dangling-whitespace: rule for trailing spaces

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

git/commits.go

@@ -57,6 +57,19 @@ var FieldNames = map[string]string{
 	"%G?": "verification_flag",
 }
 
+// Show returns the diff of a commit.
+//
+// NOTE: This could be expensive for very large commits.
+func Show(commit string) ([]byte, error) {
+	cmd := exec.Command("git", "show", commit)
+	cmd.Stderr = os.Stderr
+	out, err := cmd.Output()
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
 // CommitEntry represents a single commit's information from `git`.
 // See also FieldNames
 type CommitEntry map[string]string

main.go

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

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("+ ")
+)