[libcxx] Reject month 0 in get_date/__get_month

[DavidSpickett]

Summary

[libcxx] Reject month 0 in get_date/__get_month

This fixes #47663.

Months in dates should be >= 1 and <= 12.
We parse up to two digits then minus one, because
we want to store this as "months since January"
(0-11).

However we didn't check that the result of that
was not -1. For example if you had (MM/DD/YYYY)
00/21/2022.

Added tests for:

• Failing if month is 0
• Failing if month is 13
• Allowing a leading zero in month e.g. "01"

Note that libc++ and libstdc++ return different
values on parsing failure, and MSVC STL returns
end of stream instead.

Handle the first two by checking for defines, MSVC STL
expects these tests to fail for other reasons already:
https://github.com/microsoft/STL/blob/main/tests/libcxx/expected_results.txt#L372
so not handling that case here.

[DavidSpickett]

For https://github.com/llvm/llvm-project/issues/47663.

That's a lot of boilerplate for the tests but I figured I'd stay focused on the problem at hand. (and there are probably reasons for that style)

I did notice that libstdc++ differs in its return value for the failures. It will consume just one character, even if the month is "13" where libcxx consumes both.

$ /tmp/test_libcxx.o
Parsing the date out of '13/01/2013' in the locale en_US.utf8
Parse failed. Unparsed string: /01/2013
$ g++ /tmp/test.cpp -o /tmp/test.o && /tmp/test.o
Parsing the date out of '13/01/2013' in the locale en_US.utf8
Parse failed. Unparsed string: 3/01/2013

From https://en.cppreference.com/w/cpp/locale/time_get/get_date (not sure if I should be getting the actual standard document for this) this seems like it could be ok.

I read in a draft standard for do_get_date specifically "Returns: An iterator pointing immediately beyond the last character recognized as possibly part of a valid date.". So "possibly" seems like it would allow for both behaviours.

[DavidSpickett]

libcxx/include/locale

1928

If this way of writing the comparison seems strange, I'm matching __get_day above.

[Mordante]

Thanks for working on this!

In D124175#3464773, @DavidSpickett wrote:

For https://github.com/llvm/llvm-project/issues/47663.

From https://en.cppreference.com/w/cpp/locale/time_get/get_date (not sure if I should be getting the actual standard document for this) this seems like it could be ok.

Nothing wrong with cppreference, but for the Standard wording we usually use http://eel.is/c++draft/locale.time.get.virtuals#lib:do_get_date,time_get. (Not sure whether you know this resource.)

I read in a draft standard for do_get_date specifically "Returns: An iterator pointing immediately beyond the last character recognized as possibly part of a valid date.". So "possibly" seems like it would allow for both behaviours.

I think libstdc++'s behaviour is the correct behaviour. But fixing that should be a separate review.

libcxx/test/std/localization/locale.categories/category.time/locale.time.get.byname/get_date.pass.cpp

17–18

:-( This is not your change, but it basically means these changes aren't tested in most of our CI. I'll create a fix.

115

This should be guarded with

#if _LIBCPP_VERSION
        assert(base(i) == in+2);
#else
        assert(base(i) == in+2);
#endif

Our tests should be portable and MSVC STL and GCC use them.

[DavidSpickett]

Nothing wrong with cppreference, but for the Standard wording we usually use http://eel.is/c++draft/locale.time.get.virtuals#lib:do_get_date,time_get. (Not sure whether you know this resource.)

I didn't, that's much better since cppreference has some of the descriptions merged.

I think libstdc++'s behaviour is the correct behaviour. But fixing that should be a separate review.

I think I see the logic there now. For MM/DD/YYYY "13/01/2022", the "1" could be part of a valid date ("1/01/2022"), but "13" could not. For the "00/" case, you can have one leading zero so "0" could possibly be part of a valid date ("01/01/2022") but "00" cannot be.

libcxx/test/std/localization/locale.categories/category.time/locale.time.get.byname/get_date.pass.cpp

115

I'll confirm what MSVC does and add these guards.

[DavidSpickett]

libcxx/test/std/localization/locale.categories/category.time/locale.time.get.byname/get_date.pass.cpp

17–18

Yeah I actually tested this on Linux by commenting out that one test case. So I can at least confirm everything else works.

[DavidSpickett]

Added defines for the iterator checks to support libstdc++.
(MSVC STL has these disabled already:
https://github.com/microsoft/STL/blob/main/tests/libcxx/expected_results.txt#L372
I do know what it does though so I could add that if needed?)

[DavidSpickett]

Rebase, might pick up the AIX xfails in the process.

[DavidSpickett]

I opened https://github.com/llvm/llvm-project/issues/55036 for the difference in the return value.

I agree with you that libstdc++ is correct, made sense once I thought about the use case where you want to know which bit of the date caused the problem.

[DavidSpickett]

Format step is failing in CI because I'm adding to files that aren't formatted to begin with. https://buildkite.com/llvm-project/libcxx-ci/builds/10345#813d83ad-2ec6-4919-9769-a226d56a6da3

[philnik]

In D124175#3467378, @DavidSpickett wrote:

Format step is failing in CI because I'm adding to files that aren't formatted to begin with. https://buildkite.com/llvm-project/libcxx-ci/builds/10345#813d83ad-2ec6-4919-9769-a226d56a6da3

You can ignore this. It's only soft failing currently.

