Add support for ktlint-plugins.properties version synchronization

README.md

@@ -279,6 +279,44 @@ ktlint {
 ```
 </details>
 
+#### KtLint IntelliJ Plugin Integration
+
+If you're using the [ktlint IntelliJ plugin](https://github.com/nbadal/ktlint-intellij-plugin), you can automatically synchronize the ktlint version between your IDE and Gradle builds by creating a `ktlint-plugins.properties` file in your project root directory.
+
+The IntelliJ plugin can read and write the ktlint version to this file. When this file exists and contains a `ktlint-version` property, the Gradle plugin will automatically use that version as the default.
+
+Example `ktlint-plugins.properties` file:
+```properties
+ktlint-version=1.2.1
+```
+
+**Key benefits:**
+- Ensures consistency between IDE and build tool ktlint versions
+- Simplifies version management across your development team
+- Allows IntelliJ plugin to manage the version
+
+**Override behavior:**
+Even when the `ktlint-plugins.properties` file exists, you can still explicitly set the version in your `build.gradle` or `build.gradle.kts` file, which will take precedence:
+
+<details>
+<summary>Groovy</summary>
+
+```groovy
+ktlint {
+    version = "1.3.0" // This overrides the version in ktlint-plugins.properties
+}
+```
+</details>
+<details open>
+<summary>Kotlin</summary>
+
+```kotlin
+ktlint {
+    version.set("1.3.0") // This overrides the version in ktlint-plugins.properties
+}
+```
+</details>
+
 ### Configuration
 The following configuration block is _optional_.
 

plugin/src/main/kotlin/org/jlleitschuh/gradle/ktlint/KtlintExtension.kt

@@ -31,8 +31,19 @@ open class KtlintExtension @Inject internal constructor(
 
     /**
      * The version of KtLint to use.
+     *
+     * If a `ktlint-plugins.properties` file exists in the project root with a `ktlint-version` property,
+     * that version will be used as the default. Otherwise, defaults to "1.5.0".
+     *
+     * This property can be explicitly set in the build script to override the default behavior.
      */
-    val version: Property<String> = objectFactory.property { set("1.5.0") }
+    val version: Property<String> = objectFactory.property {
+        // Try to read version from ktlint-plugins.properties file first
+        val versionFromFile = readKtlintVersionFromPropertiesFile(
+            projectLayout.projectDirectory.asFile.toPath()
+        )
+        set(versionFromFile ?: "1.5.0")
+    }
 
     /**
      * Enable relative paths in reports

plugin/src/main/kotlin/org/jlleitschuh/gradle/ktlint/PluginUtil.kt

@@ -33,6 +33,35 @@ internal inline fun <reified T : Task> Project.registerTask(
 }
 
 internal const val EDITOR_CONFIG_FILE_NAME = ".editorconfig"
+internal const val KTLINT_PLUGINS_PROPERTIES_FILE_NAME = "ktlint-plugins.properties"
+internal const val KTLINT_PLUGINS_VERSION_PROPERTY = "ktlint-version"
+
+/**
+ * Reads the ktlint version from the ktlint-plugins.properties file if it exists.
+ * This file is used by the ktlint IntelliJ plugin to store the ktlint version.
