proper mixin compatibilityLevel, and some constants collecting

common.gradle

@@ -40,6 +40,17 @@ dependencies {
 //	include(modImplementation(fabricApi.module("fabric-resource-loader-v0", project.fabric_api_version)))
 }
 
+String MIXIN_CONFIG_PATH = 'template_mod.mixins.json'
+String LANG_DIR = 'assets/template_mod/lang'
+JavaVersion JAVA_COMPATIBILITY
+if (mcVersion >= 11800) {
+	JAVA_COMPATIBILITY = JavaVersion.VERSION_17
+} else if (mcVersion >= 11700) {
+	JAVA_COMPATIBILITY = JavaVersion.VERSION_16
+} else {
+	JAVA_COMPATIBILITY = JavaVersion.VERSION_1_8
+}
+
 loom {
 	runConfigs.all {
 		// to make sure it generates all "Minecraft Client (:subproject_name)" applications
@@ -53,16 +64,8 @@ remapJar {
 	remapperIsolation = true
 }
 
-if (mcVersion >= 11800) {
-	sourceCompatibility = JavaVersion.VERSION_17
-	targetCompatibility = JavaVersion.VERSION_17
-} else if (mcVersion >= 11700) {
-	sourceCompatibility = JavaVersion.VERSION_16
-	targetCompatibility = JavaVersion.VERSION_16
-} else {
-	sourceCompatibility = JavaVersion.VERSION_1_8
-	targetCompatibility = JavaVersion.VERSION_1_8
-}
+sourceCompatibility = JAVA_COMPATIBILITY
+targetCompatibility = JAVA_COMPATIBILITY
 
 String versionSuffix = ''
 // detect github action environment variables
@@ -94,12 +97,16 @@ processResources {
 		]
 		expand valueMap
 	}
+
+	filesMatching(MIXIN_CONFIG_PATH) {
+		expand "compatibility_level": "JAVA_${JAVA_COMPATIBILITY.ordinal() + 1}"
+	}
 }
 
 // https://github.com/Fallen-Breath/yamlang
 yamlang {
 	targetSourceSets = [sourceSets.main]
-	inputDir = 'assets/template_mod/lang'
+	inputDir = LANG_DIR
 }
 
 // ensure that the encoding is set to UTF-8, no matter what the system default is

src/main/resources/template_mod.mixins.json

@@ -2,7 +2,7 @@
   "required": true,
   "minVersion": "0.8",
   "package": "me.fallenbreath.template_mod.mixins",
-  "compatibilityLevel": "JAVA_8",
+  "compatibilityLevel": "${compatibility_level}",
   "mixins": [
     "MinecraftServerMixin"
   ],