Setup for separating base sets (#4179)

Start setting things up to split the
base types into distinct sets. This
* Renames some functions
* makes a minor change to how bases
  are "cleared" from the struct.
  Instead of removing them, it just
  hides them

Work in this PR will be used in later
PRs

---

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

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

#### Type of change

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

#### Issue(s)

* #3943
* #4178

#### Test Plan

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

src/internal/kopia/backup_bases.go

@@ -17,12 +17,12 @@ import (
 type BackupBases interface {
 	RemoveMergeBaseByManifestID(manifestID manifest.ID)
 	Backups() []BackupEntry
-	AssistBackups() []BackupEntry
+	UniqueAssistBackups() []BackupEntry
 	MinBackupVersion() int
 	MergeBases() []ManifestEntry
-	ClearMergeBases()
-	AssistBases() []ManifestEntry
-	ClearAssistBases()
+	DisableMergeBases()
+	UniqueAssistBases() []ManifestEntry
+	DisableAssistBases()
 	MergeBackupBases(
 		ctx context.Context,
 		other BackupBases,
@@ -37,6 +37,13 @@ type backupBases struct {
 	mergeBases    []ManifestEntry
 	assistBackups []BackupEntry
 	assistBases   []ManifestEntry
+
+	// 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) RemoveMergeBaseByManifestID(manifestID manifest.ID) {
@@ -71,10 +78,18 @@ func (bb *backupBases) RemoveMergeBaseByManifestID(manifestID manifest.ID) {
 }
 
 func (bb backupBases) Backups() []BackupEntry {
+	if bb.disableMergeBases {
+		return nil
+	}
+
 	return slices.Clone(bb.backups)
 }
 
-func (bb backupBases) AssistBackups() []BackupEntry {
+func (bb backupBases) UniqueAssistBackups() []BackupEntry {
+	if bb.disableAssistBases {
+		return nil
+	}
+
 	return slices.Clone(bb.assistBackups)
 }
 
@@ -95,20 +110,27 @@ func (bb *backupBases) MinBackupVersion() int {
 }
 
 func (bb backupBases) MergeBases() []ManifestEntry {
+	if bb.disableMergeBases {
+		return nil
+	}
+
 	return slices.Clone(bb.mergeBases)
 }
 
-func (bb *backupBases) ClearMergeBases() {
-	bb.mergeBases = nil
-	bb.backups = nil
+func (bb *backupBases) DisableMergeBases() {
+	bb.disableMergeBases = true
+}
+
+func (bb backupBases) UniqueAssistBases() []ManifestEntry {
+	if bb.disableAssistBases {
+		return nil
 	}
 
-func (bb backupBases) AssistBases() []ManifestEntry {
 	return slices.Clone(bb.assistBases)
 }
 
-func (bb *backupBases) ClearAssistBases() {
-	bb.assistBases = nil
+func (bb *backupBases) DisableAssistBases() {
+	bb.disableAssistBases = true
 }
 
 // MergeBackupBases reduces the two BackupBases into a single BackupBase.
@@ -116,6 +138,9 @@ func (bb *backupBases) ClearAssistBases() {
 // some migration that disrupts lookup), and that the BackupBases used to call
 // this function contains the current version.
 //
+// This call should be made prior to Disable*Bases being called on either the
+// called BackupBases or the passed in BackupBases.
+//
 // reasonToKey should be a function that, given a Reasoner, will produce some
 // string that represents Reasoner in the context of the merge operation. For
 // example, to merge BackupBases across a ProtectedResource migration, the
@@ -134,11 +159,11 @@ func (bb *backupBases) MergeBackupBases(
 	other BackupBases,
 	reasonToKey func(reason identity.Reasoner) string,
 ) BackupBases {
-	if other == nil || (len(other.MergeBases()) == 0 && len(other.AssistBases()) == 0) {
+	if other == nil || (len(other.MergeBases()) == 0 && len(other.UniqueAssistBases()) == 0) {
 		return bb
 	}
 
-	if bb == nil || (len(bb.MergeBases()) == 0 && len(bb.AssistBases()) == 0) {
+	if bb == nil || (len(bb.MergeBases()) == 0 && len(bb.UniqueAssistBases()) == 0) {
 		return other
 	}
 
