presubmit: add whitespace test in go (#3629)

Automatically submitted.

test/trailing_test.go

@@ -0,0 +1,50 @@
+package test
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"unicode"
+)
+
+func TestTrailingWhitespace(t *testing.T) {
+	err := filepath.Walk("..", hasTrailingWhitespace)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func hasTrailingWhitespace(path string, info os.FileInfo, _ error) error {
+	// Only handle regular files, skip files that are executable and skip file in the
+	// root that start with a .
+	if !info.Mode().IsRegular() {
+		return nil
+	}
+	if info.Mode().Perm()&0111 != 0 {
+		return nil
+	}
+	if strings.HasPrefix(path, "../.") {
+		return nil
+	}
+
+	println("looking at", path)
+	file, err := os.Open(path)
+	if err != nil {
+		return nil
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		text := scanner.Text()
+		trimmed := strings.TrimRightFunc(text, unicode.IsSpace)
+		if len(text) != len(trimmed) {
+			return fmt.Errorf("file %q has trailing whitespace, text: %q", path, text)
+		}
+	}
+
+	return scanner.Err()
+}