ESM / CJS syntax detection

[pi0]

Provide utilities to use regex based static analyzes detecting if potentially ESM or CommonJS syntax is used in a code

• hasESMSyntax(code: string, id?: string) (note: dynamic import is not esm syntax`
• hasCJSSyntax(code: string, id?: string)
• detectSyntax(code: string, id?: string): esm | cjs | mixed | unknown

Some reference: https://github.com/unjs/jiti/blob/main/src/utils.ts#L27

[danielroe]

For interest, there is also this more rigorous method that uses acorn to detect syntax.

[pi0]

Indeed AST parsing is most reliable but costs performance impact that we can not simply use it for DX purpose anymore in many places. These utilities are mainly needed to have a quick guess on file format and inline to use vite or rollup's AST parser and transforms.

For reference rollup commonjs plugin is also regex based for first phase https://github.com/rollup/plugins/blob/master/packages/commonjs/src/parse.js