@@ -189,11 +214,11 @@ func (bb *backupBases) MergeBackupBases(
 	res := &backupBases{
 		backups:     bb.Backups(),
 		mergeBases:  bb.MergeBases(),
-		assistBases: bb.AssistBases(),
+		assistBases: bb.UniqueAssistBases(),
 		// Note that assistBackups are a new feature and don't exist
 		// in prior versions where we were using UPN based reasons i.e.
 		// other won't have any assistBackups.
-		assistBackups: bb.AssistBackups(),
+		assistBackups: bb.UniqueAssistBackups(),
 	}
 
 	// Add new mergeBases and backups.

src/internal/kopia/backup_bases_test.go

@@ -185,22 +185,40 @@ func (suite *BackupBasesUnitSuite) TestRemoveMergeBaseByManifestID() {
 	}
 }
 
-func (suite *BackupBasesUnitSuite) TestClearMergeBases() {
+func (suite *BackupBasesUnitSuite) TestDisableMergeBases() {
+	t := suite.T()
 	bb := &backupBases{
 		backups:       make([]BackupEntry, 2),
 		mergeBases:    make([]ManifestEntry, 2),
+		assistBackups: make([]BackupEntry, 2),
+		assistBases:   make([]ManifestEntry, 2),
 	}
 
-	bb.ClearMergeBases()
-	assert.Empty(suite.T(), bb.Backups())
-	assert.Empty(suite.T(), bb.MergeBases())
+	bb.DisableMergeBases()
+	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)
 }
 
-func (suite *BackupBasesUnitSuite) TestClearAssistBases() {
-	bb := &backupBases{assistBases: make([]ManifestEntry, 2)}
+func (suite *BackupBasesUnitSuite) TestDisableAssistBases() {
+	t := suite.T()
+	bb := &backupBases{
+		backups:       make([]BackupEntry, 2),
+		mergeBases:    make([]ManifestEntry, 2),
+		assistBases:   make([]ManifestEntry, 2),
+		assistBackups: make([]BackupEntry, 2),
+	}
 
-	bb.ClearAssistBases()
-	assert.Empty(suite.T(), bb.AssistBases())
+	bb.DisableAssistBases()
+	assert.Empty(t, bb.UniqueAssistBases())
+	assert.Empty(t, bb.UniqueAssistBackups())
+
+	// Merge base should be unchanged.
+	assert.Len(t, bb.Backups(), 2)
+	assert.Len(t, bb.MergeBases(), 2)
 }
 
 func (suite *BackupBasesUnitSuite) TestMergeBackupBases() {

src/internal/kopia/base_finder_test.go

@@ -299,7 +299,7 @@ func (suite *BaseFinderUnitSuite) TestNoResult_NoBackupsOrSnapshots() {
 
 	bb := bf.FindBases(ctx, reasons, nil)
 	assert.Empty(t, bb.MergeBases())
-	assert.Empty(t, bb.AssistBases())
+	assert.Empty(t, bb.UniqueAssistBases())
 }
 
 func (suite *BaseFinderUnitSuite) TestNoResult_ErrorListingSnapshots() {
@@ -318,7 +318,7 @@ func (suite *BaseFinderUnitSuite) TestNoResult_ErrorListingSnapshots() {
 
 	bb := bf.FindBases(ctx, reasons, nil)
 	assert.Empty(t, bb.MergeBases())
-	assert.Empty(t, bb.AssistBases())
+	assert.Empty(t, bb.UniqueAssistBases())
 }
 
 func (suite *BaseFinderUnitSuite) TestGetBases() {
@@ -1061,7 +1061,7 @@ func (suite *BaseFinderUnitSuite) TestGetBases() {
 				test.expectedBaseReasons)
 			checkBackupEntriesMatch(
 				t,
-				bb.AssistBackups(),
+				bb.UniqueAssistBackups(),
 				test.backupData,
 				test.expectedAssistReasons)
 
@@ -1072,7 +1072,7 @@ func (suite *BaseFinderUnitSuite) TestGetBases() {
 				test.expectedBaseReasons)
 			checkManifestEntriesMatch(
 				t,
-				bb.AssistBases(),
+				bb.UniqueAssistBases(),
 				test.manifestData,
 				test.expectedAssistManifestReasons)
 		})

src/internal/kopia/mock_backup_base.go

@@ -14,17 +14,17 @@ func AssertBackupBasesEqual(t *testing.T, expect, got BackupBases) {
 	if expect == nil {
 		assert.Empty(t, got.Backups(), "backups")
 		assert.Empty(t, got.MergeBases(), "merge bases")
-		assert.Empty(t, got.AssistBackups(), "assist backups")
-		assert.Empty(t, got.AssistBases(), "assist bases")
+		assert.Empty(t, got.UniqueAssistBackups(), "assist backups")
+		assert.Empty(t, got.UniqueAssistBases(), "assist bases")
 
