interp: Return invalid globs when nullglob is set

Prior to this commit invalid globs were returned as null when nullglob
was set, which resulted in test expressions failing:

  $ shopt -s nullglob; [ -n butter ] && echo bubbles
  "-n": executable file not found in $PATH

After this commit invalid globs are returned verbatim when nullglob is
set.

expand/expand.go

@@ -409,14 +409,17 @@ func Fields(cfg *Config, words ...*syntax.Word) ([]string, error) {
  for _, field := range wfields {
  path, doGlob := cfg.escapedGlobField(field)
  var matches []string
+ var invalidGlob *pattern.InvalidGlobError
  if doGlob && cfg.ReadDir != nil {
  matches, err = cfg.glob(dir, path)
- if err != nil {
- return nil, err
- }
- if len(matches) > 0 || cfg.NullGlob {
- fields = append(fields, matches...)
- continue
+ if !errors.As(err, &invalidGlob) {
+ if err != nil {
+ return nil, err
+ }
+ if len(matches) > 0 || cfg.NullGlob {
+ fields = append(fields, matches...)
+ continue
+ }
  }
  }
  fields = append(fields, cfg.fieldJoin(field))
@@ -851,8 +854,7 @@ func (cfg *Config) glob(base, pat string) ([]string, error) {
  }
  expr, err := pattern.Regexp(part, pattern.Filenames)
  if err != nil {
- // If any glob part is not a valid pattern, don't glob.
- return nil, nil
+ return nil, err
  }
  rx := regexp.MustCompile("^" + expr + "$")
  var newMatches []string

interp/interp_test.go

@@ -2581,6 +2581,12 @@ set +o pipefail
  "shopt -s nullglob; touch existing-1; echo missing-* existing-*",
  "existing-1\n",
  },
+ // Ensure that setting nullglob does not return invalid globs as null
+ // strings.
+ {
+ "shopt -s nullglob; [ -n butter ] && echo bubbles",
+ "bubbles\n",
+ },
  {
  "cat <<EOF\n{foo_interp_missing,bar_interp_missing}\nEOF",
  "{foo_interp_missing,bar_interp_missing}\n",

pattern/pattern.go

@@ -20,6 +20,15 @@ import (
 // Not all functions change their behavior with all of the options below.
 type Mode uint
 
+type InvalidGlobError struct {
+ msg string
+ err error
+}
+
+func (e InvalidGlobError) Error() string { return e.msg }
+
+func (e InvalidGlobError) Unwrap() error { return e.err }
+
 const (
  Shortest Mode = 1 << iota // prefer the shortest match.
  Filenames // "*" and "?" don't match slashes; only "**" does
@@ -85,13 +94,13 @@ writeLoop:
  }
  case '\\':
  if i++; i >= len(pat) {
- return "", fmt.Errorf(`\ at end of pattern`)
+ return "", &InvalidGlobError{msg: `\ at end of pattern`}
  }
  buf.WriteString(regexp.QuoteMeta(string(pat[i])))
  case '[':
  name, err := charClass(pat[i:])
  if err != nil {
- return "", err
+ return "", &InvalidGlobError{msg: "charClass invalid", err: err}
  }
  if name != "" {
  buf.WriteString(name)
@@ -110,19 +119,19 @@ writeLoop:
  }
  buf.WriteByte(c)
  if i++; i >= len(pat) {
- return "", fmt.Errorf("[ was not matched with a closing ]")
+ return "", &InvalidGlobError{msg: "[ was not matched with a closing ]"}
  }
  switch c = pat[i]; c {
  case '!', '^':
  buf.WriteByte('^')
  if i++; i >= len(pat) {
- return "", fmt.Errorf("[ was not matched with a closing ]")
+ return "", &InvalidGlobError{msg: "[ was not matched with a closing ]"}
  }
  }
  if c = pat[i]; c == ']' {
  buf.WriteByte(']')
  if i++; i >= len(pat) {
- return "", fmt.Errorf("[ was not matched with a closing ]")
+ return "", &InvalidGlobError{msg: "[ was not matched with a closing ]"}
  }
  }
  rangeStart := byte(0)
@@ -140,7 +149,7 @@ writeLoop:
  break loopBracket
  }
  if rangeStart != 0 && rangeStart > c {
- return "", fmt.Errorf("invalid range: %c-%c", rangeStart, c)
+ return "", &InvalidGlobError{msg: fmt.Sprintf("invalid range: %c-%c", rangeStart, c)}
  }
  if c == '-' {
  rangeStart = pat[i-1]
@@ -149,7 +158,7 @@ writeLoop:
  }
  }
  if i >= len(pat) {
- return "", fmt.Errorf("[ was not matched with a closing ]")
+ return "", &InvalidGlobError{msg: "[ was not matched with a closing ]"}
  }
  case '{':
  if mode&Braces == 0 {
@@ -183,7 +192,7 @@ writeLoop:
  start, err1 := strconv.Atoi(match[1])
  end, err2 := strconv.Atoi(match[2])
  if err1 != nil || err2 != nil || start > end {
- return "", fmt.Errorf("invalid range: %q", match[0])
+ return "", &InvalidGlobError{msg: fmt.Sprintf("invalid range: %q", match[0])}
  }
  // TODO: can we do better here?
  buf.WriteString("(?:")