gatsbyjs/gatsby · error

${cFlag} is not part of the available compiler flags.

Error message

${cFlag} is not part of the available compiler flags.

What it means

Thrown by the Identifier visitor of `babel-transform-compiler-flags` (babel-transform-compiler-flags.js:59). When source code references `_CFLAGS_.<cFlag>`, the plugin checks `availableFlags.includes(cFlag)`; if the accessed flag name is not on the whitelist, the build aborts to prevent silently replacing it with an empty string.

Source

Thrown at packages/babel-preset-gatsby-package/lib/babel-transform-compiler-flags.js:59

       * @param {PluginPass} state
       */
      Identifier(
        nodePath,
        state
      ) {
        const identifier = /** @type {Identifier} */ (nodePath.node)
        const flags = /** @type {IPluginOptions} */ (state.opts).flags
        const availableFlags = /** @type {IPluginOptions} */ (state.opts).availableFlags

        if (
          identifier.name === `_CFLAGS_` &&
          t.isMemberExpression(nodePath.parent)
        ) {
          const parentNode = /** @type {MemberExpression} */ (nodePath.parent)
          const cFlag = /** @type {Identifier} */ (parentNode.property).name

          if (!availableFlags.includes(cFlag)) {
            throw new Error(
              `${cFlag} is not part of the available compiler flags.`
            )
          }

          nodePath.parentPath.replaceWith(
            t.stringLiteral(flags[cFlag] ? flags[cFlag] : ``)
          )
        }
      },
    },
  }
}

View on GitHub (pinned to 8b06340921)

Solutions

1. Add the missing flag name to the `availableFlags` array in the plugin/preset options.
2. Check for typos: the name after `_CFLAGS_.` must exactly match an entry in `availableFlags`.
3. Remove the `_CFLAGS_.<flag>` reference if the flag is no longer used.

Example fix

// before
// source: if (_CFLAGS_.ENABLE_X) { ... }
// config: availableFlags: ['PRESERVE_FILE_DOWNLOADS']

// after
// config:
availableFlags: ['PRESERVE_FILE_DOWNLOADS', 'ENABLE_X']

function allCflagRefsAreListed(sourceFiles, availableFlags) {
  const used = new Set()
  for (const src of sourceFiles) {
    for (const m of src.matchAll(/_CFLAGS_\.([A-Za-z0-9_]+)/g)) used.add(m[1])
  }
  return [...used].filter(f => !availableFlags.includes(f))
}

function isKnownFlag(flagName, availableFlags) {
  return Array.isArray(availableFlags) && availableFlags.includes(flagName)
}

When it happens

Trigger: Source code contains `_CFLAGS_.NEW_THING` but `NEW_THING` is not listed in `availableFlags`; renaming a flag in code but not in the build config; copy-pasting code that references a flag the build does not know about.

Common situations: Adding a new compiler flag to source without updating the preset's `availableFlags` list; using a flag only defined in a different build configuration; typos in the flag name on either side.

Related errors

• flags option needs to be set
• availableFlags option needs to be set
• keepDynamicImports option needs to be set
• BabelPluginRemoveGraphQLQueries: String interpolations are n
• BabelPluginRemoveGraphQLQueries: Unexpected empty graphql ta

AI-assisted analysis of gatsbyjs/gatsby@8b06340921 (2026-08-13). Data as JSON: /api/errors/ceadd585c23c99a8. Report an issue: GitHub.