Thanks for the feedback - the updated file is included at the end and at
https://gist.github.com/bburns/43c9f170361aecee3b71 - Chris added a
few comments there.

>> I tried running configure without the '--host=x86_64-w64-mingw32' etc switches
>> but got an error:
>> configure: error: Emacs does not support 'x86_64-pc-msys' systems.

This turned out to be due to not being in the right environment - I added the
step to switch to the MinGW-w64 environment and now it works without specifying
the --host, etc.

> Sorry, I don't understand: this _is_ INSTALL, isn't it?  And the
> current INSTALL does include a couple of examples.  What am I missing?

At the moment, this is a separate file - e.g. it could be nt/INSTALL64, though
if we wanted we could merge them.

When I tried using the nt/INSTALL instructions last year I was mostly confused
about the --prefix option - I didn't understand what was meant by build inside
or outside the source tree, and the example given, /d/usr, was a bit foreign to
me as a place to store programs, so Chris's example was easier to follow. I
tried to keep these instructions simple also, but referred the user to the
nt/INSTALL file for more information in a couple of places.

>> I think this was in part because MSYS2 doesn't add its folders to the PATH, and
>> if you use the PATH variable there might be both 32-bit and 64-bit DLLs on it,
> But that's a problem MSYS2 and MinGW64 should have solved already,
> right?  IOW, it's not something specific to Emacs.

Okay, straightened that out a bit, now it says

  Adding these directories to your PATH tells Emacs where to find the DLLs it
  needs to run, and some optional commands like grep and find.  These commands
  will also be available at the Windows console.

> I indeed think that the instructions should tell how to create a
> desktop shortcut for running Emacs.
> I would suggest removing this time information

Okay, added a section for making a shortcut, and removed the time info.

> I guess you didn't use "make -j8" or some such. 

That's a good option to include - I added it to the make section.

Thanks again for your help -
 
Brian

------------

               Building and Installing Emacs on 64-bit MS-Windows
                           using MSYS2 and MinGW-w64

               Copyright (c) 2015 Free Software Foundation, Inc.
                See the end of the file for license conditions.

This document describes how to compile a 64-bit GNU Emacs using MSYS2 and
MinGW-w64.  For more detailed information on the build process, and instructions
for building a 32-bit Emacs using MSYS and MinGW, see the INSTALL document in
this directory.

Do not use this recipe with Cygwin.  For building on Cygwin, use the normal
installation instructions in ../INSTALL.


* Requirements

  The total space required is 3GB: 1.8GB for MSYS2 / MinGW-w64 and 1.2GB for
  Emacs with the full repository, or less if you're using a release tarball.


* Set up the MinGW-w64 / MSYS2 build environment

  MinGW-w64 provides a complete runtime for projects built with gcc for 64-bit
  Windows - it's located at http://mingw-w64.org/.

  MSYS2 is a Cygwin-derived software distribution for Windows which provides
  build tools for MinGW-w64 - see http://msys2.github.io/.


** Download and install MinGW-w64 and MSYS2

  You can download the x86_64 version of MSYS2 (i.e. msys2-x86_64-<date>.exe)
  from

      https://sourceforge.net/projects/msys2/files/Base/x86_64

  Run this file to install MSYS2 in your preferred directory, e.g. the default
  C:\msys64 - this will install MinGW-w64 also.  Note that directory names
  containing spaces may cause problems.

  Then you'll need to add the following directories to your Windows PATH
  environment variable -

      c:\msys64\usr\bin;c:\msys64\mingw64\bin

  you can do this through Control Panel / System and Security / System /
  Advanced system settings / Environment Variables / Edit path.

  Adding these directories to your PATH tells Emacs where to find the DLLs it
  needs to run, and some optional commands like grep and find.  These commands
  will also be available at the Windows console.


** Download and install the necessary packages

  Run msys2_shell.bat in your MSYS2 directory and you will see a BASH window
  opened.

