Ignore the PATH fix if it is not set

[jneira]

• If it is not set the fix makes no sense
• Fixes stack ./install.hs stack-install-cabal failed #1436

[fendor]

Maybe adding a log message may be interesting.

[fendor]

In #1436 (comment) it is said that the path is set. Maybe dont merge this until it is clear why this issue arises?

[samuelpilz]

Is catching an exception the best way to detect if the environment variable is set? This seems a bit hacky to me, but I have no experience with the System.Environment module

[jneira]

In #1436 (comment) it is said that the path is set. Maybe dont merge this until it is clear why this issue arises?

Sure, but i think the actual code does what i expected in the first place (return Nothing if the var is not informed)

Is catching an exception the best way to detect if the environment variable is set? This seems a bit hacky to me, but I have no experience with the System.Environment module

It was a surprise to me that lookupEnv throws an Exception instead return Nothing if the variable is not set (why return Maybe String then?)

The docs for lookupEnv states:

For POSIX users, this is equivalent to getEnv.

...and getenv trhows an IOException if the variable is not set 🤦‍♂

[fendor]

...and getenv trhows an IOException if the variable is not set 🤦‍♂

then the patch makes sense. Maybe we should only catch exceptions that satisfy the predicate isDoesNotExistError? Otherwise, this PR is good to go.

[fendor]

@jneira Merge when you are ready!

[fendor]

That looks great! Thank you!