FIR IDE: add basic keyword completion

idea/idea-fir/src/org/jetbrains/kotlin/idea/completion/FirKeywordCompletion.kt

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.idea.completion
+
+import com.intellij.codeInsight.completion.CompletionResultSet
+import com.intellij.codeInsight.completion.PrefixMatcher
+import com.intellij.openapi.module.Module
+import com.intellij.psi.PsiElement
+import org.jetbrains.kotlin.config.LanguageVersionSettingsImpl
+
+object FirKeywordCompletion {
+    private val keywordCompletion = KeywordCompletion(object : KeywordCompletion.LanguageVersionSettingProvider {
+        override fun getLanguageVersionSetting(element: PsiElement) = LanguageVersionSettingsImpl.DEFAULT // TODO
+        override fun getLanguageVersionSetting(module: Module) = LanguageVersionSettingsImpl.DEFAULT // TODO
+    })
+
+    fun completeKeywords(result: CompletionResultSet, position: PsiElement, prefixMatcher: PrefixMatcher, isJvmModule: Boolean) {
+        keywordCompletion.complete(position, prefixMatcher, isJvmModule) { lookupElement ->
+            result.addElement(lookupElement)
+        }
+    }
+}

idea/idea-fir/src/org/jetbrains/kotlin/idea/completion/KotlinFirCompletionContributor.kt

@@ -26,8 +26,10 @@ import org.jetbrains.kotlin.idea.frontend.api.symbols.markers.KtNamedSymbol
 import org.jetbrains.kotlin.idea.frontend.api.symbols.markers.KtSymbolWithVisibility
 import org.jetbrains.kotlin.idea.frontend.api.types.KtClassType
 import org.jetbrains.kotlin.idea.frontend.api.types.KtType
+import org.jetbrains.kotlin.idea.project.TargetPlatformDetector
 import org.jetbrains.kotlin.idea.references.mainReference
 import org.jetbrains.kotlin.lexer.KtTokens
+import org.jetbrains.kotlin.platform.jvm.isJvm
 import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.psi.psiUtil.getReceiverExpression
 
@@ -140,8 +142,12 @@ private class KotlinCommonCompletionProvider(
     @OptIn(InvalidWayOfUsingAnalysisSession::class)
     fun addCompletions(parameters: CompletionParameters, result: CompletionResultSet) {
         val originalFile = parameters.originalFile as? KtFile ?: return
+        val isJvmModule = TargetPlatformDetector.getPlatform(originalFile).isJvm()
+
         recordOriginalFile(parameters)
 
+        FirKeywordCompletion.completeKeywords(result, parameters.position, prefixMatcher, isJvmModule = isJvmModule)
+
         val reference = (parameters.position.parent as? KtSimpleNameExpression)?.mainReference ?: return
         val nameExpression = reference.expression.takeIf { it !is KtLabelReferenceExpression } ?: return
 

idea/idea-fir/src/org/jetbrains/kotlin/idea/completion/KotlinFirLookupElementFactory.kt

@@ -16,6 +16,7 @@ import com.intellij.openapi.diagnostic.logger
 import com.intellij.openapi.editor.Document
 import com.intellij.openapi.util.TextRange
 import com.intellij.psi.PsiElement
+import org.jetbrains.kotlin.idea.completion.handlers.isTextAt
 import org.jetbrains.kotlin.idea.core.asFqNameWithRootPrefixIfNeeded
 import org.jetbrains.kotlin.idea.frontend.api.KtAnalysisSession
 import org.jetbrains.kotlin.idea.frontend.api.analyse
@@ -395,8 +396,6 @@ private object ShortNamesRenderer {
         "${if (param.isVararg) "vararg " else ""}${param.name.asString()}: ${param.annotatedType.type.render()}"
 }
 
-private fun Document.isTextAt(offset: Int, text: String) =
-    offset + text.length <= textLength && getText(TextRange(offset, offset + text.length)) == text
 
 private fun CharSequence.skipSpaces(index: Int): Int =
     (index until length).firstOrNull { val c = this[it]; c != ' ' && c != '\t' } ?: this.length