Libelektra: Swig: Warning about Specialization of Non-Template `hash`

[sanssecours]

Steps to Reproduce the Problem

1. Clone the repository

   git clone https://github.com/ElektraInitiative/libelektra.git
   

2. Create build directory

   mkdir -p build
   

3. Create the build system using the following command

   cd build
   cmake ..                            \
         -GNinja                           \
         -DENABLE_ASAN=OFF                     \
         -DENABLE_LOGGER=OFF                   \
         -DENABLE_DEBUG=ON                     \
         -DENABLE_TESTING=ON                   \
         -DBUILD_PDF=ON                        \
         -DCMAKE_EXPORT_COMPILE_COMMANDS=ON            \
         -DPDFLATEX_COMPILER=`which latexmk`           \
         -DPDFLATEX_COMPILER_OPTIONS='-pdf;-f;-quiet'      \
         -DCMAKE_PREFIX_PATH=/usr/local/opt/qt5            \
         -DTOOLS=ALL                       \
         -DBINDINGS="ALL;-swig_ruby;-swig_python;-swig_python2"    \
         -DPLUGINS="ALL"
   

4. Compile Elektra

   ninja
   

   Expected Result

Elektra compiles without any warnings

Actual Result

Ninja prints the following warning:

[153/903] Swig source
Elektra/src/bindings/cpp/include/key.hpp:1753: Warning 317: Specialization of non-template 'hash'.

.

System Information

• Elektra Version: master
• OS: macOS 10.12.4

[markus2330]

Thank you for reporting! It seems like that is a hard-to-fix one!

According to the C++11 standard, the template hash should be defined in <functional>. (E.g. see http://en.cppreference.com/w/cpp/utility/hash) This fix was applied in 5e55f326c27eaa3b6dd1e962c23524637509c33d, but it seems like different compilers have different ideas where the template is defined. Where is it in yours?

We could add more headers until every compiler/system is happy?

[sanssecours]

According to the C++11 standard, the template hash should be defined in <functional>. Where is it in yours?

I have no idea, sorry 😳. I would assume the definition is in the same file. Below I attached a copy of the functional header from my system:

• functional.txt

. A newer version of this file should be available here. As far as I can tell the file contains at least specializations of hash for various types.

We could add more headers until every compiler/system is happy?

Sounds okay in my opinion.

[markus2330]

I tried to create a forward declarations like the headers do. Can you confirm if this fixes the warning? (simply close the issue if it does)

[sanssecours]

Thank you for trying to fix this issue. Unfortunately Elektra does not compile on my machine anymore since the latest commit. The text below shows the output of the build system.

