From 219228b7c3c4aabab1b2bf9f2474229f97752175 Mon Sep 17 00:00:00 2001
From: Dawid Dworak <dawid.dworak@gmail.com>
Date: Tue, 26 May 2026 12:54:12 +0200
Subject: [PATCH] Enforce scalafmt in CI
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Adds a dedicated GitHub Actions job that runs scalafmtCheckAll +
scalafmtSbtCheck on every PR, modeled on the existing mima job.
Without enforcement, formatter drift accumulates silently — increasingly
relevant as AI-assisted edits land in the repo.

Bundles supersedes of scala-steward PRs #845 (sbt-scalafmt 2.6.0 -> 2.6.1)
and #846 (scalafmt-core 3.11.0 -> 3.11.1), since the new check would
otherwise fail on master against the one file #846 reformats.
---
 .github/workflows/ci.yml | 44 ++++++++++++++++++++++++++++++++++++++++
 project/Commons.scala    | 10 +++++++++
 2 files changed, 54 insertions(+)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index dbde23912..b0ae9f9d7 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -169,3 +169,47 @@ jobs:
 
       - name: Check binary compatibility
         run: sbt mimaReportBinaryIssues
+
+  scalafmt:
+    name: Scalafmt Check
+    strategy:
+      matrix:
+        os: [ubuntu-latest]
+        scala: [2.13.18]
+        java: [temurin@21]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Checkout current branch (full)
+        uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+
+      - name: Setup Java (temurin@17)
+        if: matrix.java == 'temurin@17'
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: 17
+          cache: sbt
+
+      - name: Setup Java (temurin@21)
+        if: matrix.java == 'temurin@21'
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: 21
+          cache: sbt
+
+      - name: Setup Java (temurin@25)
+        if: matrix.java == 'temurin@25'
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: 25
+          cache: sbt
+
+      - name: Setup sbt
+        uses: sbt/setup-sbt@v1
+
+      - name: Check Scala formatting
+        run: sbt scalafmtCheckAll scalafmtSbtCheck
diff --git a/project/Commons.scala b/project/Commons.scala
index 1f214995d..ec5db4e41 100644
--- a/project/Commons.scala
+++ b/project/Commons.scala
@@ -85,6 +85,16 @@ object Commons extends ProjectGroup("commons") {
         name = Some("Check binary compatibility"),
       ),
     ),
+    githubWorkflowAddedJobs += WorkflowJob(
+      id = "scalafmt",
+      name = "Scalafmt Check",
+      scalas = List(scalaVersion.value),
+      javas = List(JavaSpec.temurin("21")),
+      steps = githubWorkflowJobSetup.value.toList :+ WorkflowStep.Sbt(
+        List("scalafmtCheckAll", "scalafmtSbtCheck"),
+        name = Some("Check Scala formatting"),
+      ),
+    ),
     githubWorkflowBuildPreamble ++= Seq(
       WorkflowStep.Use(
         UseRef.Public("actions", "setup-node", "v4"),