+ *
+ * @param projectDir The project directory to search for the properties file
+ * @return The ktlint version string if found, null otherwise
+ */
+internal fun readKtlintVersionFromPropertiesFile(projectDir: Path): String? {
+    val propertiesFile = projectDir.resolve(KTLINT_PLUGINS_PROPERTIES_FILE_NAME)
+    if (!Files.exists(propertiesFile) || !Files.isReadable(propertiesFile)) {
+        return null
+    }
+
+    return propertiesFile.toFile().useLines { lines ->
+        lines
+            .filter { it.contains("=") }
+            .map {
+                val key = it.substringBefore("=").trim()
+                val value = it.substringAfter('=').trim()
+                key to value
+            }
+            .firstOrNull { it.first == KTLINT_PLUGINS_VERSION_PROPERTY }
+            ?.second
+            ?.takeIf { it.isNotBlank() }
+    }
+}
 
 internal fun getEditorConfigFiles(currentProjectDir: Path): Set<Path> {
     val result = mutableSetOf<Path>()

plugin/src/test/kotlin/org/jlleitschuh/gradle/ktlint/KtlintPluginsPropertiesTest.kt

@@ -0,0 +1,154 @@
+package org.jlleitschuh.gradle.ktlint
+
+import org.assertj.core.api.Assertions.assertThat
+import org.gradle.util.GradleVersion
+import org.jlleitschuh.gradle.ktlint.testdsl.CommonTest
+import org.jlleitschuh.gradle.ktlint.testdsl.GradleTestVersions
+import org.jlleitschuh.gradle.ktlint.testdsl.build
+import org.jlleitschuh.gradle.ktlint.testdsl.project
+
+@GradleTestVersions
+class KtlintPluginsPropertiesTest : AbstractPluginTest() {
+
+    @CommonTest
+    fun shouldUseVersionFromKtlintPluginsPropertiesFileWhenPresent(gradleVersion: GradleVersion) {
+        project(gradleVersion) {
+            // Create ktlint-plugins.properties file with version
+            projectPath.resolve(KTLINT_PLUGINS_PROPERTIES_FILE_NAME).writeText(
+                """
+                ktlint-version=1.2.1
+                """.trimIndent()
+            )
+
+            withCleanSources()
+
+            buildGradle.appendText(
+                """
+                
+                tasks.register("printKtlintVersion") {
+                    doLast {
+                        println("Ktlint version: " + ktlint.version.get())
+                    }
+                }
+                """.trimIndent()
+            )
+
+            build("printKtlintVersion") {
+                assertThat(output).contains("Ktlint version: 1.2.1")
+            }
+        }
+    }
+
+    @CommonTest
+    fun shouldUseDefaultVersionWhenKtlintPluginsPropertiesFileIsAbsent(gradleVersion: GradleVersion) {
+        project(gradleVersion) {
+            withCleanSources()
+
+            buildGradle.appendText(
+                """
+                
+                tasks.register("printKtlintVersion") {
+                    doLast {
+                        println("Ktlint version: " + ktlint.version.get())
+                    }
+                }
+                """.trimIndent()
+            )
+
+            build("printKtlintVersion") {
+                assertThat(output).contains("Ktlint version: 1.5.0")
+            }
+        }
+    }
+
+    @CommonTest
+    fun shouldAllowExplicitVersionOverrideEvenWhenPropertiesFileExists(gradleVersion: GradleVersion) {
+        project(gradleVersion) {
+            // Create ktlint-plugins.properties file with version
+            projectPath.resolve(KTLINT_PLUGINS_PROPERTIES_FILE_NAME).writeText(
+                """
+                ktlint-version=1.2.1
+                """.trimIndent()
+            )
+
+            withCleanSources()
+
+            buildGradle.appendText(
+                """
+                
+                ktlint {
+                    version = "1.3.0"
+                }
+                
+                tasks.register("printKtlintVersion") {
+                    doLast {
+                        println("Ktlint version: " + ktlint.version.get())
+                    }
+                }
+                """.trimIndent()
+            )
+
+            build("printKtlintVersion") {
+                assertThat(output).contains("Ktlint version: 1.3.0")
+            }
+        }
+    }
+
+    @CommonTest
+    fun shouldUseDefaultVersionWhenKtlintVersionPropertyIsBlank(gradleVersion: GradleVersion) {
+        project(gradleVersion) {
+            // Create ktlint-plugins.properties file with blank version
+            projectPath.resolve(KTLINT_PLUGINS_PROPERTIES_FILE_NAME).writeText(
+                """
+                ktlint-version=
+                """.trimIndent()
+            )
+
+            withCleanSources()
+
+            buildGradle.appendText(
+                """
+                
+                tasks.register("printKtlintVersion") {
+                    doLast {
+                        println("Ktlint version: " + ktlint.version.get())