[1/218] Building CXX object src/plugins/struct/CMakeFiles/elektra-struct-objects.dir/checker.cpp.o
FAILED: src/plugins/struct/CMakeFiles/elektra-struct-objects.dir/checker.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -DELEKTRA_STATIC -DHAVE_KDBCONFIG_H -DPLUGIN_SHORT_NAME=struct -DREADME=readme_struct.c -Isrc/include -I../src/include -Isrc/bindings/cpp/include -I../src/bindings/cpp/include -Isrc/plugins/struct -std=c++11  -Wno-deprecated-declarations -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fsanitize=integer  -Wold-style-cast -Wno-missing-field-initializers -Woverloaded-virtual  -Wsign-promo  -Wno-long-long -pedantic -Wno-variadic-macros -Wall -Wextra -Wno-overlength-strings -Wsign-compare -Wfloat-equal -Wformat-security -Wshadow -Wcomments -Wtrigraphs -Wundef -Wuninitialized -Winit-self -O2 -g -DNDEBUG   -fPIC -MD -MT src/plugins/struct/CMakeFiles/elektra-struct-objects.dir/checker.cpp.o -MF src/plugins/struct/CMakeFiles/elektra-struct-objects.dir/checker.cpp.o.d -o src/plugins/struct/CMakeFiles/elektra-struct-objects.dir/checker.cpp.o -c "Elektra/src/plugins/struct/checker.cpp"
In file included from Elektra/src/plugins/struct/checker.cpp:11:
In file included from Elektra/src/plugins/struct/checker.hpp:19:
../src/bindings/cpp/include/key.hpp:1757:8: error: explicit specialization of non-template struct 'hash'
struct hash<kdb::Key>
       ^   ~~~~~~~~~~
../src/bindings/cpp/include/key.hpp:1757:8: error: redefinition of 'hash' as different kind of symbol
../src/bindings/cpp/include/key.hpp:1751:8: note: previous definition is here
struct hash;
       ^
2 errors generated.
[2/218] Building CXX object src/plugins/struct/CMakeFiles/elektra-struct.dir/checker.cpp.o
FAILED: src/plugins/struct/CMakeFiles/elektra-struct.dir/checker.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -DHAVE_KDBCONFIG_H -DPLUGIN_SHORT_NAME=struct -DREADME=readme_struct.c -Delektra_struct_EXPORTS -Isrc/include -I../src/include -Isrc/bindings/cpp/include -I../src/bindings/cpp/include -Isrc/plugins/struct -std=c++11  -Wno-deprecated-declarations -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fsanitize=integer  -Wold-style-cast -Wno-missing-field-initializers -Woverloaded-virtual  -Wsign-promo  -Wno-long-long -pedantic -Wno-variadic-macros -Wall -Wextra -Wno-overlength-strings -Wsign-compare -Wfloat-equal -Wformat-security -Wshadow -Wcomments -Wtrigraphs -Wundef -Wuninitialized -Winit-self -O2 -g -DNDEBUG -fPIC -MD -MT src/plugins/struct/CMakeFiles/elektra-struct.dir/checker.cpp.o -MF src/plugins/struct/CMakeFiles/elektra-struct.dir/checker.cpp.o.d -o src/plugins/struct/CMakeFiles/elektra-struct.dir/checker.cpp.o -c "Elektra/src/plugins/struct/checker.cpp"
In file included from Elektra/src/plugins/struct/checker.cpp:11:
In file included from Elektra/src/plugins/struct/checker.hpp:19:
../src/bindings/cpp/include/key.hpp:1757:8: error: explicit specialization of non-template struct 'hash'
struct hash<kdb::Key>
       ^   ~~~~~~~~~~
../src/bindings/cpp/include/key.hpp:1757:8: error: redefinition of 'hash' as different kind of symbol
../src/bindings/cpp/include/key.hpp:1751:8: note: previous definition is here
struct hash;
       ^
2 errors generated.
[3/218] Building CXX object src/plugins/lua/CMakeFiles/elektra-lua.dir/lua.cpp.o
