# facett UI error codes — for idiots
## What is this?
Every broken thing in a facett screen now has a **name tag**, like `facet-map-2`.
Before, a test only knew something was wrong by reading the words on screen. If you
changed the words, the test went blind. Now each error has a permanent **code** that
never changes, so tests and other apps can point at the EXACT problem.
## The name tag looks like
```
facet-<component>-<n>
│ │
│ └── a number, counted per component (1, 2, 3, …), NEVER reused
└── which facett part (map, graph3d, geomap, korp, …)
```
Examples: `facet-map-1`, `facet-graph3d-2`, `facet-korp-1`.
## Two things always show up together
1. The **message** — the human sentence, like "map has no vessels to plot". Same as
before. Always there.
2. The **code** — the name tag `facet-map-2`. In a normal dev (debug) build it shows
on screen in **bright PINK** next to the message. In a shipped (release) build the
pink is faint, but the code is still in the data + logs + the About popup.
## How do I make one?
```rust
let e = facet_err!(map, 2, "no positions to plot");
e.render(ui); // draws the message + the pink code
```
That's it. `map` = the part, `2` = the number, then your sentence.
## Rules (do not break)
* Pick the **next unused number** for that component. Look in the LIST
(`facett-error-codes-registry.md`).
* **Never** change or reuse an old number. Codes are forever.
* Add your new code to the LIST when you make one.
## Where do I see them all?
Run `facett-demo`, open the **Errors** tab. You'll see:
* pink codes on example errors,
* the build's git hash,
* a link to the source code on codeberg for each part,
* a big TABLE (the "matrix slide") of every code.
There's also a **Manual** tab (the real facett manual) and an **About** popup (press
the `legend` button) that shows the git hash and the codeberg links.
## Why "korp/cases:facet-map-2"?
An app like korp can show the SAME facett part (say the map) in two places. So korp
sticks its own label in front: `korp/cases:facet-map-2` vs `korp/analysis:facet-map-2`.
Same map error, two spots — now a test can tell them apart. (That wiring is Phase 2;
facett just gives korp the tool.)