node-gyp build on Windows always rebuilds the final binary even if no files were changed

[DuBistKomisch]

Cloned bufferutil, ran npm install and node-gyp rebuild, then running node-gyp build:

PS C:\Users\jake\src\bufferutil> node-gyp build
gyp info it worked if it ends with ok
gyp info using node-gyp@3.5.0
gyp info using node@4.2.6 | win32 | ia32
gyp info spawn C:\Program Files (x86)\MSBuild\14.0\bin\msbuild.exe
gyp info spawn args [ 'build/binding.sln',
gyp info spawn args   '/clp:Verbosity=minimal',
gyp info spawn args   '/nologo',
gyp info spawn args   '/p:Configuration=Release;Platform=Win32' ]
Building the projects in this solution one at a time. To enable parallel build, please add the "/m" switch.
     Creating library C:\Users\jake\src\bufferutil\build\Release\bufferutil.lib and object C:\Users\jake\src\bufferutil\build\Release\bufferutil.exp
  Generating code
  Finished generating code
  bufferutil.vcxproj -> C:\Users\jake\src\bufferutil\build\Release\\bufferutil.node
  bufferutil.vcxproj -> C:\Users\jake\src\bufferutil\build\Release\bufferutil.pdb (Full PDB)
gyp info ok

No source files were modified, but it still rebuilds the binaries. On Linux and Mac this would be a no-op as it recognises nothing has changed.

Is this a limitation of gyp itself? Surely msbuild is capable of this. Is there some setting I can put in binding.gyp to override this?

This is an issue because it slows down build scripts with unnecessary rebuilds. We have a fairly big native addon so it adds about 20 seconds.

[joaocgreis]

Notice that bufferutil.cc and win_delay_load_hook.cc don't get rebuilt into object files (they would appear above Creating library ...), only linking is done every time.

I noticed that this doesn't happen when nodedir is a full node source tree, only when it's downloaded by node-gyp and investigated a bit. Turns out that node-gyp is somehow updating the lastwritetime of node.lib before running MSBuild, forcing the linker to run. This looks like something that can be improved.

[DuBistKomisch]

Yeah luckily, build time would be several minutes if it rebuilt all the object files!

Had a look and you're right, write time on the node.lib gets updated each time I do a build, weird. Could it be being copied internally each time? I'll have a poke around.

[DuBistKomisch]

Yeah there's some 5 year old copyNodeLib function in lib/build.js which copies the node.lib for the right architecture before each build. I'll put together a PR with a check that the right file is already there.

[bnoordhuis]

There is an open pull request about that: #951

[DuBistKomisch]

Tried it with npm install -g https://github.com/pmed/node-gyp#target-arch-windows (from #964) and it seems to fix the problem. I look forward to either of them landing I guess.

[bnoordhuis]

@joaocgreis Perhaps you can test/review #951 or #964? I think my preference is for the latter.

[joaocgreis]

Fixed by c307b30...386746c (#964)