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SyntaxHighlightedTextEditor

Experimental API

This composable is annotated with @ExperimentalHighlightApi. The API surface may change without a deprecation cycle.

SyntaxHighlightedTextEditor is an editable code field (built on BasicTextField) with live syntax highlighting. As users type, highlighting updates after a short debounce while preserving cursor and selection.

Full API in Dokka:

When to use it

  • You want an editable code field with built-in async highlighting.
  • You want a ready-made Surface plus BasicTextField wrapper.
  • You want to keep editor state (TextFieldValue) while highlighting updates in background.

Key parameters

  • value and onValueChange - editor state and updates.
  • language - highlight.js language id.
  • theme - explicit theme or value from HighlightThemeProvider.
  • debounceMs - typing pause before highlight call.
  • contentPadding and shape - layout and clipping of editor surface.
  • horizontalScrollState and verticalScrollState - hoisted scroll states for external control or observation of editor scroll position.
  • keyboardOptions - keyboard / IME behavior. Defaults to SyntaxHighlightedTextEditorDefaults.CodeKeyboardOptions (autocorrect off, autocapitalization off, Ascii keyboard) - the right defaults for source code. Override via .copy(imeAction = ...) to keep the code-friendly settings while customising one field.
  • cursorBrush - text cursor color. Defaults to null, which derives the cursor from the theme's text color so it stays visible on both light and dark themes. Pass an explicit Brush (e.g. SolidColor(MaterialTheme.colorScheme.primary)) to override.
  • onHighlightComplete and onError - observability hooks. onHighlightComplete receives a HighlightResult (timing, span count, language); see the API docs.
  • indentation - indentation string to insert when the Tab key is pressed. Defaults to 4 spaces (" ").
  • autoIndentEnabled - whether to automatically copy the leading indentation of the previous line when inserting a newline. Defaults to true.
  • tabKeyInterceptionEnabled - whether to intercept the hardware Tab key to insert spaces instead of shifting focus to the next view. Defaults to true. Note that arrow keys (Up, Down, Left, Right) are also intercepted to prevent focus from escaping the editor when boundaries are reached.

For anything else BasicTextField exposes (enabled, readOnly, singleLine, maxLines, decorationBox, etc.) drop one level down to rememberSyntaxHighlightedEditorValue and render your own field - the editor is intentionally opinionated.

Opting in

// Option 1 - opt in at the call site
@OptIn(ExperimentalHighlightApi::class)
@Composable
fun MyScreen() {
    SyntaxHighlightedTextEditor(...)
}

// Option 2 - propagate to your own API
@ExperimentalHighlightApi
@Composable
fun MyEditorScreen() {
    SyntaxHighlightedTextEditor(...)
}

// Option 3 - file-wide opt-in (before package statement)
@file:OptIn(ExperimentalHighlightApi::class)

import dev.hossain.highlight.ui.ExperimentalHighlightApi
import dev.hossain.highlight.ui.HighlightThemeProvider
import dev.hossain.highlight.ui.SyntaxHighlightedTextEditor
import dev.hossain.highlight.ui.rememberTomorrowNightTheme
import dev.hossain.highlight.ui.rememberTomorrowTheme

@OptIn(ExperimentalHighlightApi::class)
@Composable
fun EditorScreen() {
    var editorValue by remember { mutableStateOf(TextFieldValue("fun hello() = println(\"Hello!\")")) }

    HighlightThemeProvider(
        lightHighlightTheme = rememberTomorrowTheme(),
        darkHighlightTheme  = rememberTomorrowNightTheme(),
    ) {
        SyntaxHighlightedTextEditor(
            value          = editorValue,
            onValueChange  = { editorValue = it },
            language       = "kotlin",
            modifier       = Modifier
                .fillMaxWidth()
                .border(1.dp, MaterialTheme.colorScheme.outline, RoundedCornerShape(8.dp)),
            shape          = RoundedCornerShape(8.dp),
            contentPadding = PaddingValues(12.dp),
        )
    }
}

