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HighlightLanguage

HighlightLanguage is a pure Kotlin helper that maps file extensions to highlight.js language identifiers.

It is a convenience API. SyntaxHighlightedCode and HighlightEngine.highlight() still accept a plain String language id, so you can always pass supported highlight.js names directly.

Full API in Dokka:

When to use it

  • You have filenames or file extensions and need a best-effort language id.
  • You want locale-safe, case-insensitive extension lookup.
  • You want a simple fallback to plaintext for unknown extensions.

Core behavior

  • fromExtension(extension) returns a highlight.js language id or null.
  • Lookup is case-insensitive and locale-safe (Locale.ROOT).
  • Pass extension without a leading dot.
HighlightLanguage.fromExtension("kt")   // "kotlin"
HighlightLanguage.fromExtension("KT")   // "kotlin"
HighlightLanguage.fromExtension("py")   // "python"
HighlightLanguage.fromExtension("xyz")  // null

val file = File("MainActivity.kt")
val language = HighlightLanguage.fromExtension(file.extension) ?: "plaintext"

SyntaxHighlightedCode(
    code     = file.readText(),
    language = language,
)

Practical guidance

  • Prefer mapping by extension only when language is not known from other metadata.
  • For user-selected languages, pass the chosen id directly.
  • For unknown or mixed content, consider HighlightEngine.highlightAuto() instead.

Common pitfalls

  • Passing extension with dot (".kt") instead of "kt".
  • Assuming the helper mirrors every upstream highlight.js alias at all times.
  • Forgetting a fallback path (?: "plaintext") for unknown extensions.