ARROW-6323: [R] Expand file paths when passing to readers

[nealrichardson]

Note that there is no test in the test suite that asserts that ~ is expanded correctly because we can only write to tempfiles in the tests, but It Works on My Machine ™️ .

cc @romainfrancois

[nealrichardson]

Debugging the windows build failure, stand by

[codecov-io]

Codecov Report

Merging #5169 into master will decrease coverage by 12.41%.
The diff coverage is 83.33%.

@@ Coverage Diff @@## master #5169 +/- ##
===========================================
- Coverage 87.63% 75.22% -12.42% 
===========================================
Files 1022 57 -965 Lines 146258 3604 -142654 Branches 1437 0 -1437 ===========================================
- Hits 128174 2711 -125463 + Misses 17722 893 -16829 + Partials 362 0 -362

Impacted Files	Coverage Δ
r/R/feather.R	63.41% <ø> (-1.71%)	⬇️
r/R/csv.R	97.22% <ø> (-0.15%)	⬇️
r/R/RecordBatchWriter.R	72.22% <ø> (+2.22%)	⬆️
r/R/json.R	90% <ø> (-1.31%)	⬇️
r/R/read_table.R	100% <ø> (ø)	⬆️
r/R/write_arrow.R	96.42% <ø> (-0.13%)	⬇️
r/R/compression.R	90.9% <ø> (-1.4%)	⬇️
r/R/RecordBatchReader.R	70.58% <ø> (-1.64%)	⬇️
r/R/parquet.R	73.07% <100%> (ø)	⬆️
r/R/io.R	74.28% <75%> (ø)	⬆️
... and 965 more

---

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[fsaintjacques]

Is it expected from R libraries to expand path? If so, I have no objection to merge this.

[nealrichardson]

Yes:

> write.csv(iris, file="~/Downloads/iris.csv")
> read.csv("~/Downloads/iris.csv")
XSepal.LengthSepal.WidthPetal.LengthPetal.WidthSpecies115.13.51.40.2setosa224.93.01.40.2setosa334.73.21.30.2setosa444.63.11.50.2setosa555.03.61.40.2setosa665.43.91.70.4setosa...

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 75.22%. Comparing base (3c9236d) to head (635d954).

Files with missing lines	Patch %	Lines
r/R/io.R	75.00%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (3c9236d) and HEAD (635d954). Click for more details.

HEAD has 5 uploads less than BASE

Flag	BASE (3c9236d)	HEAD (635d954)
	6	1

Additional details and impacted files

@@ Coverage Diff @@## master #5169 +/- ##
===========================================
- Coverage 87.63% 75.22% -12.42% 
===========================================
Files 1022 57 -965 Lines 146258 3604 -142654 Branches 1437 0 -1437 ===========================================
- Hits 128174 2711 -125463 + Misses 17722 893 -16829 + Partials 362 0 -362 

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