cmake: fix to use variable for the curl namespace

[vszakats]

Replace (wrong) literal with a variable to specify the curl
namespace.

Follow-up to 1199308 #11505

Reported-by: balikalina on Github
Fixes 1199308#r123923098
Closes #11629

[balikalina]

Some projects need to export alias
add_library(ALIAS) in config file in some cases cause an error

CMake Error at ***/build/parts/curl/install/lib64/cmake/CURL/CURLConfig.cmake:62 (add_library):
[25/26]   add_library cannot create ALIAS target "CURL::libcurl" because target
[25/26]   "CURL::libcurl_static" is imported but not globally visible.
[25/26] Call Stack (most recent call first):
[25/26]   /usr/share/cmake3/Modules/FindCURL.cmake:58 (find_package)
[25/26]   pull/tests/integration/CMakeLists.txt:29 (find_package)
[25/26] -- Found CURL: ***/build/parts/curl/install/lib64/cmake/CURL/CURLConfig.cmake (found version "8.3.0-DEV")  
[25/26] CMake Error at ***/build/parts/curl/install/lib64/cmake/CURL/CURLConfig.cmake:62 (add_library):
[25/26]   add_library cannot create ALIAS target "CURL::libcurl" because target
[25/26]   "CURL::libcurl_static" is imported but not globally visible.
[25/26] Call Stack (most recent call first):
[25/26]   /usr/share/cmake3/Modules/FindCURL.cmake:58 (find_package)
[25/26]   push/CMakeLists.txt:2 (find_package)

there is an issue about exporting the alias
https://gitlab.kitware.com/cmake/cmake/-/issues/18996

so could you consider please set property EXPORT_NAME instead of add_library(ALIAS)?

line 222 lib/CMakeLists.txt

add_library(${LIB_NAME} ALIAS ${LIB_SELECTED})
add_library(${PROJECT_NAME}::${LIB_NAME} ALIAS ${LIB_SELECTED})

#export libcurl alias as target name
set_property(TARGET ${LIB_SELECTED}
  PROPERTY
  EXPORT_NAME ${LIB_NAME})

if(CURL_ENABLE_EXPORT_TARGET)

if added, must remove the

add_library(@PROJECT_NAME@::libcurl ALIAS @PROJECT_NAME@::@LIB_SELECTED@)

from CMake/curl-config.cmake.in

[vszakats]

Thank you, is this what you had in mind?: #11646

[balikalina]

Thank you, is this what you had in mind?: #11646

yes, exactly
if it doesn't crash any other builds for other build systems/os
may be should take some pause while waiting for other opinions

[vszakats]

There was an issue reported with this solution over at libssh2: libssh2/libssh2#1154 (comment)

With a difference suggestion for a fix.

[balikalina]

There was an issue reported with this solution over at libssh2: libssh2/libssh2#1154 (comment)

With a difference suggestion for a fix.

if I move setting property EXPORT_NAME from lib/CMakeLists.txt to CMake/curl-config.cmake.in in a such way

include("${CMAKE_CURRENT_LIST_DIR}/@TARGETS_EXPORT_NAME@.cmake")
check_required_components("@PROJECT_NAME@")

# Alias for either shared or static library
#add_library(@PROJECT_NAME@::libcurl ALIAS @PROJECT_NAME@::@LIB_SELECTED@)
set_property(TARGET @PROJECT_NAME@::@LIB_SELECTED@ PROPERTY EXPORT_NAME @PROJECT_NAME@::libcurl)

receive error:

[25/26] CMake Error at ***/build/parts/curl/install/lib64/cmake/CURL/CURLConfig.cmake:63 (set_property):
[25/26]   EXPORT_NAME property can't be set on imported targets
[25/26]   ("CURL::libcurl_static")

[balikalina]

both CMakefiles.txt add target library (example for static)

add_library(${LIB_STATIC} STATIC ${SOURCES})

then libcurl declares aliases

add_library(${LIB_NAME} ALIAS ${LIB_SELECTED})
add_library(${PROJECT_NAME}::${LIB_NAME} ALIAS ${LIB_SELECTED})

when ssh2 doesn't do this

and the last they both install target

so the only difference is the absence of ALIAS add_library() call in CMakeLists.txt

[vszakats]

Thanks for investigating @balikalina and pointing to these bits.

I read docs and came up with a minimal test, but the bad news is that I couldn't reproduce, and all patch suggestions break the test, while the master build works OK. I tested this with libssh2 only, because based on the CMake error message, this looks like the same issue in both libcurl and libssh2 (despite minor differences in their CMakeLists.txts).

I closed the related PR, but feel free to discuss / investigate further in #11646.