OpenAPITools/openapi-generator · error · IllegalArgumentException

Invalid operationIdNaming: " + operationIdNaming + ". Must b

Error message

Invalid operationIdNaming: " + operationIdNaming + ". Must be PascalCase, camelCase or snake_case

What it means

The R generator's setOperationIdNaming() only accepts the literal strings 'PascalCase', 'camelCase', or 'snake_case' (exact casing); anything else throws IllegalArgumentException. The chosen value also drives the WithHttpInfo suffix used in generated function names ('_with_http_info' for snake_case).

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/RClientCodegen.java:666

    }

    public void setExceptionPackageToUse(String exceptionPackage) {
        if (DEFAULT.equals(exceptionPackage))
            this.useDefaultExceptionHandling = true;
        if (RLANG.equals(exceptionPackage)) {
            supportingFiles.add(new SupportingFile("api_exception.mustache", File.separator + "R", "api_exception.R"));
            this.useRlangExceptionHandling = true;
        }
    }

    public boolean getUseOneOfDiscriminatorLookup() {
        return this.useOneOfDiscriminatorLookup;
    }

    public void setOperationIdNaming(final String operationIdNaming) {
        if (!("PascalCase".equals(operationIdNaming) || "camelCase".equals(operationIdNaming) ||
                "snake_case".equals(operationIdNaming))) {
            throw new IllegalArgumentException("Invalid operationIdNaming: " + operationIdNaming +
                    ". Must be PascalCase, camelCase or snake_case");
        }

        if ("snake_case".equals(operationIdNaming)) {
            additionalProperties.put("WithHttpInfo", "_with_http_info");
        } else {
            additionalProperties.put("WithHttpInfo", "WithHttpInfo");
        }

        this.operationIdNaming = operationIdNaming;
    }

    @Override
    public String escapeQuotationMark(String input) {
        // remove " to avoid code injection
        return input.replace("\"", "");
    }

View on GitHub (pinned to fcec517be3)

Solutions

1. Use one of the exact tokens: operationIdNaming=PascalCase, operationIdNaming=camelCase, or operationIdNaming=snake_case
2. Check for stray whitespace/quotes in the config file around the value
3. If unset, omit the option to keep the default naming

Example fix

# before
openapi-generator-cli generate -i api.yaml -g r -c operationIdNaming=snake-case
# after
openapi-generator-cli generate -i api.yaml -g r -c operationIdNaming=snake_case

# bash: exact-token whitelist
OP_NAMING="${OP_NAMING:-}"
[[ -z "${OP_NAMING}" || "${OP_NAMING}" == PascalCase || "${OP_NAMING}" == camelCase || "${OP_NAMING}" == snake_case ]] \
  || { echo 'operationIdNaming must be PascalCase, camelCase or snake_case (exact)'; exit 1; }

try {
    RClientCodegen codegen = new RClientCodegen();
    codegen.setOperationIdNaming("snake_case"); // one of the three exact tokens
    new DefaultGenerator().opts(input).generate();
} catch (IllegalArgumentException e) {
    // 'Invalid operationIdNaming' - use the exact token and rerun
}

When it happens

Trigger: openapi-generator-cli generate -i api.yaml -g r -c operationIdNaming=Pascalcase / snake-case / snake / kebab-case. The comparison is String.equals, so any casing or spelling deviation fails.

Common situations: Users typing the style descriptively ('SnakeCase', 'SCREAMING_SNAKE') instead of the exact token; configs migrated from other generators whose naming options accept different vocabularies (e.g. --operation-id-name vs operationIdNaming).

Related errors

• Invalid HTTP library " + getLibrary() + ". Only httr, httr2
• Invalid model property naming '{name}'. Must be 'original',
• Invalid model property naming '{naming}'. Must be 'original'
• Invalid model property naming '{name}'. Must be 'original',
• Invalid model property naming '{naming}'. Must be 'original'

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/cd3c1b1cfd27612d. Report an issue: GitHub.