feat(devin-lang): improve code completion for DevInTypes.VARIABLE_ID #101

The completion provider now uses the `MyInsertHandler` to insert a newline and move the caret
after inserting a variable identifier, providing a better user experience for code completion
within DevInTypes.VARIABLE_ID. Additionally, the completion provider now iterates over all
injectable languages and adds them as lookup elements, each with its type text and an insert
handler, improving the overall functionality of the completion feature.

Author: phodal

exts/devin-lang/src/main/kotlin/cc/unitmesh/language/DevInCompletionContributor.kt

@@ -12,11 +12,7 @@ class DevInCompletionContributor : CompletionContributor() {
     private val INPUT_DUMMY_IDENTIFIER = "AutoDevDummy"
 
     init {
-        extend(
-            CompletionType.BASIC,
-            psiElement(DevInTypes.VARIABLE_ID),
-            VariableProvider()
-        )
+        extend(CompletionType.BASIC, psiElement(DevInTypes.VARIABLE_ID), VariableProvider())
     }
 
     override fun beforeCompletion(context: CompletionInitializationContext) {

exts/devin-lang/src/main/kotlin/cc/unitmesh/language/completion/CodeLanguageProvider.kt

@@ -1,16 +1,30 @@
 package cc.unitmesh.language.completion
 
-import com.intellij.codeInsight.completion.CompletionParameters
-import com.intellij.codeInsight.completion.CompletionProvider
-import com.intellij.codeInsight.completion.CompletionResultSet
+import com.intellij.codeInsight.completion.*
+import com.intellij.codeInsight.lookup.LookupElement
+import com.intellij.codeInsight.lookup.LookupElementBuilder
+import com.intellij.lang.LanguageUtil
 import com.intellij.util.ProcessingContext
 
-class CodeLanguageProvider: CompletionProvider<CompletionParameters>() {
+class CodeLanguageProvider : CompletionProvider<CompletionParameters>() {
     override fun addCompletions(
         parameters: CompletionParameters,
         context: ProcessingContext,
         result: CompletionResultSet,
     ) {
-        TODO("Not yet implemented")
+        for (language in LanguageUtil.getInjectableLanguages()) {
+            val id = language.id
+            val handler = LookupElementBuilder.create(id)
+                .withTypeText(language.displayName, true)
+                .withInsertHandler(MyInsertHandler())
+            result.addElement(handler)
+        }
+    }
+
+    private class MyInsertHandler : InsertHandler<LookupElement> {
+        override fun handleInsert(context: InsertionContext, item: LookupElement) {
+            context.document.insertString(context.tailOffset, "\n\n")
+            context.editor.caretModel.moveCaretRelatively(1, 0, false, false, false)
+        }
     }
 }