun) await migration.revert(path, repoOptions, isBrowser)
       } catch (e) {
+        const lastSuccessfullyRevertedVersion = migration.version
+        log(`An exception was raised during execution of migration. Setting the repo\'s version to last successfully reverted version: ${lastSuccessfullyRevertedVersion}`)
+        await repoVersion.setVersion(path, lastSuccessfullyRevertedVersion)
+
         e.message = `During reversion to version ${migration.version} exception was raised: ${e.message}`
         throw e
       }
+
       typeof onProgress === 'function' && onProgress(migration, counter, totalMigrations) // Reports on migration process
       log(`Reverting to version ${migration.version} finished`)
     }

test/index.spec.js

@@ -249,14 +249,16 @@ describe('index.js', () => {
     it('should unlock repo when error is thrown', async () => {
       getVersionStub.returns(4)
       const options = createOptions()
-      options.migrations[3].revert = sinon.stub().rejects()
+      options.migrations[2].revert = sinon.stub().rejects()
 
       await expect(migrator.revert('/some/path', 2, options))
         .to.eventually.be.rejected()
 
       expect(lockCloseStub.calledOnce).to.be.true()
       expect(lockStub.calledOnce).to.be.true()
-      expect(setVersionStub.called).to.be.false()
+
+      // The last successfully reverted migration should be set as repo's version
+      expect(setVersionStub.calledOnceWith('/some/path', 3)).to.be.true()
     })
   })
 
@@ -388,7 +390,9 @@ describe('index.js', () => {
 
       expect(lockCloseStub.calledOnce).to.be.true()
       expect(lockStub.calledOnce).to.be.true()
-      expect(setVersionStub.called).to.be.false()
+
+      // The last successfully migrated migration should be set as repo's version
+      expect(setVersionStub.calledOnceWith('/some/path', 3)).to.be.true()
     })
   })
 })