1601907 - non-constexpr function 'length' cannot be used in a constant expression

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Sylvestre Ledru [:Sylvestre]]

Building with clang trunk

 /var/lib/jenkins/workspace/firefox-clang-last/js/src/builtin/intl/NumberFormat.cpp:403:25: error: constexpr function never produces a constant expression [-Winvalid-constexpr]
 static constexpr size_t MaxUnitLength() {
                         ^
 /var/lib/jenkins/workspace/firefox-clang-last/js/src/builtin/intl/NumberFormat.cpp:408:31: note: non-constexpr function 'length' cannot be used in a constant expression
     length = std::max(length, std::char_traits<char>::length(unit.subtype));
                               ^
 /usr/bin/../lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/bits/char_traits.h:266:7: note: declared here
       length(const char_type* __s)
       ^
 In file included from Unified_cpp_js_src5.cpp:2:
 /var/lib/jenkins/workspace/firefox-clang-last/js/src/builtin/intl/NumberFormat.cpp:419:18: error: variable-sized object may not be initialized
   char unitChars[MaxUnitLength() + 1] = {};
                  ^~~~~~~~~~~~~~~~~~~
 2 errors generated.

Maybe caused by the C++17 migration?
with clang version 10.0.0-[phone]+41eeded8043-1exp120191205105719.1634

Comment 1

[Nathan Froyd [:froydnj]]

This is because GCC 6.x's libstdc++ is not C++17 conformant. We could just disable the constexpr code path here (I have a local patch to do just that).

Comment 2

[Sylvestre Ledru [:Sylvestre]]

Attachment: Bug 1601907 - Disable a code path when built with libstdc++ 6 and below r?froydnj

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/c1db977cabfe
Disable a code path when built with libstdc++ 6 and below r=froydnj

Comment 4

[Narcis Beleuzu [:NarcisB]]

https://hg.mozilla.org/mozilla-central/rev/c1db977cabfe

Comment 5

[Rico Tzschichholz]

This change actually causes the mentioned build failure on Ubuntu with clang 9 and libstdc++ 6 (gcc 8.3.0 and 9.2.1)

https://launchpadlibrarian.net/455261494/buildlog_ubuntu-focal-amd64.firefox-trunk_73.0~a1~hg20191211r506473-0ubuntu0.20.04.1~umd1_BUILDING.txt.gz

Building with clang 8 and libstdc++6 (gcc 5.4.0) seems to be not affected.

Comment 6

[Sylvestre Ledru [:Sylvestre]]

(In reply to Rico Tzschichholz from comment #5)

This change actually causes the mentioned build failure on Ubuntu with clang 9 and libstdc++ 6 (gcc 8.3.0 and 9.2.1)

could you please open a new bug for this?
thanks

Comment 7

[Rico Tzschichholz]

https://bugzilla.mozilla.org/show_bug.cgi?id=1603371