Inconsistent quote and escape handling in parameter expansion

[Ondrej Oprala]

Hi all,
I've attempted to write a patch fixing an issue mentioned here 
http://lists.gnu.org/archive/html/bug-bash/2012-02/msg00106.html a while 
back. It basically wraps parameter expansion around a new context of 
it's own, using it to make another condition for single-quote 
substitution. While it's by no means perfect, it makes parameter 
expansion a bit more sane IMHO. The change should eventually have a new 
compat option, since it breaks a few test cases (I suppose making it 
fully backwards-compatible is impossible). I'd really appreciate some 
comments and advice on the patch's approach and/or necessary improvements.

Thanks,
Ondrej
>From 3ac7b13686ad4ea477f12bfba759f14e2d05062a Mon Sep 17 00:00:00 2001
From: Ondrej Oprala <oopr...@redhat.com>
Date: Thu, 1 Nov 2012 14:39:27 +0100
Subject: [PATCH] Bash-4.2 patch 40

---
 subst.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/subst.c b/subst.c
index 937c71d..7010dae 100644
--- a/subst.c
+++ b/subst.c
@@ -7933,6 +7933,8 @@ expand_word_internal (word, quoted, isexp, 
contains_dollar_at, expanded_somethin
 
   char twochars[2];
 
+  static int p_exp; /* parameter expansion context. */
+
   DECLARE_MBSTATE;
 
   istring = (char *)xmalloc (istring_size = DEFAULT_INITIAL_ARRAY_SIZE);
@@ -8131,9 +8133,12 @@ add_string:
          pflags = (word->flags & W_NOCOMSUB) ? PF_NOCOMSUB : 0;
          if (word->flags & W_NOSPLIT2)
            pflags |= PF_NOSPLIT2;
+         p_exp = 1;
          tword = param_expand (string, &sindex, quoted, expanded_something,
                               &temp_has_dollar_at, &quoted_dollar_at,
                               &had_quoted_null, pflags);
+         if (!string[sindex])
+           p_exp = 0;
          has_dollar_at += temp_has_dollar_at;
 
          if (tword == &expand_wdesc_error || tword == &expand_wdesc_fatal)
@@ -8225,7 +8230,8 @@ add_string:
            {
              SCOPY_CHAR_I (twochars, CTLESC, c, string, sindex, string_size);
            }
-         else if ((quoted & (Q_HERE_DOCUMENT|Q_DOUBLE_QUOTES)) && 
((sh_syntaxtab[c] & tflag) == 0))
+         else if ((quoted & (Q_HERE_DOCUMENT|Q_DOUBLE_QUOTES)) && 
((sh_syntaxtab[c] & tflag) == 0) &&
+                       !(c == '\'' && p_exp))
            {
              SCOPY_CHAR_I (twochars, '\\', c, string, sindex, string_size);
            }
-- 
1.7.11.7