What causes "Not one of " + values" in bazelbuild/bazel?

Use one of the values listed verbatim in the error message ("Not one of [a, b]").

bazelbuild/bazel · error · OptionsParsingException

Not one of " + values

Error message

Not one of " + values

What it means

Thrown by Converters.StringSetConverter.convert when the input is not one of the exact strings the converter was constructed with. Many enum-like Bazel flags are implemented as a closed set of allowed strings; anything not in that ImmutableSet is rejected with a message that conveniently lists all valid values.

Source

Thrown at src/main/java/com/google/devtools/common/options/Converters.java:429

    }
  }

  /** Checks whether a string is part of a set of strings. */
  public static class StringSetConverter extends Converter.Contextless<String> {

    private final ImmutableSet<String> values;

    public StringSetConverter(String... values) {
      this.values = ImmutableSet.copyOf(values);
    }

    @Override
    public String convert(String input) throws OptionsParsingException {
      if (values.contains(input)) {
        return input;
      }

      throw new OptionsParsingException("Not one of " + values);
    }

    @Override
    public String getTypeDescription() {
      return joinEnglishList(values);
    }
  }

  /** Checks whether a string is a valid regex pattern and compiles it. */
  public static class RegexPatternConverter extends Converter.Contextless<RegexPatternOption> {

    @Override
    public RegexPatternOption convert(String input) throws OptionsParsingException {
      try {
        return RegexPatternOption.create(
            Pattern.compile(StringEncoding.internalToUnicode(input), Pattern.DOTALL));
      } catch (PatternSyntaxException e) {
        throw new OptionsParsingException("Not a valid regular expression: " + e.getMessage());

View on GitHub (pinned to e6e199d060)

Solutions

Use one of the values listed verbatim in the error message ("Not one of [a, b]").
Check the flag's help text (its type description lists the same values) after upgrading Bazel.
Parameterize scripts from the same constant list the flag defines to prevent drift.

Example fix

# before
bazel build --strategy=Local //...
# after
bazel build --strategy=local //...   # match exact spelling/case from the error's value list

Defensive patterns

Strategy: validation

Validate before calling

boolean isAllowedValue(String input, Set<String> allowed) {
  return input != null && allowed.contains(input); // exact, case-sensitive match
}

Type guard

boolean isEnumSetFlagValue(String s, java.util.Set<String> allowed) {
  return s != null && allowed.contains(s);
}

Prevention

Derive script constants from the flag's documented value list.
The error message lists every valid value; read it before retrying.
Re-verify closed-set values after Bazel version upgrades.

When it happens

Trigger: Passing --my_flag=compresse to a flag whose StringSetConverter was built with {"compressed","uncompressed"}; passing values with different casing, whitespace, or an equals-sign variant not in the set.

Common situations: Typos and case mismatches; values valid in an older/newer Bazel version removed or renamed; scripts constructing values dynamically that sometimes produce empty strings.

Related errors

AI-assisted analysis of bazelbuild/bazel@e6e199d060 (2026-08-14). Data as JSON: /api/errors/6a44dce2db6cca8d. Report an issue: GitHub.