cli: detect installing from postinstall hook

[bahmutov]

• Closes Make caching Cypress binary in node_modules easier #2634

User facing changelog

"Normalizes" installation when running with custom relative Cypress cache folder. For example if you want to install Cypress and cache it in the current folder, rather than in ~/.cache

export CYPRESS_CACHE_FOLDER=cache/Cypress
npm i cypress
npx cypress run

Additional details

Before this change, during npm i cypress, the installation was executed in ./node_modules/cypress folder, which is a normal NPM behavior in postinstall hook. But this of course is very surprising to the user who expected the relative path CYPRESS_CACHE_FOLDER=cache/Cypress to resolve in the current folder, and not with respect to node_modules/cypress.

How has the user experience changed?

PR Tasks

• Have tests been added/updated?

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PR Review Checklist

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User Experience

• The feature/bugfix is self-documenting from within the product.
• The change provides the end user with a way to fix their problem (no dead ends).

Functionality

• The code works and performs its intended function with the correct logic.
• Performance has been factored in (for example, the code cleans up after itself to not cause memory leaks).
• The code guards against edge cases and invalid input and has tests to cover it.

Maintainability

• The code is readable (too many nested 'if's are a bad sign).
• Names used for variables, methods, etc, clearly describe their function.
• The code is easy to understood and there are relevant comments explaining.
• New algorithms are documented in the code with link(s) to external docs (flowcharts, w3c, chrome, firefox).
• There are comments containing link(s) to the addressed issue (in tests and code).

Quality

• The change does not reimplement code.
• There's not a module from the ecosystem that should be used instead.
• There is no redundant or duplicate code.
• There are no irrelevant comments left in the code.
• Tests are testing the code’s intended functionality in the best way possible.

Internal

• The original issue has been tagged with a release in ZenHub.

[andrew-codes]

Looks good and there appears to be test coverage for both the absolute path and a relative path test case for CYPRESS_CACHE_FOLDER.

[jennifer-shehane]

Is this a breaking change? Will this break peoples current installs that have already accommodated to the current behavior?

[kuceb]

@jennifer-shehane I would say its a patch fix. If the breaking change was clearly a bug it's fair for the version not to be breaking

[bahmutov]

yeah @jennifer-shehane people who did CYPRESS_CACHE_FOLDER=../../cache/Cypress (which I honestly think is very rare) would need to remove dots and "simply" use CYPRESS_CACHE_FOLDER=cache/Cypress for all actions