feat(build): add a homebrew ktfmt plugin

The general idea of the implementation is borrowed from https://github.com/cortinico/ktfmt-gradle

build-logic/kotlin-plugins/build.gradle.kts

@@ -20,7 +20,7 @@ afterEvaluate {
   tasks.withType<KotlinCompile>().configureEach {
     kotlinOptions {
       jvmTarget = JavaVersion.VERSION_11.toString()
-      freeCompilerArgs = freeCompilerArgs + "-Xsam-conversions=class"
+      freeCompilerArgs = freeCompilerArgs + "-Xsam-conversions=class" + "-opt-in=kotlin.RequiresOptIn"
     }
   }
 }
@@ -43,6 +43,10 @@ gradlePlugin {
       id = "com.github.android-password-store.kotlin-library"
       implementationClass = "app.passwordstore.gradle.KotlinLibraryPlugin"
     }
+    register("ktfmt") {
+      id = "com.github.android-password-store.ktfmt"
+      implementationClass = "app.passwordstore.gradle.KtfmtPlugin"
+    }
     register("spotless") {
       id = "com.github.android-password-store.spotless"
       implementationClass = "app.passwordstore.gradle.SpotlessPlugin"
@@ -57,9 +61,12 @@ gradlePlugin {
 dependencies {
   implementation(libs.build.agp)
   implementation(libs.build.detekt)
+  implementation(libs.build.diffutils)
   implementation(libs.build.kotlin)
+  implementation(libs.build.ktfmt)
   implementation(libs.build.r8)
   implementation(libs.build.spotless)
   implementation(libs.build.vcu)
   implementation(libs.build.versions)
+  implementation(libs.kotlin.coroutines.core)
 }

build-logic/kotlin-plugins/src/main/kotlin/app/passwordstore/gradle/KtfmtPlugin.kt

@@ -0,0 +1,32 @@
+package app.passwordstore.gradle
+
+import app.passwordstore.gradle.ktfmt.KtfmtCheckTask
+import app.passwordstore.gradle.ktfmt.KtfmtFormatTask
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.register
+
+class KtfmtPlugin : Plugin<Project> {
+
+  override fun apply(target: Project) {
+    target.tasks.register<KtfmtFormatTask>("ktfmtFormat") {
+      source =
+        project.layout.projectDirectory.asFileTree
+          .filter { file ->
+            file.extension == "kt" ||
+              file.extension == "kts" && !file.canonicalPath.contains("build")
+          }
+          .asFileTree
+    }
+    target.tasks.register<KtfmtCheckTask>("ktfmtCheck") {
+      source =
+        project.layout.projectDirectory.asFileTree
+          .filter { file ->
+            file.extension == "kt" ||
+              file.extension == "kts" && !file.canonicalPath.contains("build")
+          }
+          .asFileTree
+      projectDirectory.set(target.layout.projectDirectory)
+    }
+  }
+}

build-logic/kotlin-plugins/src/main/kotlin/app/passwordstore/gradle/ktfmt/KtfmtCheckTask.kt

@@ -0,0 +1,68 @@
+package app.passwordstore.gradle.ktfmt
+
+import com.facebook.ktfmt.format.Formatter
+import com.facebook.ktfmt.format.FormattingOptions
+import java.io.File
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.async
+import kotlinx.coroutines.awaitAll
+import kotlinx.coroutines.coroutineScope
+import kotlinx.coroutines.runBlocking
+import org.gradle.api.file.DirectoryProperty
+import org.gradle.api.file.FileCollection
+import org.gradle.api.tasks.IgnoreEmptyDirectories
+import org.gradle.api.tasks.InputFiles
+import org.gradle.api.tasks.Internal
+import org.gradle.api.tasks.PathSensitive
+import org.gradle.api.tasks.PathSensitivity
+import org.gradle.api.tasks.SourceTask
+import org.gradle.api.tasks.TaskAction
+
+@OptIn(ExperimentalCoroutinesApi::class)
+abstract class KtfmtCheckTask : SourceTask() {
+
+  @get:PathSensitive(PathSensitivity.RELATIVE)
+  @get:InputFiles
+  @get:IgnoreEmptyDirectories
+  protected val inputFiles: FileCollection
+    get() = super.getSource()
+
+  @get:Internal abstract val projectDirectory: DirectoryProperty
+
+  @TaskAction
+  fun execute() {
+    runBlocking(Dispatchers.IO.limitedParallelism(PARALLEL_TASK_LIMIT)) {
+      coroutineScope {
+        val results = inputFiles.map { async { checkFile(it) } }.awaitAll()
+        if (results.any { (notFormatted, _) -> notFormatted }) {
+          results
+            .map { (_, diffs) -> diffs }
+            .forEach { diffs -> KtfmtDiffer.printDiff(diffs, logger) }
+          error("[ktfmt] Found unformatted files")
+        }
+      }
+    }
+  }
+
+  private fun checkFile(input: File): Pair<Boolean, List<KtfmtDiffEntry>> {
+    val originCode = input.readText()
+    val formattedCode =
+      Formatter.format(
+        FormattingOptions(
+          style = FormattingOptions.Style.GOOGLE,
+          maxWidth = 100,
+          continuationIndent = 2,
+        ),
+        originCode
+      )
+    val pathNormalizer = { file: File -> file.toRelativeString(projectDirectory.asFile.get()) }
+    return (originCode != formattedCode) to
+      KtfmtDiffer.computeDiff(input, formattedCode, pathNormalizer)
+  }
+
+  companion object {
+
+    private const val PARALLEL_TASK_LIMIT = 4
+  }
+}

build-logic/kotlin-plugins/src/main/kotlin/app/passwordstore/gradle/ktfmt/KtfmtDiffEntry.kt

