lib: deep-copy process.config during configure

[DeeDeeG]

Checklist

• npm install && npm test passes
• tests are included
• documentation is changed or added
• commit message follows commit guidelines

Description of change

In lib/configure.js, when creating the local config object as a copy of process.config, use JSON.parse(JSON.stringify(process.config) rather than Object.assign({}, process.config).

Makes it so we won't modify properties of child objects of the original process.config. (Modifying process.config or its children is deprecated as of Node 16.)

Background

Testing with the latest Node v16 nightly build revealed that the deprecation warning from nodejs/node#36902 was still showing with the latest node-gyp v8.0.0 during the config or rebuild commands.

// ...
gyp info find Python using Python version 3.9.0 found at "/usr/local/bin/python3"
(node:21174) [DEP0150] DeprecationWarning: Setting process.config is deprecated. In the future the property will be read-only.
(Use `node --trace-deprecation ...` to show where the warning was created)
gyp info spawn /usr/local/bin/python3
// ...

With the --trace-deprecation flag:

// ...
gyp info find Python using Python version 3.9.0 found at "/usr/local/bin/python3"
(node:21184) [DEP0150] DeprecationWarning: Setting process.config is deprecated. In the future the property will be read-only.
    at Object.maybeWarn (node:internal/bootstrap/node:79:15)
    at Object.set (node:internal/bootstrap/node:103:10)
    at createConfigFile (/Users/[user]/node-gyp/lib/configure.js:117:21)
    at /Users/[user]/node-gyp/lib/configure.js:84:9
    at FSReqCallback.oncomplete (node:fs:183:23)
gyp info spawn /usr/local/bin/python3
// ...

In Node v16, the process.config object has a proxy function which warns once if it, or any of its properties, or any of its child objects' properties, are modified. And it turns out that Object.assign() does not deep copy any nested objects of the object you assign from. Nested objects are copied by reference rather than by value. So by modifying (for example) our local config.defaults.cflags array, we are also modifying process.config.target_defaults.cflags.

See the discussion at the bottom of #2322 for more details.

[DeeDeeG]

Hi again, thanks for merging.

I just wanted to mention: Apparently JSON.stringify can error out if you ask it to stringify an object with a BigInt or a circular reference in it.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#exceptions

I don't think people should be putting either of those things in their process.config object. And altering process.config is of course deprecated as of Node 16, but it is still possible to do.

So, for dealing with this unlikely/bizarre case, we could consider handling the error somehow or using a purpose-built library for deep-copying objects. I don't really think that's worth it, but I thought I would raise the issue. (I forgot to mention it earlier.)