commits: add a fallback if rev-list fails due to shallow depth

Fixes: #53

When CI only fetches some shallow depth of commits in a repo, don't fail
on `git rev-list` on commits that are outside that range.

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

git/commits.go

@@ -15,13 +15,19 @@ import (
 // If commitrange is a single commit, all ancestor commits up through the hash provided.
 // If commitrange is an empty commit range, then nil is returned.
 func Commits(commitrange string) ([]CommitEntry, error) {
+	// TEST if it has _enough_ of a range from rev-list
+	commitrange, err := checkRevList(commitrange)
+	if err != nil {
+		logrus.Errorf("failed to validate the git commit range: %s", err)
+		return nil, err
+	}
 	cmdArgs := []string{"git", "rev-list", commitrange}
 	if debug() {
 		logrus.Infof("[git] cmd: %q", strings.Join(cmdArgs, " "))
 	}
 	output, err := exec.Command(cmdArgs[0], cmdArgs[1:]...).Output()
 	if err != nil {
-		logrus.Errorf("mm[git] cmd: %q", strings.Join(cmdArgs, " "))
+		logrus.Errorf("[git] cmd: %q", strings.Join(cmdArgs, " "))
 		return nil, err
 	}
 	if len(output) == 0 {
@@ -39,6 +45,39 @@ func Commits(commitrange string) ([]CommitEntry, error) {
 	return commits, nil
 }
 
+// Since the commitrange requested may be longer than the depth being cloned in CI,
+// check for an error, if so do a git log to get the oldest available commit for a reduced range.
+func checkRevList(commitrange string) (string, error) {
+	cmdArgs := []string{"git", "rev-list", commitrange}
+	if debug() {
+		logrus.Infof("[git] cmd: %q", strings.Join(cmdArgs, " "))
+	}
+	_, err := exec.Command(cmdArgs[0], cmdArgs[1:]...).Output()
+	if err == nil {
+		// no issues, return now
+		return commitrange, nil
+	}
+	cmdArgs = []string{"git", "log", "--pretty=oneline"}
+	if debug() {
+		logrus.Infof("[git] cmd: %q", strings.Join(cmdArgs, " "))
+	}
+	output, err := exec.Command(cmdArgs[0], cmdArgs[1:]...).Output()
+	if err != nil {
+		logrus.Errorf("[git] cmd: %q", strings.Join(cmdArgs, " "))
+		return "", err
+	}
+	// This "output" is now the list of available commits and short description.
+	// We want the last commit hash only.. (i.e. `| tail -n1 | awk '{ print $1 }'`)
+	chunks := strings.Split(strings.TrimSpace(string(output)), "\n")
+	if len(chunks) == 1 {
+		return strings.Split(chunks[0], " ")[0], nil
+	}
+	last := chunks[len(chunks)-1]
+	lastCommit := strings.Split(last, " ")[0]
+
+	return fmt.Sprintf("%s..HEAD", lastCommit), nil
+}
+
 // FieldNames are for the formating and rendering of the CommitEntry structs.
 // Keys here are from git log pretty format "format:..."
 var FieldNames = map[string]string{

main.go

@@ -3,10 +3,10 @@ package main
 import (
 	"flag"
 	"fmt"
-	"log"
 	"os"
 	"strings"
 
+	"github.com/sirupsen/logrus"
 	_ "github.com/vbatts/git-validation/rules/danglingwhitespace"
 	_ "github.com/vbatts/git-validation/rules/dco"
 	_ "github.com/vbatts/git-validation/rules/messageregexp"
@@ -62,7 +62,7 @@ func main() {
 		rules = validate.FilterRules(validate.RegisteredRules, validate.SanitizeFilters(*flRun))
 	}
 	if os.Getenv("DEBUG") != "" {
-		log.Printf("%#v", rules) // XXX maybe reduce this list
+		logrus.Printf("%#v", rules) // XXX maybe reduce this list
 	}
 
 	var commitRange = *flCommitRange
@@ -80,13 +80,14 @@ func main() {
 		}
 	}
 
+	logrus.Infof("using commit range: %s", commitRange)
 	runner, err := validate.NewRunner(*flDir, rules, commitRange, *flVerbose)
 	if err != nil {
-		log.Fatal(err)
+		logrus.Fatal(err)
 	}
 
 	if err := runner.Run(); err != nil {
-		log.Fatal(err)
+		logrus.Fatal(err)
 	}
 	_, fail := runner.Results.PassFail()
 	if fail > 0 {