FAILED: src/plugins/lua/CMakeFiles/elektra-lua.dir/lua.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -DHAVE_KDBCONFIG_H -DPLUGIN_SHORT_NAME=lua -DREADME=readme_lua.c -DSWIG_TYPE_TABLE=kdb -Delektra_lua_EXPORTS -Isrc/include -I../src/include -Isrc/bindings/cpp/include -I../src/bindings/cpp/include -I/usr/local/include -Isrc/plugins/lua -std=c++11  -Wno-deprecated-declarations -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fsanitize=integer  -Wold-style-cast -Wno-missing-field-initializers -Woverloaded-virtual  -Wsign-promo  -Wno-long-long -pedantic -Wno-variadic-macros -Wall -Wextra -Wno-overlength-strings -Wsign-compare -Wfloat-equal -Wformat-security -Wshadow -Wcomments -Wtrigraphs -Wundef -Wuninitialized -Winit-self -O2 -g -DNDEBUG -fPIC   -Wno-shadow -Wno-old-style-cast -Wno-unused-variable -MD -MT src/plugins/lua/CMakeFiles/elektra-lua.dir/lua.cpp.o -MF src/plugins/lua/CMakeFiles/elektra-lua.dir/lua.cpp.o.d -o src/plugins/lua/CMakeFiles/elektra-lua.dir/lua.cpp.o -c "Elektra/src/plugins/lua/lua.cpp"
In file included from Elektra/src/plugins/lua/lua.cpp:20:
../src/bindings/cpp/include/key.hpp:1757:8: error: explicit specialization of non-template struct 'hash'
struct hash<kdb::Key>
       ^   ~~~~~~~~~~
../src/bindings/cpp/include/key.hpp:1757:8: error: redefinition of 'hash' as different kind of symbol
../src/bindings/cpp/include/key.hpp:1751:8: note: previous definition is here
struct hash;
       ^
2 errors generated.
[4/218] Building CXX object src/plugins/lua/CMakeFiles/elektra-lua-objects.dir/lua.cpp.o
FAILED: src/plugins/lua/CMakeFiles/elektra-lua-objects.dir/lua.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -DELEKTRA_STATIC -DHAVE_KDBCONFIG_H -DPLUGIN_SHORT_NAME=lua -DREADME=readme_lua.c -DSWIG_TYPE_TABLE=kdb -Isrc/include -I../src/include -Isrc/bindings/cpp/include -I../src/bindings/cpp/include -I/usr/local/include -Isrc/plugins/lua -std=c++11  -Wno-deprecated-declarations -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fsanitize=integer  -Wold-style-cast -Wno-missing-field-initializers -Woverloaded-virtual  -Wsign-promo  -Wno-long-long -pedantic -Wno-variadic-macros -Wall -Wextra -Wno-overlength-strings -Wsign-compare -Wfloat-equal -Wformat-security -Wshadow -Wcomments -Wtrigraphs -Wundef -Wuninitialized -Winit-self -O2 -g -DNDEBUG   -fPIC -Wno-shadow -Wno-old-style-cast -Wno-unused-variable -MD -MT src/plugins/lua/CMakeFiles/elektra-lua-objects.dir/lua.cpp.o -MF src/plugins/lua/CMakeFiles/elektra-lua-objects.dir/lua.cpp.o.d -o src/plugins/lua/CMakeFiles/elektra-lua-objects.dir/lua.cpp.o -c "Elektra/src/plugins/lua/lua.cpp"
In file included from Elektra/src/plugins/lua/lua.cpp:20:
../src/bindings/cpp/include/key.hpp:1757:8: error: explicit specialization of non-template struct 'hash'
struct hash<kdb::Key>
       ^   ~~~~~~~~~~
../src/bindings/cpp/include/key.hpp:1757:8: error: redefinition of 'hash' as different kind of symbol
../src/bindings/cpp/include/key.hpp:1751:8: note: previous definition is here
struct hash;
       ^
2 errors generated.
[5/218] Building CXX object src/plugins/python2/CMakeFiles/elektra-python2-objects.dir/python.cpp.o
