Do generators expression work with BASE_DIRS in target_sources

Usage
1

I can post a longer example of this issue if needed but I wanted to see if what I am doing is just not expected to work. I have a CMakeLists.txt like

target_sources(HelloWorld PUBLIC 
   FILE_SET generated_export_headers 
   TYPE HEADERS
   BASE_DIRS 
        $<BUILD_INTERFACE:${CMAKE_BINARY_DIR}/HelloWorld> 
        $<INSTALL_INTERFACE:${CMAKE_BINARY_DIR}>
   FILES ${CMAKE_BINARY_DIR}/HelloWorld/helloworld_export.h)

When I use this it seems whatever I do the BUILD_INTERFACE is used in the install step. That is the install happens in the root install include directory never in a subdirectory called “HelloWorld” which is what I would have expected.

I assume I am doing something very dumb but in my defense BASE_DIRS is barley documented at all.

So should I expect generator expressions to work in BASE_DIRS?

2

I don’t think it makes sense to have separate build/install interfaces for BASE_DIRS. What is the goal here? To require helloworld_export.h when including in the source tree, but HelloWorld/helloworld_export.h when it is installed? Given that the header is meant to be included by public headers, how are both spellings going to be satisfied by the files that include it?

3

Some background. I was upgrading a project to use FILE_SET hopefully to simplify things.
I have attached an example project. I build into an out of source build directory and generate the Visual Studio solution using cmake -G "Visual Studio 17 2022" ../src
Note I can make all this work using some target_include_directories and the like but I was really trying to use FILE_SET as much as possible to learn stuff about it. This might just be pushing FILE_SET usage beyond what it is intended for?

So there is one project HelloWorld that lives in a sub directory HelloWorld The project uses

target_sources(HelloWorld PUBLIC 
   FILE_SET HEADERS 
   BASE_DIRS 
       ${CMAKE_SOURCE_DIR} 
   FILES HelloWorld.h)

for it’s one header. This all works well.
On install the HelloWorld.h header if install in include/HelloWorld/HelloWorld.h which is what I expect. This is using

install(
    TARGETS HelloWorld
    EXPORT HelloWorldExport
    FILE_SET HEADERS
)

The HelloWorld CMake also generates an export header using

generate_export_header(HelloWorld)

The helloworld_export.h is generated in the ${CMAKE_CURRENT_BINARY_DIR} as expected.
Now in HelloWorld.cpp this header is included as

#include "helloworld_export.h"

Using the double quotes in the #include here is the way I have seen in every project I have worked on. So to find this file I need ${CMAKE_CURRENT_BINARY_DIR} in the include path so I can do the following to achieve this

target_sources(HelloWorld PUBLIC 
   FILE_SET generated_export_headers 
   TYPE HEADERS
   ${CMAKE_CURRENT_BINARY_DIR}
   FILES ${CMAKE_CURRENT_BINARY_DIR}/helloworld_export.h)

So I add this file set to the install to get

install(
    TARGETS HelloWorld
    EXPORT HelloWorldExport
    FILE_SET HEADERS
    FILE_SET generated_export_headers
)

However the install is then

1>-- Up-to-date: .../install/include/HelloWorld/HelloWorld.h
1>-- Up-to-date: .../install/include/helloworld_export.h

However this is not what I want. I want the helloworld_export.h to be in the HelloWorld directory beside the HelloWorld.h file. So the install path I want includes the HelloWorld directory. This can be done using the following

target_sources(HelloWorld PUBLIC 
   FILE_SET generated_export_headers 
   TYPE HEADERS
   BASE_DIRS ${CMAKE_BINARY_DIR}
   FILES ${CMAKE_CURRENT_BINARY_DIR}/helloworld_export.h)

This does what I want on install

1>-- Up-to-date: .../install/include/HelloWorld/HelloWorld.h
1>-- Up-to-date: .../install/include/HelloWorld/helloworld_export.h

However that makes the build fail as it can not longer find helloworld_export.h. So I thought I would use a different BASE_DIR for build and install like so

target_sources(HelloWorld PUBLIC 
   FILE_SET generated_export_headers 
   TYPE HEADERS
   BASE_DIRS $<BUILD_LOCAL_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}> $<INSTALL_INTERFACE:${CMAKE_BINARY_DIR}>
   FILES ${CMAKE_CURRENT_BINARY_DIR}/helloworld_export.h)

However that still installs

1>-- Up-to-date: .../install/include/HelloWorld/HelloWorld.h
1>-- Up-to-date: .../install/include/helloworld_export.h

So it seems like the generator expressions aren’t working like the BUILD_LOCAL_INTERFACE still triggers in an install command.

Example.zip (1.8 KB)

4

Try this:

install(
    TARGETS HelloWorld
    EXPORT HelloWorldExport
    FILE_SET HEADERS
    FILE_SET generated_export_headers
      DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/HelloWorld"
)

It’s not clear to me why the default destination for HEADERS would be different than any other type-HEADERS file set though…

5

Ah, this is the problem. The path to HelloWorld.h from the basedir is HelloWorld/HelloWorld.h, so it is installed as such. Either use ${CMAKE_CURRENT_SOURCE_DIR} as a base directory or do:

Basically, the path from the containing BASE_DIR to the file is a “cononical name” for the header and should be included as such.