Allow for dry run

[lorenzwalthert]

Closes #633 and implements an API change.

New argument dry in style_file() and friends to control write back and failing in case of modification. The argument takes these values:

• off (default): Current behavior. Write back to file as side effect. Return tibble with summary invisible (as now).
• on: Never modify files, also return tibble summary as if things were written back.
• fail: Same as on, but fail fast with error if modification would occur on write-back.

Any feedback on the design welcome, I am not so sure this is optimal. @krlmlr since this is an API change, I'd like to have your opinion on that if possible.

[codecov-io]

Codecov Report

Merging #634 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #634   +/-   ##
=======================================
  Coverage   90.64%   90.65%           
=======================================
  Files          47       47           
  Lines        2171     2173    +2     
=======================================
+ Hits         1968     1970    +2     
  Misses        203      203           

Impacted Files	Coverage Δ
R/ui-styling.R	100.00% <ø> (ø)
R/io.R	87.75% <100.00%> (+0.52%)	⬆️

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[lorenzwalthert]

@select-id-from-users you can try this if you want. Will merge into master later.

[select-id-from-users]

@lorenzwalthert Works like a charm, thank you very much!

tux:/tmp/renv$ Rscript -e 'styler::style_file("test.R", dry="fail")'
Styling  1  files:
 test.R Error: File `test.R` would be modified by styler and `dry` = 'fail'.
Backtrace:
     █
  1. └─styler::style_file("test.R", dry = "fail")
  2.   └─styler:::transform_files(...)
  3.     └─purrr::map_lgl(...)
  4.       └─styler:::.f(.x[[i]], ...)
  5.         └─styler:::transform_code(path, fun = fun, ..., dry = dry)
  6.           └─styler:::transform_utf8(path, fun = fun, ..., dry = dry)
  7.             ├─map_lgl(path, transform_utf8_one, fun = fun, dry = dry) %>% set_names(path)
  8.             │ └─base::eval(lhs, parent, parent)
  9.             │   └─base::eval(lhs, parent, parent)
 10.             └─purrr::map_lgl(path, transform_utf8_one, fun = fun, dry = dry)
 11.               └─styler:::.f(.x[[i]], ...)
 12.                 └─rlang::with_handlers(...)
 13.                   └─bas
Execution halted
tux:/tmp/renv$ echo $?
1
tux:/tmp/renv$ Rscript -e 'styler::style_file("test.R", dry="off")'
Styling  1  files:
 test.R ℹ 
────────────────────────────────────────
Status	Count	Legend 
✔ 	0	File unchanged.
ℹ 	1	File changed.
✖ 	0	Styling threw an error.
────────────────────────────────────────
Please review the changes carefully!
tux:/tmp/renv$ Rscript -e 'styler::style_file("test.R", dry="fail")'
Styling  1  files:
 test.R ✔ 
────────────────────────────────────────
Status	Count	Legend 
✔ 	1	File unchanged.
ℹ 	0	File changed.
✖ 	0	Styling threw an error.
────────────────────────────────────────
tux:/tmp/renv$ echo $?
0

[lorenzwalthert]

Error: File test.R would be modified by styler and dry = 'fail'.

Maybe we can come up with a better error:

Error: File `test.R` would be modified by styler and argument `dry` is set to 'fail'.

Also, do you find on, off and dry self-explanatory?

[select-id-from-users]

I guess since the error is thrown only when dry="fail" you don't have to mention that dry is set to 'fail'? I have no strong opinion here, and would be happy either way.

I find the options self-explanatory yes. Maybe "on" could be "warn"? Although warnings can also result in non-zero exit code when you run devtools::check(error_on="note"). Also here I don't have strong opinion. Naming things is hard.