[ruby-core:103365] [Ruby master Bug#16651] Extensions Do Not Compile on Mingw64 with mingw64-make

[nobu@ruby-lang.org]

Issue #16651 has been updated by nobu (Nobuyoshi Nakada).


Building io-console with 2.7.2 from RubyInstaller:
```
$ ruby -v ../src/ext/io/console/extconf.rb
ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x64-mingw32]
checking for HAVE_RUBY_FIBER_SCHEDULER_H... no
checking for rb_scheduler_timeout()... no
creating Makefile

$ grep -e ^topdir -e ^arch_hdrdir Makefile
topdir = /C/Ruby27-x64/include/ruby-2.7.0
arch_hdrdir = C:/Ruby27-x64/include/ruby-2.7.0/x64-mingw32

$ make
compiling ../src/ext/io/console/console.c
linking shared-object io/console.so
```
It succeeds with no problem.

`/C/` is not wrong in msys make, I'm not sure why the first description had the wrong path without the leading slash.

----------------------------------------
Bug #16651: Extensions Do Not Compile on Mingw64 with mingw64-make
https://bugs.ruby-lang.org/issues/16651#change-91456

* 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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