ci: properly cache plts (2nd attempt)

.github/workflows/ci.yml

@@ -28,6 +28,12 @@ jobs:
             _build
             deps
           key: ${{ runner.os }}-${{ matrix.elixir }}-${{ matrix.erlang }}-${{ hashFiles('mix.lock') }}
+      - uses: actions/cache@v4
+        with:
+          # Don't cache PLTs based on mix.lock hash, as Dialyzer can incrementally update old ones
+          key: ${{ runner.os }}-${{ matrix.elixir }}-${{ matrix.erlang }}-plt
+          path: plts
+        if: ${{ matrix.lint }}
       - uses: erlef/setup-beam@v1
         with:
           otp-version: ${{ matrix.erlang }}

.gitignore

@@ -24,3 +24,5 @@ tower-*.tar
 
 # Temporary files, for example, from tests.
 /tmp/
+
+/plts

mix.exs

@@ -15,6 +15,9 @@ defmodule Tower.MixProject do
       elixirc_paths: elixirc_paths(Mix.env()),
       deps: deps(),
       package: package(),
+      dialyzer: [
+        plt_local_path: "plts"
+      ],
 
       # Docs
       name: "Tower",