FAILED: src/plugins/python2/CMakeFiles/elektra-python2-objects.dir/python.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -DELEKTRA_STATIC -DHAVE_KDBCONFIG_H -DPLUGIN_SHORT_NAME=python2 -DPYTHON_PLUGIN_NAME=python2 -DPYTHON_PLUGIN_SYMBOL_NAME=Python2 -DREADME=readme_python2.c -DSWIG_RUNTIME=\"runtime.h\" -DSWIG_TYPE_TABLE=kdb -Isrc/include -I../src/include -Isrc/bindings/cpp/include -I../src/bindings/cpp/include -I/System/Library/Frameworks/Python.framework/Headers -Isrc/plugins/python2 -std=c++11  -Wno-deprecated-declarations -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fsanitize=integer  -Wold-style-cast -Wno-missing-field-initializers -Woverloaded-virtual  -Wsign-promo  -Wno-long-long -pedantic -Wno-variadic-macros -Wall -Wextra -Wno-overlength-strings -Wsign-compare -Wfloat-equal -Wformat-security -Wshadow -Wcomments -Wtrigraphs -Wundef -Wuninitialized -Winit-self -O2 -g -DNDEBUG   -fPIC -Wno-shadow -Wno-old-style-cast -Wno-unused-variable -MD -MT src/plugins/python2/CMakeFiles/elektra-python2-objects.dir/python.cpp.o -MF src/plugins/python2/CMakeFiles/elektra-python2-objects.dir/python.cpp.o.d -o src/plugins/python2/CMakeFiles/elektra-python2-objects.dir/python.cpp.o -c "Elektra/src/plugins/python2/python.cpp"
In file included from Elektra/src/plugins/python2/python.cpp:9:
In file included from Elektra/src/plugins/python2/../python/python.cpp:23:
../src/bindings/cpp/include/key.hpp:1757:8: error: explicit specialization of non-template struct 'hash'
struct hash<kdb::Key>
       ^   ~~~~~~~~~~
../src/bindings/cpp/include/key.hpp:1757:8: error: redefinition of 'hash' as different kind of symbol
../src/bindings/cpp/include/key.hpp:1751:8: note: previous definition is here
struct hash;
       ^
2 errors generated.
[6/218] Building CXX object src/plugins/python2/CMakeFiles/elektra-python2.dir/python.cpp.o
FAILED: src/plugins/python2/CMakeFiles/elektra-python2.dir/python.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -DHAVE_KDBCONFIG_H -DPLUGIN_SHORT_NAME=python2 -DPYTHON_PLUGIN_NAME=python2 -DPYTHON_PLUGIN_SYMBOL_NAME=Python2 -DREADME=readme_python2.c -DSWIG_RUNTIME=\"runtime.h\" -DSWIG_TYPE_TABLE=kdb -Delektra_python2_EXPORTS -Isrc/include -I../src/include -Isrc/bindings/cpp/include -I../src/bindings/cpp/include -I/System/Library/Frameworks/Python.framework/Headers -Isrc/plugins/python2 -std=c++11  -Wno-deprecated-declarations -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fsanitize=integer  -Wold-style-cast -Wno-missing-field-initializers -Woverloaded-virtual  -Wsign-promo  -Wno-long-long -pedantic -Wno-variadic-macros -Wall -Wextra -Wno-overlength-strings -Wsign-compare -Wfloat-equal -Wformat-security -Wshadow -Wcomments -Wtrigraphs -Wundef -Wuninitialized -Winit-self -O2 -g -DNDEBUG -fPIC   -Wno-shadow -Wno-old-style-cast -Wno-unused-variable -MD -MT src/plugins/python2/CMakeFiles/elektra-python2.dir/python.cpp.o -MF src/plugins/python2/CMakeFiles/elektra-python2.dir/python.cpp.o.d -o src/plugins/python2/CMakeFiles/elektra-python2.dir/python.cpp.o -c "Elektra/src/plugins/python2/python.cpp"
In file included from Elektra/src/plugins/python2/python.cpp:9:
In file included from Elektra/src/plugins/python2/../python/python.cpp:23:
../src/bindings/cpp/include/key.hpp:1757:8: error: explicit specialization of non-template struct 'hash'
struct hash<kdb::Key>
       ^   ~~~~~~~~~~
../src/bindings/cpp/include/key.hpp:1757:8: error: redefinition of 'hash' as different kind of symbol
../src/bindings/cpp/include/key.hpp:1751:8: note: previous definition is here
struct hash;
       ^
2 errors generated.
[7/218] Building CXX object src/plugins/struct/CMakeFiles/elektra-struct.dir/struct.cpp.o
