shortsubject: add a subject length check

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

main.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/vbatts/git-validation/git"
 	_ "github.com/vbatts/git-validation/rules/dco"
+	_ "github.com/vbatts/git-validation/rules/shortsubject"
 	"github.com/vbatts/git-validation/validate"
 )
 

rules/shortsubject/rule.go

@@ -0,0 +1,30 @@
+package shortsubject
+
+import (
+	"github.com/vbatts/git-validation/git"
+	"github.com/vbatts/git-validation/validate"
+)
+
+var (
+	// DcoRule is the rule being registered
+	ShortSubjectRule = validate.Rule{
+		Name:        "short-subject",
+		Description: "commit subjects are strictly less than 90 (github ellipsis length)",
+		Run:         ValidateShortSubject,
+	}
+)
+
+func init() {
+	validate.RegisterRule(ShortSubjectRule)
+}
+
+func ValidateShortSubject(c git.CommitEntry) (vr validate.Result) {
+	if len(c["subject"]) >= 90 {
+		vr.Pass = false
+		vr.Msg = "commit subject exceeds 90 characters"
+		return
+	}
+	vr.Pass = true
+	vr.Msg = "commit subject is not more than 90 characters"
+	return
+}