[ruby-core:103359] [Ruby master Bug#16651] Extensions Do Not Compile on Mingw64 with mingw64-make

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


I suppose it is by luck that `arch_hdrdir` of the form `C:/foo/bar` is not causing problems with `make` from MSYS. In fact, in my environment (not Windows) `gem install rails && rails new foo` succeeds when `VPATH` is modified such that it does not contain `$(arch_hdrdir)/ruby`, or not even `$(hdrdir)/ruby`. I wonder if any extension in the world requires these paths contained in `VPATH`.

The proposed modification might be OK for `make` from MSYS if the definition of `VPATH` can be modified so that it never contains any drive letters. Note that some extensions (e.g. [sassc](https://github.com/sass/sassc-ruby)) add additional paths to `VPATH`. And assuming that the modification is applied, I doubt if `mingw32-make` will successfully build an extension which really depends on `VPATH` containing multiple paths.

user:cfis Could you please try to `gem install sassc` with `mingw32-make`? If it really does not work with multiple paths in `VPATH`, then it should fail to build that extension. Unfortunately I do not have access to Windows machines connected to the Internet.

----------------------------------------
Bug #16651: Extensions Do Not Compile on Mingw64 with mingw64-make
https://bugs.ruby-lang.org/issues/16651#change-91450

* 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:

```makefile
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:

```ruby
      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:

```makefile
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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