fix(editor): migrate IDELanguage to Kotlin

editor/src/main/java/com/itsaky/androidide/editor/language/CommonCompletionProvider.kt

@@ -16,6 +16,7 @@
  */
 package com.itsaky.androidide.editor.language
 
+import com.itsaky.androidide.editor.language.utils.CompletionHelper
 import com.itsaky.androidide.lsp.api.ILanguageServer
 import com.itsaky.androidide.lsp.models.CompletionItem
 import com.itsaky.androidide.lsp.models.CompletionParams
@@ -27,11 +28,9 @@ import com.itsaky.androidide.models.Position
 import com.itsaky.androidide.progress.ProcessCancelledException
 import com.itsaky.androidide.utils.ILogger
 import io.github.rosemoe.sora.lang.completion.CompletionCancelledException
-import io.github.rosemoe.sora.lang.completion.CompletionHelper
 import io.github.rosemoe.sora.text.CharPosition
 import io.github.rosemoe.sora.text.ContentReference
 import java.nio.file.Path
-import java.util.function.Predicate
 
 /**
  * Common implementation of completion provider which requests completions to provided language
@@ -39,10 +38,15 @@ import java.util.function.Predicate
  *
  * @author Akash Yadav
  */
-class CommonCompletionProvider(private val server: ILanguageServer,
-  private val cancelChecker: CompletionCancelChecker) {
+internal class CommonCompletionProvider(
+  private val server: ILanguageServer,
+  private val cancelChecker: CompletionCancelChecker
+) {
 
-  private val log = ILogger.newInstance(javaClass.simpleName)
+  companion object {
+
+    private val log = ILogger.newInstance("CommonCompletionProvider")
+  }
 
   /**
    * Computes completion items using the provided language server instance.
@@ -53,18 +57,19 @@ class CommonCompletionProvider(private val server: ILanguageServer,
    * @return The computed completion items. May return an empty list if the there was an error
    * computing the completion items.
    */
-  fun complete(
-    content: ContentReference?,
+  inline fun complete(
+    content: ContentReference,
     file: Path,
     position: CharPosition,
-    prefixMatcher: Predicate<Char?>
+    prefixMatcher: (Char) -> Boolean
   ): List<CompletionItem> {
     val completionResult =
       try {
         setupLookupForCompletion(file)
-        val prefix = CompletionHelper.computePrefix(content, position) { prefixMatcher.test(it) }
+        val prefix = CompletionHelper.computePrefix(content, position, prefixMatcher)
         val params =
-          CompletionParams(Position(position.line, position.column, position.index), file, cancelChecker)
+          CompletionParams(Position(position.line, position.column, position.index), file,
+            cancelChecker)
         params.content = content
         params.prefix = prefix
         server.complete(params)

