C++ Package Manager
C++ Shell

README.md

CPM

Build Status

A C++ Package Manager based on CMake and Git.

CPM is designed to promote small, well-tested, composable C++ modules. CPM allows you to link against multiple different versions of the same static library without symbol conflicts. You can include other C++ modules that may depend on older or newer versions of the same modules you are using. Additionally, CPM will automatically download and build C++ modules for you. To explore CPM's ecosystem head over to the CPM website: http://cpm.rocks .

You can manage C or C++ libraries that do not utilize CPM. A number of 'external' modules are already listed on the website. These modules abstract away the details of downloading, building, and linking against various projects. Just be aware that you cannot statically link against multiple different versions of these 'external' modules because they are not built as CPM modules and do not manage symbols like real CPM modules do.

For an example of a module with various interdependencies, check out cpm-es-render. Here's an example dependency graph that the cpm website automatically generated for this module:

cpm-es-render dependency graph

Table of Contents

Brief Example

Below is a sample of a CMakeLists.txt file that uses 3 modules. These modules are: platform specific OpenGL headers, an axis aligned bounding box implementation, and G-truc's GLSL vector math library. See the next section for a full explanation of how to use CPM. The following CMakeLists.txt is self-contained and will build as-is:

  cmake_minimum_required(VERSION 2.8.7 FATAL_ERROR)
  project(foo)

  #------------------------------------------------------------------------------
  # Required CPM Setup - no need to modify - See: https://github.com/iauns/cpm
  #------------------------------------------------------------------------------
  set(CPM_DIR "${CMAKE_CURRENT_BINARY_DIR}/cpm_packages" CACHE TYPE STRING)
  find_package(Git)
  if(NOT GIT_FOUND)
    message(FATAL_ERROR "CPM requires Git.")
  endif()
  if (NOT EXISTS ${CPM_DIR}/CPM.cmake)
    message(STATUS "Cloning repo (https://github.com/iauns/cpm)")
    execute_process(
      COMMAND "${GIT_EXECUTABLE}" clone https://github.com/iauns/cpm ${CPM_DIR}
      RESULT_VARIABLE error_code
      OUTPUT_QUIET ERROR_QUIET)
    if(error_code)
      message(FATAL_ERROR "CPM failed to get the hash for HEAD")
    endif()
  endif()
  include(${CPM_DIR}/CPM.cmake)

  #------------------------------------------------------------------------------
  # CPM Modules
  #------------------------------------------------------------------------------

  # ++ MODULE: OpenGL platform
  CPM_AddModule("gl_platform"
    GIT_REPOSITORY "https://github.com/iauns/cpm-gl-platform"
    GIT_TAG "1.3.5")

  # ++ MODULE: aabb
  CPM_AddModule("aabb"
    GIT_REPOSITORY "https://github.com/iauns/cpm-glm-aabb"
    GIT_TAG "1.0.3")

  # ++ EXTERNAL-MODULE: GLM
  CPM_AddModule("glm"
    GIT_REPOSITORY "https://github.com/iauns/cpm-glm"
    GIT_TAG "1.0.2"
    USE_EXISTING_VER TRUE)

  CPM_Finish()

  #-----------------------------------------------------------------------
  # Setup source
  #-----------------------------------------------------------------------

  # NOTE: Feel free to ignore this section. It simply creates a main.cpp source
  # file from scratch instead of relying on the source being present. This is
  # done only to keep this CMakeLists.txt self-contained.

  file(WRITE src/main.cpp "#include <iostream>\n")
  file(APPEND src/main.cpp "#include <glm-aabb/AABB.hpp>\n")
  file(APPEND src/main.cpp "#include <glm/glm.hpp>\n\n")
  file(APPEND src/main.cpp "namespace glm_aabb = CPM_AABB_NS;\n\n")
  file(APPEND src/main.cpp "int main(int argc, char** av)\n")
  file(APPEND src/main.cpp "{\n")
  file(APPEND src/main.cpp "  glm_aabb::AABB aabb(glm::vec3(-1.0), glm::vec3(1.0));\n")
  file(APPEND src/main.cpp "  aabb.extend(glm::vec3(-2.0, 3.0, -0.5));\n")
  file(APPEND src/main.cpp "  glm_aabb::AABB aabb2(glm::vec3(1.0), 1.0);\n")
  file(APPEND src/main.cpp "  std::cout << \"AABB Interesction: \" << aabb.intersect(aabb2) << std::endl;\n")
  file(APPEND src/main.cpp "  return 0;\n")
  file(APPEND src/main.cpp "}\n")

  set(Sources src/main.cpp)

  #-----------------------------------------------------------------------
  # Setup executable
  #-----------------------------------------------------------------------
  set(EXE_NAME cpm-test)
  add_executable(${EXE_NAME} ${Sources})
  target_link_libraries(${EXE_NAME} ${CPM_LIBRARIES})

Using CPM

Quick Setup

To use CPM in your C++ project, include the following at the top of your CMakeLists.txt:

  #------------------------------------------------------------------------------
  # Required CPM Setup - no need to modify - See: https://github.com/iauns/cpm
  #------------------------------------------------------------------------------
  set(CPM_DIR "${CMAKE_CURRENT_BINARY_DIR}/cpm-packages" CACHE TYPE STRING)
  find_package(Git)
  if(NOT GIT_FOUND)
    message(FATAL_ERROR "CPM requires Git.")
  endif()
  if (NOT EXISTS ${CPM_DIR}/CPM.cmake)
    message(STATUS "Cloning repo (https://github.com/iauns/cpm)")
    execute_process(
      COMMAND "${GIT_EXECUTABLE}" clone https://github.com/iauns/cpm ${CPM_DIR}
      RESULT_VARIABLE error_code
      OUTPUT_QUIET ERROR_QUIET)
    if(error_code)
      message(FATAL_ERROR "CPM failed to get the hash for HEAD")
    endif()
  endif()
  include(${CPM_DIR}/CPM.cmake)

