func_quote_for_eval and sed_quote_subst

[Noah Misch]

The name func_quote_for_eval brings to my mind this invariant:

 Given any $foo, $bar and $foo compare identically after these commands:
  func_quote_for_eval "$foo"
  eval "bar=$func_quote_for_eval_result"

It is not so for $foo containing metacharacters with meaning within double
quotes.  Naturally, then, $foo and $bar compare identically after these
command:

  foo_subst=`echo "X$foo" | $Xsed -e "$sed_quote_subst"`
  func_quote_for_eval "$foo_subst"
  eval "bar=$func_quote_for_eval_result"

Perusing ltmain.m4sh, I see that a sed_quote_subst precedes most calls to
func_quote_for_eval.  Does there exist a func_quote_for_eval on an argument that
we correctly do not filter through sed_quote_subst?  If not, should
func_quote_for_eval actually do the sed_quote_subst?

One a related point, why
sed_quote_subst='s/\([\\`\\"$\\\\]\)/\\\1/g'
instead of this?
sed_quote_subst='s/\([`"$\]\)/\\\1/g'

As best I can tell, the extra backslashes in the former do not quote anything;
they just add more literal backslashes to the character class.

Here's a sample (untested) patch implementing the sed_quote_subst out-factoring:

--- config/general.m4sh.~1.4.~  2004-10-08 13:01:49.000000000 -0400
+++ config/general.m4sh 2004-10-16 15:16:50.840649600 -0400
@@ -252,7 +252,7 @@ func_mktempdir ()
 # Aesthetically quote ARG to be evaled later.
 func_quote_for_eval ()
 {
-  my_arg="$1"
+  my_arg=`$ECHO "X$1" | $Xsed -e "$sed_quote_subst"`
 
   case $my_arg in
     # Double-quote args containing other shell metacharacters.
--- config/ltmain.m4sh.~1.11.~  2004-10-16 11:02:05.000000000 -0400
+++ config/ltmain.m4sh  2004-10-16 15:30:23.198763200 -0400
@@ -1090,7 +1090,6 @@ func_mode_compile ()
       esac    #  case $arg_mode
 
       # Aesthetically quote the previous argument.
-      lastarg=`$ECHO "X$lastarg" | $Xsed -e "$sed_quote_subst"`
       func_quote_for_eval "$lastarg"
       base_compile="$base_compile $func_quote_for_eval_result"
     done # for arg
@@ -1511,8 +1510,8 @@ func_mode_execute ()
        ;;
       esac
       # Quote arguments (to preserve shell metacharacters).
-      file=`$ECHO "X$file" | $Xsed -e "$sed_quote_subst"`
-      args="$args \"$file\""
+      func_quote_for_eval "$file"
+      args="$args $func_quote_for_eval_result"
     done
 
     if test -z "$run"; then
@@ -1637,7 +1636,6 @@ func_mode_install ()
        # Allow the use of GNU shtool's install command.
        $ECHO "X$nonopt" | $Xsed | $GREP shtool > /dev/null; then
       # Aesthetically quote it.
-      arg=`$ECHO "X$nonopt" | $Xsed -e "$sed_quote_subst"`
       func_quote_for_eval "$arg"
       install_prog="$func_quote_for_eval_result "
       arg="$1"
@@ -1649,7 +1647,6 @@ func_mode_install ()
 
     # The real first argument should be the name of the installation program.
     # Aesthetically quote it.
-    arg=`$ECHO "X$arg" | $Xsed -e "$sed_quote_subst"`
     func_quote_for_eval "$arg"
     install_prog="$install_prog$func_quote_for_eval_result"
 
@@ -1693,7 +1690,6 @@ func_mode_install ()
       esac
 
       # Aesthetically quote the argument.
-      arg=`$ECHO "X$arg" | $Xsed -e "$sed_quote_subst"`
       func_quote_for_eval "$arg"
       install_prog="$install_prog $func_quote_for_eval_result"
     done
@@ -2198,7 +2194,6 @@ func_mode_link ()
     while test "$#" -gt 0; do
       arg="$1"
       shift
-      qarg=`$ECHO "X$arg" | $Xsed -e "$sed_quote_subst"`
       func_quote_for_eval "$qarg"
       libtool_args="$libtool_args $func_quote_for_eval_result"
 
@@ -2716,7 +2711,7 @@ func_mode_link ()
        ;;
 
       -Wc,*)
-       args=`$ECHO "X$arg" | $Xsed -e "$sed_quote_subst" -e 's/^-Wc,//'`
+       args=`$ECHO "X$arg" | $Xsed -e 's/^-Wc,//'`
        arg=
        save_ifs="$IFS"; IFS=','
        for flag in $args; do
@@ -2730,7 +2725,7 @@ func_mode_link ()
        ;;
 
       -Wl,*)
-       args=`$ECHO "X$arg" | $Xsed -e "$sed_quote_subst" -e 's/^-Wl,//'`
+       args=`$ECHO "X$arg" | $Xsed -e s/^-Wl,//'`
        arg=
        save_ifs="$IFS"; IFS=','
        for flag in $args; do
@@ -2765,7 +2760,6 @@ func_mode_link ()
       # -q* pass through compiler args for the IBM compiler
       # -m* pass through architecture-specific compiler args for GCC
       -64|-mips[[0-9]]|-xarch=*|-xtarget=*|+DA*|+DD*|-q*|-m*)
-        arg=`$ECHO "X$arg" | $Xsed -e "$sed_quote_subst"`
         func_quote_for_eval "$arg"
        arg="$func_quote_for_eval_result"
         compile_command="$compile_command $arg"
@@ -2776,7 +2770,6 @@ func_mode_link ()
 
       # Some other compiler flag.
       -* | +*)
-        arg=`$ECHO "X$arg" | $Xsed -e "$sed_quote_subst"`
         func_quote_for_eval "$arg"
        arg="$func_quote_for_eval_result"
        ;;
@@ -2910,7 +2903,6 @@ func_mode_link ()
       *)
        # Unknown arguments in both finalize_command and compile_command need
        # to be aesthetically quoted because they are evaled later.
-       arg=`$ECHO "X$arg" | $Xsed -e "$sed_quote_subst"`
        func_quote_for_eval "$arg"
        arg="$func_quote_for_eval_result"
        ;;
@@ -5593,8 +5585,8 @@ EOF
          elif eval var_value=\$$var; test -z "$var_value"; then
            relink_command="$var=; export $var; $relink_command"
          else
-           var_value=`$ECHO "X$var_value" | $Xsed -e "$sed_quote_subst"`
-           relink_command="$var=\"$var_value\"; export $var; $relink_command"
+           func_quote_for_eval "$var_value"
+           relink_command="$var=$func_quote_for_eval_result; export $var; 
$relink_command"
          fi
        done
        relink_command="(cd `pwd`; $relink_command)"
@@ -6283,8 +6275,8 @@ fi\
        elif eval var_value=\$$var; test -z "$var_value"; then
          relink_command="$var=; export $var; $relink_command"
        else
-         var_value=`$ECHO "X$var_value" | $Xsed -e "$sed_quote_subst"`
-         relink_command="$var=\"$var_value\"; export $var; $relink_command"
+         func_quote_for_eval "$var_value"
+         relink_command="$var=$func_quote_for_eval_result; export $var; 
$relink_command"
        fi
       done
       # Quote the link command for shipping.