editor/src/main/java/com/itsaky/androidide/editor/language/IDELanguage.java

@@ -1,134 +0,0 @@
-/*
- *  This file is part of AndroidIDE.
- *
- *  AndroidIDE is free software: you can redistribute it and/or modify
- *  it under the terms of the GNU General Public License as published by
- *  the Free Software Foundation, either version 3 of the License, or
- *  (at your option) any later version.
- *
- *  AndroidIDE is distributed in the hope that it will be useful,
- *  but WITHOUT ANY WARRANTY; without even the implied warranty of
- *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- *  GNU General Public License for more details.
- *
- *  You should have received a copy of the GNU General Public License
- *   along with AndroidIDE.  If not, see <https://www.gnu.org/licenses/>.
- */
-package com.itsaky.androidide.editor.language;
-
-import android.os.Bundle;
-import androidx.annotation.NonNull;
-import com.itsaky.androidide.editor.api.IEditor;
-import com.itsaky.androidide.editor.ui.IDECompletionPublisher;
-import com.itsaky.androidide.lookup.Lookup;
-import com.itsaky.androidide.lsp.api.ILanguageServer;
-import com.itsaky.androidide.preferences.internal.EditorPreferencesKt;
-import com.itsaky.androidide.progress.ICancelChecker;
-import com.itsaky.androidide.utils.ILogger;
-import io.github.rosemoe.sora.lang.Language;
-import io.github.rosemoe.sora.lang.completion.CompletionCancelledException;
-import io.github.rosemoe.sora.lang.completion.CompletionPublisher;
-import io.github.rosemoe.sora.lang.format.Formatter;
-import io.github.rosemoe.sora.text.CharPosition;
-import io.github.rosemoe.sora.text.ContentReference;
-import java.nio.file.Paths;
-import java.util.ArrayList;
-
-/**
- * Base class for language implementations in the IDE.
- *
- * @author Akash Yadav
- */
-public abstract class IDELanguage implements Language {
-
-  private static final ILogger LOG = ILogger.newInstance("IDELanguage");
-  private Formatter formatter;
-
-  @Override
-  public void requireAutoComplete(
-      @NonNull final ContentReference content,
-      @NonNull final CharPosition position,
-      @NonNull final CompletionPublisher publisher,
-      @NonNull final Bundle extraArguments)
-      throws CompletionCancelledException {
-    try {
-      final var cancelChecker = new CompletionCancelChecker(publisher);
-      Lookup.getDefault().register(ICancelChecker.class, cancelChecker);
-      doComplete(content, position, publisher, cancelChecker, extraArguments);
-    } finally {
-      Lookup.getDefault().unregister(ICancelChecker.class);
-    }
-  }
-
-  private void doComplete(
-      final @NonNull ContentReference content,
-      final @NonNull CharPosition position,
-      final @NonNull CompletionPublisher publisher,
-      final @NonNull CompletionCancelChecker cancelChecker,
-      final @NonNull Bundle extraArguments) {
-    final var server = getLanguageServer();
-    if (server == null) {
-      LOG.warn("Cannot provide completions. No language server available.");
-      return;
-    }
-
-    final var path = extraArguments.getString(IEditor.KEY_FILE, null);
-    if (path == null) {
-      LOG.warn("Cannot provide completions. No file provided.");
-      return;
-    }
-
-    final var completionProvider = new CommonCompletionProvider(server, cancelChecker);
-    final var file = Paths.get(path);
-
-    final var completionItems =
-        completionProvider.complete(content, file, position, this::checkIsCompletionChar);
-
-    publisher.setUpdateThreshold(1);
-
-    ((IDECompletionPublisher) publisher).addLSPItems(completionItems);
-  }
-
-  protected ILanguageServer getLanguageServer() {
-    return null;
-  }
-
-  /**
-   * Check if the given character is a completion character.
-   *
-   * @param c The character to check.
-   * @return <code>true</code> if the character is completion char, <code>false</code> otherwise.
-   */
-  protected boolean checkIsCompletionChar(char c) {
-    return false;
-  }
-
-  @Override
-  public boolean useTab() {
-    return !EditorPreferencesKt.getUseSoftTab();
-  }
-
-  @NonNull
-  @Override
-  public Formatter getFormatter() {
-    if (formatter != null) {
-      return formatter;
-    }
-
-    return formatter = new LSPFormatter(getLanguageServer());
-  }
-
-  public int getTabSize() {
-    return EditorPreferencesKt.getTabSize();
-  }
-
-  @Override
-  public int getIndentAdvance(@NonNull final ContentReference content, final int line,
-      final int column) {
-    return getIndentAdvance(content.getLine(line).substring(0, column));
-  }
-
-  public int getIndentAdvance(@NonNull String line) {
-    return 0;
-  }
-}

