Improve UX experience when packages are not installed via projen

Documentation for lots of NPM packages often include instructions for how to install the package, say by running npm i -D my-fancy-package. Installing stuff this way is the norm for most people. But if you’re new to projen (e.g. you’re contributing to an existing repo and maybe didn’t realize it had projen or what projen did), you might run the command without realizing that doing that will not register the dependency with projen.

To improve the UX, I think it could be useful if projen automatically detects when a dependency got added to package.json when it wasn’t expected. Maybe it could give a warning, suggesting that you should add the package(s) to .projenrc.js instead.

(For a lot of other config files, I believe this issue doesn’t apply because they are set as readonly, so it’s clear when you shouldn’t edit a file - but package.json must be editable for technical reasons IIRC).

In terms of implementation, I think this could be calculated during the synthesis process, when you run npx projen, by running a check against the internal .projen/deps.json file.

I haven’t given a ton of thought on whether this could have implications / cause conflicts in other user development flows, but I figured I’d drop the idea here anyways. Any kind of warning could get very annoying if it has false positives / shows up unnecessarily.

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Also independently of this, could it be useful to have a page in the docs for projen newbies that lists out common development tasks and how you might do them differently if you’re working on a projen-based javascript project vs a traditional javascript project? ex.

Operation	In a traditional project…	In a projen project…
Installing dependencies	In the command line, run npm install package-name or npm install --save-dev package-name.	In .projenrc.js, add project.addDeps('package-name') or project.addDevDeps('package-name')
Exclude a file from git tracking	Edit .gitignore to add file, directory, or other pattern.	In projenrc.js, add project.gitignore.exclude('file-to-ignore')
…etc.	…etc.	…etc.

[brianfoody]

A more intuitive experience for me would be to add an npx projen install command so that I can stay in my happy land of installing through command line. Manually adding of deps is the only thing I don’t really like so far.

[github-actions[bot]]

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