Add and apply scalafmt

.github/workflows/format.yml

@@ -0,0 +1,23 @@
+name: Scalafmt
+
+permissions: {}
+
+on:
+  pull_request:
+    branches: ['**']
+
+jobs:
+  build:
+    name: Code is formatted
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout current branch (full)
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          persist-credentials: false
+
+      - name: Check project is formatted
+        uses: jrouly/scalafmt-native-action@v3
+        with:
+          arguments: '--list --mode diff-ref=origin/main'

.scalafmt.conf

@@ -0,0 +1,26 @@
+version = 3.7.17
+runner.dialect = scala212
+maxColumn = 120
+project.git = true
+
+# http://docs.scala-lang.org/style/scaladoc.html recommends the JavaDoc style.
+# scala/scala is written that way too https://github.com/scala/scala/blob/v2.12.2/src/library/scala/Predef.scala
+docstrings.style = Asterisk
+
+# This also seems more idiomatic to include whitespace in import x.{ yyy }
+spaces.inImportCurlyBraces = true
+
+align.tokens."+" = [
+  {
+    code   = "%"
+    owners = [
+      { regex = "Term.ApplyInfix" }
+    ]
+  },
+  {
+    code   = "%%"
+    owners = [
+      { regex = "Term.ApplyInfix" }
+    ]
+  }
+]

build.sbt

@@ -36,7 +36,8 @@ scalacOptions ++= List(
   "-unchecked",
   "-deprecation",
   "-language:_",
-  "-encoding", "UTF-8"
+  "-encoding",
+  "UTF-8"
 )
 
 // publish settings

project/plugins.sbt

@@ -1,2 +1,3 @@
 addSbtPlugin("com.github.sbt" % "sbt-github-actions" % "0.22.0")
-addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.5.12")
+addSbtPlugin("com.github.sbt" % "sbt-ci-release"     % "1.5.12")
+addSbtPlugin("org.scalameta"  % "sbt-scalafmt"       % "2.5.2")