fix: restore git-diff mode to fix v1.0.1 Vela regression

internal/plugin/gitdiff/diff.go

@@ -0,0 +1,56 @@
+// Package gitdiff produces a unified diff by running git locally, reproducing
+// the behaviour of the old scripts/start.sh that was removed in v1.0.1.
+package gitdiff
+
+import (
+	"bytes"
+	"io"
+	"os/exec"
+
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+)
+
+// Loader fetches the PR diff by running `git fetch` + `git diff` in the
+// current working directory. git must be on $PATH and the remote "origin" must
+// be reachable (credentials via .netrc, SSH key, or the git credential helper
+// already configured in the calling environment).
+type Loader struct {
+	baseBranch string
+	module     string
+}
+
+func NewLoader(baseBranch, module string) *Loader {
+	return &Loader{baseBranch: baseBranch, module: module}
+}
+
+// Load fetches origin/<baseBranch> and returns a unified=0 diff against HEAD.
+// When module is non-empty it is passed as a path filter to git diff, matching
+// the behaviour of the old start.sh for Gradle multi-module projects.
+func (l *Loader) Load() (io.Reader, error) {
+	if l.baseBranch == "" {
+		return nil, errors.New("base branch is required for PARAMETER_DIFF_SOURCE=git (set PARAMETER_BASE_BRANCH or VELA_PULL_REQUEST_TARGET)")
+	}
+
+	fetchArgs := []string{"fetch", "--no-tags", "origin", l.baseBranch}
+	logrus.Infof("running git %v", fetchArgs)
+	fetchCmd := exec.Command("git", fetchArgs...) //nolint:gosec // args are controlled internally, not user input
+	if out, err := fetchCmd.CombinedOutput(); err != nil {
+		return nil, errors.Wrapf(err, "git fetch failed: %s", string(out))
+	}
+
+	diffArgs := []string{"--no-pager", "diff", "--unified=0", "origin/" + l.baseBranch}
+	if l.module != "" {
+		diffArgs = append(diffArgs, l.module)
+	}
+	logrus.Infof("running git %v", diffArgs)
+	diffCmd := exec.Command("git", diffArgs...) //nolint:gosec // args are controlled internally, not user input
+	var stdout, stderr bytes.Buffer
+	diffCmd.Stdout = &stdout
+	diffCmd.Stderr = &stderr
+	if err := diffCmd.Run(); err != nil {
+		return nil, errors.Wrapf(err, "git diff failed: %s", stderr.String())
+	}
+
+	return &stdout, nil
+}

internal/plugin/runner.go

@@ -15,6 +15,7 @@ import (
 	"github.com/target/pull-request-code-coverage/internal/plugin/coverage/jacoco"
 	"github.com/target/pull-request-code-coverage/internal/plugin/coverage/lcov"
 	"github.com/target/pull-request-code-coverage/internal/plugin/coverage/pythoncov"
+	"github.com/target/pull-request-code-coverage/internal/plugin/gitdiff"
 	"github.com/target/pull-request-code-coverage/internal/plugin/githubdiff"
 	"github.com/target/pull-request-code-coverage/internal/plugin/pluginhttp"
 	"github.com/target/pull-request-code-coverage/internal/plugin/pluginjson"
@@ -101,14 +102,39 @@ func (*DefaultRunner) Run(propertyGetter func(string) (string, bool), changedSou
 
 	diffSource, found := propertyGetter("PARAMETER_DIFF_SOURCE")
 	if !found || diffSource == "" {
-		logrus.Info("PARAMETER_DIFF_SOURCE was missing, defaulting to stdin")
-		diffSource = "stdin"
+		// Auto-detect: when running in Vela CI (VELA_PULL_REQUEST_TARGET is set by
+		// the Vela runtime) fall back to the git diff mode so pipelines that relied
+		// on the old start.sh entrypoint continue to work without any config change.
+		if velaTarget, hasVelaTarget := propertyGetter("VELA_PULL_REQUEST_TARGET"); hasVelaTarget && velaTarget != "" {
+			logrus.Info("PARAMETER_DIFF_SOURCE was missing but VELA_PULL_REQUEST_TARGET is set, defaulting to git")
+			diffSource = "git"
+		} else {
+			logrus.Info("PARAMETER_DIFF_SOURCE was missing, defaulting to stdin")
+			diffSource = "stdin"
+		}
 	}
 
 	switch diffSource {
 	case "stdin":
 		// changedSourceLinesSource already points at the piped-in diff (stdin);
 		// nothing to do. This is the original, default behavior.
+	case "git":
+		// Runs git fetch + git diff locally, reproducing what start.sh did before
+		// it was removed in v1.0.1. The base branch is read from PARAMETER_BASE_BRANCH
+		// first, then VELA_PULL_REQUEST_TARGET for backward compatibility.
+		baseBranch, hasBranch := propertyGetter("PARAMETER_BASE_BRANCH")
+		if !hasBranch || baseBranch == "" {
+			baseBranch, _ = propertyGetter("VELA_PULL_REQUEST_TARGET")
+		}
+
+		logrus.Infof("PARAMETER_DIFF_SOURCE is git, diffing against origin/%s", baseBranch)
+
+		diffReader, fetchErr := gitdiff.NewLoader(baseBranch, module).Load()
+		if fetchErr != nil {
+			return errors.Wrap(fetchErr, "Failed fetching diff via git")
+		}
+
+		changedSourceLinesSource = diffReader
 	case "github":
 		if !ghAPIKeyFound || !repoPRFound || !repoOwnerFound || !repoNameFound {
 			return errors.New("PARAMETER_DIFF_SOURCE=github requires a GitHub API key (PARAMETER_GH_API_KEY), BUILD_PULL_REQUEST_NUMBER, REPOSITORY_ORG and REPOSITORY_NAME")
@@ -123,7 +149,7 @@ func (*DefaultRunner) Run(propertyGetter func(string) (string, bool), changedSou
 