 		return
 	}
 
 	if got == nil {
-		if len(expect.Backups()) > 0 &&
-			len(expect.MergeBases()) > 0 &&
-			len(expect.AssistBackups()) > 0 &&
-			len(expect.AssistBases()) > 0 {
+		if len(expect.Backups()) > 0 ||
+			len(expect.MergeBases()) > 0 ||
+			len(expect.UniqueAssistBackups()) > 0 ||
+			len(expect.UniqueAssistBases()) > 0 {
 			assert.Fail(t, "got was nil but expected non-nil result %v", expect)
 		}
 
@@ -33,8 +33,8 @@ func AssertBackupBasesEqual(t *testing.T, expect, got BackupBases) {
 
 	assert.ElementsMatch(t, expect.Backups(), got.Backups(), "backups")
 	assert.ElementsMatch(t, expect.MergeBases(), got.MergeBases(), "merge bases")
-	assert.ElementsMatch(t, expect.AssistBackups(), got.AssistBackups(), "assist backups")
-	assert.ElementsMatch(t, expect.AssistBases(), got.AssistBases(), "assist bases")
+	assert.ElementsMatch(t, expect.UniqueAssistBackups(), got.UniqueAssistBackups(), "assist backups")
+	assert.ElementsMatch(t, expect.UniqueAssistBases(), got.UniqueAssistBases(), "assist bases")
 }
 
 func NewMockBackupBases() *MockBackupBases {
@@ -52,22 +52,22 @@ func (bb *MockBackupBases) WithBackups(b ...BackupEntry) *MockBackupBases {
 
 func (bb *MockBackupBases) WithMergeBases(m ...ManifestEntry) *MockBackupBases {
 	bb.backupBases.mergeBases = append(bb.MergeBases(), m...)
-	bb.backupBases.assistBases = append(bb.AssistBases(), m...)
+	bb.backupBases.assistBases = append(bb.UniqueAssistBases(), m...)
 
 	return bb
 }
 
 func (bb *MockBackupBases) WithAssistBackups(b ...BackupEntry) *MockBackupBases {
-	bb.backupBases.assistBackups = append(bb.AssistBackups(), b...)
+	bb.backupBases.assistBackups = append(bb.UniqueAssistBackups(), b...)
 	return bb
 }
 
 func (bb *MockBackupBases) WithAssistBases(m ...ManifestEntry) *MockBackupBases {
-	bb.backupBases.assistBases = append(bb.AssistBases(), m...)
+	bb.backupBases.assistBases = append(bb.UniqueAssistBases(), m...)
 	return bb
 }
 
 func (bb *MockBackupBases) ClearMockAssistBases() *MockBackupBases {
-	bb.backupBases.ClearAssistBases()
+	bb.backupBases.DisableAssistBases()
 	return bb
 }

src/internal/kopia/wrapper.go

@@ -178,7 +178,7 @@ func (w Wrapper) ConsumeBackupCollections(
 			mergeBase = bases.MergeBases()
 		}
 
-		assistBase = bases.AssistBases()
+		assistBase = bases.UniqueAssistBases()
 	}
 
 	dirTree, err := inflateDirTree(

src/internal/operations/backup.go

@@ -732,7 +732,7 @@ func mergeDetails(
 	// leaves us in a bit of a pickle if the user has run any concurrent backups
 	// with overlapping Reasons that turn into assist bases, but the modTime check
 	// in DetailsMergeInfoer should handle that.
-	for _, base := range bases.AssistBackups() {
+	for _, base := range bases.UniqueAssistBackups() {
 		added, err := mergeItemsFromBase(
 			ctx,
 			false,

src/internal/operations/manifests.go

@@ -39,13 +39,13 @@ func produceManifestsAndMetadata(
 	if !useMergeBases || !getMetadata {
 		logger.Ctx(ctx).Debug("full backup requested, dropping merge bases")
 
-		bb.ClearMergeBases()
+		bb.DisableMergeBases()
 	}
 
 	if dropAssistBases {
 		logger.Ctx(ctx).Debug("no caching requested, dropping assist bases")
 
-		bb.ClearAssistBases()
+		bb.DisableAssistBases()
 	}
 
 	return bb, meta, useMergeBases, nil