quarkusio/quarkus · error · IllegalArgumentException

Converting to ${toFormat} is not supported

Error message

Converting to ${toFormat} is not supported

What it means

JavadocTransformer.transform dispatches Javadoc conversion by target format: ASCIIDOC and MARKDOWN are supported; anything else (null or an unknown JavadocFormat) hits the default branch and throws IllegalArgumentException.

Source

Thrown at core/processor/src/main/java/io/quarkus/annotation/processor/documentation/config/formatter/JavadocTransformer.java:17

package io.quarkus.annotation.processor.documentation.config.formatter;

import io.quarkus.annotation.processor.documentation.config.model.JavadocFormat;

public final class JavadocTransformer {

    private JavadocTransformer() {
    }

    public static String transform(String javadoc, JavadocFormat fromFormat, JavadocFormat toFormat) {
        switch (toFormat) {
            case ASCIIDOC:
                return JavadocToAsciidocTransformer.toAsciidoc(javadoc, fromFormat);
            case MARKDOWN:
                return JavadocToMarkdownTransformer.toMarkdown(javadoc, fromFormat);
            default:
                throw new IllegalArgumentException("Converting to " + toFormat + " is not supported");
        }
    }
}

View on GitHub (pinned to e1c734241f)

Solutions

1. Pass JavadocFormat.ASCIIDOC or JavadocFormat.MARKDOWN as the target format
2. Check for null/default format before calling transform
3. Update JavadocTransformer's switch to handle any newly added format enum constant
4. Audit the caller to see where the bad format value originates

Example fix

// before
JavadocFormat toFormat = null; // unset
String out = JavadocTransformer.transform(javadoc, from, toFormat);
// after
JavadocFormat toFormat = JavadocFormat.ASCIIDOC;
String out = JavadocTransformer.transform(javadoc, from, toFormat);

Objects.requireNonNull(toFormat, "toFormat must be set");
if (toFormat != JavadocFormat.ASCIIDOC && toFormat != JavadocFormat.MARKDOWN) {
    throw new IllegalArgumentException("Unsupported target format: " + toFormat);
}

try {
    return JavadocTransformer.transform(javadoc, from, toFormat);
} catch (IllegalArgumentException e) {
    if (e.getMessage() != null && e.getMessage().startsWith("Converting to")) {
        return JavadocTransformer.transform(javadoc, from, JavadocFormat.ASCIIDOC);
    }
    throw e;
}

When it happens

Trigger: Calling JavadocTransformer.transform(javadoc, fromFormat, toFormat) with toFormat that is neither ASCIIDOC nor MARKDOWN — typically a null format from an unset configuration or a newly added enum constant not yet handled in the switch.

Common situations: Custom doc tooling passing an uninitialized format variable; adding a new JavadocFormat constant to the enum without updating the transformer switch; configuration mistake in a documentation generation pipeline.

Related errors

• Conversion from Markdown to Asciidoc is not supported
• Unable to find javadoc for config item ${enclosingElement} $
• Unable to read the resolved model from: ${resolvedModelPath}
• Could not parse HTML entity &${abbrev}; in ${text}
• Unable to parse: ${javadocPath}

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/5e440144c2057ddf. Report an issue: GitHub.