The first step in developing a custom language plugin is registering a file type associated with the language.

The IDE typically determines the type of a file by looking at its file name or extension.

FileType Interface

FileType (consulo.virtualFileSystem.fileType.FileType) is the base interface for all file types. It defines:

Method	Description
getId()	Returns the unique identifier for this file type. Must be unique across all registered file types.
getDisplayName()	Returns the user-readable display name. By default returns a LocalizeValue of the ID.
getDescription()	Returns the user-readable description. Deprecated in favor of getDisplayName().
getDefaultExtension()	Returns the default file extension (without the leading dot).
getIcon()	Returns the icon used for showing files of this type.
isBinary()	Returns true if files of this type contain binary data. Used for source control, to-do scanning, and other purposes.
isReadOnly()	Returns true if this file type is read-only. Read-only file types are not shown in the "File Types" settings dialog.
getCharset(VirtualFile file, byte[] content)	Returns the character set for the specified file.

LanguageFileType

A custom language file type is a class derived from LanguageFileType (consulo.language.file.LanguageFileType), which passes a Language (consulo.language.Language) subclass to its base class constructor.

LanguageFileType extends FileType and adds language association:

Method	Description
LanguageFileType(Language language)	Creates a language file type for the specified language.
LanguageFileType(Language language, boolean secondary)	Creates a language file type. If secondary is true, this file type will never be returned as the associated file type for the language. Used when a file type reuses the language of another file type.
getLanguage()	Returns the Language instance associated with this file type.
isSecondary()	Returns true if this is a secondary file type for its language.
extractCharsetFromFileContent(Project project, VirtualFile file, CharSequence content)	Override to extract the charset from file content (e.g., for files that declare their encoding in a header).

Registration with @ExtensionImpl

To register a file type, implement a FileTypeFactory subclass annotated with @ExtensionImpl. The FileTypeFactory (consulo.virtualFileSystem.fileType.FileTypeFactory) base class is annotated with @ExtensionAPI(ComponentScope.APPLICATION).

The FileTypeFactory defines a single method:

Method	Description
createFileTypes(FileTypeConsumer consumer)	Called during initialization. Use the consumer to register file types with their associated extensions or matchers.

The FileTypeConsumer provides three consume overloads:

Method	Description
consume(FileType fileType)	Registers the file type with its default extension.
consume(FileType fileType, String extensions)	Registers the file type with a semicolon-delimited list of extensions.
consume(FileType fileType, FileNameMatcher... matchers)	Registers the file type with custom file name matchers for advanced matching.

Example

import consulo.annotation.component.ExtensionImpl;
import consulo.virtualFileSystem.fileType.FileTypeConsumer;
import consulo.virtualFileSystem.fileType.FileTypeFactory;

import jakarta.annotation.Nonnull;

@ExtensionImpl
public class MyLanguageFileTypeFactory extends FileTypeFactory {
    @Override
    public void createFileTypes(@Nonnull FileTypeConsumer consumer) {
        consumer.consume(MyLanguageFileType.INSTANCE, "mylang");
    }
}

Where MyLanguageFileType is defined as:

import consulo.language.file.LanguageFileType;
import consulo.localize.LocalizeValue;
import consulo.ui.image.Image;

import jakarta.annotation.Nonnull;

public class MyLanguageFileType extends LanguageFileType {
    public static final MyLanguageFileType INSTANCE = new MyLanguageFileType();

    private MyLanguageFileType() {
        super(MyLanguage.INSTANCE);
    }

    @Nonnull
    @Override
    public String getId() {
        return "MY_LANGUAGE";
    }

    @Nonnull
    @Override
    public LocalizeValue getDescription() {
        return LocalizeValue.localizeTODO("My Language file");
    }

    @Nonnull
    @Override
    public String getDefaultExtension() {
        return "mylang";
    }

    @Nonnull
    @Override
    public Image getIcon() {
        return MyLanguageIcons.FILE;
    }
}

File Type Detection by Content

For cases where a file type cannot be determined by extension alone, implement FileTypeDetector (consulo.virtualFileSystem.fileType.FileTypeDetector), annotated with @ExtensionAPI(ComponentScope.APPLICATION):

Method	Description
detect(VirtualFile file, ByteSequence firstBytes, CharSequence firstCharsIfText)	Detects file type by content. firstBytes contains the initial bytes of the file. firstCharsIfText contains the text conversion if the content is text, or null otherwise. Returns the detected FileType or null.
getDetectedFileTypes()	Returns the collection of file types this detector can detect, or null if it can detect multiple types.
getDesiredContentPrefixLength()	Returns the number of leading bytes needed for reliable detection. Defaults to 1024.
getVersion()	Returns the detector version. Increment when detection logic changes.

Another approach is to implement FileTypeIdentifiableByVirtualFile (consulo.virtualFileSystem.fileType.FileTypeIdentifiableByVirtualFile) in your FileType implementation. This interface adds a single method isMyFileType(VirtualFile file) that allows determining the file type based on the virtual file itself (e.g., by examining the file path or name patterns).

Verification

To verify that the file type is registered correctly, implement the getIcon() method in your LanguageFileType subclass and verify that the correct icon (see Working with Icons and Images) is displayed for files associated with your file type.

Examples:

• Custom Language Support Tutorial: Language and File Type