Improve promotion comment.

internal/pkg/githubapi/github.go

@@ -1109,14 +1109,40 @@ func prBody(keys []int, newPrMetadata prMetadata, newPrBody string) string {
 
 	for i, k := range keys {
 		sp = newPrMetadata.PreviousPromotionMetadata[k].SourcePath
-		x := newPrMetadata.PreviousPromotionMetadata[k].TargetPaths
+		x := identifyCommonPaths(newPrMetadata.PromotedPaths, newPrMetadata.PreviousPromotionMetadata[k].TargetPaths)
 		tp = strings.Join(x, fmt.Sprintf("`  \n%s`", strings.Repeat(mkTab, i+1)))
 		newPrBody = newPrBody + fmt.Sprintf("%s↘️  #%d  `%s` ➡️  \n%s`%s`  \n", strings.Repeat(mkTab, i), k, sp, strings.Repeat(mkTab, i+1), tp)
 	}
 
 	return newPrBody
 }
 
+// identifyCommonPaths takes a slice of promotion paths and target paths and
+// returns a slice containing paths in common.
+func identifyCommonPaths(promotionPaths []string, targetPaths []string) []string {
+	if (len(promotionPaths) == 0) || (len(targetPaths) == 0) {
+		return nil
+	}
+	var commonPaths []string
+	for _, pp := range promotionPaths {
+		if pp == "" {
+			continue
+		}
+		for _, tp := range targetPaths {
+			if tp == "" {
+				continue
+			}
+			// strings.HasPrefix is used to check that the target path and promotion path match instead of
+			// using 'pp ==  tp' because the promotion path is targetPath + component.
+			if strings.HasPrefix(pp, tp) {
+				commonPaths = append(commonPaths, tp)
+			}
+		}
+	}
+
+	return commonPaths
+}
+
 func createPrObject(ghPrClientDetails GhPrClientDetails, newBranchRef string, newPrTitle string, newPrBody string, defaultBranch string, assignee string) (*github.PullRequest, error) {
 	newPrConfig := &github.NewPullRequest{
 		Body:  github.String(newPrBody),

internal/pkg/githubapi/github_test.go

@@ -235,6 +235,9 @@ func TestPrBody(t *testing.T) {
 	t.Parallel()
 	keys := []int{1, 2, 3}
 	newPrMetadata := prMetadata{
+		// note: "targetPath3" is missing from the list of promoted paths, so it should not
+		// be included in the new PR body.
+		PromotedPaths: []string{"targetPath1", "targetPath2", "targetPath4", "targetPath5", "targetPath6"},
 		PreviousPromotionMetadata: map[int]promotionInstanceMetaData{
 			1: {
 				SourcePath:  "sourcePath1",
@@ -338,3 +341,72 @@ func TestCommitStatusTargetURL(t *testing.T) {
 		})
 	}
 }
+
+func Test_identifyCommonPaths(t *testing.T) {
+	t.Parallel()
+	type args struct {
+		promoPaths  []string
+		targetPaths []string
+	}
+	tests := []struct {
+		name string
+		args args
+		want []string
+	}{
+		{
+			name: "same paths",
+			args: args{
+				promoPaths:  []string{"path1/component/path", "path2/component/path", "path3/component/path"},
+				targetPaths: []string{"path1", "path2", "path3"},
+			},
+			want: []string{"path1", "path2", "path3"},
+		},
+		{
+			name: "paths1 is empty",
+			args: args{
+				promoPaths:  []string{},
+				targetPaths: []string{"path1", "path2", "path3"},
+			},
+			want: nil,
+		},
+		{
+			name: "paths2 is empty",
+			args: args{
+				promoPaths:  []string{"path1/component/some", "path2/some/other", "path3"},
+				targetPaths: []string{},
+			},
+			want: nil,
+		},
+		{
+			name: "paths2 missing elements",
+			args: args{
+				promoPaths:  []string{"path1", "path2", "path3"},
+				targetPaths: []string{""},
+			},
+			want: nil,
+		},
+		{
+			name: "path1 missing elements",
+			args: args{
+				promoPaths:  []string{""},
+				targetPaths: []string{"path1", "path2"},
+			},
+			want: nil,
+		},
+		{
+			name: "path1 and path2 common elements",
+			args: args{
+				promoPaths:  []string{"path1/component/path", "path3/component/also"},
+				targetPaths: []string{"path1", "path2", "path3"},
+			},
+			want: []string{"path1", "path3"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			got := identifyCommonPaths(tt.args.promoPaths, tt.args.targetPaths)
+			assert.Equal(t, got, tt.want)
+		})
+	}
+}

internal/pkg/githubapi/testdata/pr_body.golden.md

@@ -2,7 +2,6 @@
     `targetPath1`  
     `targetPath2`  
     ↘️  #2  `sourcePath2` ➡️  
-        `targetPath3`  
         `targetPath4`  
         ↘️  #3  `sourcePath3` ➡️  
             `targetPath5`