m4: avoid spurious output with unrecognized format specifiers.

* modules/format.c (format): Advance the loop invariants past an
unrecognized format specifier to avoid printing the specifier
character on the next pass.
* doc/m4.texi (Format): Don't expect unrecognized specifiers to
be output by format macro.
* tests/null.out: Don't expect unrecognized null specifier to be
output.
* tests/generate.awk (new_test): Treat `ignore' in expected error
output the same as Autotest.
* doc/m4.texi (Format): Use special `ignore' string rather than
unsupported @comment xerr magic.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>

4 files changed, 10 insertions, 2 deletions

diff --git a/doc/m4.texi b/doc/m4.texi
index bc2fccaf..06d871db 100644
--- a/doc/m4.texi
+++ b/doc/m4.texi
@@ -7512,7 +7512,7 @@ Likewise, escape sequences are not yet recognized.
 @example
 format(`%p', `0')
 @error{}m4:stdin:1: warning: format: unrecognized specifier in '%p'
-@result{}p
+@result{}
 format(`%*d', `')
 @error{}m4:stdin:2: warning: format: empty string treated as 0
 @error{}m4:stdin:2: warning: format: too few arguments: 2 < 3
@@ -7527,10 +7527,10 @@ format(`%.1f', `2a')
 @comment Unfortunately, 8-bit bytes are hard to check for; but the
 @comment exit status is enough to sniff the crash in broken versions.
 
-@comment xerr: ignore
 @example
 format(`%'format(`%c', `128'))
 @result{}
+@error{}ignore
 @end example
 @end ignore
 
diff --git a/modules/format.c b/modules/format.c
index b13b2630..92e2d474 100644
--- a/modules/format.c
+++ b/modules/format.c
@@ -338,6 +338,11 @@ format (m4 *context, m4_obstack *obs, int argc, m4_macro_args *argv)
           m4_warn (context, 0, me, _("unrecognized specifier in %s"),
                    quotearg_style_mem (locale_quoting_style, f, M4ARGLEN (1)));
           valid_format = false;
+          if (f_len > 0)
+            {
+              fmt++;
+              f_len--;
+            }
           continue;
         }
       fmt++;
diff --git a/tests/generate.awk b/tests/generate.awk
index 6dcddf4e..ab25661f 100755
--- a/tests/generate.awk
+++ b/tests/generate.awk
@@ -170,6 +170,9 @@ function new_test(input, status, output, error, options, xfail, examples) {
   output = normalize(output);
   error = normalize(error);
 
+  if (error == "ignore\n")
+    error = "ignore";
+
   if (options ~ / (import|load|modtest|mpeval|perl|shadow|stdlib|time)/)
     printf ("AT_CHECK_DYNAMIC_MODULE\n");
   if (options ~ / mpeval/)
diff --git a/tests/null.out b/tests/null.out
index 993d9fe0..784ab7ab 100644
--- a/tests/null.out
+++ b/tests/null.out