Bug #16651: Extensions Do Not Compile on Mingw64

• Status: Open
• Priority: Normal
• Assignee: -
• Target version: -
• ruby -v: ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x64-mingw32]
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN

[cfis (Charlie Savage)]

When mkmf.rb creates a Makefile for an extension, it will generate something that looks like this:

srcdir = .
topdir = C/MSYS64/USR/LOCAL/ruby-2.7.0/include/ruby-2.7.0
hdrdir = $(topdir)
arch_hdrdir = C:/MSYS64/USR/LOCAL/ruby-2.7.0/include/ruby-2.7.0/x64-mingw32

Notice the topdir path is c/ without the ":" Its only the topdir that does this, all other paths in the makefile use the "c:/" style.

mkmf.rb intentionally does that, see line 1098:

  def mkintpath(path)
    # mingw uses make from msys and it needs special care
    # converts from C:\some\path to /C/some/path
    path = path.dup
    path.tr!('\\', '/')
    path.sub!(/\A([A-Za-z]):(?=\/)/, '/\1') <-------- This line
    path
  end

But this is wrong, and causes errors like this (this is compiling the debase gem but it doesn't matter what c extension you use):

make: *** No rule to make target 'C/MSYS64/USR/LOCAL/ruby-2.7.0/include/ruby-2.7.0/ruby.h', needed by 'breakpoint.o'. Stop.

The fix is simple, just delete that line. The makefile should look like this:

srcdir = .
topdir = C:/MSYS64/USR/LOCAL/ruby-2.7.0/include/ruby-2.7.0
hdrdir = $(topdir)
arch_hdrdir = C:/MSYS64/USR/LOCAL/ruby-2.7.0/include/ruby-2.7.0/x64-mingw32

Note I'm not the first person to see this, but I've just been manually fixing it over the years. Would be good to really fix it.

https://github.com/oneclick/rubyinstaller2/issues/105
https://github.com/oneclick/rubyinstaller2/issues/47
https://github.com/tmm1/http_parser.rb/issues/55

Note some of those tickets put the blame on using mingw-make versus msys make. But on my system, neither work with the "c/" style path but both work with the "c:/" style path.