---
title: "MGS1018: dead output glob"
description: A project declares an output glob that matches nothing while its other outputs match files. A target that inherits the glob fails its snapshot on a cold cache, long after the mistake was made.
tags: [MGS1018, magusfile, outputs, cache, snapshot, doctor, spells]
---

# MGS1018: dead output glob

A project declares an output glob that matches **no** files, while other globs the
same project declares **do** match. The glob is almost always inherited from a bound
spell that this project never satisfies.

## Why this matters, and why it hides

Declared outputs are per project, and a bound spell contributes its `provides` globs to
every target on that project. A target that declares nothing of its own
(`ctx.writesFiles`) inherits the whole set. So a check-only target - a test, a lint -
inherits an output glob it was never going to write.

That is harmless until the target has to **snapshot**, which only happens on a cache
**miss**. As long as the target keeps replaying, the code path never runs. The first
thing to see the failure is a cold cache: a fresh clone, a new CI runner, or
`magus clean --cache`. By then the declaration that caused it may be months old, and the
error arrives somewhere that looks unrelated to it.

This diagnostic moves that discovery forward, to the moment the glob stops matching.

## Example

A project binds the `typescript` spell, which provides `dist/**`, but emits its bundles
to `gen/`:

```buzz
magus\project({
    "spells": [typescript],   // contributes dist/** to every target
    "outputs": ["gen/**"],    // what this project actually writes
});

// No ctx.writesFiles, so this inherits dist/** - a glob it never produces.
export fun test(ctx: magus\Context, args: [str]) > void {
    magus\cmd("buzz", args: ["-t", "render.buzz"]);
}
```

## Resolve it

Pick whichever is true of your project:

- **The target does produce files.** Declare them, so its snapshot records the real
  artifact instead of an inherited glob:

  ```buzz
  ctx.writesFiles("gen/assets/mermaid.js");
  ```

- **The target produces nothing** (a test, a check). Nothing to declare - the inherited
  glob simply should not have applied. magus only treats an empty result as an error when
  the target declared the outputs itself, so this case is already safe; the diagnostic is
  pointing at the project-level glob, not at your target.

- **The project never writes that glob at all.** The spell binding is contributing an
  output shape this project does not use. Either the binding is wrong, or the spell's
  `mgs_listProvidedGlobs` does not describe how this project builds.

## Why the check stays quiet on an unbuilt tree

If **nothing** a project declares has been produced yet, the project simply has not been
built, and every glob matching zero is expected. Reporting then would fire on every fresh
clone and teach people to ignore the check. It only speaks when some outputs exist and one
glob still matches nothing - which is the case that indicates a real mistake rather than
an empty tree.

## See also

- [Cache model](../../../concepts/cache.md) - what `provides` means and how a snapshot works
- [Spells](../../../concepts/spells.md) - what a bound spell contributes to a project
- [MGS1005](MGS1005.md) - a per-target output glob that duplicates a project-wide one