[CMake] Fix ExtensionDependencies.inc with multiple extensions

[aeubanks]

Summary

When polly is enabled and LLVM_BYE_LINK_INTO_TOOLS=ON is on, ExtensionDependencies.inc does not compile.

$ ninja tools/llvm-config/CMakeFiles/llvm-config.dir/llvm-config.cpp.o
tools/llvm-config/ExtensionDependencies.inc:8:1: error: excess elements in struct initializer
{{"Bye", {"Bye",nullptr}}},

ExtensionDependencies.inc pre-patch:

std::array<ExtensionDescriptor, 2> AvailableExtensions{
{{"Polly", {"support", "core", ...,nullptr}}},
{{"Bye", {"Bye",nullptr}}},
};

ExtensionDependencies.inc with this patch:

std::array<ExtensionDescriptor, 2> AvailableExtensions{
ExtensionDescriptor{"Polly", {"support", "core", ...,nullptr}},
ExtensionDescriptor{"Bye", {"Bye",nullptr}},
};

[Meinersbur]

From the array element type, the compiler should know which type to brace-initialize. There seems to be one set of braces too much, makes me wonder how it ever worked.

In any case. the solution looks save, LGTM.

[aeubanks]

fix whitespace

[serge-sans-paille]

In D91641#2401024, @Meinersbur wrote:

There seems to be one set of braces too much, makes me wonder how it ever worked.

The « extra » set of brace was for list initialization, using that rule (from https://en.cppreference.com/w/cpp/language/list_initialization)

Otherwise, the constructors of T are considered, in two phases: 

    All constructors that take std::initializer_list as the only argument, or as the first argument if the remaining arguments have default values, are examined, and matched by overload resolution against a single argument of type std::initializer_list 

   If the previous stage does not produce a match, all constructors of T participate in overload resolution against the set of arguments that consists of the elements of the braced-init-list, with the restriction that only non-narrowing conversions are allowed. If this stage produces an explicit constructor  as the best match for a copy-list-initialization, compilation fails (note, in simple copy-initialization, explicit constructors are not considered at all).

Anyway, explicit is better than implicit, so this diff is definitively fine :-)

[Meinersbur]

In D91641#2401724, @serge-sans-paille wrote:

In D91641#2401024, @Meinersbur wrote:

There seems to be one set of braces too much, makes me wonder how it ever worked.

The « extra » set of brace was for list initialization, using that rule (from https://en.cppreference.com/w/cpp/language/list_initialization)

Otherwise, the constructors of T are considered, in two phases: 

    All constructors that take std::initializer_list as the only argument, or as the first argument if the remaining arguments have default values, are examined, and matched by overload resolution against a single argument of type std::initializer_list 

   If the previous stage does not produce a match, all constructors of T participate in overload resolution against the set of arguments that consists of the elements of the braced-init-list, with the restriction that only non-narrowing conversions are allowed. If this stage produces an explicit constructor  as the best match for a copy-list-initialization, compilation fails (note, in simple copy-initialization, explicit constructors are not considered at all).

Thanks for clarifying.

llvm/cmake/modules/AddLLVM.cmake

if(ARG_GEN_CONFIG)
               const char* Name;\n\
               const char* RequiredLibraries[1 + 1 + ${llvm_plugin_max_deps_length}];\n\
            };\n\
            std::array<ExtensionDescriptor, ${llvm_static_extension_count}> AvailableExtensions{\n")
 
       foreach(llvm_extension ${LLVM_STATIC_EXTENSIONS})
         get_property(llvm_plugin_deps TARGET ${llvm_extension} PROPERTY LINK_LIBRARIES)
 
-        file(APPEND "${ExtensionDeps}.tmp" "{{\"${llvm_extension}\", {")
+  file(APPEND "${ExtensionDeps}.tmp" "ExtensionDescriptor{\"${llvm_extension}\", {")
         foreach(llvm_plugin_dep ${llvm_plugin_deps})
             # Turn library dependency back to component name, if possible.
             # That way llvm-config can avoid redundant dependencies.
             STRING(REGEX REPLACE "^-l" ""  plugin_dep_name ${llvm_plugin_dep})
             STRING(REGEX MATCH "^LLVM" is_llvm_library ${plugin_dep_name})
             if(is_llvm_library)
                 STRING(REGEX REPLACE "^LLVM" ""  plugin_dep_name ${plugin_dep_name})
                 STRING(TOLOWER ${plugin_dep_name} plugin_dep_name)
             endif()
             file(APPEND "${ExtensionDeps}.tmp" "\"${plugin_dep_name}\", ")
         endforeach()
 
         # Self + mandatory trailing null, because the number of RequiredLibraries differs between extensions.
-        file(APPEND "${ExtensionDeps}.tmp" \"${llvm_extension}\", "nullptr}}},\n")
+        file(APPEND "${ExtensionDeps}.tmp" \"${llvm_extension}\", "nullptr}},\n")
       endforeach()
       file(APPEND "${ExtensionDeps}.tmp" "};\n")
 
       # only replace if there's an actual change
       execute_process(COMMAND ${CMAKE_COMMAND} -E copy_if_different
           "${ExtensionDeps}.tmp"
           "${ExtensionDeps}")
       file(REMOVE "${ExtensionDeps}.tmp")