stdio-common: Also reject exp char w/o significand in i18n scanf [BZ #13988]

Fix the handling of real 'scanf' input such as "+.e" as per BZ #13988
for the i18n case as well, complementing commit 6ecec3b616ae ("Don't
accept exp char without preceding digits in scanf float parsing"), where
the 'e' character is incorrectly consumed from input.  Add a test case
matching stdio-common/bug26.c, with bits from localedata/tst-sscanf.c.

Reviewed-by: Joseph Myers <josmyers@redhat.com>

3 files changed, 63 insertions, 3 deletions

diff --git a/localedata/Makefile b/localedata/Makefile
index 9401437..4a23593 100644
--- a/localedata/Makefile
+++ b/localedata/Makefile
@@ -236,6 +236,7 @@ tests = \
   bug-iconv-trans \
   bug-setlocale1 \
   bug-usesetlocale \
+  tst-bz13988 \
   tst-c-utf8-consistency \
   tst-digits \
   tst-iconv-emojis-trans \
diff --git a/localedata/tst-bz13988.c b/localedata/tst-bz13988.c
new file mode 100644
index 0000000..8d6f399
--- /dev/null
+++ b/localedata/tst-bz13988.c
@@ -0,0 +1,53 @@
+/* Localized test for BZ #13988.
+   Copyright (C) 2025 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <locale.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <libc-diag.h>
+#include <support/check.h>
+
+#define PD "\xd9\xab"
+
+static int
+do_test (void)
+{
+  if (setlocale (LC_ALL, "fa_IR.UTF-8") == NULL)
+    FAIL_EXIT1 ("setlocale (LC_ALL, \"fa_IR.UTF-8\")");
+
+  char s[] = "+" PD "e";
+  FILE *f = fmemopen (s, strlen (s), "r");
+
+  /* Avoid: "warning: 'I' flag used with '%f' gnu_scanf format [-Wformat=]";
+     cf. GCC PR c/119514.  */
+  DIAG_PUSH_NEEDS_COMMENT;
+  DIAG_IGNORE_NEEDS_COMMENT (4.9, "-Wformat");
+
+  /* This should fail to parse a floating-point number, and leave 'e' in the
+     input.  */
+  double d;
+  TEST_VERIFY_EXIT (fscanf (f, "%Ilf", &d) == 0);
+  TEST_VERIFY_EXIT (fgetc (f) == 'e');
+
+  DIAG_POP_NEEDS_COMMENT;
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/stdio-common/vfscanf-internal.c b/stdio-common/vfscanf-internal.c
index 87f23b5..6817fc1 100644
--- a/stdio-common/vfscanf-internal.c
+++ b/stdio-common/vfscanf-internal.c
@@ -2409,7 +2409,7 @@ digits_extended_fail:
 		      if (got_e && charbuf.current[-1] == exp_char
 			  && (c == L_('-') || c == L_('+')))
 			char_buffer_add (&charbuf, c);
-		      else if (char_buffer_size (&charbuf) > got_sign && !got_e
+		      else if (got_digit && !got_e
 			       && (CHAR_T) TOLOWER (c) == exp_char)
 			{
 			  char_buffer_add (&charbuf, exp_char);
@@ -2426,7 +2426,10 @@ digits_extended_fail:
 			      if (c == wcdigits[n])
 				{
 				  if (n < 10)
-				    char_buffer_add (&charbuf, L_('0') + n);
+				    {
+				      char_buffer_add (&charbuf, L_('0') + n);
+				      got_digit = 1;
+				    }
 				  else if (n == 11 && !got_dot)
 				    {
 				      char_buffer_add (&charbuf, decimal);
@@ -2461,7 +2464,10 @@ digits_extended_fail:
 				    width = avail;
 
 				  if (n < 10)
-				    char_buffer_add (&charbuf, L_('0') + n);
+				    {
+				      char_buffer_add (&charbuf, L_('0') + n);
+				      got_digit = 1;
+				    }
 				  else if (n == 11 && !got_dot)
 				    {
 				      /* Add all the characters.  */