main.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"errors"
 	"fmt"
 	"log"
 	"os"
@@ -9,7 +8,9 @@ import (
 	"strings"
 
 	git "github.com/go-git/go-git/v5"
+	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/object"
+	"github.com/go-git/go-git/v5/plumbing/storer"
 	gha "github.com/sethvargo/go-githubactions"
 )
 
@@ -25,27 +26,35 @@ func main() {
 	}
 
 	// Retrieve the commit history.
-	ref, err := r.Head()
+	head, err := r.Head()
 	if err != nil {
 		log.Fatalf("Failed to retrieve HEAD reference: %v", err)
 	}
 
 	// Create iterator over commits.
-	commits, err := r.Log(&git.LogOptions{From: ref.Hash()})
+	commits, err := r.Log(&git.LogOptions{From: head.Hash()})
 	if err != nil {
 		log.Fatalf("Failed to retrieve commit history: %v", err)
 	}
 
 	// Limit number of iterations.
 	from := gha.GetInput("from")
+	log.Printf("Resolving revision '%s'", from)
+
+	var lca *object.Commit
+	if from != "" {
+		lca = getMergeBase(r, head, from)
+	}
+
+	log.Printf("Resolved: %s", lca.Hash)
 
 	// Processing result.
 	var fail bool
 
 	_ = commits.ForEach(func(c *object.Commit) error {
 		// Stop iterator when limit is reached.
-		if len(from) != 0 && strings.HasPrefix(c.ID().String(), from) {
+		if lca != nil && c.Hash == lca.Hash {
-			return errors.New("stop")
+			return storer.ErrStop
 		}
 
 		// Parse commit data.
@@ -63,16 +72,18 @@ func main() {
 		header := lines[0]
 		if !rxHeader.MatchString(header) {
 			fail = true
-			fmt.Printf("Error: invalid header %s [%s]\n", header, id)
+			fmt.Printf("Error: invalid header '%s' [%s]\n", header, id)
 			return nil
 		}
 
 		// Check commit sign-off.
 		if !rxSignOff.MatchString(lines[len(lines)-1]) {
 			fail = true
-			fmt.Printf("Error: missing sign-off %s [%s]\n", header, id)
+			fmt.Printf("Error: missing sign-off '%s' [%s]\n", header, id)
+			return nil
 		}
 
+		fmt.Printf("OK: '%s' [%s]\n", header, id)
 		return nil
 	})
 
@@ -82,3 +93,29 @@ func main() {
 	}
 }
 
+func getMergeBase(r *git.Repository, head *plumbing.Reference, from string) *object.Commit {
+	h, err := r.ResolveRevision(plumbing.Revision(from))
+	if err != nil {
+		h, err = r.ResolveRevision(plumbing.Revision(plumbing.NewBranchReferenceName(from)))
+		if err != nil {
+			log.Fatalf("Failed to resolve a reference '%s': %v", from, err)
+		}
+	}
+
+	to, err := r.CommitObject(*h)
+	if err != nil {
+		log.Fatalf("Failed to get commit object: %v", err)
+	}
+
+	other, err := r.CommitObject(head.Hash())
+	if err != nil {
+		log.Fatalf("Failed to get HEAD commit object: %v", err)
+	}
+
+	cc, err := to.MergeBase(other)
+	if err != nil {
+		log.Fatalf("Failed to determine merge-base: %v", err)
+	}
+
+	return cc[0]
+}