OpenAPITools/openapi-generator · error · IllegalArgumentException

Invalid file naming '{}'. Must be 'camelCase' or 'kebab-case

Error message

Invalid file naming '{}'. Must be 'camelCase' or 'kebab-case'

What it means

The typescript-nestjs client generator supports exactly two file naming strategies, 'camelCase' and 'kebab-case', enforced by setFileNaming (TypeScriptNestjsClientCodegen.java:533). The 'fileNaming' additional property selects how model file names are derived in convertUsingFileNamingConvention; any other value throws this IllegalArgumentException during processOpts.

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/TypeScriptNestjsClientCodegen.java:537

     */
    private void validateClassSuffixArgument(String argument, String value) {
        if (!value.matches(CLASS_NAME_SUFFIX_PATTERN)) {
            throw new IllegalArgumentException(
                    String.format(Locale.ROOT, "%s class suffix only allows alphanumeric characters.", argument)
            );
        }
    }

    /**
     * Set the file naming type.
     *
     * @param fileNaming the file naming to use
     */
    private void setFileNaming(String fileNaming) {
        if ("camelCase".equals(fileNaming) || "kebab-case".equals(fileNaming)) {
            this.fileNaming = fileNaming;
        } else {
            throw new IllegalArgumentException("Invalid file naming '" +
                    fileNaming + "'. Must be 'camelCase' or 'kebab-case'");
        }
    }

    /**
     * Converts the original name according to the current <code>fileNaming</code> strategy.
     *
     * @param originalName the original name to transform
     * @return the transformed name
     */
    private String convertUsingFileNamingConvention(String originalName) {
        String name = this.removeModelPrefixSuffix(originalName);
        if ("kebab-case".equals(fileNaming)) {
            name = dashize(underscore(name));
        } else {
            name = camelize(name, LOWERCASE_FIRST_LETTER);
        }
        return name;

View on GitHub (pinned to fcec517be3)

Solutions

  1. Set fileNaming to exactly 'camelCase' or 'kebab-case' (case-sensitive, kebab needs the dash).
  2. If you omitted the option but still see the error, search your spec's vendor extensions or config file for a 'fileNaming' key with a stray value.

Example fix

# before
openapi-generator-cli generate -g typescript-nestjs -DfileNaming=snake_case

# after
openapi-generator-cli generate -g typescript-nestjs -DfileNaming=kebab-case
Defensive patterns

Strategy: validation

Validate before calling

case "$FILE_NAMING" in
  camelCase|kebab-case|"") ;;
  *) echo "ERROR: fileNaming must be 'camelCase' or 'kebab-case'" >&2; exit 1;;
esac

Type guard

const FILE_NAMING_VALUES = ['camelCase', 'kebab-case'] as const;
type FileNaming = typeof FILE_NAMING_VALUES[number];
const isFileNaming = (v: string): v is FileNaming =>
  (FILE_NAMING_VALUES as readonly string[]).includes(v);

Prevention

When it happens

Trigger: Running with -DfileNaming=snake_case, -DfileNaming=PascalCase, or a typo like -DfileNaming=kebabcase. The check is an exact string comparison, so casing matters.

Common situations: Porting specs/build scripts from other generators (e.g. typescript-fetch, java) whose file naming options accept different vocabularies like 'snake_case' or 'PascalCase'; assuming kebabcase without the dash works.

Related errors

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/d026998c4ce34039. Report an issue: GitHub.