Syntax error in cjs code for netlify-adapter can break deploys

[goynang]

There is an error in the CJS code generated for netlify-adapter where line 6 of .netlify/handler.js ends up as...

var ./server/app.js = require('./server/app.js');

...which is a syntax error and leads to bad deploy unless you force esbuild to be used instead. The CJS version of handler.js (before code replacements take place) looks like...

var APP = require('APP');

...whereas the ESM version looks like...

import { App } from 'APP';

The code substitution is based on replacing APP with ./server/app.js (lines 53-55 of adapter-netlify/index.js) so mistakenly replaces both uses within the require statement (the variable and the path).

It looks like rollup is altering the import from App to APP when it changes it to a require statement for CJS.

In addition it looks like the adapter is hardcoded to build CJS functions targeted for node 12...

const output = esbuild.transformSync(input, { format: 'cjs', target: 'node12' }).code;

...rather than something newer or respecting netlify.toml

Originally posted by @goynang in #2687 (comment)