Writing IntelliJ Idea plugin . Part 1

IntelliJ Idea is not a free IDE - but since 15 years (or longer) the are able to sell against free IDEs like eclipse.
Because it is just better and easy to expand. And sometimes there is a need for support of some awkward programming language - and you have to bite a bullet and roll your own plugin.


Here we have it - programming language for custom tool (which is not going to go away any time soon, and still good to make money). Language itself is fully functional, but syntax was borrowed from pascal (nobody is sure when it was developed, but must be in pre-java days), and keywords are partly in german language. Case insensitive. It calls for sane idea plugin, with syntax coloring, indexing and navigation.


Fortunately JetBrains folks provide good step by step guide - but since we are busy, we will not read explanation part (as always) and start coding our plugin

First 2 steps were easy, and wothout any adventures. I just followed explanations in 1 & 2 - and in some 20 minutes I had my file recognized, and opened and provided with icon.

  1. Created file type
package de.mmtalk.intellij;

import com.intellij.lang.properties.charset.Native2AsciiCharset;
import com.intellij.openapi.fileEditor.impl.LoadTextUtil;
import com.intellij.openapi.fileTypes.LanguageFileType;
import com.intellij.openapi.util.IconLoader;
import com.intellij.openapi.vfs.CharsetToolkit;
import com.intellij.openapi.vfs.VirtualFile;
import com.intellij.openapi.vfs.encoding.EncodingRegistry;
import org.jetbrains.annotations.NotNull;

import javax.swing.*;
import java.nio.charset.Charset;

public class MMTalkFileType extends LanguageFileType {

    public static final LanguageFileType INSTANCE = new MMTalkFileType();
    private static final String DEFAULT_EXTENSION = "mmtalk";
    public static final Icon ICON = IconLoader.getIcon("/icons/mmtalk.png");

    public MMTalkFileType() {

    public String getName() {
        return "MMTalk";

    public String getDescription() {
        return PropertiesBundle.message("mmtalk.description");

    public String getDefaultExtension() {
        return DEFAULT_EXTENSION;

    public Icon getIcon() {
        return ICON;

    public String getCharset(@NotNull VirtualFile file, @NotNull final byte[] content) {
        LoadTextUtil.DetectResult guessed = LoadTextUtil.guessFromContent(file, content);
        Charset charset = guessed.hardCodedCharset == null ? EncodingRegistry.getInstance().getDefaultCharsetForPropertiesFiles(file) : guessed.hardCodedCharset;
        if (charset == null) {
            charset = CharsetToolkit.getDefaultSystemCharset();
        if (EncodingRegistry.getInstance().isNative2Ascii(file)) {
            charset = Native2AsciiCharset.wrap(charset);
        return charset.name();


( Icon and exgtension are defined here, make your icon 16x16 PNG, zlu maz need higher resolution for QHD displays tough. )

  1. And factory for it ““java package de.mmtalk.intellij;

import com.intellij.openapi.fileTypes.FileTypeConsumer; import com.intellij.openapi.fileTypes.FileTypeFactory; import org.jetbrains.annotations.NotNull;

public class MMTalkFileTypeFactory extends FileTypeFactory { @Override public void createFileTypes(@NotNull FileTypeConsumer fileTypeConsumer) { fileTypeConsumer.consume(MMTalkFileType.INSTANCE); } }

3. Custom language definition

package de.mmtalk.intellij;

import com.intellij.lang.Language;

public class MMTalkLanguage  extends Language{

    public static final MMTalkLanguage INSTANCE = new MMTalkLanguage();

    public MMTalkLanguage() {

And registered mime type just in case

  1. And of course everything goes into plugin.xml

    <extensions defaultExtensionNs="com.intellij">
        <fileTypeFactory implementation="de.mmtalk.intellij.MMTalkFileTypeFactory"/>

Now compile, run and enjoy you new icon in toolbar: