gatsbyjs/gatsby · error

unable to find prism language '${diffLanguage}' for highligh

Error message

unable to find prism language '${diffLanguage}' for highlighting. applying generic code block

What it means

Prism fallback warning during code highlighting: the block's diff language (the language inside a diff fence) failed to load via loadPrismLanguage. The diffLanguage is added to the unsupported set (warn once), then the code is escaped and rendered as a generic code block without diff or target-language highlighting.

Source

Thrown at packages/gatsby-remark-prismjs/src/highlight-code.js:55

      const lang = language.toLowerCase()
      if (!unsupportedLanguages.has(lang)) {
        console.warn(message, `applying generic code block`)
        unsupportedLanguages.add(lang)
      }
      return escapeHTML(code, additionalEscapeCharacters)
    }
  }

  // (Try to) load diffLanguage on demand.
  if (diffLanguage && !Prism.languages[diffLanguage]) {
    try {
      loadPrismLanguage(diffLanguage)
    } catch (e) {
      const message = `unable to find prism language '${diffLanguage}' for highlighting.`

      const lang = diffLanguage.toLowerCase()
      if (!unsupportedLanguages.has(lang)) {
        console.warn(message, `applying generic code block`)
        unsupportedLanguages.add(lang)
      }
      // Ignore diffLanguage when it does not exist.
      diffLanguage = null
    }
  }

  const grammar = Prism.languages[language]
  const highlighted = Prism.highlight(
    code,
    grammar,
    diffLanguage ? `${language}-${diffLanguage}` : language
  )
  const codeSplits = handleDirectives(highlighted, lineNumbersHighlight)

  let finalCode = ``
  const lastIdx = codeSplits.length - 1 // Don't add back the new line character after highlighted lines
  // as they need to be display: block and full-width.

View on GitHub (pinned to e85d62f177)

Solutions

1. Fix the diff language identifier or remove it from the fence info string

When it happens

Trigger: Thrown at packages/gatsby-remark-prismjs/src/highlight-code.js:55 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of gatsbyjs/gatsby@e85d62f177 (2026-08-26). Data as JSON: /api/errors/a5ec3ebd481f9289. Report an issue: GitHub.