format is locale aware

[Bruno Haible]

Hi,

After building m4-1.4.19 on DragonFly BSD 6.0, with LC_ALL=fr_FR.UTF-8,
"make check" shows a test failure:

Checking ../../checks/180.format
@ ../doc/m4.texi:6066: Origin of test
../../checks/180.format: stdout mismatch
--- m4-tmp.452851/m4-xout       2021-06-08 03:26:41.805343000 +0200
+++ m4-tmp.452851/m4-out        2021-06-08 03:26:41.797573000 +0200
@@ -1,8 +1,8 @@
 
 The string "The brown fox jumped over the lazy dog" uses 38 characters
 1
-56790
+56789
 5000
 success
-success
-20
+0P+0
+10
@ ../doc/m4.texi:6066: Origin of test
../../checks/180.format: stderr mismatch
--- m4-tmp.452851/m4-xerr       2021-06-08 03:26:41.805343000 +0200
+++ m4-tmp.452851/m4-err        2021-06-08 03:26:41.797573000 +0200
@@ -0,0 +1,5 @@
+m4:stdin:4: non-numeric argument 56789.9876
+m4:stdin:9: non-numeric argument 1.999
+m4:stdin:10: non-numeric argument 1.999
+m4:stdin:11: non-numeric argument 1.999
+m4:stdin:12: non-numeric argument 0xa.P+1

And indeed, the src/m4 program behaves in a locale dependent manner:

$ src/m4
format(`%.0f', `9.9')
src/m4:stdin:1: non-numeric argument 9.9
9
format(`%.0f', `9,9')
10
format(`%.1f', `4')
4,0

I see the same behaviour also on a glibc system.

1) Is the number parsing and printing of numbers in 'format' supposed to
be locale dependent? If yes, it would be good to document it in
https://www.gnu.org/software/m4/manual/html_node/Format.html .
If no, the fix would be in main.c: Add a
  setlocale (LC_NUMERIC, "C");
after setlocale (LC_ALL, "").

2) Why do I see the test 180 fail on DragonFly BSD but not on a glibc
system? In both cases, I have LC_ALL set to fr_FR.UTF-8, and this locale
exists (verified with 'locale -a').

Bruno