[PATCH v3 07/10] stdio-common: Also reject exp char w/o significand in i18n scanf [BZ #13988]

[Maciej W. Rozycki]

From: Maciej W. Rozycki <macro@redhat.com>

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.
---
This is needed to prevent a localedata/tst-sscanf regression with 10/10,
but it is of course a fix for a bug on its own.  I don't know why GCC is 
unhappy with the 'I' modifier, this doesn't appear documented anywhere.

New change in v3.
---
 localedata/Makefile             |    1 
 localedata/tst-bz13988.c        |   51 ++++++++++++++++++++++++++++++++++++++++
 stdio-common/vfscanf-internal.c |   12 +++++++--
 3 files changed, 61 insertions(+), 3 deletions(-)

glibc-scanf-bz13988-i18n.diff
Index: glibc/localedata/Makefile
===================================================================
--- glibc.orig/localedata/Makefile
+++ glibc/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 \
Index: glibc/localedata/tst-bz13988.c
===================================================================
--- /dev/null
+++ glibc/localedata/tst-bz13988.c
@@ -0,0 +1,51 @@
+/* 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");
+
+  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>
Index: glibc/stdio-common/vfscanf-internal.c
===================================================================
--- glibc.orig/stdio-common/vfscanf-internal.c
+++ glibc/stdio-common/vfscanf-internal.c
@@ -2409,7 +2409,7 @@ __vfscanf_internal (FILE *s, const char
 		      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 @@ __vfscanf_internal (FILE *s, const char
 			      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 @@ __vfscanf_internal (FILE *s, const char
 				    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.  */