[PATCH 2 of 2] alias: expand "$@" as list of parameters quoted individually (BC) (issue4200)

[Siddharth Agarwal]

# HG changeset patch
# User Siddharth Agarwal <sid0 at fb.com>
# Date 1407997312 25200
#      Wed Aug 13 23:21:52 2014 -0700
# Node ID 38b9b34c3351935a54a2d4da185452a753c98970
# Parent  c3fbbb727b54c25c93ef64a7353e62503e0fa441
alias: expand "$@" as list of parameters quoted individually (BC) (issue4200)

Before this patch, there was no way to pass in all the positional parameters as
separate words down to another command.

(1) $@ (without quotes) would expand to all the parameters separated by a space.
    This would work fine for arguments without spaces, but arguments with spaces
    in them would be split up by POSIX shells into separate words.
(2) '$@' (in single quotes) would expand to all the parameters within a pair of
    single quotes. POSIX shells would then treat the entire list of arguments
    as one word.
(3) "$@" (in double quotes) would expand similarly to (2).

With this patch, we expand "$@" (in double quotes) as all positional
parameters, quoted individually with util.shellquote, and separated by spaces.
Under standard field-splitting conditions, POSIX shells will tokenize each
argument into exactly one word.

This is a backwards-incompatible change, but the old behavior was arguably a
bug: Bourne-derived shells have expanded "$@" as a tokenized list of positional
parameters for a very long time. I could find this behavior specified in IEEE
Std 1003.1-2001, and this probably goes back to much further before that.

diff --git a/mercurial/dispatch.py b/mercurial/dispatch.py
--- a/mercurial/dispatch.py
+++ b/mercurial/dispatch.py
@@ -331,6 +331,27 @@
         args = shlex.split(cmd)
     return args + givenargs
 
+def aliasinterpolate(name, args, cmd):
+    '''interpolate args into cmd for shell aliases
+
+    This also handles $0, $@ and "$@".
+    '''
+    # util.interpolate can't deal with "$@" (with quotes) because it's only
+    # built to match prefix + patterns.
+    replacemap = dict(('$%d' % (i + 1), arg) for i, arg in enumerate(args))
+    replacemap['$0'] = name
+    replacemap['$$'] = '$'
+    replacemap['$@'] = ' '.join(args)
+    # Typical Unix shells interpolate "$@" (with quotes) as all the positional
+    # parameters, separated out into words. Emulate the same behavior here by
+    # quoting the arguments individually. POSIX shells will then typically
+    # tokenize each argument into exactly one word.
+    replacemap['"$@"'] = ' '.join(util.shellquote(arg) for arg in args)
+    # escape '\$' for regex
+    regex = '|'.join(replacemap.keys()).replace('$', r'\$')
+    r = re.compile(regex)
+    return r.sub(lambda x: replacemap[x.group()], cmd)
+
 class cmdalias(object):
     def __init__(self, name, definition, cmdtable):
         self.name = self.cmd = name
@@ -376,10 +397,7 @@
                                  % (int(m.groups()[0]), self.name))
                         return ''
                 cmd = re.sub(r'\$(\d+|\$)', _checkvar, self.definition[1:])
-                replace = dict((str(i + 1), arg) for i, arg in enumerate(args))
-                replace['0'] = self.name
-                replace['@'] = ' '.join(args)
-                cmd = util.interpolate(r'\$', replace, cmd, escape_prefix=True)
+                cmd = aliasinterpolate(self.name, args, cmd)
                 return util.system(cmd, environ=env, out=ui.fout)
             self.fn = fn
             return
diff --git a/mercurial/help/config.txt b/mercurial/help/config.txt
--- a/mercurial/help/config.txt
+++ b/mercurial/help/config.txt
@@ -229,8 +229,9 @@
 Positional arguments like ``$1``, ``$2``, etc. in the alias definition
 expand to the command arguments. Unmatched arguments are
 removed. ``$0`` expands to the alias name and ``$@`` expands to all
-arguments separated by a space. These expansions happen before the
-command is passed to the shell.
+arguments separated by a space. ``"$@"`` (with quotes) expands to all
+arguments quoted individually and separated by a space. These expansions
+happen before the command is passed to the shell.
 
 Shell aliases are executed in an environment where ``$HG`` expands to
 the path of the Mercurial that was used to execute the alias. This is
diff --git a/tests/test-alias.t b/tests/test-alias.t
--- a/tests/test-alias.t
+++ b/tests/test-alias.t
@@ -30,6 +30,7 @@
   > echo1 = !printf '\$1\n'
   > echo2 = !printf '\$2\n'
   > echo13 = !printf '\$1 \$3\n'
+  > echotokens = !printf "%s\n" "\$@"
   > count = !hg log -r "\$@" --template=. | wc -c | sed -e 's/ //g'
   > mcount = !hg log \$@ --template=. | wc -c | sed -e 's/ //g'
   > rt = root
@@ -241,6 +242,22 @@
   foo baz
   $ hg echo2 foo
   
+  $ hg echotokens
+  
+  $ hg echotokens foo 'bar $1 baz'
+  foo
+  bar $1 baz
+  $ hg echotokens 'test $2' foo
+  test $2
+  foo
+  $ hg echotokens 'test $@' foo '$@'
+  test $@
+  foo
+  $@
+  $ hg echotokens 'test "$@"' foo '"$@"'
+  test "$@"
+  foo
+  "$@"
   $ echo bar > bar
   $ hg commit -qA -m bar
   $ hg count .