Don't mark lines from other commits as modified

Author: prymitive

internal/discovery/git_branch_test.go

@@ -1270,6 +1270,56 @@ groups:
 				},
 			},
 		},
+		{
+			title: "rule partially replaced",
+			setup: func(t *testing.T) {
+				commitFile(t, "rules.yml", `
+groups:
+- name: v1
+  rules:
+  - record: up:sum
+    expr: |
+      sum(
+        up
+      )
+`, "v1")
+
+				_, err := git.RunGit("checkout", "-b", "v2")
+				require.NoError(t, err, "git checkout v2")
+
+				commitFile(t, "rules.yml", `
+groups:
+- name: v1
+  rules:
+  - record: up:count
+    expr: |
+      count(
+        up
+      )
+`, "v2")
+			},
+			finder: discovery.NewGitBranchFinder(git.RunGit, git.NewPathFilter(includeAll, nil, nil), "main", 4, parser.PrometheusSchema, model.UTF8Validation, nil),
+			entries: []discovery.Entry{
+				{
+					State: discovery.Added,
+					Path: discovery.Path{
+						Name:          "rules.yml",
+						SymlinkTarget: "rules.yml",
+					},
+					ModifiedLines: []int{5, 7},
+					Rule:          mustParse(4, "  - record: up:count\n    expr: |\n      count(\n        up\n      )\n"),
+				},
+				{
+					State: discovery.Removed,
+					Path: discovery.Path{
+						Name:          "rules.yml",
+						SymlinkTarget: "rules.yml",
+					},
+					ModifiedLines: []int{5, 7},
+					Rule:          mustParse(4, "  - record: up:sum\n    expr: |\n      sum(\n        up\n      )\n"),
+				},
+			},
+		},
 	}
 
 	for _, tc := range testCases {

internal/git/changes.go

@@ -273,14 +273,17 @@ func getModifiedLines(cmd CommandRunner, commits []string, fpath, atCommit strin
 
 	linesBefore := bytes.Split(bodyBefore, []byte("\n"))
 	linesAfter := bytes.Split(bodyAfter, []byte("\n"))
+	slog.Debug("Number of lines", slog.Int("before", len(linesBefore)), slog.Int("after", len(linesAfter)))
 
 	modLines := make([]int, 0, len(lines))
 	for _, line := range lines {
-		if !slices.Contains(commits, line.Commit) && line.Line == line.PrevLine {
+		slog.Debug("Checking line", slog.String("commit", line.Commit), slog.Int("prev", line.PrevLine), slog.Int("line", line.Line))
+		if !slices.Contains(commits, line.Commit) {
 			continue
 		}
 
 		if line.PrevLine <= len(linesBefore) && line.Line <= len(linesAfter) {
+			slog.Debug("Checking line content", slog.String("before", string(linesBefore[line.PrevLine-1])), slog.String("after", string(linesAfter[line.Line-1])))
 			if bytes.Equal(linesBefore[line.PrevLine-1], linesAfter[line.Line-1]) {
 				continue
 			}

internal/git/changes_test.go

@@ -646,6 +646,46 @@ func TestChanges(t *testing.T) {
 			},
 			err: "",
 		},
+		{
+			title: "rule partially replaced",
+			setup: func(t *testing.T) git.CommandRunner {
+				mustRun(t, "init", "--initial-branch=main", ".")
+				require.NoError(t, os.WriteFile("main.txt", []byte("l1\nl2\nl3\n"), 0o644))
+				mustRun(t, "add", "main.txt")
+				gitCommit(t, "init")
+
+				mustRun(t, "checkout", "-b", "v2")
+				require.NoError(t, os.WriteFile("main.txt", []byte("l1\nl3\n"), 0o644))
+				mustRun(t, "add", "main.txt")
+				gitCommit(t, "edit")
+
+				mustRun(t, "mv", "main.txt", "pr.txt")
+				gitCommit(t, "rename")
+
+				return debugGitRun(t)
+			},
+			changes: []*git.FileChange{
+				{
+					Commits: []string{"1", "2"},
+					Path: git.PathDiff{
+						Before: git.Path{
+							Name: "main.txt",
+							Type: git.File,
+						},
+						After: git.Path{
+							Name: "pr.txt",
+							Type: git.File,
+						},
+					},
+					Body: git.BodyDiff{
+						Before:        []byte("l1\nl2\nl3\n"),
+						After:         []byte("l1\nl3\n"),
+						ModifiedLines: []int{1, 2},
+					},
+				},
+			},
+			err: "",
+		},
 	}
 
 	for _, tc := range testCases {