+                    }
+                }
+                """.trimIndent()
+            )
+
+            build("printKtlintVersion") {
+                assertThat(output).contains("Ktlint version: 1.5.0")
+            }
+        }
+    }
+
+    @CommonTest
+    fun shouldUseDefaultVersionWhenPropertiesFileHasNoKtlintVersionProperty(gradleVersion: GradleVersion) {
+        project(gradleVersion) {
+            // Create ktlint-plugins.properties file without ktlint-version
+            projectPath.resolve(KTLINT_PLUGINS_PROPERTIES_FILE_NAME).writeText(
+                """
+                some-other-property=value
+                """.trimIndent()
+            )
+
+            withCleanSources()
+
+            buildGradle.appendText(
+                """
+                
+                tasks.register("printKtlintVersion") {
+                    doLast {
+                        println("Ktlint version: " + ktlint.version.get())
+                    }
+                }
+                """.trimIndent()
+            )
+
+            build("printKtlintVersion") {
+                assertThat(output).contains("Ktlint version: 1.5.0")
+            }
+        }
+    }
+}

plugin/src/test/kotlin/org/jlleitschuh/gradle/ktlint/PluginUtilTest.kt

@@ -40,4 +40,99 @@ internal class PluginUtilTest {
             delete()
         }
     }
+
+    @Test
+    fun `test readKtlintVersionFromPropertiesFile returns version when file exists`() {
+        temporaryFolder.resolve(KTLINT_PLUGINS_PROPERTIES_FILE_NAME).apply {
+            createNewFile()
+            writeText(
+                """
+                ktlint-version=1.2.1
+                """.trimIndent()
+            )
+            val version = readKtlintVersionFromPropertiesFile(temporaryFolder.toPath())
+            Assertions.assertEquals("1.2.1", version) {
+                "correctly reads version from properties file"
+            }
+            delete()
+        }
+    }
+
+    @Test
+    fun `test readKtlintVersionFromPropertiesFile returns null when file does not exist`() {
+        val version = readKtlintVersionFromPropertiesFile(temporaryFolder.toPath())
+        Assertions.assertNull(version) {
+            "returns null when properties file does not exist"
+        }
+    }
+
+    @Test
+    fun `test readKtlintVersionFromPropertiesFile returns null when version property is missing`() {
+        temporaryFolder.resolve(KTLINT_PLUGINS_PROPERTIES_FILE_NAME).apply {
+            createNewFile()
+            writeText(
+                """
+                some-other-property=value
+                """.trimIndent()
+            )
+            val version = readKtlintVersionFromPropertiesFile(temporaryFolder.toPath())
+            Assertions.assertNull(version) {
+                "returns null when ktlint-version property is missing"
+            }
+            delete()
+        }
+    }
+
+    @Test
+    fun `test readKtlintVersionFromPropertiesFile handles whitespace correctly`() {
+        temporaryFolder.resolve(KTLINT_PLUGINS_PROPERTIES_FILE_NAME).apply {
+            createNewFile()
+            writeText(
+                """
+                ktlint-version = 1.3.0
+                """.trimIndent()
+            )
+            val version = readKtlintVersionFromPropertiesFile(temporaryFolder.toPath())
+            Assertions.assertEquals("1.3.0", version) {
+                "correctly handles whitespace around equals sign"
+            }
+            delete()
+        }
+    }
+
+    @Test
+    fun `test readKtlintVersionFromPropertiesFile returns null when version is blank`() {
+        temporaryFolder.resolve(KTLINT_PLUGINS_PROPERTIES_FILE_NAME).apply {
+            createNewFile()
+            writeText(
+                """
+                ktlint-version=
+                """.trimIndent()
+            )
+            val version = readKtlintVersionFromPropertiesFile(temporaryFolder.toPath())
+            Assertions.assertNull(version) {
+                "returns null when ktlint-version is blank"
+            }
+            delete()
+        }
+    }
+
+    @Test
+    fun `test readKtlintVersionFromPropertiesFile handles multiple properties`() {
+        temporaryFolder.resolve(KTLINT_PLUGINS_PROPERTIES_FILE_NAME).apply {
+            createNewFile()
+            writeText(
+                """
+                some-property=value1
+                ktlint-version=1.4.0
+                another-property=value2
+                """.trimIndent()
+            )
+            val version = readKtlintVersionFromPropertiesFile(temporaryFolder.toPath())
+            Assertions.assertEquals("1.4.0", version) {
+                "correctly finds ktlint-version among multiple properties"
+            }
+            delete()
+        }
+    }
 }