missing CMakeLists option for deep plc

[reg31]

Hi,

There is no option to set OPUS_DEEP_PLC, and add_sources_group(opus lpcnet ${deep_plc_headers} ${deep_plc_sources}) is defined twice:

if (OPUS_DEEP_PLC OR OPUS_DRED OR OPUS_OSCE)
add_sources_group(opus lpcnet ${deep_plc_headers} ${deep_plc_sources})
set(OPUS_DNN TRUE)
else()
set(OPUS_DNN FALSE)
endif()

if (OPUS_DNN)
add_sources_group(opus lpcnet ${deep_plc_headers} ${deep_plc_sources})
target_compile_definitions(opus PRIVATE ENABLE_DEEP_PLC)
endif()

https://github.com/xiph/opus/blob/main/CMakeLists.txt#L399

The file is missing something like:

set(OPUS_DEEP_PLC_HELP_STR "enable deep plc.")
option(OPUS_DEEP_PLC ${OPUS_DEEP_PLC_HELP_STR} OFF)
add_feature_info(OPUS_DEEP_PLC OPUS_DEEP_PLC ${OPUS_DEEP_PLC_HELP_STR})

[xnorpx]

I saw this as well.

I didn't write this code, but we should compare what autoconf does and mimic that.