# `MishkaCmsCore.Runtime.Resources.Validations.TemplateCompiles`
[🔗](https://github.com/mishka-group/mishka_cms_core/blob/v0.0.1/lib/mishka_cms_core/runtime/resources/__validations/template_compiles.ex#L5)

Refuses a layout, component or error page whose markup HEEx will not take, at the action boundary.

`MishkaCmsCore.Runtime.Resources.Validations.PageCodeCompiles` has done this for a `Page` since it
existed, and it is the reason a page cannot even be seeded broken. The other three had nothing:
the row was stored, `MishkaCmsCore.Runtime.RuntimeStatus` reported `Ready`, the compile then failed
into `MishkaCmsCore.Runtime.States.CompileFailureState`, and the site went on serving the module it
already had. The author is told nothing at any point in that.

## Why this is the syntax half and not the whole compile

`PageCodeCompiles` builds the whole LiveView, which is about a second of work and the right price
for a page — its handlers and helpers are author-written Elixir that only a real compile can judge.
A layout, a component and an error page are markup plus, at most, helpers; the failure that
actually happens is markup the tokenizer accepts and the engine does not:

    {@a + }              parses as an expression, is not Elixir      → caught by `to_heex/1`
    <div :foo={@a}>      a special attribute that does not exist     → caught HERE, and nowhere else
    <div :for={@a}>      `:for` without a generator                  → the same
    <:header>x</:header> a slot entry outside a component            → the same

`CodeCheck.template/1` is `Phoenix.LiveView.TagEngine.compile/2` — the call every one of this
runtime's compilers makes — with no module built around it, so it costs milliseconds. What it
cannot see is anything semantic, which is what the compile pipeline is for.

## An error page is a list

It keeps `error_pages`, one entry per status, so "the template" is several of them; each is checked
and the first fault names the status it came from, because "line 4" means nothing when the reader
has five documents open in one record.

## What is deliberately NOT checked

`root_layout_template` is not HEEx and must not be judged as if it were.
`MishkaCmsCore.Runtime.Compilers.ErrorCompiler` compiles it with `EEx.compile_string/2` and
`Phoenix.HTML.Engine` — the classic engine — precisely *because* it relies on EEx interpolation
inside an attribute (`content="<%= Phoenix.Controller.get_csrf_token() %>"`), which HEEx rejects
and which the shipped seeds use. Every per-status template beside it goes through the TagEngine and
is checked here; the root layout is a different language in the same record.

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*Consult [api-reference.md](api-reference.md) for complete listing*