cannot compile 0.10.7 with uClibc++

[neheb]

Describe the bug

/home/mangix/devstuff/openwrt/staging_dir/toolchain-mips_24kc_gcc-9.3.0_musl/lib/gcc/mips-openwrt-linux-musl/9.3.0/../../../../mips-openwrt-linux-musl/bin/ld: src/lib_json/libjsoncpp.a(json_value.cpp.o): in function `Json::Value::operator<(Json::Value const&) const':
json_value.cpp:(.text+0x5dc): undefined reference to `bool std::operator< <Json::Value::CZString, Json::Value, std::less<Json::Value::CZString>, std::allocator<Json::Value> >(std::map<Json::Value::CZString, Json::Value, std::less<Json::Value::CZString>, std::allocator<Json::Value> > const&, std::map<Json::Value::CZString, Json::Value, std::less<Json::Value::CZString>, std::allocator<Json::Value> > const&)'
collect2: error: ld returned 1 exit status

This was after several changes with defines to get it to build. Also backported b082693

Maybe something else is needed...

Desktop (please complete the following information):

• OS: OpenWrt
• Meson version - latest. 0.54
• Ninja version - latest 1.10

[neheb]

Real error:

src/lib_json/json_value.cpp:937:16: warning: returning reference to temporary [-Wreturn-local-addr]
  937 |   return (*it).second;
      |          ~~~~~~^~~~~~
src/lib_json/json_value.cpp: In member function 'const Json::Value* Json::Value::find(const char*, const char*) const':
src/lib_json/json_value.cpp:1010:17: error: taking address of rvalue [-fpermissive]
 1010 |   return &(*it).second;

I tried to work around it by using normal iterators but that didn't work.

[BillyDonahue]

For reference (fudging the line number a bit):

src/lib_json/json_value.cpp:937

jsoncpp/src/lib_json/json_value.cpp

Line 1059 in 90ca694

return (*it).second;

and

src/lib_json/json_value.cpp:1010

jsoncpp/src/lib_json/json_value.cpp

Line 1085 in 90ca694

return &(*it).second;

[BillyDonahue]

json_value.cpp:(.text+0x5dc): undefined reference to
bool std::operator< <K,V,C,A> (
    std::map<K,V,C,A> const &,
    std::map<K,V,C,A> const &);
[ with
  K = Json::Value::CZString,
  V = Json::Value,
  C = std::less<Json::Value::CZString>,
  A = std::allocator<Json::Value>
]

It should be the standard library's job to define the operator< between std::map objects.
Check your link line?

I don't see how the "real error" cited would contribute to a link error like this.

As far as I can tell, I don't think those return statements are returning local memory.
It may be that the version of jsoncpp this is happening on is not current master branch?

[neheb]

The way I got that link error was by changing two const_iterator to iterator. Otherwise I get those two return errors.

The version is the release version. Version 1.9.2 does not even compile.