hooks: allow Unix style environment variables on external Windows hooks

This will help making common hooks between Windows and non-Windows platforms.

Having to build the shellenviron dict here and in procutil.system() is a bit
unfortunate, but the only other option is to fix up the command inside
procutil.system().  It seems more important that the note about the hook being
run reflects what is actually run.

The patch from last summer added the hooks on the command line, but it looks
like HG_ARGS has since learned about --config args, and the output was just
confusing.  Therefore, it's now loaded from a file in the histedit test for
clarity.

mercurial/help/config.txt

@@ -886,6 +886,12 b' They contain the type of hook which trig'
 of the hook in the config, respectively. In the example above, this will
 be ``$HG_HOOKTYPE=incoming`` and ``$HG_HOOKNAME=incoming.email``.
 
+.. container:: windows
+
+  Some basic Unix syntax is supported for portability, including ``$VAR``
+  and ``${VAR}`` style variables.  To use a literal ``$``, it must be
+  escaped with a back slash or inside of a strong quote.
+
 ``changegroup``
   Run after a changegroup has been added via push, pull or unbundle.  The ID of
   the first new changeset is in ``$HG_NODE`` and last is in ``$HG_NODE_LAST``.

mercurial/hook.py

@@ -120,8 +120,6 b' def pythonhook(ui, repo, htype, hname, f'
     return r, False
 
 def _exthook(ui, repo, htype, name, cmd, args, throw):
-    ui.note(_("running hook %s: %s\n") % (name, cmd))
-
     starttime = util.timer()
     env = {}
 
@@ -141,6 +139,12 b' def _exthook(ui, repo, htype, name, cmd,'
             v = stringutil.pprint(v)
         env['HG_' + k.upper()] = v
 
+    if pycompat.iswindows:
+        environ = procutil.shellenviron(env)
+        cmd = util.platform.shelltocmdexe(cmd, environ)
+
+    ui.note(_("running hook %s: %s\n") % (name, cmd))
+
     if repo:
         cwd = repo.root
     else:

tests/test-histedit-fold.t

@@ -478,14 +478,7 b' This is an excuse to test hook with hist'
   1:199b6bb90248 b
   0:6c795aa153cb a
 
-Setup the proper environment variable symbol for the platform, to be subbed
-into the hook command.
-#if windows
-  $ NODE="%HG_NODE%"
-#else
-  $ NODE="\$HG_NODE"
-#endif
-  $ hg histedit 6c795aa153cb --config hooks.commit="echo commit $NODE" --commands - 2>&1 << EOF | fixbundle
+  $ hg histedit 6c795aa153cb --config hooks.commit='echo commit $HG_NODE' --commands - 2>&1 << EOF | fixbundle
   > pick 199b6bb90248 b
   > fold a1a953ffb4b0 c
   > pick 6c795aa153cb a
@@ -496,8 +489,24 b' into the hook command.'
   1:9599899f62c0 a
   0:79b99e9c8e49 b
 
+Test unix -> windows style variable substitution in external hooks.
+
+  $ cat > $TESTTMP/tmp.hgrc <<'EOF'
+  > [hooks]
+  > pre-add = echo no variables
+  > post-add = echo ran $HG_ARGS, literal \$non-var, 'also $non-var', $HG_RESULT
+  > EOF
+
+TODO: Windows should output double quotes around "also $non-var"
   $ echo "foo" > amended.txt
-  $ hg add amended.txt
+  $ HGRCPATH=$TESTTMP/tmp.hgrc hg add -v amended.txt
+  running hook pre-add: echo no variables
+  no variables
+  adding amended.txt
+  running hook post-add: echo ran %HG_ARGS%, literal $non-var, 'also $non-var', %HG_RESULT% (windows !)
+  running hook post-add: echo ran $HG_ARGS, literal \$non-var, 'also $non-var', $HG_RESULT (no-windows !)
+  ran add -v amended.txt, literal $non-var, 'also $non-var', 0 (windows !)
+  ran add -v amended.txt, literal $non-var, also $non-var, 0 (no-windows !)
   $ hg ci -q --config extensions.largefiles= --amend -I amended.txt
   The fsmonitor extension is incompatible with the largefiles extension and has been disabled. (fsmonitor !)
 

tests/test-rebase-interruptions.t

@@ -333,12 +333,7 b' Test rebase interrupted by hooks'
 
   $ cp -R a3 hook-pretxncommit
   $ cd hook-pretxncommit
-#if windows
-  $ NODE="%HG_NODE%"
-#else
-  $ NODE="\$HG_NODE"
-#endif
-  $ hg rebase --source 2 --dest 5 --tool internal:other --config "hooks.pretxncommit=hg log -r $NODE | grep \"summary:     C\""
+  $ hg rebase --source 2 --dest 5 --tool internal:other --config 'hooks.pretxncommit=hg log -r $HG_NODE | grep "summary:     C"'
   rebasing 2:965c486023db "C"
   summary:     C
   rebasing 6:a0b2430ebfb8 "F" (tip)