fix(bitbucket-datacenter): detect changes on merged PR push

When a pull request is merged in Bitbucket Data Center, the resulting
push event contains a merge commit that reports no file changes. This
caused on-path-change and on-cel-expression filters to silently skip
PipelineRuns because the changed files list was always empty.

The fix detects merge commits (commits with multiple parents) during
payload parsing and uses the Bitbucket /changes API with since/until
params to diff the previous HEAD against the current HEAD, retrieving
the actual files modified by the merged PR.

Key changes:
- Parse merge commits in push payloads to capture previousHeadCommit
- Add getMergeCommitChanges using /changes API with proper pagination
- Add DiffStats/Pagination types for the /changes API response
- Update TearDown to skip deletion of already-merged PRs
- Allow CreatePR to target a custom base branch for merge test scenarios
- Add E2E test for on-path-change annotation surviving a PR merge push
- Add unit tests for getMergeCommitChanges and merge commit GetFiles path

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: zakisk

go.mod

@@ -13,6 +13,7 @@ require (
 	github.com/google/cel-go v0.28.0
 	github.com/google/go-cmp v0.7.0
 	github.com/google/go-github/scrape v0.0.0-20260403152401-96a365122246
+	github.com/google/go-github/v84 v84.0.0
 	github.com/google/go-github/v85 v85.0.0
 	github.com/hako/durafmt v0.0.0-20210608085754-5c1018a4e16b
 	github.com/jenkins-x/go-scm v1.15.17
@@ -78,7 +79,6 @@ require (
 	github.com/go-openapi/swag/typeutils v0.25.5 // indirect
 	github.com/go-openapi/swag/yamlutils v0.25.5 // indirect
 	github.com/go-viper/mapstructure/v2 v2.5.0 // indirect
-	github.com/google/go-github/v84 v84.0.0 // indirect
 	github.com/oklog/ulid/v2 v2.1.1 // indirect
 	github.com/prometheus/otlptranslator v1.0.0 // indirect
 	github.com/rickb777/plural v1.4.10 // indirect

pkg/provider/bitbucketdatacenter/bitbucketdatacenter.go

@@ -41,6 +41,7 @@ type Provider struct {
 	apiURL                    string
 	provenance                string
 	projectKey                string
+	previousHeadCommit        string
 	repo                      *v1alpha1.Repository
 	triggerEvent              string
 	cachedChangedFiles        *changedfiles.ChangedFiles
@@ -422,7 +423,13 @@ func (v *Provider) fetchChangedFiles(ctx context.Context, runevent *info.Event)
 	case triggertype.Push:
 		opts := &scm.ListOptions{Page: 1, Size: apiResponseLimit}
 		for {
-			changes, _, err := v.Client().Git.ListChanges(ctx, orgAndRepo, runevent.SHA, opts)
+			var changes []*scm.Change
+			var err error
+			if v.previousHeadCommit != "" {
+				changes, _, err = v.getMergeCommitChanges(ctx, runevent.Organization, runevent.Repository, v.previousHeadCommit, runevent.SHA, opts)
+			} else {
+				changes, _, err = v.Client().Git.ListChanges(ctx, orgAndRepo, runevent.SHA, opts)
+			}
 			if err != nil {
 				return changedfiles.ChangedFiles{}, fmt.Errorf("failed to list changes for commit %s: %w", runevent.SHA, err)
 			}

pkg/provider/bitbucketdatacenter/bitbucketdatacenter_test.go

@@ -745,10 +745,33 @@ func TestGetFiles(t *testing.T) {
 		},
 	}
 
+	mergeCommitPushEvent := &info.Event{
+		SHA:           "MERGESHA456",
+		Organization:  "pac",
+		Repository:    "test",
+		TriggerTarget: triggertype.Push,
+	}
+
+	mergeCommitFiles := []*bbtest.DiffStat{
+		{
+			Path: bbtest.DiffPath{ToString: "merge-added.go"},
+			Type: "ADD",
+		},
+		{
+			Path: bbtest.DiffPath{ToString: "merge-modified.txt"},
+			Type: "MODIFY",
+		},
+		{
+			Path: bbtest.DiffPath{ToString: "merge-deleted.md"},
+			Type: "DELETE",
+		},
+	}
+
 	tests := []struct {
 		name                   string
 		event                  *info.Event
 		changeFiles            []*bbtest.DiffStat
+		previousHeadCommit     string
 		wantAddedFilesCount    int
 		wantDeletedFilesCount  int
 		wantModifiedFilesCount int
@@ -794,6 +817,23 @@ func TestGetFiles(t *testing.T) {
 			wantError:              true,
 			errMsg:                 "failed to list changes for pull request: No message available",
 		},
+		{
+			name:                   "good/merge commit push event",
+			event:                  mergeCommitPushEvent,
+			changeFiles:            mergeCommitFiles,
+			previousHeadCommit:     "PREVIOUSHEAD789",
+			wantAddedFilesCount:    1,
+			wantDeletedFilesCount:  1,
+			wantModifiedFilesCount: 1,
+			wantRenamedFilesCount:  0,
+		},
+		{
+			name:               "bad/merge commit push event api error",
+			event:              mergeCommitPushEvent,
+			previousHeadCommit: "PREVIOUSHEAD789",
+			wantError:          true,
+			errMsg:             "failed to list changes for commit MERGESHA456: failed to get merge commit changes: status code: 401",
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -802,10 +842,24 @@ func TestGetFiles(t *testing.T) {
 			defer tearDown()
 
