Help find and troubleshoot pprof installation

[wlandau]

Summary

To address #13 and #14, this PR exports 3 functions:

• pprof_path(): return the path to pprof if it exists and "" otherwise.
• assert_pprof(): error if pprof is not found.
• test_pprof(): tests the pprof() function on a small example to make sure the pprof installation is usable.

By default, each function prints console messages whenever it struggles to find pprof. Set verbose = FALSE to turn these messages off.

Related GitHub issues and pull requests

• Ref: Verify system dependencies #13, Use existing pprof installation? #14

Checklist

• I understand and agree to proffer's code of conduct.
• I have listed any substantial changes in the development news.
• I have added testthat unit tests to tests/testthat for any new functionality. Feel free to use skip("interactive only") for any tests that cannot be fully automated.
• This pull request is not a draft.

[wlandau]

pprof_path() still does not work on Windows. I need to investigate when I get back to a Windows machine.

[codecov-io]

Codecov Report

Merging #15 into master will decrease coverage by 3.89%.
The diff coverage is 47.72%.

@@            Coverage Diff            @@
##           master      #15     +/-   ##
=========================================
- Coverage   46.42%   42.52%   -3.9%     
=========================================
  Files           3        4      +1     
  Lines          56       87     +31     
=========================================
+ Hits           26       37     +11     
- Misses         30       50     +20

Impacted Files	Coverage Δ
R/pprof.R	0% <0%> (-25%)	⬇️
R/utils.R	100% <100%> (ø)	⬆️
R/troubleshoot.R	45.94% <45.94%> (ø)

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[wlandau]

As of f76bde5, proffer searches for pprof on Windows too (if pprof_path is not set). So I think this PR completely solves #14. Maybe #13 as well, unless we want an all-in-one check for future system dependencies we may add in addition to pprof.

[wlandau]

@krlmlr, what do you think about these new functions for proffer?

[krlmlr]

Thanks.

We can simplify the Windows installation a bit if we look at default locations for the executables if they're not on the $PATH. This seems possible for Go and doesn't look too difficult for Graphviz. Also, we could provide an installation helper that installs {RProtoBuf} and directs the user to installers for Windows, or tells which packages to install on Linux and macOS.

I'll take a stab.