 		changedSourceLinesSource = diffReader
 	default:
-		return errors.Errorf("Unknown PARAMETER_DIFF_SOURCE %q (expected \"stdin\" or \"github\")", diffSource)
+		return errors.Errorf("Unknown PARAMETER_DIFF_SOURCE %q (expected \"stdin\", \"git\", or \"github\")", diffSource)
 	}
 
 	changedLines, changedLinesErr := unifieddiff.NewChangedSourceLinesLoader(module, sourceDirs).Load(changedSourceLinesSource)

internal/plugin/runner_diffsource_test.go

@@ -9,6 +9,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	"github.com/target/pull-request-code-coverage/internal/test/mocks"
 )
 
@@ -56,7 +57,7 @@ func TestDefaultRunner_Run_DiffSourceUnknown(t *testing.T) {
 	propGetter.On("GetProperty", "PARAMETER_DIFF_SOURCE").Return("banana", true)
 
 	err := NewRunner().Run(propGetter.GetProperty, strings.NewReader(""), os.Stdout)
-	assert.EqualError(t, err, "Unknown PARAMETER_DIFF_SOURCE \"banana\" (expected \"stdin\" or \"github\")")
+	assert.EqualError(t, err, "Unknown PARAMETER_DIFF_SOURCE \"banana\" (expected \"stdin\", \"git\", or \"github\")")
 
 	propGetter.AssertExpectations(t)
 }
@@ -117,3 +118,46 @@ func TestDefaultRunner_Run_DiffSourceGithub_FetchesDiff(t *testing.T) {
 
 	propGetter.AssertExpectations(t)
 }
+
+// When PARAMETER_DIFF_SOURCE is absent but VELA_PULL_REQUEST_TARGET is set the
+// runner should auto-select the "git" path. We verify this by using a branch
+// name that is guaranteed to not exist on any remote, so git fetch always fails
+// and the error message proves the "git" path was taken (not the silent "stdin"
+// path that would return 0 lines with no error).
+func TestDefaultRunner_Run_DiffSourceAutodetect_VelaTarget(t *testing.T) {
+	propGetter := mocks.NewMockPropertyGetter()
+
+	propGetter.On("GetProperty", "PARAMETER_COVERAGE_FILE").Return("../test/jacocoTestReport.xml", true)
+	propGetter.On("GetProperty", "PARAMETER_COVERAGE_TYPE").Return("jacoco", true)
+	propGetter.On("GetProperty", "PARAMETER_SOURCE_DIRS").Return("src/main/java", true)
+	// No PARAMETER_DIFF_SOURCE — auto-detect should kick in.
+	// Use a branch that cannot exist on any remote so git fetch always fails.
+	propGetter.On("GetProperty", "VELA_PULL_REQUEST_TARGET").Return("this-branch-does-not-exist-xyzzy-99999", true)
+	propGetter.On("GetProperty", "PARAMETER_BASE_BRANCH").Return("", false)
+
+	err := NewRunner().Run(propGetter.GetProperty, strings.NewReader(""), os.Stdout)
+	// require (not assert) so the test stops here on nil — prevents a nil-deref
+	// panic on the Contains check below.
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "Failed fetching diff via git")
+
+	propGetter.AssertExpectations(t)
+}
+
+// PARAMETER_DIFF_SOURCE=git with an explicit PARAMETER_BASE_BRANCH should also
+// take the git path and surface a meaningful error when the branch is empty.
+func TestDefaultRunner_Run_DiffSourceGit_MissingBaseBranch(t *testing.T) {
+	propGetter := mocks.NewMockPropertyGetter()
+
+	propGetter.On("GetProperty", "PARAMETER_COVERAGE_FILE").Return("../test/jacocoTestReport.xml", true)
+	propGetter.On("GetProperty", "PARAMETER_COVERAGE_TYPE").Return("jacoco", true)
+	propGetter.On("GetProperty", "PARAMETER_SOURCE_DIRS").Return("src/main/java", true)
+	propGetter.On("GetProperty", "PARAMETER_DIFF_SOURCE").Return("git", true)
+	propGetter.On("GetProperty", "PARAMETER_BASE_BRANCH").Return("", false)
+	propGetter.On("GetProperty", "VELA_PULL_REQUEST_TARGET").Return("", false)
+
+	err := NewRunner().Run(propGetter.GetProperty, strings.NewReader(""), os.Stdout)
+	assert.EqualError(t, err, "Failed fetching diff via git: base branch is required for PARAMETER_DIFF_SOURCE=git (set PARAMETER_BASE_BRANCH or VELA_PULL_REQUEST_TARGET)")
+
+	propGetter.AssertExpectations(t)
+}