 			stats := &bbtest.DiffStats{
+				Pagination: bbtest.Pagination{
+					LastPage: true,
+				},
 				Values: tt.changeFiles,
 			}
 
-			if tt.event.TriggerTarget == triggertype.Push {
+			if tt.event.TriggerTarget == triggertype.Push && tt.previousHeadCommit != "" {
+				mux.HandleFunc("/projects/pac/repos/test/changes", func(w http.ResponseWriter, r *http.Request) {
+					if tt.wantError {
+						w.WriteHeader(http.StatusUnauthorized)
+						return
+					}
+					assert.Equal(t, r.URL.Query().Get("since"), tt.previousHeadCommit)
+					assert.Equal(t, r.URL.Query().Get("until"), tt.event.SHA)
+					b, _ := json.Marshal(stats)
+					fmt.Fprint(w, string(b))
+				})
+			} else if tt.event.TriggerTarget == triggertype.Push {
 				mux.HandleFunc("/projects/pac/repos/test/commits/IAMSHA123/changes", func(w http.ResponseWriter, _ *http.Request) {
 					if tt.wantError {
 						w.WriteHeader(http.StatusUnauthorized)
@@ -831,7 +885,7 @@ func TestGetFiles(t *testing.T) {
 			provider := sdkmetric.NewMeterProvider(sdkmetric.WithReader(reader))
 			otel.SetMeterProvider(provider)
 
-			v := &Provider{client: client, baseURL: tURL, triggerEvent: string(tt.event.TriggerTarget)}
+			v := &Provider{client: client, baseURL: tURL, triggerEvent: string(tt.event.TriggerTarget), previousHeadCommit: tt.previousHeadCommit}
 			changedFiles, err := v.GetFiles(ctx, tt.event)
 			if tt.wantError {
 				assert.Equal(t, err.Error(), tt.errMsg)
@@ -855,33 +909,37 @@ func TestGetFiles(t *testing.T) {
 				}
 			}
 
-			var rm metricdata.ResourceMetrics
-			err = reader.Collect(ctx, &rm)
-			assert.NilError(t, err, "error collecting metrics")
-
-			assert.Equal(t, len(rm.ScopeMetrics), 1)
-			assert.Equal(t, len(rm.ScopeMetrics[0].Metrics), 1)
-			assert.Equal(t, rm.ScopeMetrics[0].Metrics[0].Name, "pipelines_as_code_git_provider_api_request_count")
-			count, ok := rm.ScopeMetrics[0].Metrics[0].Data.(metricdata.Sum[int64])
-			assert.Assert(t, ok)
-			assert.Equal(t, count.DataPoints[0].Value, int64(1))
-
-			_, _ = v.GetFiles(ctx, tt.event)
-			// recollect the metrics af
-			err = reader.Collect(ctx, &rm)
-			assert.NilError(t, err, "error collecting metrics")
-
-			assert.Equal(t, len(rm.ScopeMetrics), 1)
-			assert.Equal(t, len(rm.ScopeMetrics[0].Metrics), 1)
-			assert.Equal(t, rm.ScopeMetrics[0].Metrics[0].Name, "pipelines_as_code_git_provider_api_request_count")
-			count, ok = rm.ScopeMetrics[0].Metrics[0].Data.(metricdata.Sum[int64])
-			assert.Assert(t, ok)
-			if tt.wantError {
-				// no caching on error so we expect 2 metrics
-				assert.Equal(t, count.DataPoints[0].Value, int64(2))
-			} else {
-				// caching on success so we expect 1 metric
+			// getMergeCommitChanges uses v.client.Do directly (not v.Client()),
+			// so no API usage metrics are recorded for that path.
+			if tt.previousHeadCommit == "" {
+				var rm metricdata.ResourceMetrics
+				err = reader.Collect(ctx, &rm)
+				assert.NilError(t, err, "error collecting metrics")
+
+				assert.Equal(t, len(rm.ScopeMetrics), 1)
+				assert.Equal(t, len(rm.ScopeMetrics[0].Metrics), 1)
+				assert.Equal(t, rm.ScopeMetrics[0].Metrics[0].Name, "pipelines_as_code_git_provider_api_request_count")
+				count, ok := rm.ScopeMetrics[0].Metrics[0].Data.(metricdata.Sum[int64])
+				assert.Assert(t, ok)
 				assert.Equal(t, count.DataPoints[0].Value, int64(1))
+
+				_, _ = v.GetFiles(ctx, tt.event)
+				// recollect the metrics af
+				err = reader.Collect(ctx, &rm)
+				assert.NilError(t, err, "error collecting metrics")
+
+				assert.Equal(t, len(rm.ScopeMetrics), 1)
+				assert.Equal(t, len(rm.ScopeMetrics[0].Metrics), 1)
+				assert.Equal(t, rm.ScopeMetrics[0].Metrics[0].Name, "pipelines_as_code_git_provider_api_request_count")
+				count, ok = rm.ScopeMetrics[0].Metrics[0].Data.(metricdata.Sum[int64])
+				assert.Assert(t, ok)
+				if tt.wantError {
+					// no caching on error so we expect 2 metrics
+					assert.Equal(t, count.DataPoints[0].Value, int64(2))
+				} else {
+					// caching on success so we expect 1 metric
+					assert.Equal(t, count.DataPoints[0].Value, int64(1))
+				}
 			}
 		})
 	}