editor/src/main/java/com/itsaky/androidide/editor/language/IDELanguage.kt

@@ -0,0 +1,124 @@
+/*
+ *  This file is part of AndroidIDE.
+ *
+ *  AndroidIDE is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  AndroidIDE is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *   along with AndroidIDE.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package com.itsaky.androidide.editor.language
+
+import android.os.Bundle
+import com.itsaky.androidide.editor.api.IEditor
+import com.itsaky.androidide.editor.ui.IDECompletionPublisher
+import com.itsaky.androidide.lookup.Lookup
+import com.itsaky.androidide.lsp.api.ILanguageServer
+import com.itsaky.androidide.preferences.internal.tabSize
+import com.itsaky.androidide.preferences.internal.useSoftTab
+import com.itsaky.androidide.progress.ICancelChecker
+import com.itsaky.androidide.utils.ILogger
+import io.github.rosemoe.sora.lang.Language
+import io.github.rosemoe.sora.lang.completion.CompletionCancelledException
+import io.github.rosemoe.sora.lang.completion.CompletionPublisher
+import io.github.rosemoe.sora.lang.format.Formatter
+import io.github.rosemoe.sora.text.CharPosition
+import io.github.rosemoe.sora.text.ContentReference
+import java.nio.file.Paths
+
+/**
+ * Base class for language implementations in the IDE.
+ *
+ * @author Akash Yadav
+ */
+abstract class IDELanguage : Language {
+
+  private var formatter: Formatter? = null
+
+  protected open val languageServer: ILanguageServer?
+    get() = null
+
+  open fun getTabSize(): Int {
+    return tabSize
+  }
+
+  @Throws(CompletionCancelledException::class)
+  override fun requireAutoComplete(
+    content: ContentReference,
+    position: CharPosition,
+    publisher: CompletionPublisher,
+    extraArguments: Bundle
+  ) {
+    try {
+      val cancelChecker = CompletionCancelChecker(publisher)
+      Lookup.getDefault().register(ICancelChecker::class.java, cancelChecker)
+      doComplete(content, position, publisher, cancelChecker, extraArguments)
+    } finally {
+      Lookup.getDefault().unregister(
+        ICancelChecker::class.java)
+    }
+  }
+
+  private fun doComplete(
+    content: ContentReference,
+    position: CharPosition,
+    publisher: CompletionPublisher,
+    cancelChecker: CompletionCancelChecker,
+    extraArguments: Bundle
+  ) {
+    val server = languageServer
+    if (server == null) {
+      LOG.warn("Cannot provide completions. No language server available.")
+      return
+    }
+    val path = extraArguments.getString(IEditor.KEY_FILE, null)
+    if (path == null) {
+      LOG.warn("Cannot provide completions. No file provided.")
+      return
+    }
+    val completionProvider = CommonCompletionProvider(server, cancelChecker)
+    val file = Paths.get(path)
+    val completionItems = completionProvider.complete(content, file, position) { checkIsCompletionChar(it) }
+    publisher.setUpdateThreshold(1)
+    (publisher as IDECompletionPublisher).addLSPItems(completionItems)
+  }
+
+  /**
+   * Check if the given character is a completion character.
+   *
+   * @param c The character to check.
+   * @return `true` if the character is completion char, `false` otherwise.
+   */
+  protected open fun checkIsCompletionChar(c: Char): Boolean {
+    return false
+  }
+
+  override fun useTab(): Boolean {
+    return !useSoftTab
+  }
+
+  override fun getFormatter(): Formatter {
+    return formatter ?: LSPFormatter(languageServer).also { formatter = it }
+  }
+
+  override fun getIndentAdvance(content: ContentReference, line: Int,
+    column: Int): Int {
+    return getIndentAdvance(content.getLine(line).substring(0, column))
+  }
+
+  open fun getIndentAdvance(line: String): Int {
+    return 0
+  }
+
+  companion object {
+
+    private val LOG = ILogger.newInstance("IDELanguage")
+  }
+}

editor/src/main/java/com/itsaky/androidide/editor/language/treesitter/JavaLanguage.kt

@@ -26,6 +26,7 @@ import com.itsaky.androidide.lsp.api.ILanguageServer
 import com.itsaky.androidide.lsp.api.ILanguageServerRegistry
 import com.itsaky.androidide.lsp.java.JavaLanguageServer
 import com.itsaky.androidide.treesitter.java.TSLanguageJava
+import io.github.rosemoe.sora.lang.Language.INTERRUPTION_LEVEL_SLIGHT
 import io.github.rosemoe.sora.util.MyCharacter
 import io.github.rosemoe.sora.widget.SymbolPairMatch
 
@@ -45,9 +46,8 @@ class JavaLanguage(context: Context) :
     val FACTORY = Factory { JavaLanguage(it) }
   }
 
-  override fun getLanguageServer(): ILanguageServer? {
-    return ILanguageServerRegistry.getDefault().getServer(JavaLanguageServer.SERVER_ID)
-  }
+  override val languageServer: ILanguageServer?
+    get() = ILanguageServerRegistry.getDefault().getServer(JavaLanguageServer.SERVER_ID)
 
   override fun checkIsCompletionChar(c: Char): Boolean {
     return MyCharacter.isJavaIdentifierPart(c) || c == '.'