With an explicit theme (no provider)

@OptIn(ExperimentalHighlightApi::class)
@Composable
fun SqlEditor() {
    var editorValue by remember { mutableStateOf(TextFieldValue("SELECT * FROM users")) }

    SyntaxHighlightedTextEditor(
        value         = editorValue,
        onValueChange = { editorValue = it },
        language      = "sql",
        theme         = rememberTomorrowTheme(),
    )
}

Customize the editor text style

SyntaxHighlightedTextEditorDefaults.DefaultTextStyle is the pre-allocated singleton the editor uses by default (monospace family). Build on top of it with .copy(...) to override only what you need - using the singleton avoids allocating a fresh TextStyle on every recomposition while typing.

import dev.hossain.highlight.ui.SyntaxHighlightedTextEditorDefaults

@OptIn(ExperimentalHighlightApi::class)
@Composable
fun LargerEditor() {
    var editorValue by remember { mutableStateOf(TextFieldValue("")) }
    // Wrap in remember so typing recompositions don't allocate a fresh TextStyle
    // every frame. Add keys (e.g. remember(fontSize) { ... }) when the derived
    // style depends on changing inputs.
    val editorStyle = remember {
        SyntaxHighlightedTextEditorDefaults.DefaultTextStyle.copy(fontSize = 15.sp)
    }

    SyntaxHighlightedTextEditor(
        value         = editorValue,
        onValueChange = { editorValue = it },
        language      = "kotlin",
        textStyle     = editorStyle,
    )
}

How the highlight pipeline behaves

SyntaxHighlightedTextEditor delegates pipeline logic to rememberSyntaxHighlightedEditorValue() and renders the returned value in a Surface plus BasicTextField wrapper.

Core behavior:

  1. A debounce window waits debounceMs after typing stops, then calls HighlightEngine.highlight().
  2. Rapid keystrokes cancel prior coroutine work, so only the latest text is highlighted.
  3. Stale snapshot checks keep language and theme changes safe.
  4. While new results are in flight, previously computed spans are reused where valid, so only the actively edited region is briefly unstyled.

Common pitfalls

  • Use contentPadding for inner spacing; .padding() on modifier changes outer layout instead.
  • Keep shape aligned with any border shape to avoid background bleed at rounded corners.
  • Outside HighlightThemeProvider, a standalone engine/WebView is created and managed by lifecycle.

Why aren't enabled, readOnly, singleLine, etc. exposed?

SyntaxHighlightedTextEditor is a deliberate convenience composable: it ships code-friendly defaults (keyboardOptions, cursorBrush, monospace textStyle, debounce window, theme-aware surface) and exposes only the parameters needed to tune them. It is not a parameterized clone of BasicTextField.

For any other BasicTextField parameter you might want - enabled, readOnly, singleLine, maxLines, minLines, keyboardActions, visualTransformation, onTextLayout, interactionSource, decorationBox - drop one level down to rememberSyntaxHighlightedEditorValue and render your own field. The helper returns a TextFieldValue with highlighting applied and cursor / selection preserved; you compose it into whatever field shape you need.

This split keeps the convenience composable's surface small (and stable - it doesn't grow as Compose Foundation adds new BasicTextField parameters) while still giving you full control when you need it.

Lower-level helper for custom text fields

Use rememberSyntaxHighlightedEditorValue() when you want your own field component (OutlinedTextField, third-party editor, etc.) and only need highlighted TextFieldValue output.

@OptIn(ExperimentalHighlightApi::class)
@Composable
fun MyCustomEditor() {
    var editorValue by remember { mutableStateOf(TextFieldValue("")) }
    val displayValue = rememberSyntaxHighlightedEditorValue(
        value    = editorValue,
        language = "kotlin",
    )

    OutlinedTextField(
        value         = displayValue,
        onValueChange = { editorValue = it },
        label         = { Text("Code") },
    )
}