Add auto version generator

[no changelog]

buildSrc/src/lookupversion.kt

@@ -0,0 +1,31 @@
+/*
+ * SPDX-FileCopyrightText: 2024 Linnea Gräf <nea@nea.moe>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+fun execString(vararg args: String): String {
+    val pb = ProcessBuilder(*args)
+        .redirectOutput(ProcessBuilder.Redirect.PIPE)
+        .start()
+    pb.waitFor()
+    return pb.inputStream.readAllBytes().decodeToString().trim()
+}
+
+private val tag = "([0-9.]+)\\.0".toRegex()
+private val tagOffset = "([0-9.]+)\\.0-([0-9]+)..+".toRegex()
+
+inline fun <T> Regex.useMatcher(string: String, block: (MatchResult) -> T): T? {
+    return matchEntire(string)?.let(block)
+}
+
+fun getGitTagInfo(): String {
+    val str = execString("git", "describe", "--tags", "HEAD")
+    tag.useMatcher(str) {
+        return it.groupValues[0]
+    }
+    tagOffset.useMatcher(str) {
+        return it.groupValues[1] + "." + it.groupValues[2]
+    }
+    return "nogitversion"
+}