feat: jsr305 compat for kotlinc

- feat: treat jsr305 as strict
- feat: consider pkl's annotations for jsr305 compat

Signed-off-by: Sam Gammon <sam@elide.dev>

Author: sgammon

buildSrc/src/main/kotlin/pklKotlinLibrary.gradle.kts

@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 import org.gradle.accessors.dm.LibrariesForLibs
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import org.jetbrains.kotlin.gradle.tasks.KotlinJvmCompile
 
 plugins {
   id("pklJavaLibrary")
@@ -38,3 +40,26 @@ dependencies {
 tasks.compileKotlin {
   enabled = true // disabled by pklJavaLibrary
 }
+
+tasks.withType<KotlinJvmCompile>().configureEach {
+  compilerOptions {
+    // must match the minimum JVM bytecode target for Pkl
+    jvmTarget = JvmTarget.JVM_17
+
+    // enable java parameter names for stronger Kotlin-Java interop and debugging
+    javaParameters = true
+
+    // consider kotlin warnings errors if not otherwise suppressed
+    allWarningsAsErrors = true
+
+    freeCompilerArgs.addAll(
+      listOf(
+        // enable strict nullability checking and integration with pkl's own annotations
+        "-Xjsr305=strict",
+        "-Xjsr305=@org.pkl.core.util.Nullable:strict",
+        "-Xjsr305=@org.pkl.core.util.Nonnull:strict",
+      )
+    )
+  }
+}
+