editor/src/main/java/com/itsaky/androidide/editor/language/treesitter/JsonLanguage.kt

@@ -20,6 +20,7 @@ package com.itsaky.androidide.editor.language.treesitter
 import android.content.Context
 import com.itsaky.androidide.editor.language.treesitter.TreeSitterLanguage.Factory
 import com.itsaky.androidide.treesitter.json.TSLanguageJson
+import io.github.rosemoe.sora.lang.Language.INTERRUPTION_LEVEL_STRONG
 
 /**
  * [TreeSitterLanguage] implementation for JSON files.
@@ -28,10 +29,13 @@ import com.itsaky.androidide.treesitter.json.TSLanguageJson
  */
 class JsonLanguage(context: Context) :
   TreeSitterLanguage(context, TSLanguageJson.getInstance(), TS_TYPE) {
+
   companion object {
+
     const val TS_TYPE = "json"
 
-    @JvmField val FACTORY = Factory { JsonLanguage(it) }
+    @JvmField
+    val FACTORY = Factory { JsonLanguage(it) }
   }
 
   override fun getInterruptionLevel(): Int {

editor/src/main/java/com/itsaky/androidide/editor/language/treesitter/KotlinLanguage.kt

@@ -18,7 +18,9 @@
 package com.itsaky.androidide.editor.language.treesitter
 
 import android.content.Context
+import com.itsaky.androidide.editor.language.treesitter.TreeSitterLanguage.Factory
 import com.itsaky.androidide.treesitter.kotlin.TSLanguageKotlin
+import io.github.rosemoe.sora.lang.Language.INTERRUPTION_LEVEL_STRONG
 
 /**
  * [TreeSitterLanguage] implementation for Kotlin.
@@ -29,6 +31,7 @@ open class KotlinLanguage(context: Context) :
   TreeSitterLanguage(context, TSLanguageKotlin.getInstance(), TS_TYPE_KT) {
 
   companion object {
+
     val FACTORY = Factory { KotlinLanguage(it) }
     const val TS_TYPE_KT = "kt"
     const val TS_TYPE_KTS = "kts"

editor/src/main/java/com/itsaky/androidide/editor/language/treesitter/TSLanguageRegistry.kt

@@ -27,6 +27,7 @@ import com.itsaky.androidide.editor.language.treesitter.internal.TSLanguageRegis
 interface TSLanguageRegistry {
 
   companion object {
+
     @JvmStatic
     val instance by lazy { TSLanguageRegistryImpl() }
   }

editor/src/main/java/com/itsaky/androidide/editor/language/treesitter/TreeSitterLanguage.kt

@@ -33,6 +33,7 @@ import com.itsaky.androidide.treesitter.TSQueryCursor
 import com.itsaky.androidide.treesitter.TSQueryMatch
 import com.itsaky.androidide.utils.ILogger
 import io.github.rosemoe.sora.editor.ts.TsTheme
+import io.github.rosemoe.sora.lang.Language.INTERRUPTION_LEVEL_STRONG
 import io.github.rosemoe.sora.lang.analysis.AnalyzeManager
 import io.github.rosemoe.sora.text.ContentReference
 import io.github.rosemoe.sora.text.TextUtils
@@ -78,7 +79,7 @@ abstract class TreeSitterLanguage(context: Context, lang: TSLanguage, type: Stri
   }
 
   open fun finalizeIndent(indent: Int): Int {
-    return indent * tabSize
+    return indent * getTabSize()
   }
 
   override fun getAnalyzeManager(): AnalyzeManager {
@@ -106,7 +107,7 @@ abstract class TreeSitterLanguage(context: Context, lang: TSLanguage, type: Stri
       content.toString(),
       line,
       column,
-      decrementBy = TextUtils.countLeadingSpaceCount(content.getLine(line), tabSize)
+      decrementBy = TextUtils.countLeadingSpaceCount(content.getLine(line), getTabSize())
     )
   }
 

editor/src/main/java/com/itsaky/androidide/editor/language/treesitter/TreeSitterLanguageSpec.kt

