From 43995b04fc9795de8791e8a9d82206f95d8acaf1 Mon Sep 17 00:00:00 2001
From: Fernandez Ludovic <ldez@users.noreply.github.com>
Date: Fri, 31 Jan 2025 05:56:38 +0100
Subject: [PATCH] feat: merge-base option

---
 patch.go      | 46 ++++++++++++++++++++++++++++++++++++++++------
 patch_test.go |  2 +-
 revgrep.go    | 14 +++++++++++---
 3 files changed, 52 insertions(+), 10 deletions(-)

diff --git a/patch.go b/patch.go
index c0cbf76..81a2acd 100644
--- a/patch.go
+++ b/patch.go
@@ -12,6 +12,12 @@ import (
 	"strings"
 )
 
+type patchOption struct {
+	revisionFrom string
+	revisionTo   string
+	mergeBase    string
+}
+
 // GitPatch returns a patch from a git repository.
 // If no git repository was found and no errors occurred, nil is returned,
 // else an error is returned revisionFrom and revisionTo defines the git diff parameters,
@@ -20,7 +26,7 @@ import (
 // If revisionFrom is set but revisionTo is not,
 // untracked files will be included, to exclude untracked files set revisionTo to HEAD~.
 // It's incorrect to specify revisionTo without a revisionFrom.
-func GitPatch(ctx context.Context, revisionFrom, revisionTo string) (io.Reader, []string, error) {
+func GitPatch(ctx context.Context, option patchOption) (io.Reader, []string, error) {
 	// check if git repo exists
 	if err := exec.CommandContext(ctx, "git", "status", "--porcelain").Run(); err != nil {
 		// don't return an error, we assume the error is not repo exists
@@ -45,11 +51,23 @@ func GitPatch(ctx context.Context, revisionFrom, revisionTo string) (io.Reader,
 		newFiles = append(newFiles, string(file))
 	}
 
-	if revisionFrom != "" {
-		args := []string{revisionFrom}
+	if option.mergeBase != "" {
+		var base string
+		base, err = getMergeBase(ctx, option.mergeBase)
+		if err != nil {
+			return nil, nil, err
+		}
+
+		if base != "" {
+			option.revisionFrom = base
+		}
+	}
+
+	if option.revisionFrom != "" {
+		args := []string{option.revisionFrom}
 
-		if revisionTo != "" {
-			args = append(args, revisionTo)
+		if option.revisionTo != "" {
+			args = append(args, option.revisionTo)
 		}
 
 		args = append(args, "--")
@@ -59,7 +77,7 @@ func GitPatch(ctx context.Context, revisionFrom, revisionTo string) (io.Reader,
 			return nil, nil, errDiff
 		}
 
-		if revisionTo == "" {
+		if option.revisionTo == "" {
 			return patch, newFiles, nil
 		}
 
@@ -159,3 +177,19 @@ func isSupportedByGit(ctx context.Context, major, minor, patch int) bool {
 
 	return currentMajor*1_000_000_000+currentMinor*1_000_000+currentPatch*1_000 >= major*1_000_000_000+minor*1_000_000+patch*1_000
 }
+
+func getMergeBase(ctx context.Context, base string) (string, error) {
+	cmd := exec.CommandContext(ctx, "git", "merge-base", base, "HEAD")
+
+	patch := new(bytes.Buffer)
+	errBuff := new(bytes.Buffer)
+
+	cmd.Stdout = patch
+	cmd.Stderr = errBuff
+
+	if err := cmd.Run(); err != nil {
+		return "", fmt.Errorf("error executing %q: %w: %w", strings.Join(cmd.Args, " "), err, readAsError(errBuff))
+	}
+
+	return strings.TrimSpace(patch.String()), nil
+}
diff --git a/patch_test.go b/patch_test.go
index 988e698..99cfc10 100644
--- a/patch_test.go
+++ b/patch_test.go
@@ -20,7 +20,7 @@ func TestGitPatch_nonGitDir(t *testing.T) {
 
 	t.Cleanup(func() { _ = os.Chdir(wd) })
 
-	patch, newFiles, err := GitPatch(context.Background(), "", "")
+	patch, newFiles, err := GitPatch(context.Background(), patchOption{})
 	if err != nil {
 		t.Errorf("error expected nil, got: %v", err)
 	}
diff --git a/revgrep.go b/revgrep.go
index 184db1c..ca4ac79 100644
--- a/revgrep.go
+++ b/revgrep.go
@@ -29,10 +29,12 @@ type Checker struct {
 	Debug io.Writer
 	// RevisionFrom check revision starting at, leave blank for auto-detection ignored if patch is set.
 	RevisionFrom string
-	// WholeFiles indicates that the user wishes to see all issues that comes up anywhere in any file that has been changed in this revision or patch.
-	WholeFiles bool
 	// RevisionTo checks revision finishing at, leave blank for auto-detection ignored if patch is set.
 	RevisionTo string
+	// MergeBase checks revision starting at the best common ancestor, leave blank for auto-detection ignored if patch is set.
+	MergeBase string
+	// WholeFiles indicates that the user wishes to see all issues that comes up anywhere in any file that has been changed in this revision or patch.
+	WholeFiles bool
 	// Regexp to match path, line number, optional column number, and message.
 	Regexp string
 	// AbsPath is used to make an absolute path of an issue's filename to be relative in order to match patch file.
@@ -228,8 +230,14 @@ func (c *Checker) loadPatch(ctx context.Context) error {
 		return nil
 	}
 
+	option := patchOption{
+		revisionFrom: c.RevisionFrom,
+		revisionTo:   c.RevisionTo,
+		mergeBase:    c.MergeBase,
+	}
+
 	var err error
-	c.Patch, c.NewFiles, err = GitPatch(ctx, c.RevisionFrom, c.RevisionTo)
+	c.Patch, c.NewFiles, err = GitPatch(ctx, option)
 	if err != nil {
 		return fmt.Errorf("could not read git repo: %w", err)
 	}