# Errors

> The error codes textlane raises and what each one means.

Textlane raises `textlane.TextlaneError`, whose `code` names what went wrong, so a caller can
tell the cases apart without reading the message:

```python
import textlane

code = ""
try:
    textlane.textlane().use("md.nope")
except textlane.TextlaneError as error:
    code = error.code
code
# unknown-plugin
```

| Code                    | When                                                                   |
| ----------------------- | ---------------------------------------------------------------------- |
| `unknown-plugin`        | `use` names a plugin textlane does not have                            |
| `invalid-plugin`        | `use` gets something that is neither a plugin, a list nor a preset     |
| `invalid-options`       | a plugin's options do not match its types, when the pipeline is built  |
| `frozen-processor`      | `use` or a `data` setter is called on a frozen processor               |
| `missing-parser`        | `parse` or `process` runs with no parser in the pipeline               |
| `missing-compiler`      | `stringify` or `process` runs with no compiler in the pipeline         |
| `invalid-stage`         | a stage gets a tree it does not take, such as hast before `md.to_html` |
| `async-in-sync`         | `process` or `run` meets a stage with asynchronous work                |
| `invalid-tree`          | a tree given to `run` or `stringify` is not valid unist                |
| `unsupported-node`      | a tree given to `run` or `stringify` holds a node with no `type`       |
| `unknown-node`          | a compiler meets a node type it cannot write                           |
| `tree-too-deep`         | a tree nests too deep to pass between Rust and Python                  |
| `mdx-failed`            | `mdx.compile` meets JavaScript it cannot compile                       |
| `unsafe-number`         | `nl.indefinite_article` meets a number too large to read               |
| `highlight-failed`      | `html.highlight` cannot color a code block                             |
| `highlight-unavailable` | `html.highlight`'s grammars and themes failed to load                  |

Syntax errors in MDX carry the upstream's source and rule as their code, as
`micromark-extension-mdx-expression:acorn` for an expression that does not parse.

Options are checked when the pipeline is built, the first time it runs or freezes, not when
`use` is called.