FAILED: src/plugins/struct/CMakeFiles/elektra-struct.dir/struct.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -DHAVE_KDBCONFIG_H -DPLUGIN_SHORT_NAME=struct -DREADME=readme_struct.c -Delektra_struct_EXPORTS -Isrc/include -I../src/include -Isrc/bindings/cpp/include -I../src/bindings/cpp/include -Isrc/plugins/struct -std=c++11  -Wno-deprecated-declarations -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fsanitize=integer  -Wold-style-cast -Wno-missing-field-initializers -Woverloaded-virtual  -Wsign-promo  -Wno-long-long -pedantic -Wno-variadic-macros -Wall -Wextra -Wno-overlength-strings -Wsign-compare -Wfloat-equal -Wformat-security -Wshadow -Wcomments -Wtrigraphs -Wundef -Wuninitialized -Winit-self -O2 -g -DNDEBUG -fPIC -MD -MT src/plugins/struct/CMakeFiles/elektra-struct.dir/struct.cpp.o -MF src/plugins/struct/CMakeFiles/elektra-struct.dir/struct.cpp.o.d -o src/plugins/struct/CMakeFiles/elektra-struct.dir/struct.cpp.o -c "Elektra/src/plugins/struct/struct.cpp"
In file included from Elektra/src/plugins/struct/struct.cpp:13:
../src/bindings/cpp/include/key.hpp:1757:8: error: explicit specialization of non-template struct 'hash'
struct hash<kdb::Key>
       ^   ~~~~~~~~~~
../src/bindings/cpp/include/key.hpp:1757:8: error: redefinition of 'hash' as different kind of symbol
../src/bindings/cpp/include/key.hpp:1751:8: note: previous definition is here
struct hash;
       ^
2 errors generated.
[8/218] Building CXX object src/plugins/struct/CMakeFiles/elektra-struct-objects.dir/struct.cpp.o
FAILED: src/plugins/struct/CMakeFiles/elektra-struct-objects.dir/struct.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -DELEKTRA_STATIC -DHAVE_KDBCONFIG_H -DPLUGIN_SHORT_NAME=struct -DREADME=readme_struct.c -Isrc/include -I../src/include -Isrc/bindings/cpp/include -I../src/bindings/cpp/include -Isrc/plugins/struct -std=c++11  -Wno-deprecated-declarations -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fsanitize=integer  -Wold-style-cast -Wno-missing-field-initializers -Woverloaded-virtual  -Wsign-promo  -Wno-long-long -pedantic -Wno-variadic-macros -Wall -Wextra -Wno-overlength-strings -Wsign-compare -Wfloat-equal -Wformat-security -Wshadow -Wcomments -Wtrigraphs -Wundef -Wuninitialized -Winit-self -O2 -g -DNDEBUG   -fPIC -MD -MT src/plugins/struct/CMakeFiles/elektra-struct-objects.dir/struct.cpp.o -MF src/plugins/struct/CMakeFiles/elektra-struct-objects.dir/struct.cpp.o.d -o src/plugins/struct/CMakeFiles/elektra-struct-objects.dir/struct.cpp.o -c "Elektra/src/plugins/struct/struct.cpp"
In file included from Elektra/src/plugins/struct/struct.cpp:13:
../src/bindings/cpp/include/key.hpp:1757:8: error: explicit specialization of non-template struct 'hash'
struct hash<kdb::Key>
       ^   ~~~~~~~~~~
../src/bindings/cpp/include/key.hpp:1757:8: error: redefinition of 'hash' as different kind of symbol
../src/bindings/cpp/include/key.hpp:1751:8: note: previous definition is here
struct hash;
       ^
2 errors generated.
[9/218] Building CXX object src/plugins/tcl/CMakeFiles/elektra-tcl.dir/tcl.cpp.o
