Lack of handling of "requires" in mbed_app.json

[LDong-Arm]

Description

The Mbed configuration system has a "requires" field (see example) to restrict compilation to certain libraries instead of the whole Mbed OS. This also affects what macros get defined, i.e. macros are only generated from mbed_lib.json of libraries we build.

The current version of mbed-tools defines macros from all libraries, regardless of "defines". This causes issues (see discussion in ARMmbed/mbed-os#13934) when we need to define a macro only when the library is enabled.

Note: If this issue is resolved, we should not need #78 anymore. But there's a more fundamental issue: the "requires": [...] field duplicates the purpose CMake dependency lists:

target_link_libraries(${APP_TARGET}
    PRIVATE
        mbed-os
        mbed-netsocket
)

Such duplication means users would list dependencies twice, once for CMake, once in "requires". How could we handle this?

Issue request type

• Enhancement
• Bug

[LDong-Arm]

@Patater @hugueskamba