@@ -0,0 +1,3 @@
+package app.passwordstore.gradle.ktfmt
+
+data class KtfmtDiffEntry(val input: String, val lineNumber: Int, val message: String)

build-logic/kotlin-plugins/src/main/kotlin/app/passwordstore/gradle/ktfmt/KtfmtDiffer.kt

@@ -0,0 +1,35 @@
+package app.passwordstore.gradle.ktfmt
+
+import com.github.difflib.DiffUtils
+import com.github.difflib.patch.ChangeDelta
+import com.github.difflib.patch.DeleteDelta
+import com.github.difflib.patch.InsertDelta
+import java.io.File
+import org.gradle.api.logging.Logger
+
+object KtfmtDiffer {
+  fun computeDiff(
+    inputFile: File,
+    formattedCode: String,
+    pathNormalizer: (File) -> String
+  ): List<KtfmtDiffEntry> {
+    val originCode = inputFile.readText()
+    return DiffUtils.diff(originCode, formattedCode, null).deltas.map {
+      val line = it.source.position + 1
+      val message: String =
+        when (it) {
+          is ChangeDelta -> "Line changed: ${it.source.lines.first()}"
+          is DeleteDelta -> "Line deleted"
+          is InsertDelta -> "Line added"
+          else -> ""
+        }
+      KtfmtDiffEntry(pathNormalizer(inputFile), line, message)
+    }
+  }
+
+  fun printDiff(entries: List<KtfmtDiffEntry>, logger: Logger) {
+    entries.forEach { entry ->
+      logger.error("${entry.input}:${entry.lineNumber} - ${entry.message}")
+    }
+  }
+}

build-logic/kotlin-plugins/src/main/kotlin/app/passwordstore/gradle/ktfmt/KtfmtFormatTask.kt

@@ -0,0 +1,56 @@
+package app.passwordstore.gradle.ktfmt
+
+import com.facebook.ktfmt.format.Formatter
+import com.facebook.ktfmt.format.FormattingOptions
+import java.io.File
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.async
+import kotlinx.coroutines.awaitAll
+import kotlinx.coroutines.coroutineScope
+import kotlinx.coroutines.runBlocking
+import org.gradle.api.file.FileCollection
+import org.gradle.api.tasks.IgnoreEmptyDirectories
+import org.gradle.api.tasks.InputFiles
+import org.gradle.api.tasks.PathSensitive
+import org.gradle.api.tasks.PathSensitivity
+import org.gradle.api.tasks.SourceTask
+import org.gradle.api.tasks.TaskAction
+
+@OptIn(ExperimentalCoroutinesApi::class)
+abstract class KtfmtFormatTask : SourceTask() {
+
+  @get:PathSensitive(PathSensitivity.RELATIVE)
+  @get:InputFiles
+  @get:IgnoreEmptyDirectories
+  protected val inputFiles: FileCollection
+    get() = super.getSource()
+
+  @TaskAction
+  fun execute() {
+    runBlocking(Dispatchers.IO.limitedParallelism(PARALLEL_TASK_LIMIT)) {
+      coroutineScope { inputFiles.map { async { formatFile(it) } }.awaitAll() }
+    }
+  }
+
+  private fun formatFile(input: File) {
+    val originCode = input.readText()
+    val formattedCode =
+      Formatter.format(
+        FormattingOptions(
+          style = FormattingOptions.Style.GOOGLE,
+          maxWidth = 100,
+          continuationIndent = 2,
+        ),
+        originCode
+      )
+    if (originCode != formattedCode) {
+      input.writeText(formattedCode)
+    }
+  }
+
+  companion object {
+
+    private const val PARALLEL_TASK_LIMIT = 4
+  }
+}

build.gradle.kts

@@ -5,8 +5,9 @@
 @file:Suppress("DSL_SCOPE_VIOLATION", "UnstableApiUsage")
 
 plugins {
-  id("com.github.android-password-store.kotlin-common")
   id("com.github.android-password-store.git-hooks")
+  id("com.github.android-password-store.kotlin-common")
+  id("com.github.android-password-store.ktfmt")
   id("com.github.android-password-store.spotless")
   id("com.github.android-password-store.versions")
   alias(libs.plugins.hilt) apply false

gradle/libs.versions.toml

@@ -39,8 +39,10 @@ aps-sublimeFuzzy = "com.github.android-password-store:sublime-fuzzy:2.2.1"
 aps-zxingAndroidEmbedded = "com.github.android-password-store:zxing-android-embedded:4.2.1"
 build-agp = { module = "com.android.tools.build:gradle", version.ref = "agp" }
 build-detekt = "io.gitlab.arturbosch.detekt:detekt-gradle-plugin:1.21.0"
+build-diffutils = "io.github.java-diff-utils:java-diff-utils:4.12"
 build-download = "de.undercouch:gradle-download-task:5.3.0"
 build-kotlin = { module = "org.jetbrains.kotlin:kotlin-gradle-plugin", version.ref = "kotlin" }
+build-ktfmt = "com.facebook:ktfmt:0.41"
 build-mavenpublish = "com.vanniktech:gradle-maven-publish-plugin:0.22.0"
 build-metalava = "me.tylerbwong.gradle.metalava:plugin:0.3.2"
 build-okhttp = "com.squareup.okhttp3:okhttp:4.10.0"