HMCL-dev/HMCL · error · IllegalArgumentException

Illegal pattern (Unclosed )

Error message

Illegal pattern (Unclosed ${char}): ${value}

What it means

Thrown as IllegalArgumentException from replaceTokens when a '{' or '\'' starts a token/quoted section that is never closed before the end of the string: the scanning inner loop reaches the end of the value without finding the matching '}' or '\''. The literal is structurally invalid.

Solutions

1. Correct the literal in install_profile.json so every '{' has a matching '}' and quotes are paired
2. Regenerate the installer profile or use the official installer jar
3. Validate the JSON content of install_profile.json inside the installer
4. If you control the code, pre-validate balanced braces/quotes before calling parseLiteral

Example fix

// before
"{MINECRAFT_JAR"
// after
"{MINECRAFT_JAR}"

static boolean balanced(String s) {
    int braces = 0, quotes = 0;
    for (int i = 0; i < s.length(); i++) {
        char c = s.charAt(i);
        if (c == '\\') i++;
        else if (c == '{') braces++;
        else if (c == '}') braces--;
        else if (c == '\'') quotes++;
    }
    return braces == 0 && quotes % 2 == 0;
}

try { task.run(); } catch (IllegalArgumentException e) { if (e.getMessage() != null && e.getMessage().contains("Illegal pattern (Unclosed")) reportUnclosedToken(e.getMessage()); else throw e; }

When it happens

Trigger: A processor arg or data value contains '{' without a matching '}' (e.g. "{MINECRAFT_JAR" ) or an odd number of quote characters ("'literal" ), so the inner loop hits y == value.length() during parseLiteral of install_profile.json content.

Common situations: Hand-edited or malformed install_profile.json processor args; a placeholder whose closing brace was lost in editing or JSON escaping; template values pasted partially.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• Illegal pattern (Bad escape)
• Illegal pattern: Missing Key
• Artifact name is malformed
• Bad Build-Number
• Expected typed ID prefix '" + expectedPrefix + "'

AI-assisted analysis of HMCL-dev/HMCL@24702dc5a0 (2026-09-10). Data as JSON: /api/errors/03367714ba514ce5. Report an issue: GitHub.

Appendix: source

Thrown at HMCLCore/src/main/java/org/jackhuang/hmcl/download/neoforge/NeoForgeOldInstallTask.java:225

        this.installer = installer;
        this.selfVersion = selfVersion;

        setSignificance(TaskSignificance.MAJOR);
    }

    private static String replaceTokens(Map<String, String> tokens, String value) {
        StringBuilder buf = new StringBuilder();
        for (int x = 0; x < value.length(); x++) {
            char c = value.charAt(x);
            if (c == '\\') {
                if (x == value.length() - 1)
                    throw new IllegalArgumentException("Illegal pattern (Bad escape): " + value);
                buf.append(value.charAt(++x));
            } else if (c == '{' || c == '\'') {
                StringBuilder key = new StringBuilder();
                for (int y = x + 1; y <= value.length(); y++) {
                    if (y == value.length())
                        throw new IllegalArgumentException("Illegal pattern (Unclosed " + c + "): " + value);
                    char d = value.charAt(y);
                    if (d == '\\') {
                        if (y == value.length() - 1)
                            throw new IllegalArgumentException("Illegal pattern (Bad escape): " + value);
                        key.append(value.charAt(++y));
                    } else {
                        if (c == '{' && d == '}') {
                            x = y;
                            break;
                        }
                        if (c == '\'' && d == '\'') {
                            x = y;
                            break;
                        }
                        key.append(d);
                    }
                }
                if (c == '\'') {

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