Merged pull_request events should resolve to the target branch.

Author: linkdata

internal/gitsemver/gitsemver.go

@@ -1,9 +1,11 @@
 package gitsemver
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
+	"os"
 	"strconv"
 	"strings"
 )
@@ -172,26 +174,52 @@ func (vs *GitSemVer) GetTag(repo string) (tag string, match bool, err error) {
 	return
 }
 
+type gitHubPullRequestEvent struct {
+	PullRequest struct {
+		Merged bool `json:"merged"`
+	} `json:"pull_request"`
+}
+
+func (vs *GitSemVer) isMergedGitHubPullRequest() bool {
+	eventName := strings.TrimSpace(vs.Env.Getenv("GITHUB_EVENT_NAME"))
+	if eventName == "pull_request" || eventName == "pull_request_target" {
+		if eventPath := strings.TrimSpace(vs.Env.Getenv("GITHUB_EVENT_PATH")); eventPath != "" {
+			if b, err := os.ReadFile(eventPath); /* #nosec G304 */ err == nil {
+				var event gitHubPullRequestEvent
+				if err = json.Unmarshal(b, &event); err == nil {
+					return event.PullRequest.Merged
+				}
+			}
+		}
+	}
+	return false
+}
+
 func (vs *GitSemVer) getBranchGitHub(repo string) (branchName string, err error) {
 	// Pull request events expose the source branch as GITHUB_HEAD_REF.
 	// Prefer this so PR builds are not mistaken for base-branch releases.
-	if branchName = strings.TrimSpace(vs.Env.Getenv("GITHUB_HEAD_REF")); branchName == "" {
-		if branchName = strings.TrimSpace(vs.Env.Getenv("GITHUB_REF_NAME")); branchName != "" {
-			if strings.TrimSpace(vs.Env.Getenv("GITHUB_REF_TYPE")) == "tag" {
-				var branches []string
-				if branches, err = vs.Git.GetBranchesFromTag(repo, branchName); err == nil {
-					for _, branchName = range branches {
-						if vs.IsReleaseBranch(branchName) {
-							return
-						}
+	if branchName = strings.TrimSpace(vs.Env.Getenv("GITHUB_HEAD_REF")); branchName != "" {
+		// Merged pull_request events should resolve to the target branch.
+		if vs.isMergedGitHubPullRequest() {
+			branchName = strings.TrimSpace(vs.Env.Getenv("GITHUB_BASE_REF"))
+		}
+		return
+	}
+	if branchName = strings.TrimSpace(vs.Env.Getenv("GITHUB_REF_NAME")); branchName != "" {
+		if strings.TrimSpace(vs.Env.Getenv("GITHUB_REF_TYPE")) == "tag" {
+			var branches []string
+			if branches, err = vs.Git.GetBranchesFromTag(repo, branchName); err == nil {
+				for _, branchName = range branches {
+					if vs.IsReleaseBranch(branchName) {
+						return
 					}
 				}
-				branchName = ""
 			}
-		} else {
-			// Fallback for contexts that only expose a base branch.
-			branchName = strings.TrimSpace(vs.Env.Getenv("GITHUB_BASE_REF"))
+			branchName = ""
 		}
+	} else {
+		// Fallback for contexts that only expose a base branch.
+		branchName = strings.TrimSpace(vs.Env.Getenv("GITHUB_BASE_REF"))
 	}
 	return
 }

internal/gitsemver/gitsemver_test.go

@@ -196,9 +196,20 @@ func Test_VersionStringer_GetBranch(t *testing.T) {
 	name, err = vs.GetBranch(".")
 	isEqual(t, err, nil)
 	isEqual(t, "feature/foo", name)
+	eventPath := filepath.Join(t.TempDir(), "event.json")
+	if err = os.WriteFile(eventPath, []byte(`{"pull_request":{"merged":true}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	env["GITHUB_EVENT_NAME"] = "pull_request"
+	env["GITHUB_EVENT_PATH"] = eventPath
+	name, err = vs.GetBranch(".")
+	isEqual(t, err, nil)
+	isEqual(t, "main", name)
 	delete(env, "GITHUB_HEAD_REF")
 	delete(env, "GITHUB_BASE_REF")
 	delete(env, "GITHUB_REF_NAME")
+	delete(env, "GITHUB_EVENT_NAME")
+	delete(env, "GITHUB_EVENT_PATH")
 	git.branch = ""
 
 	git.branch = "detached"