@@ -30,7 +30,7 @@ import java.io.Closeable
  */
 class TreeSitterLanguageSpec
 @JvmOverloads constructor(val spec: TsLanguageSpec,
-                          indentsQueryScm: String = ""
+  indentsQueryScm: String = ""
 ) : Closeable {
 
   // <editor-fold desc="Proxy properties">
@@ -38,7 +38,8 @@ class TreeSitterLanguageSpec
     get() = spec.language
   // </editor-fold>
 
-  val indentsQuery: TSQuery? = if (indentsQueryScm.isBlank()) TSQuery.EMPTY else TSQuery.create(language, indentsQueryScm)
+  val indentsQuery: TSQuery? = if (indentsQueryScm.isBlank()) TSQuery.EMPTY else TSQuery.create(
+    language, indentsQueryScm)
     .let { if (it.canAccess()) it else null }
 
   init {

editor/src/main/java/com/itsaky/androidide/editor/language/treesitter/XMLLanguage.kt

@@ -23,6 +23,7 @@ import com.itsaky.androidide.lsp.api.ILanguageServer
 import com.itsaky.androidide.lsp.api.ILanguageServerRegistry
 import com.itsaky.androidide.lsp.xml.XMLLanguageServer
 import com.itsaky.androidide.treesitter.xml.TSLanguageXml
+import io.github.rosemoe.sora.lang.Language.INTERRUPTION_LEVEL_STRONG
 import io.github.rosemoe.sora.util.MyCharacter
 
 /**
@@ -33,6 +34,9 @@ import io.github.rosemoe.sora.util.MyCharacter
 class XMLLanguage(context: Context) :
   TreeSitterLanguage(context, lang = TSLanguageXml.getInstance(), type = TS_TYPE) {
 
+  override val languageServer: ILanguageServer?
+    get() = ILanguageServerRegistry.getDefault().getServer(XMLLanguageServer.SERVER_ID)
+
   companion object {
 
     const val TS_TYPE = "xml"
@@ -41,10 +45,6 @@ class XMLLanguage(context: Context) :
     val FACTORY = Factory { XMLLanguage(it) }
   }
 
-  override fun getLanguageServer(): ILanguageServer? {
-    return ILanguageServerRegistry.getDefault().getServer(XMLLanguageServer.SERVER_ID)
-  }
-
   override fun checkIsCompletionChar(c: Char): Boolean {
     return MyCharacter.isJavaIdentifierPart(c) || c == '<' || c == '/'
   }

editor/src/main/java/com/itsaky/androidide/editor/language/treesitter/internal/TSLanguageRegistryImpl.kt

@@ -47,7 +47,7 @@ class TSLanguageRegistryImpl : TSLanguageRegistry {
     fileType: String
   ): TreeSitterLanguage.Factory<T> {
     return (registry[fileType] ?: throw TSLanguageRegistry.NotRegisteredException(fileType))
-      as TreeSitterLanguage.Factory<T>
+        as TreeSitterLanguage.Factory<T>
   }
 
   override fun destroy() {

editor/src/main/java/com/itsaky/androidide/editor/language/treesitter/predicates/AnyOfPredicate.kt

@@ -42,14 +42,14 @@ object AnyOfPredicate : TreeSitterPredicate() {
 
   override fun canHandle(steps: List<TsClientPredicateStep>): Boolean {
     return steps.size > 4 &&
-      steps.let {
-        it[0].predicateType == TSQueryPredicateStep.Type.String &&
-          it[1].predicateType == TSQueryPredicateStep.Type.Capture &&
-          it[it.lastIndex].predicateType == TSQueryPredicateStep.Type.Done &&
-          it.subList(2, it.lastIndex - 1).all { step ->
-            step.predicateType == TSQueryPredicateStep.Type.String
-          }
-      }
+        steps.let {
+          it[0].predicateType == TSQueryPredicateStep.Type.String &&
+              it[1].predicateType == TSQueryPredicateStep.Type.Capture &&
+              it[it.lastIndex].predicateType == TSQueryPredicateStep.Type.Done &&
+              it.subList(2, it.lastIndex - 1).all { step ->
+                step.predicateType == TSQueryPredicateStep.Type.String
+              }
+        }
   }
 
   override fun doPredicateInternal(

editor/src/main/java/com/itsaky/androidide/editor/language/treesitter/predicates/EqualPredicate.kt

