[Bug c++/114439] New: [14 Regression] icu4c-73.2 build failure: invalid initializer for array member

["slyfox at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114439

            Bug ID: 114439
           Summary: [14 Regression] icu4c-73.2 build failure: invalid
                    initializer for array member
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
  Target Milestone: ---

Initially observed build failure on icu4c-73.2 using gcc
r14-9636-gc2e28df90a1640 .

The build fails there as:

regexst.cpp: In constructor
'icu_73::RegexStaticSets::RegexStaticSets(UErrorCode*)':
regexst.cpp:75:52: error: invalid initializer for array member
'icu_73::UnicodeSet icu_73::RegexStaticSets::fPropSets [13]'
   75 | RegexStaticSets::RegexStaticSets(UErrorCode *status) {
      |                                                    ^
regexst.cpp:75:52: error: invalid initializer for array member
'icu_73::Regex8BitSet icu_73::RegexStaticSets::fPropSets8 [13]'
regexst.cpp:75:52: error: invalid initializer for array member
'icu_73::UnicodeSet icu_73::RegexStaticSets::fRuleSets [3]'

Minimized example:

$ cat regexst.cpp.cpp
struct UnicodeSet {
  int *list = stackList;
  int stackList[];
};
struct RegexStaticSets {
  RegexStaticSets() {}
  UnicodeSet fPropSets[2]{};
};

$ g++-14 -std=c++11 -c regexst.cpp.cpp -o bug.o
regexst.cpp.cpp: In constructor 'RegexStaticSets::RegexStaticSets()':
regexst.cpp.cpp:6:21: error: invalid initializer for array member 'UnicodeSet
RegexStaticSets::fPropSets [2]'
    6 |   RegexStaticSets() {}
      |                     ^

For comparison gcc-13 looks fine:

$ g++-13 -std=c++11 -c regexst.cpp.cpp -o bug.o

Compiler version:

$ g++-14 -v
Using built-in specs.
COLLECT_GCC=/<<NIX>>/gcc-14.0.1/bin/g++
COLLECT_LTO_WRAPPER=/<<NIX>>/gcc-14.0.1/libexec/gcc/x86_64-unknown-linux-gnu/14.0.1/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../source/configure --prefix=/<<NIX>>/gcc-14.0.1
--with-gmp-include=/<<NIX>>/gmp-6.3.0-dev/include
--with-gmp-lib=/<<NIX>>/gmp-6.3.0/lib
--with-mpfr-include=/<<NIX>>/mpfr-4.2.1-dev/include
--with-mpfr-lib=/<<NIX>>/mpfr-4.2.1/lib --with-mpc=/<<NIX>>/libmpc-1.3.1
--with-native-system-header-dir=/<<NIX>>/glibc-2.39-dev/include
--with-build-sysroot=/
--with-gxx-include-dir=/<<NIX>>/gcc-14.0.1/include/c++/14.0.1/
--program-prefix= --enable-lto --disable-libstdcxx-pch
--without-included-gettext --with-system-zlib --enable-checking=release
--enable-static --enable-languages=c,c++ --disable-multilib --enable-plugin
--disable-libcc1 --with-isl=/<<NIX>>/isl-0.20 --disable-bootstrap
--build=x86_64-unknown-linux-gnu --host=x86_64-unknown-linux-gnu
--target=x86_64-unknown-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.1 99999999 (experimental) (GCC)