Added support for extern declarations and enhanced .lyng.d merging

- Implemented `extern` support for functions, classes, objects, enums, and properties in the `MiniAST`.
- Updated `MiniAST` to include `isExtern` field for applicable nodes.
- Enabled merging of `.lyng.d` declaration files into main `.lyng` scripts.
- Adjusted tests to validate `extern` behavior and documentation handling.
- Minor fixes to parser logic for improved robustness.

lyng-idea/src/main/kotlin/net/sergeych/lyng/idea/util/LyngAstManager.kt

@@ -19,6 +19,7 @@ package net.sergeych.lyng.idea.util
 
 import com.intellij.openapi.util.Key
 import com.intellij.psi.PsiFile
+import com.intellij.psi.PsiManager
 import kotlinx.coroutines.runBlocking
 import net.sergeych.lyng.Compiler
 import net.sergeych.lyng.Source
@@ -45,7 +46,11 @@ object LyngAstManager {
             val provider = IdeLenientImportProvider.create()
             val src = Source(file.name, text)
             runBlocking { Compiler.compileWithMini(src, provider, sink) }
-            sink.build()
+            val script = sink.build()
+            if (script != null && !file.name.endsWith(".lyng.d")) {
+                mergeDeclarationFiles(file, script)
+            }
+            script
         } catch (_: Throwable) {
             sink.build()
         }
@@ -59,6 +64,26 @@ object LyngAstManager {
         return built
     }
 
+    private fun mergeDeclarationFiles(file: PsiFile, mainScript: MiniScript) {
+        val psiManager = PsiManager.getInstance(file.project)
+        var current = file.virtualFile?.parent
+        val seen = mutableSetOf<String>()
+
+        while (current != null) {
+            for (child in current.children) {
+                if (child.name.endsWith(".lyng.d") && child != file.virtualFile && seen.add(child.path)) {
+                    val psiD = psiManager.findFile(child) ?: continue
+                    val scriptD = getMiniAst(psiD)
+                    if (scriptD != null) {
+                        mainScript.declarations.addAll(scriptD.declarations)
+                        mainScript.imports.addAll(scriptD.imports)
+                    }
+                }
+            }
+            current = current.parent
+        }
+    }
+
     fun getBinding(file: PsiFile): BindingSnapshot? {
         val doc = file.viewProvider.document ?: return null
         val stamp = doc.modificationStamp

lyng-idea/src/main/resources/META-INF/plugin.xml

@@ -42,7 +42,7 @@
 
     <extensions defaultExtensionNs="com.intellij">
         <!-- Language and file type -->
-        <fileType implementationClass="net.sergeych.lyng.idea.LyngFileType" name="Lyng" extensions="lyng" fieldName="INSTANCE" language="Lyng"/>
+        <fileType implementationClass="net.sergeych.lyng.idea.LyngFileType" name="Lyng" extensions="lyng;lyng.d" fieldName="INSTANCE" language="Lyng"/>
 
         <!-- Minimal parser/PSI to fully wire editor services for the language -->
         <lang.parserDefinition language="Lyng" implementationClass="net.sergeych.lyng.idea.psi.LyngParserDefinition"/>