[CMake] Ensuring an external project is built and installed before trying to call "find_package" on it

[Timothy Wrona]

I am working on a CMake project that depends on a couple other projects I
have previously written. I would like to include those other projects using
"ExternalProject_Add", but I am having some issues.

The basic layout of the project is this:

cmake_minimum_required(VERSION 3.14.0)

project(ProjectWithDependencies)

include(ExternalProject)
ExternalProject_Add(Dependency1
    GIT_REPOSITORY <URL to git repo>
)
ExternalProject_Add(Dependency2
    GIT_REPOSITORY <URL to git repo>
)

find_package(Dependency1 Required)
find_package(Dependency2 Required)

# Use targets

I was under the assumption that "ExternalProject_Add" would automatically
build and install the dependencies before getting to the "find_package"
calls (they are CMake projects so the default build and install commands
should be fine) but this doesn't seem to be how it works.

When I get to "find_package" it fails because the dependency hasn't been
installed yet.

How can I ensure that the dependencies are fully compiled and installed
before attempting to find them? (Note: FetchContent doesn't work here
because the two projects "Dependency1" and "Dependency2" have targets with
the same name which causes FetchContent to fail.)

Any help is appreciated.

Thanks,
Tim
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