[ruby-core:103316] [Ruby master Bug#16651] Extensions Do Not Compile on Mingw64 with mingw64-make

Issue #16651 has been updated by xtkoba (Tee KOBAYASHI).


I suppose `arch_hdrdir` also should have been canonicalized by `mkintpath`, because otherwise it would cause trouble with `VPATH` in `Makefile` which is defined as:

```make
VPATH = $(srcdir):$(arch_hdrdir)/ruby:$(hdrdir)/ruby
```

And I believe that the notation of `VPATH` as above does not work well with `mingw32-make`, because [it allows only one path](http://mingw.5.n7.nabble.com/mingw32-make-VPATH-doesn-t-work-td6550.html).

It seems clear that `mingw32-make` is not supported in the current build system of Ruby. I doubt if the maintainers have tried to support it ever.

One way of supporting both `make` from MSYS and `mingw32-make` would be to stop using `VPATH`, although I have no idea whether this is possible. FYI, `VPATH` seems to cause another trouble (Bug #12179), and it would be desirable if we could throw it away.

----------------------------------------
Bug #16651: Extensions Do Not Compile on Mingw64 with mingw64-make
https://bugs.ruby-lang.org/issues/16651#change-91405

* Author: cfis (Charlie Savage)
* Status: Open
* Priority: Normal
* ruby -v: ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x64-mingw32]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
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.




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