Error Handling

mdbook-mermaid-mmdr is designed to never fail the build, even when a diagram is invalid.

Inline Error Messages

When a mermaid code block fails to render, the preprocessor replaces it with an HTML error block:

<pre class="mermaid-error">Error: &lt;error details&gt;</pre>

A warning is also logged to stderr. The rest of the book continues to build normally.

Styling Errors

You can style error blocks in a custom mdbook theme:

.mermaid-error {
    color: #cc0000;
    background: #fff0f0;
    border: 1px solid #cc0000;
    padding: 1em;
    border-radius: 4px;
}

Debugging

Set the RUST_LOG environment variable to see detailed output:

RUST_LOG=debug mdbook build

The preprocessor logs theme resolution, rendering attempts, and any SVG post-processing at the debug and warn levels.