Turn merge bases into assist bases when disabling them (#4182)

Have disable merge bases turn all merge
bases into assist bases instead of
completely removing them. This allows
us to continue getting benefits of
kopia assisted incrementals and fixes
the not having the backup models for
details merging

---

#### Does this PR need a docs update or release note?

- [x] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [ ] ⛔ No

#### Type of change

- [ ] 🌻 Feature
- [x] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Supportability/Tests
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

#### Issue(s)

* fixes #4178
* #3943

#### Test Plan

- [ ] 💪 Manual
- [x] ⚡ Unit test
- [x] 💚 E2E

CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 - Contacts backups no longer slices root-folder data if outlook is set to languages other than english.
+- Failed backups if the --disable-incrementals flag was passed when there was a valid merge base under some conditions.
 
 ## [v0.12.0] (beta) - 2023-08-29
 

src/internal/kopia/backup_bases.go

@@ -48,9 +48,6 @@ type backupBases struct {
 	// disableAssistBases denote whether any assist bases should be returned to
 	// kopia during snapshot operation.
 	disableAssistBases bool
-	// disableMergeBases denotes whether any bases should be returned from calls
-	// to MergeBases().
-	disableMergeBases bool
 }
 
 func (bb *backupBases) SnapshotAssistBases() []ManifestEntry {
@@ -99,10 +96,6 @@ func (bb *backupBases) ConvertToAssistBase(manifestID manifest.ID) {
 }
 
 func (bb backupBases) Backups() []BackupEntry {
-	if bb.disableMergeBases {
-		return nil
-	}
-
 	return slices.Clone(bb.backups)
 }
 
@@ -131,15 +124,20 @@ func (bb *backupBases) MinBackupVersion() int {
 }
 
 func (bb backupBases) MergeBases() []ManifestEntry {
-	if bb.disableMergeBases {
-		return nil
-	}
-
 	return slices.Clone(bb.mergeBases)
 }
 
 func (bb *backupBases) DisableMergeBases() {
-	bb.disableMergeBases = true
+	// Turn all merge bases into assist bases. We don't want to remove them
+	// completely because we still want to allow kopia assisted incrementals
+	// unless that's also explicitly disabled. However, we can't just leave them
+	// in the merge set since then we won't return the bases when merging backup
+	// details.
+	bb.assistBases = append(bb.assistBases, bb.mergeBases...)
+	bb.assistBackups = append(bb.assistBackups, bb.backups...)
+
+	bb.mergeBases = nil
+	bb.backups = nil
 }
 
 func (bb backupBases) UniqueAssistBases() []ManifestEntry {

src/internal/kopia/backup_bases_test.go

@@ -8,6 +8,7 @@ import (
 	"github.com/kopia/kopia/snapshot"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/suite"
+	"golang.org/x/exp/slices"
 
 	"github.com/alcionai/corso/src/internal/model"
 	"github.com/alcionai/corso/src/internal/tester"
@@ -201,10 +202,20 @@ func (suite *BackupBasesUnitSuite) TestConvertToAssistBase() {
 
 func (suite *BackupBasesUnitSuite) TestDisableMergeBases() {
 	t := suite.T()
+
+	merge := []BackupEntry{
+		{Backup: &backup.Backup{BaseModel: model.BaseModel{ID: "m1"}}},
+		{Backup: &backup.Backup{BaseModel: model.BaseModel{ID: "m2"}}},
+	}
+	assist := []BackupEntry{
+		{Backup: &backup.Backup{BaseModel: model.BaseModel{ID: "a1"}}},
+		{Backup: &backup.Backup{BaseModel: model.BaseModel{ID: "a2"}}},
+	}
+
 	bb := &backupBases{
-		backups:       make([]BackupEntry, 2),
+		backups:       slices.Clone(merge),
 		mergeBases:    make([]ManifestEntry, 2),
-		assistBackups: make([]BackupEntry, 2),
+		assistBackups: slices.Clone(assist),
 		assistBases:   make([]ManifestEntry, 2),
 	}
 
@@ -212,12 +223,15 @@ func (suite *BackupBasesUnitSuite) TestDisableMergeBases() {
 	assert.Empty(t, bb.Backups())
 	assert.Empty(t, bb.MergeBases())
 
-	// Assist base set should be unchanged.
-	assert.Len(t, bb.UniqueAssistBackups(), 2)
-	assert.Len(t, bb.UniqueAssistBases(), 2)
-	// Merge bases should still appear in the assist base set passed in for kopia
-	// snapshots.
+	// Assist base set now has what used to be merge bases.
+	assert.Len(t, bb.UniqueAssistBases(), 4)
 	assert.Len(t, bb.SnapshotAssistBases(), 4)
+	// Merge bases should appear in the set of backup bases used for details
+	// merging.
+	assert.ElementsMatch(
+		t,
+		append(slices.Clone(merge), assist...),
+		bb.UniqueAssistBackups())
 }
 
 func (suite *BackupBasesUnitSuite) TestDisableAssistBases() {

src/internal/model/model.go

@@ -36,7 +36,22 @@ const (
 const (
 	ServiceTag    = "service"
 	BackupTypeTag = "backup-type"
+	// AssistBackup denotes that this backup should only be used for kopia
+	// assisted incrementals since it doesn't contain the complete set of data
+	// being backed up.
+	//
+	// This tag should only be used for finding backups during a
+	// manifest search. It shouldn't be used to differentiate between backups once
+	// the manifest search completes.
 	AssistBackup = "assist-backup"
+	// MergeBackup denotes that this backup can be used as a merge base during an
+	// incremental backup. It contains a complete snapshot of the data in the
+	// external service. Merge bases can also be used as assist bases during an
+	// incremental backup or demoted to being only an assist base.
+	//
+	// This tag should only be used for finding backups during a
+	// manifest search. It shouldn't be used to differentiate between backups once
+	// the manifest search completes.
 	MergeBackup = "merge-backup"
 )