dangling-whitespace: rule for trailing spaces

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

rules/danglingwhitespace/rule.go

@@ -0,0 +1,49 @@
+package danglingwhitespace
+
+import (
+	"bytes"
+	"fmt"
+
+	"github.com/vbatts/git-validation/git"
+	"github.com/vbatts/git-validation/validate"
+)
+
+var (
+	// DanglingWhitespace is the rule for checking the presence of dangling
+	// whitespaces on line endings.
+	DanglingWhitespace = validate.Rule{
+		Name:        "dangling-whitespace",
+		Description: "checking the presence of dangling whitespaces on line endings",
+		Run:         ValidateDanglingWhitespace,
+	}
+)
+
+func init() {
+	validate.RegisterRule(DanglingWhitespace)
+}
+
+func ValidateDanglingWhitespace(c git.CommitEntry) (vr validate.Result) {
+	diff, err := git.Show(c["commit"])
+	if err != nil {
+		return validate.Result{Pass: false, Msg: err.Error(), CommitEntry: c}
+	}
+
+	vr.CommitEntry = c
+	vr.Pass = true
+	for _, line := range bytes.Split(diff, newLine) {
+		if !bytes.HasPrefix(line, diffAddLine) || bytes.Equal(line, diffAddLine) {
+			continue
+		}
+		if len(bytes.TrimSpace(line)) != len(line) {
+			vr.Pass = false
+			vr.Msg = fmt.Sprintf("line %q has trailiing spaces", string(line))
+		}
+	}
+	vr.Msg = "all added diff lines do not have trailing spaces"
+	return
+}
+
+var (
+	newLine     = []byte("\n")
+	diffAddLine = []byte("+ ")
+)