oracle/graal · error · IllegalArgumentException

--java.SpecCompliance: Mode can be 'strict' or 'hotspot'.

Error message

--java.SpecCompliance: Mode can be 'strict' or 'hotspot'.

What it means

The OptionType converter for the --java.SpecCompliance option tries SpecComplianceMode.valueOf(s.toUpperCase()) and wraps any IllegalArgumentException when the string is neither 'strict' nor 'hotspot' (case-insensitive). The option controls whether Espresso mimics HotSpot behavior on points where it deviates from the JVMS.

Source

Thrown at espresso/src/com.oracle.truffle.espresso/src/com/oracle/truffle/espresso/EspressoOptions.java:286

        return new ArrayList<>(Arrays.asList(strings.split(File.pathSeparator)));
    }

    private static List<String> splitBySemiColon(String strings) {
        return new ArrayList<>(Arrays.asList(strings.split(EspressoOptions.SEMI_COLON)));
    }

    public enum SpecComplianceMode {
        STRICT,
        HOTSPOT
    }

    private static final OptionType<SpecComplianceMode> SPEC_COMPLIANCE_OPTION_TYPE = new OptionType<>("SpecCompliance", new Function<String, SpecComplianceMode>() {
        @Override
        public SpecComplianceMode apply(String s) {
            try {
                return SpecComplianceMode.valueOf(s.toUpperCase(Locale.ROOT));
            } catch (IllegalArgumentException e) {
                throw new IllegalArgumentException("--java.SpecCompliance: Mode can be 'strict' or 'hotspot'.");
            }
        }
    });

    @Option(help = "Force mimicking of hotspot behavior on unrespected specs points", //
                    category = OptionCategory.EXPERT, //
                    stability = OptionStability.EXPERIMENTAL, //
                    usageSyntax = "hotspot|strict") //
    public static final OptionKey<SpecComplianceMode> SpecCompliance = new OptionKey<>(SpecComplianceMode.HOTSPOT, SPEC_COMPLIANCE_OPTION_TYPE);

    public enum VerifyMode {
        NONE,
        REMOTE, // Verifies all bytecodes not loaded by the bootstrap class loader.
        ALL
    }

    private static final OptionType<VerifyMode> VERIFY_MODE_OPTION_TYPE = new OptionType<>("VerifyMode", new Function<String, VerifyMode>() {
        @Override

View on GitHub (pinned to a66e9ccd1d)

Solutions

1. Use exactly --java.SpecCompliance=strict or --java.SpecCompliance=hotspot (case-insensitive).
2. Remove the flag to keep the default value, which is hotspot.
3. Check mx/graalvm flag documentation for the current option name and allowed values.

Example fix

# before
--java.SpecCompliance=default

# after
--java.SpecCompliance=strict

// Java launcher
if (!List.of("strict", "hotspot").contains(specCompliance.toLowerCase(Locale.ROOT))) {
    throw new ConfigException("SpecCompliance must be strict|hotspot");
}

static boolean validSpecCompliance(String s) {
    return s != null && s.matches("(?i)(strict|hotspot)");
}

When it happens

Trigger: Passing --java.SpecCompliance=<value> (or context option java.SpecCompliance) where value is anything other than strict/hotspot, e.g. 'default', 'true', 'STRICT ' with trailing space.

Common situations: Copy-pasting JVM flags that have no Espresso equivalent; typos in CI launch configuration; scripts written against a different GraalVM version where accepted values differ.

Related errors

• -Xverify: Mode can be 'none', 'remote' or 'all'.
• --java.LivenessAnalysis can only be 'none'|'false', 'auto' o
• Not starting with digits: {size}
• Unit prefix can be at most one character: {size}
• Unrecognized unit prefix: {size} use `T`, `G`, `M`, or `k`.

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/6444081039fcf4dc. Report an issue: GitHub.