pkg/provider/bitbucketdatacenter/diff_api.go

@@ -0,0 +1,89 @@
+package bitbucketdatacenter
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/url"
+
+	"github.com/jenkins-x/go-scm/scm"
+	"github.com/openshift-pipelines/pipelines-as-code/pkg/provider/bitbucketdatacenter/types"
+)
+
+// getMergeCommitChanges gets the changes between two commits for a merge commit.
+// this endpoint is not implemented in the go-scm package, so we need to use the raw HTTP request.
+// but we're using the client from the go-scm package to make the request.
+func (v *Provider) getMergeCommitChanges(ctx context.Context, org, repo, fromCommit, toCommit string, opts *scm.ListOptions) ([]*scm.Change, *scm.Response, error) {
+	params := url.Values{}
+	params.Set("since", fromCommit)
+	params.Set("until", toCommit)
+	params.Set("start", fmt.Sprintf("%d", (opts.Page-1)*opts.Size))
+	params.Set("limit", fmt.Sprintf("%d", opts.Size))
+	path := fmt.Sprintf("rest/api/1.0/projects/%s/repos/%s/changes?%s",
+		url.PathEscape(org),
+		url.PathEscape(repo),
+		params.Encode())
+
+	resp, err := v.client.Do(ctx, &scm.Request{
+		Method: "GET",
+		Path:   path,
+		Header: http.Header{
+			"Content-Type":      {"application/json"},
+			"x-atlassian-token": {"no-check"},
+		},
+	})
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to get merge commit changes: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.Status > 300 {
+		var errResp struct {
+			Errors []struct {
+				Message string `json:"message"`
+			} `json:"errors"`
+		}
+		errMsg := fmt.Sprintf("status code: %d", resp.Status)
+		if decErr := json.NewDecoder(resp.Body).Decode(&errResp); decErr == nil && len(errResp.Errors) > 0 {
+			errMsg = fmt.Sprintf("%s, message: %s", errMsg, errResp.Errors[0].Message)
+		}
+		return nil, nil, fmt.Errorf("failed to get merge commit changes: %s", errMsg)
+	}
+
+	out := new(types.DiffStats)
+
+	err = json.NewDecoder(resp.Body).Decode(out)
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to decode merge commit changes: %w", err)
+	}
+
+	if !out.LastPage {
+		resp.Page.First = 1
+		resp.Page.Next = opts.Page + 1
+	}
+
+	return convertDiffstats(out), resp, nil
+}
+
+func convertDiffstats(from *types.DiffStats) []*scm.Change {
+	to := make([]*scm.Change, 0, len(from.Values))
+	for _, v := range from.Values {
+		to = append(to, convertDiffstat(v))
+	}
+	return to
+}
+
+func convertDiffstat(from *types.DiffStat) *scm.Change {
+	to := &scm.Change{
+		Path:     from.Path.ToString,
+		Added:    from.Type == "ADD",
+		Modified: from.Type == "MODIFY",
+		Renamed:  from.Type == "MOVE",
+		Deleted:  from.Type == "DELETE",
+	}
+	if from.SrcPath != nil {
+		to.PreviousPath = from.SrcPath.ToString
+	}
+	return to
+}