  In the BASH prompt, use the following command to install the necessary
  packages (you can copy and paste it into the shell with Shift + Insert):

      pacman -S base-devel \
      mingw-w64-x86_64-toolchain \
      mingw-w64-x86_64-xpm-nox \
      mingw-w64-x86_64-libtiff \
      mingw-w64-x86_64-giflib \
      mingw-w64-x86_64-libpng \
      mingw-w64-x86_64-libjpeg-turbo \
      mingw-w64-x86_64-librsvg \
      mingw-w64-x86_64-libxml2 \
      mingw-w64-x86_64-gnutls

  The packages include the base developer tools (autoconf, automake, grep, make,
  etc.), the compiler toolchain (gcc, gdb, etc.), several image libraries, an
  xml library, and the GnuTLS (transport layer security) library.  Only the
  first three packages are required (base-devel, toolchain, xpm-nox) - the rest
  are optional.

  You now have a complete build environment for Emacs.


* Install git (optional) and disable autocrlf

  If you're going to be building the development version of Emacs from the git
  repository, and you don't already have git on your system, you can install it
  in your MSYS2 environment with:

      pacman -S git

  The autocrlf feature of Git may interfere with the configure file, so it is
  best to disable this feature by running the command:

      git config core.autocrlf false


* Get the Emacs source code

  Now you can either get an existing release version of the Emacs source code
  from the GNU ftp site, or get the more current version and history from the
  git repository.

  You can always find the most recent information on these sources from the GNU
  Savannah Emacs site, https://savannah.gnu.org/projects/emacs.


** From the FTP site

  The Emacs ftp site is located at http://ftp.gnu.org/gnu/emacs/ - download the
  version you want to build and put the file into a location like C:\emacs\,
  then uncompress it with tar. This will put the Emacs source into a folder like
  C:\emacs\emacs-24.5:

      cd /c/emacs
      tar xf emacs-24.5.tar.xz


** From the git repository

  To download the git repository, do something like the following - this will
  put the Emacs source into C:\emacs\emacs-25:

      mkdir /c/emacs
      cd /c/emacs
      git clone git://git.sv.gnu.org/emacs.git emacs-25


* Build Emacs

  Now you're ready to build and install Emacs with autogen, configure, make,
  and make install.

  First we need to switch to the MinGW-w64 environment - exit the MSYS2 BASH
  console and run mingw64_shell.bat in the C:\msys64 folder, then cd back to
  your Emacs source directory, e.g.:

      cd /c/emacs/emacs-25


** Run autogen

  Run autogen to generate the configure script (note: this step is not necessary
  if you are using a release source tarball, as the configure file is included):

      ./autogen.sh


** Run configure

  Now you can run configure, which will build the various Makefiles - note that
  the example given here is just a simple one - for more information on the
  options available please see the nt/INSTALL file.

  The --prefix option specifies a location for the resulting binary files, which
  'make install' will use - in this example we set it to C:\emacs\emacs-25. If a
  prefix is not specified the files will be put in the standard Unix directories
  located in your C:\msys64 directory, but this is not recommended.

  Note also that we need to disable Imagemagick because Emacs does not yet
  support it on Windows.

      PKG_CONFIG_PATH=/mingw64/lib/pkgconfig \
      ./configure \
      --prefix=/c/emacs/emacs-25 \
      --without-imagemagick


** Run make

  This will compile Emacs and build the executables, putting them in the src
  directory:

      make

  To speed up the process, you can try running

      make -jN

  where N is the number of cores in your system - if your MSYS2 make supports
  parallel execution it will run significantly faster.


** Run make install

  Now you can run make install, which will copy the executable and other files
  to the location specified in the configure step.  This will create the bin,
  libexec, share, and var directories:

      make install

  You can also say

      make install prefix=/c/somewhere

  to install them somewhere else.


* Test Emacs

  To test it out, run

      ./bin/runemacs.exe -Q

  and if all went well, you will have a new 64-bit version of Emacs.


* Make a shortcut

  To make a shortcut to run the new Emacs, right click on the location where you
  want to put it, e.g. the Desktop, select New / Shortcut, then select
  runemacs.exe in the bin folder of the new Emacs, and give it a name.

  You can set any command line options by right clicking on the resulting
  shortcut, select Properties, then add any options to the Target command,
  e.g. --debug-init.


* Credits

  Thanks to Chris Zheng for the original build outline as used by the
  emacsbinw64 project, located at:

  https://sourceforge.net/p/emacsbinw64/wiki/Build%20guideline%20for%20MSYS2-MinGW-w64%20system/


* License

  This file is part of GNU Emacs.

  GNU Emacs is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  GNU Emacs is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.