FetchContent a directory but add a subdirectory

[rturrado (Roberto Turrado Camblor)]

@craig.scott

EDIT: Oh, I see that reordering would be a problem in this case. You need HIGHS_SOURCE_DIR and HIGHS_BINARY_DIR to be populated before the downloaded source has been loaded. You could let FetchContent handle the downloading only, but take control of the add_subdirectory() part by setting SOURCE_SUBDIR to a non-existent subdirectory. That will prevent FetchContent_MakeAvailable() from calling add_subdirectory(). The main advantage to using FetchContent_MakeAvailable() is

Many thanks for your comments @craig.scott.

Are you then proposing something like this?

FetchContent_Declare(highs
    GIT_REPOSITORY https://github.com/ERGO-Code/HiGHS.git
    GIT_TAG "45a127b78060942721f75f46a04b274c2bb963d8"
    SOURCE_SUBDIR this-directory-does-not-exist
)

# FechContentMakeAvailable will set
# highs_SOURCE_DIR to _deps/highs-src/this-directory-does-not-exist, and
# highs_BINARY_DIR to _deps/highs-build/this-directory-does-not-exist
FetchContent_MakeAvailable(highs)

# Properly setting
# highs_SOURCE_DIR to _deps/highs-src/src, and
# higs_BINARY_DIR to _deps/highs-build/src
set(highs_SOURCE_DIR "${highs_SOURCE_DIR}/../src")
set(highs_BINARY_DIR "${highs_BINARY_DIR}/../src")

# Now carry on doing what we were doing with FetchContent_Populate
set(HIGHS_SOURCE_DIR "${highs_SOURCE_DIR}/..")
set(HIGHS_BINARY_DIR "${highs_BINARY_DIR}/..")
add_subdirectory("${highs_SOURCE_DIR}/src" "${highs_BINARY_DIR}/src" SYSTEM)