Utilize fs.copyFileSync if available.

[stefanpenner]

• Currently would only be utilized on windows
• available in node 8.5.x
• prefer Copy-On-Write if available
• good benchmarks use fcopy for faster file copying yarnpkg/yarn#3290

Although node-copy-file-sync module exists, it uses more modern JS features. Which this library cannot yet support (without major version bump)

[fixes #34]

[stefanpenner]

@kanongil / @kellyselden / @lifeart et.al got any cycles to give this a try? See if this helps windows perf.

[kellyselden]

Sure. What would be the best way to test this other than running the test suite?

[stefanpenner]

@kellyselden

• on a current checkout
• run cold build and share the times
• run rebuild and share the times
• then update all copies of symlink-or-copy in your node_modules
• disable symlinks
• run cold build and share the times
• run rebuild and share the times

I'll also try to put together some benchmarks this week.

[lifeart]

@stefanpenner

no-symlink node 10 win 8.1

old first build 56337ms
old first build 47514ms
old first build 46859ms
old rebuild 15407ms
old rebuild 11573ms
old rebuild 11350ms

new first build  48338ms
new first build  51485ms
new first build  47898ms
new rebuild  12211ms
new rebuild  10830ms
new rebuild  11595ms


using-symlink node 10 win 8.1

old first build 37375ms
old first build 37517ms
old first build 36819ms
old rebuild 8208ms
old rebuild 8419ms
old rebuild 7828ms

new first build  36811ms
new first build  36631ms
new first build  36289ms
new rebuild  8514ms
new rebuild  8451ms
new rebuild  8617ms

[lifeart]

Master Branch

Tests failing without symlinks

Using symlinks - ok

FS-COPY-SYNC Branch

without symlinks

Using symlinks

[stefanpenner]

I'll have to re-test this on new versions of OSX, but when tested last time it was a wash or worse for smallish files.

It may be the case that we perform the operation based on curtain heuristics?