Re: [PATCH] Generic mechanism to detect shell features

[Paolo Bonzini]

> Did you have a look at Eric Sunshine's _AS_SHELL_BEST proposal?

No, I noted it a few hours after posting mine.

> I haven't had time to review either proposal thoroughly, but a quick
> glance suggests that the _AS_SHELL_BEST patch is a bit more polished

Surely.

> and better fixes the bugs discussed in the "Shell function reporting" thread

Both do (or at least should, I could not test on a bad shell).

> <http://mail.gnu.org/archive/html/autoconf-patches/2004-01/threads.html#00014>,
> but your _AS_DETECT_BETTER_SHELL proposal has the nicer idea of a
> generic detection mechanism.

And of the death of AS_INIT_WITH_SHELL_FN and of all the temporary bits of 
m4sh.m4
(they are all condensed in AS_SHELL_FN_SPY).

> Ideally we'd see a single proposal that does both.

I'd agree with applying Eric's patch and working incrementally from there.  What
follows is a brief review:

+AS_IF([test $as_fn_exitcode -eq 0],
+  m4_ifval([$1], [$1], [:]),
+  m4_ifval([$2], [$2], [:]))
+])# _AS_SHELL_FN_WORKS

The idea of AS_IF is to avoid those m4_ifvals, just do AS_IF([...], [$1], [$2]).

+_AS_SHELL_FN_SUPPORTED && as_shell_func=x
+_AS_LINENO_WORKS && as_shell_lineno=x

Use _AS_SHELL_FN_SUPPORTED_FOR_SHELL([$SHELL]) in case the syntax is not 
supported,
and drop _AS_SHELL_FN_SUPPORTED.  I also suggest that you do

    CONFIG_SHELL="$SHELL"
    _AS_SHELL_FN_SUPPORTED && as_shell_func="$SHELL"
    _AS_LINENO_WORKS && as_shell_lineno="$SHELL"

This way, ...

+  x|'') m4_default([$1]) ;;
+  *) m4_default([$2]) ;;

... you can drop as_shell_best, use CONFIG_SHELL instead, then just do 
AS_IF([test
"$CONFIG_SHELL" = "$SHELL"], [$1], [$2]).

+# Find the most desirable shell for running this script.
+AS_IF([test -z "$CONFIG_SHELL"],
+  [_AS_SHELL_BEST([],
+    [AS_UNSET([BASH_ENV])
+    AS_UNSET([ENV])
+    CONFIG_SHELL=$as_shell_best
+    export CONFIG_SHELL
+    exec "$CONFIG_SHELL" "$as_myself" ${1+"$@"}],
+    [$1])])

(Of course, don't assign CONFIG_SHELL here).

Otherwise looks great.

Paolo