# `ExQuality.Plt`
[🔗](https://github.com/riddler/ex_quality/blob/v0.15.0/lib/ex_quality/plt.ex#L1)

Recognises PLT work in dialyxir's output.

The PLT is dialyxir's cache of everything it has already analysed. Building
one takes minutes; analysing against a warm one takes seconds. The Dialyzer
stage prints a single line when it finishes, so on a cold checkout or a fresh
CI container that line arrives several minutes after the run appears to have
stalled, with nothing to say the wait is a one-time cost.

This module names the lines dialyxir prints while it builds, so the stage can
say what is happening while it is happening (`build_watcher/1`) and report
afterwards that the run paid for a build (`built?/1`).

A PLT build is not a reason to distrust the analysis that follows it, so a
run that built one still passes or fails on its warnings alone. It is only
reported, because it explains a duration a reader would otherwise read as a
hang, and because it is the thing `mix quality.plt` exists to move out of the
run.

# `build_line?`

```elixir
@spec build_line?(String.t()) :: boolean()
```

Whether a single line of dialyxir output says a PLT is being built.

    iex> ExQuality.Plt.build_line?("Adding 1042 modules to dialyxir_erlang-25.3.plt")
    true

    iex> ExQuality.Plt.build_line?("Checking 365 modules in dialyxir_erlang-25.3.plt")
    false

# `build_watcher`

```elixir
@spec build_watcher((-> any())) :: (String.t() -> :ok)
```

Returns a line handler that calls `fun` once, on the first build line it sees.

Suitable as `ExQuality.OutputCollector`'s `:on_line` handler, which is what
makes the announcement arrive while the build is running rather than after it.
Later build lines are ignored: a build prints several, and a stage that
announced each of them would report progress as noise.

# `built?`

```elixir
@spec built?(String.t()) :: boolean()
```

Whether a run's output shows that a PLT was built.

    iex> ExQuality.Plt.built?("Checking PLT...\nPLT is up to date!")
    false

# `message`

```elixir
@spec message() :: String.t()
```

The progress message for a build in flight.

    iex> ExQuality.Plt.message()
    "building PLT (this is a one-time cost)"

---

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