FAILED: src/plugins/tcl/CMakeFiles/elektra-tcl.dir/tcl.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -DHAVE_KDBCONFIG_H -DPLUGIN_SHORT_NAME=tcl -DREADME=readme_tcl.c -Delektra_tcl_EXPORTS -Isrc/include -I../src/include -Isrc/bindings/cpp/include -I../src/bindings/cpp/include -Isrc/plugins/tcl -std=c++11  -Wno-deprecated-declarations -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fsanitize=integer  -Wold-style-cast -Wno-missing-field-initializers -Woverloaded-virtual  -Wsign-promo  -Wno-long-long -pedantic -Wno-variadic-macros -Wall -Wextra -Wno-overlength-strings -Wsign-compare -Wfloat-equal -Wformat-security -Wshadow -Wcomments -Wtrigraphs -Wundef -Wuninitialized -Winit-self -O2 -g -DNDEBUG -fPIC   -isystem  /usr/local/include -MD -MT src/plugins/tcl/CMakeFiles/elektra-tcl.dir/tcl.cpp.o -MF src/plugins/tcl/CMakeFiles/elektra-tcl.dir/tcl.cpp.o.d -o src/plugins/tcl/CMakeFiles/elektra-tcl.dir/tcl.cpp.o -c "Elektra/src/plugins/tcl/tcl.cpp"
In file included from Elektra/src/plugins/tcl/tcl.cpp:9:
In file included from Elektra/src/plugins/tcl/tcl.hpp:14:
In file included from ../src/bindings/cpp/include/keyset.hpp:18:
../src/bindings/cpp/include/key.hpp:1757:8: error: explicit specialization of non-template struct 'hash'
struct hash<kdb::Key>
       ^   ~~~~~~~~~~
../src/bindings/cpp/include/key.hpp:1757:8: error: redefinition of 'hash' as different kind of symbol
../src/bindings/cpp/include/key.hpp:1751:8: note: previous definition is here
struct hash;
       ^
2 errors generated.
[10/218] Building CXX object src/plugins/tcl/CMakeFiles/elektra-tcl.dir/action.cpp.o
FAILED: src/plugins/tcl/CMakeFiles/elektra-tcl.dir/action.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -DHAVE_KDBCONFIG_H -DPLUGIN_SHORT_NAME=tcl -DREADME=readme_tcl.c -Delektra_tcl_EXPORTS -Isrc/include -I../src/include -Isrc/bindings/cpp/include -I../src/bindings/cpp/include -Isrc/plugins/tcl -std=c++11  -Wno-deprecated-declarations -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fsanitize=integer  -Wold-style-cast -Wno-missing-field-initializers -Woverloaded-virtual  -Wsign-promo  -Wno-long-long -pedantic -Wno-variadic-macros -Wall -Wextra -Wno-overlength-strings -Wsign-compare -Wfloat-equal -Wformat-security -Wshadow -Wcomments -Wtrigraphs -Wundef -Wuninitialized -Winit-self -O2 -g -DNDEBUG -fPIC   -isystem  /usr/local/include -MD -MT src/plugins/tcl/CMakeFiles/elektra-tcl.dir/action.cpp.o -MF src/plugins/tcl/CMakeFiles/elektra-tcl.dir/action.cpp.o.d -o src/plugins/tcl/CMakeFiles/elektra-tcl.dir/action.cpp.o -c "Elektra/src/plugins/tcl/action.cpp"
In file included from Elektra/src/plugins/tcl/action.cpp:9:
In file included from ../src/bindings/cpp/include/keyset.hpp:18:
../src/bindings/cpp/include/key.hpp:1757:8: error: explicit specialization of non-template struct 'hash'
struct hash<kdb::Key>
       ^   ~~~~~~~~~~
../src/bindings/cpp/include/key.hpp:1757:8: error: redefinition of 'hash' as different kind of symbol
../src/bindings/cpp/include/key.hpp:1751:8: note: previous definition is here
struct hash;
       ^
2 errors generated.

[markus2330]

Thanks for reporting, I reverted it.

[sanssecours]

I looked a bit more into this. It seems the warning is a product of Swig and not dependent on either the compiler or the OS, since building Elektra on Ubuntu with GCC produces the same warning.

[markus2330]

"low priority" and "1.0.0" is contradictory. "1.0.0" is only for features we need to release "1.0.0". "low priority" features do not need a milestone, they are done whenever someone wants do it.

[sanssecours]

Commit 918ff0da already fixed this issue anyway 😄.