Only update file header dates when they are modified

Prevents the giant "year" update commits.

Author: DenWav

buildSrc/src/main/kotlin/mcdev-core.gradle.kts

@@ -3,7 +3,7 @@
  *
  * https://mcdev.io/
  *
- * Copyright (C) 2025 minecraft-dev
+ * Copyright (C) 2026 minecraft-dev
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Lesser General Public License as published
@@ -19,6 +19,7 @@
  */
 
 import org.cadixdev.gradle.licenser.header.HeaderStyle
+import org.cadixdev.gradle.licenser.tasks.LicenseTask
 import org.gradle.accessors.dm.LibrariesForLibs
 import org.jetbrains.kotlin.gradle.dsl.JvmDefaultMode
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
@@ -128,14 +129,58 @@ intellijPlatform {
 }
 
 license {
-    header.set(resources.text.fromFile(rootProject.layout.projectDirectory.file("copyright.txt")))
+    header.set(resources.text.fromString($$"""
+        Minecraft Development for IntelliJ
+
+        https://mcdev.io/
+
+        Copyright (C) ${year} minecraft-dev
+
+        This program is free software: you can redistribute it and/or modify
+        it under the terms of the GNU Lesser General Public License as published
+        by the Free Software Foundation, version 3.0 only.
+
+        This program is distributed in the hope that it will be useful,
+        but WITHOUT ANY WARRANTY; without even the implied warranty of
+        MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+        GNU General Public License for more details.
+
+        You should have received a copy of the GNU Lesser General Public License
+        along with this program.  If not, see <https://www.gnu.org/licenses/>.
+    """.trimIndent()))
+
+    properties {
+        set("year", "2026")
+    }
+
     style["flex"] = HeaderStyle.BLOCK_COMMENT.format
     style["bnf"] = HeaderStyle.BLOCK_COMMENT.format
 
     val endings = listOf("java", "kt", "kts", "groovy", "gradle.kts", "xml", "properties", "html", "flex", "bnf")
     include(endings.map { "**/*.$it" })
 }
 
+tasks.withType(LicenseTask::class).configureEach {
+    val changedFiles = if (rootProject.ext.has("changedFiles")) {
+        @Suppress("UNCHECKED_CAST")
+        rootProject.ext["changedFiles"] as Set<File>
+    } else {
+        val unstagedFiles = git("diff", "--name-only").lines()
+        val stagedFiles = git("diff", "--staged", "--name-only").lines()
+        var changedFiles = (unstagedFiles + stagedFiles)
+            .filter { it.isNotBlank() }
+            .map(project::file)
+            .toSet()
+        rootProject.ext["changedFiles"] = changedFiles
+        changedFiles
+    }
+    doFirst {
+        files = files.filter {
+            it in changedFiles
+        }
+    }
+}
+
 idea {
     module {
         excludeDirs.add(file(intellijPlatform.sandboxContainer.get()))

buildSrc/src/main/kotlin/util.kt

@@ -3,7 +3,7 @@
  *
  * https://mcdev.io/
  *
- * Copyright (C) 2025 minecraft-dev
+ * Copyright (C) 2026 minecraft-dev
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Lesser General Public License as published
@@ -18,6 +18,10 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+import java.io.ByteArrayOutputStream
+import java.io.InputStream
+import java.io.OutputStream
+import java.nio.charset.Charset
 import org.gradle.api.Project
 import org.gradle.api.tasks.TaskContainer
 import org.gradle.api.tasks.util.PatternFilterable
@@ -65,3 +69,11 @@ fun Project.parser(bnf: String, pack: String): TaskDelegate<ParserExec> {
         this.grammarKit.setFrom(grammarKit)
     }
 }
+
+fun Project.git(vararg args: String): String {
+    val output = providers.exec {
+        commandLine("git", *args)
+        isIgnoreExitValue = true
+    }
+    return output.standardOutput.asText.get()
+}