[Mordante]

I'll have another look after the open review comments have been addressed, but the patch looks already nice.

libcxx/test/std/localization/locale.categories/category.time/locale.time.get.byname/get_date.pass.cpp

17–18

I just landed D124331, which fixes the tests on Linux. Can you rebase this patch on top of that to see whether the CI is happy too?

[DavidSpickett]

Rebase.

[DavidSpickett]

libcxx/test/std/localization/locale.categories/category.time/locale.time.get.byname/get_date.pass.cpp

115

I'm assuming no MSVC guards is ok.

[DavidSpickett]

You can ignore this. It's only soft failing currently.

Cool, thanks for confirming that.

[Mordante]

Sorry I missed your update, but LGTM! Please rebase to test the CI is green before landing.

libcxx/test/std/localization/locale.categories/category.time/locale.time.get.byname/get_date.pass.cpp

17–18

Odd this XFAIL should be gone upstream.

[DavidSpickett]

Rebase

[DavidSpickett]

libcxx/test/std/localization/locale.categories/category.time/locale.time.get.byname/get_date.pass.cpp

17–18

Must have rebased too soon, it's gone now.

libcxx/include/locale

 template <class _CharT, class _InputIterator>
 void
 time_get<_CharT, _InputIterator>::__get_month(int& __m,
                                               iter_type& __b, iter_type __e,
                                               ios_base::iostate& __err,
                                               const ctype<char_type>& __ct) const
 {
     int __t = __get_up_to_n_digits(__b, __e, __err, __ct, 2) - 1;
-    if (!(__err & ios_base::failbit) && __t <= 11)
+    if (!(__err & ios_base::failbit) && 0 <= __t && __t <= 11)
         __m = __t;
     else
         __err |= ios_base::failbit;
 }
 
 template <class _CharT, class _InputIterator>
 void
 time_get<_CharT, _InputIterator>::__get_year(int& __y,

libcxx/test/std/localization/locale.categories/category.time/locale.time.get.byname/get_date.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // NetBSD does not support LC_TIME at the moment
 // XFAIL: netbsd
 // XFAIL: LIBCXX-AIX-FIXME
 
 // REQUIRES: locale.en_US.UTF-8
 // REQUIRES: locale.fr_FR.UTF-8
 // REQUIRES: locale.ru_RU.UTF-8
 // REQUIRES: locale.zh_CN.UTF-8
 
 // <locale>
 
 // class time_get_byname<charT, InputIterator>
 
 // iter_type
 // get_date(iter_type s, iter_type end, ios_base& str,
 //          ios_base::iostate& err, tm* t) const;
 
 #include <locale>
#endif
         t = std::tm();
         I i = f.get_date(I(in), I(in+sizeof(in)/sizeof(in[0])-1), ios, err, &t);
         assert(base(i) == in+sizeof(in)/sizeof(in[0])-1);
         assert(t.tm_mon == 5);
         assert(t.tm_mday == 10);
         assert(t.tm_year == 109);
         assert(err == std::ios_base::eofbit);
     }
+    // Months must be > 0 and <= 12.
+    {
+        const my_facet f(LOCALE_en_US_UTF_8, 1);
+        const char in[] = "00/21/2022";
+        err = std::ios_base::goodbit;
+        t = std::tm();
+        I i = f.get_date(I(in), I(in+sizeof(in)/sizeof(in[0])-1), ios, err, &t);
+#if _LIBCPP_VERSION
+          // libc++ points to the '/' after the month.
+          assert(base(i) == in+2);
+#else
+          // libstdc++ points to the second character.
+          assert(base(i) == in+1);
+#endif
+        // tm is not modified.
+        assert(t.tm_mon == 0);
+        assert(t.tm_mday == 0);
+        assert(t.tm_year == 0);
+        assert(err == std::ios_base::failbit);
+    }
+    {
+        const my_facet f(LOCALE_en_US_UTF_8, 1);
+        const char in[] = "13/21/2022";
+        err = std::ios_base::goodbit;
+        t = std::tm();
+        I i = f.get_date(I(in), I(in+sizeof(in)/sizeof(in[0])-1), ios, err, &t);
+#if _LIBCPP_VERSION
+          // libc++ points to the '/' after the month.
+          assert(base(i) == in+2);
+#else
+          // libstdc++ points to the second character.
+          assert(base(i) == in+1);
+#endif
+        assert(base(i) == in+2);
+        assert(t.tm_mon == 0);
+        assert(t.tm_mday == 0);
+        assert(t.tm_year == 0);
+        assert(err == std::ios_base::failbit);
+    }
+    // Leading zero is allowed.
+    {
+        const my_facet f(LOCALE_en_US_UTF_8, 1);
+        const char in[] = "03/21/2022";
+        err = std::ios_base::goodbit;
+        t = std::tm();
+        I i = f.get_date(I(in), I(in+sizeof(in)/sizeof(in[0])-1), ios, err, &t);
+        assert(base(i) == in+sizeof(in)/sizeof(in[0])-1);
+        assert(t.tm_mon == 2);
+        assert(t.tm_mday == 21);
+        assert(t.tm_year == 122);
+        assert(err == std::ios_base::eofbit);
+    }
   return 0;
 }