Don't set updated in backup details for cached items (#2119)

## Description

If an item is discovered to be cached in kopia (i.e. kopia-assisted incremental), set the backup details for the item to note that it was not updated.

Cached items are discovered by checking the item path and mod time against the snapshots passed into kopia's Upload function

## 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

<!--- Please check the type of change your PR introduces: --->
- [ ] 🌻 Feature
- [x] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Test
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

## Issue(s)

* closes #2115 

## Test Plan

<!-- How will this be tested prior to merging.-->
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E

src/internal/kopia/upload.go

@@ -121,6 +121,7 @@ type itemDetails struct {
 	info     *details.ItemInfo
 	repoPath path.Path
 	prevPath path.Path
+	cached   bool
 }
 
 type corsoProgress struct {
@@ -179,7 +180,7 @@ func (cp *corsoProgress) FinishedFile(relativePath string, err error) {
 		d.repoPath.String(),
 		d.repoPath.ShortRef(),
 		parent.ShortRef(),
-		true,
+		!d.cached,
 		*d.info,
 	)
 
@@ -187,7 +188,7 @@ func (cp *corsoProgress) FinishedFile(relativePath string, err error) {
 	cp.deets.AddFoldersForItem(
 		folders,
 		*d.info,
-		true, // itemUpdated = true
+		!d.cached,
 	)
 }
 
@@ -199,6 +200,20 @@ func (cp *corsoProgress) FinishedHashingFile(fname string, bs int64) {
 	atomic.AddInt64(&cp.totalBytes, bs)
 }
 
+// Kopia interface function used as a callback when kopia detects a previously
+// uploaded file that matches the current file and skips uploading the new
+// (duplicate) version.
+func (cp *corsoProgress) CachedFile(fname string, size int64) {
+	defer cp.UploadProgress.CachedFile(fname, size)
+
+	d := cp.get(fname)
+	if d == nil {
+		return
+	}
+
+	d.cached = true
+}
+
 func (cp *corsoProgress) put(k string, v *itemDetails) {
 	cp.mu.Lock()
 	defer cp.mu.Unlock()

src/internal/kopia/upload_test.go

@@ -433,29 +433,58 @@ var finishedFileTable = []struct {
 }
 
 func (suite *CorsoProgressUnitSuite) TestFinishedFile() {
-	for _, test := range finishedFileTable {
-		suite.T().Run(test.name, func(t *testing.T) {
-			bd := &details.Builder{}
-			cp := corsoProgress{
-				UploadProgress: &snapshotfs.NullUploadProgress{},
-				deets:          bd,
-				pending:        map[string]*itemDetails{},
+	table := []struct {
+		name   string
+		cached bool
+	}{
+		{
+			name:   "all updated",
+			cached: false,
+		},
+		{
+			name:   "all cached",
+			cached: true,
+		},
+	}
+
+	for _, cachedTest := range table {
+		suite.T().Run(cachedTest.name, func(outerT *testing.T) {
+			for _, test := range finishedFileTable {
+				outerT.Run(test.name, func(t *testing.T) {
+					bd := &details.Builder{}
+					cp := corsoProgress{
+						UploadProgress: &snapshotfs.NullUploadProgress{},
+						deets:          bd,
+						pending:        map[string]*itemDetails{},
+					}
+
+					ci := test.cachedItems(suite.targetFileName, suite.targetFilePath)
+
+					for k, v := range ci {
+						cp.put(k, v.info)
+					}
+
+					require.Len(t, cp.pending, len(ci))
+
+					for k, v := range ci {
+						if cachedTest.cached {
+							cp.CachedFile(k, 42)
+						}
+
+						cp.FinishedFile(k, v.err)
+					}
+
+					assert.Empty(t, cp.pending)
+
+					entries := bd.Details().Entries
+
+					assert.Len(t, entries, test.expectedNumEntries)
+
+					for _, entry := range entries {
+						assert.Equal(t, !cachedTest.cached, entry.Updated)
+					}
+				})
 			}
-
-			ci := test.cachedItems(suite.targetFileName, suite.targetFilePath)
-
-			for k, v := range ci {
-				cp.put(k, v.info)
-			}
-
-			require.Len(t, cp.pending, len(ci))
-
-			for k, v := range ci {
-				cp.FinishedFile(k, v.err)
-			}
-
-			assert.Empty(t, cp.pending)
-			assert.Len(t, bd.Details().Entries, test.expectedNumEntries)
 		})
 	}
 }

src/internal/kopia/wrapper_test.go

@@ -241,16 +241,20 @@ func (suite *KopiaIntegrationSuite) TestBackupCollections() {
 		name                  string
 		expectedUploadedFiles int
 		expectedCachedFiles   int
+		// Whether entries in the resulting details should be marked as updated.
+		deetsUpdated bool
 	}{
 		{
 			name:                  "Uncached",
 			expectedUploadedFiles: 47,
 			expectedCachedFiles:   0,
+			deetsUpdated:          true,
 		},
 		{
 			name:                  "Cached",
 			expectedUploadedFiles: 0,
 			expectedCachedFiles:   47,
+			deetsUpdated:          false,
 		},
 	}
 
@@ -274,13 +278,19 @@ func (suite *KopiaIntegrationSuite) TestBackupCollections() {
 			assert.Equal(t, 0, stats.IgnoredErrorCount)
 			assert.Equal(t, 0, stats.ErrorCount)
 			assert.False(t, stats.Incomplete)
+
 			// 47 file and 6 folder entries.
+			details := deets.Details().Entries
 			assert.Len(
 				t,
-				deets.Details().Entries,
+				details,
 				test.expectedUploadedFiles+test.expectedCachedFiles+6,
 			)
 
+			for _, entry := range details {
+				assert.Equal(t, test.deetsUpdated, entry.Updated)
+			}
+
 			checkSnapshotTags(
 				t,
 				suite.ctx,