# HG changeset patch
# User Matt Harbison <matt_harbison@yahoo.com>
# Date 2020-11-21 20:34:54
# Node ID 4f6816e8440bf5b13a1b192cdc8f01a4b9fed34c
# Parent  063cf294d5e0b0861cfe55605209766f141245a4

make: switch the PYTHON default to `py.exe -3` on Windows

Python3 _is_ named `python.exe` on Windows, but that isn't necessarily on PATH
when installing from python.org.  I do happen to have a python.exe on PATH in
`$LOCALAPPDATA/Microsoft/WindowsApps`, but it appears to be 0 bytes (likely
because of permission issues), and doesn't run:

    $ python -V
     - Cannot open

Pulkit hit the same error as I did though, so it isn't just my system:

    $ make -C . local
    make: Entering directory `/home/Dell/repos/hg-committed`
    python setup.py  \
              build_py -c -d . \
              build_ext  -i \
              build_hgexe  -i \
              build_mo
     - Cannot openmake: *** [local] Error 1

The `py.exe` dispatcher lives in the Windows directory (so it is on PATH), looks
up the python.org installation, and invokes that interpreter directly.  I get a
warning with py39, but if it's our issue, it was an existing one:

    $ make -C .. local
    make: Entering directory `/c/Users/Matt/hg'
    py -3 setup.py  \
              build_py -c -d . \
              build_ext  -i \
              build_hgexe  -i \
              build_mo
    C:\Users\Matt\AppData\Local\Programs\Python\Python39\lib\site-packages\setuptools\distutils_patch.py:25:
        UserWarning: Distutils was imported before Setuptools. This usage is discouraged and may
        exhibit undesirable behaviors or errors. Please use Setuptools' objects directly or at least
        import Setuptools first.
      warnings.warn(

The end result is a py3 based hg.exe that annoyingly won't run because it can't
find python39.dll.  It will run tests (the ones without the `python3` shbang
line anyway), because the test runner adjusts PATH to include the python running
it.

Differential Revision: https://phab.mercurial-scm.org/D9361

diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -8,9 +8,9 @@ export PREFIX=/usr/local
 
 # Default to Python 3.
 #
-# Windows ships Python 3 as `python.exe`.
+# Windows ships Python 3 as `python.exe`, which may not be on PATH.  py.exe is.
 ifeq ($(OS),Windows_NT)
-PYTHON?=python
+PYTHON?=py -3
 else
 PYTHON?=python3
 endif