@@ -43,12 +43,12 @@ object EqualPredicate : TreeSitterPredicate() {
 
   override fun canHandle(steps: List<TsClientPredicateStep>): Boolean {
     return steps.size == 4 &&
-      steps[0].predicateType == TSQueryPredicateStep.Type.String &&
-      steps[1].predicateType == TSQueryPredicateStep.Type.Capture &&
-      steps[2].predicateType.let {
-        it == TSQueryPredicateStep.Type.Capture || it == TSQueryPredicateStep.Type.String
-      } &&
-      steps[3].predicateType == TSQueryPredicateStep.Type.Done
+        steps[0].predicateType == TSQueryPredicateStep.Type.String &&
+        steps[1].predicateType == TSQueryPredicateStep.Type.Capture &&
+        steps[2].predicateType.let {
+          it == TSQueryPredicateStep.Type.Capture || it == TSQueryPredicateStep.Type.String
+        } &&
+        steps[3].predicateType == TSQueryPredicateStep.Type.Done
   }
 
   override fun doPredicateInternal(
@@ -63,7 +63,7 @@ object EqualPredicate : TreeSitterPredicate() {
       predicateSteps[2].let {
         check(
           it.predicateType == TSQueryPredicateStep.Type.String ||
-            it.predicateType == TSQueryPredicateStep.Type.Capture
+              it.predicateType == TSQueryPredicateStep.Type.Capture
         ) {
           "Second predicate step of #eq? predicate must be a string or a capture"
         }

editor/src/main/java/com/itsaky/androidide/editor/language/treesitter/predicates/InvertingPredicate.kt

@@ -28,7 +28,8 @@ import io.github.rosemoe.sora.editor.ts.predicate.TsSyntheticCaptureContainer
  *
  * @author Akash Yadav
  */
-open class InvertingPredicate(override val name: String, private val predicate: TreeSitterPredicate) :
+open class InvertingPredicate(override val name: String,
+  private val predicate: TreeSitterPredicate) :
   TreeSitterPredicate() {
 
   override fun canHandle(steps: List<TsClientPredicateStep>): Boolean {

editor/src/main/java/com/itsaky/androidide/editor/language/treesitter/predicates/TreeSitterPredicate.kt

@@ -70,8 +70,8 @@ abstract class TreeSitterPredicate : TsPredicate {
 
     if (
       predicateSteps.isEmpty() ||
-        predicateSteps[0].content != "${name}?" ||
-        !canHandle(predicateSteps)
+      predicateSteps[0].content != "${name}?" ||
+      !canHandle(predicateSteps)
     ) {
       return PredicateResult.UNHANDLED
     }

editor/src/main/java/com/itsaky/androidide/editor/language/utils/CompletionHelper.kt

@@ -0,0 +1,51 @@
+/*
+ *  This file is part of AndroidIDE.
+ *
+ *  AndroidIDE is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  AndroidIDE is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *   along with AndroidIDE.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package com.itsaky.androidide.editor.language.utils
+
+import io.github.rosemoe.sora.text.CharPosition
+import io.github.rosemoe.sora.text.ContentReference
+
+/**
+ * Utility functions for completion providers.
+ *
+ * @author Akash Yadav
+ */
+object CompletionHelper {
+
+  /**
+   * Searches backward on the line, with the given checker to check chars.
+   * Returns the longest text that matches the requirement.
+   *
+   * This is a variant of [CompletionHelper.computePrefix][io.github.rosemoe.sora.lang.completion.CompletionHelper.computePrefix]
+   * which inlines the predicate for better performance.
+   */
+  inline fun computePrefix(
+    ref: ContentReference, pos: CharPosition,
+    checker: (Char) -> Boolean
+  ): String {
+    var begin = pos.column
+    val line = ref.getLine(pos.line)
+    while (begin > 0) {
+      if (!checker(line[begin - 1])) {
+        break
+      }
+      begin--
+    }
+    return line.substring(begin, pos.column)
+  }
+}