README.md confusing sentence in msys2 for Windows

[barik]

The last sentence says:

# or CMake installed and in PATH you can remove them from this list. Note
# that it is important that the `python2` and `cmake` packages **not** used.
# The build has historically been known to fail with these packages.

I'm unclear on the sentence starting with Note. The sentence seems to be missing a verb: are not used? But if that is true, it looks like the pacman command below wants to install them anyway.

[frewsxcv]

cc @alexcrichton who wrote these sentences. The description in the commit message also seems relevant to this Issue. I don't know much about MSYS2, but it looks like it might be the case that there exists a python2 package, but it shouldn't be used. Instead, one should install mingw-w64-x86_64-python2.

[petrochenkov]

Yep, python2 and mingw-w64-x86_64-python2 are different packages.
MSYS2 has three subsystems/environments with separate sets of packages - msys2, mingw32 and mingw64 (more about them here).
Rust is usually built in mingw64 environment (or mingw32; msys2 is used for development of MSYS2 itself) and has to use mingw64 version of Python.

(Curiously, mingw-w64-x86_64-make fails trying to build Rust (at least it did the last time I tried it), so make from msys2 environment has to be used. Also mingw-w64-x86_64-python2 and mingw-w64-x86_64-gdb have completely broken interactive shell unlike python2 and gdb, so you have to deal with all subsystems anyway sooner or later :D)

[petrochenkov]

@barik
Does my answer resolves the issue (modulo the missing verb)?
I'm not sure all these technicalities need to be put into README.

EDIT: Oh, the question was asked on Aug 29, it probably doesn't matter now.

[barik]

@petrochenkov Thanks, yes that resolves the issue. I guess when reading it originally, I didn't realize python2 was actually referring to a package in the MSYS ecosystem. Wonder if something like the following would help clarify for future readers, without having to get into too many technicalities:

Note that it is important that you do not use the python2 and cmake packages from the msys2 subsystem. The build has historically been known to fail with these packages.