  #------------------------------------------------------------------------------
  # CPM Modules
  #------------------------------------------------------------------------------

  # TODO: Include any modules here...

  CPM_Finish()

Then add the ${CPM_LIBRARIES} variable to your target_link_libraries similar to the following:

target_link_libraries(my_project ${CPM_LIBRARIES}) 

And you're done. You will be able to start using CPM modules right away by adding the following snippet to the CPM Modules section of your CMakeLists.txt:

  CPM_AddModule("aabb"
    GIT_REPOSITORY "https://github.com/iauns/cpm-glm-aabb"
    GIT_TAG "1.0.2")

This snippet will automatically download, build, and link version 1.0.2 of a simple axis aligned bounding box implementation named aabb. A new namespace is generated for aabb and a preprocessor definition for this namespace is automatically added to your project. The preprocessor namespace definition always follows the form CPM_<NAME>_NS where <NAME> is the capitalized first argument of your call to CPM_AddModule.

For example, in the 'aabb' snippet above, the first argument to CPM_AddModule was "aabb" so the preprocessor definition CPM_AABB_NS would be added to our project. This declares the namepsace under which CPM has bound the 'aabb' module. For instance, aabb's only class is named AABB. So the fully qualified name for the AABB class would be: CPM_AABB_NS::AABB. You may want to rename the namespace to something more appropriate: namespace glm_aabb = CPM_AABB_NS;. But that's entirely up to you. Depending on your needs, using the CPM namespace as-is may be all you need.

Be sure to place all calls to CPM_AddModule before your call to CPM_Finish. The # TODO: Include any modules here... section mentioned in the first snippet indicates where you should place calls to CPM_AddModule.

Why even bother with these preprocessor namespace definitions? The reason is so that we can leverage multiple different versions of a single CPM module in the same static linkage unit. Why would we want to let users utilize multiple versions of our module in the first place? In many cases, users won't know that they are actually using multiple different versions of your module. For example, a more recent version of your module may be included directly by the user, but an older version of your module may be pulled in as a dependency of another module the user is relying on. If you're interested, you can see CPM's dependency graph for your project.

Things To Note

Includes

Every module's root directory will be added to your include path. It is common that every module's github page describes what file or files you should include in your project. The paths to these files will be relative to the module's root directory. So you can copy the include directive directly from the module's github page into your code. For example, to access AABB's functionality we would include its interface header file like so:

#include <glm-aabb/AABB.hpp>

Compiler Flags

If you have compiler flags you wish to apply to all modules, then add them directly before the CPM section in your CMakeListst.txt. Since each call to CPM_AddModule uses add_subdirectory internally, every module will inherit your compiler flags (for good or bad).

CPM Externals

If the library you are interested in isn't a CPM module, try browsing through the CPM externals listed on http://cpmcpp.com. Just use CPM_AddModule as you would with any other module. Note that you will likely want to use the USE_EXISTING_VER parameter to CPM_AddModule in conjunction with external modules.

If you don't find a formula for your favorite library, kindly consider contributing one to our CPM modules repository.

Tag Advice

While it may be tempting to use the origin/master tag to track the most recent changes to a module, it is not recommended. Using version tags for a module (such as 1.0.2) and upgrading modules when necessary will save you time in the long run. If you track origin/master and upstream decides to release a major version which includes significant API changes then your builds will likely break immediately. But if versioned tags are used, you will maintain your build integrity even through upstream version upgrades.

Advantages

  • Automatically manages code retrieval and building of CPM modules and externals.
  • Allows the use of multiple different versions of the same statically linked module in the same executable.
  • Built entirely in CMake. Nothing else is required.
  • All CPM module code will be included in any generated project solution.
  • Will automatically detect preprocessor naming conflicts.
  • Optionally cache downloaded modules and repositories to a central directory.

Limitations

  • Only supports git (with very limited support for SVN).

Building CPM Modules

If you only want to use pre-existing CPM modules and aren't interested in building modules yourself, feel free to skip this section. But, if you are interested in building CPM modules then please read on as some guidelines and requirements are listed below.

CMakeLists.txt Entry

There must be a CMakeLists.txt at the root of your module project and this CMakeLists.txt file must contain all relevant CPM directives and code (see below). Do not use issue calls to CPM (CPM_*) in a subdirectory (add_subdirectory).

Add the following to the top of the CMakeLists.txt for your module:

  #-----------------------------------------------------------------------
  # CPM configuration
  #-----------------------------------------------------------------------
  set(CPM_MODULE_NAME <name>)
  set(CPM_LIB_TARGET_NAME ${CPM_MODULE_NAME})

  if ((DEFINED CPM_DIR) AND (DEFINED CPM_UNIQUE_ID) AND (DEFINED CPM_TARGET_NAME))
    set(CPM_LIB_TARGET_NAME ${CPM_TARGET_NAME})
    set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${CPM_DIR})
    include(CPM)
  else()
    set(CPM_DIR "${CMAKE_CURRENT_BINARY_DIR}/cpm-packages" CACHE TYPE STRING)
    find_package(Git)
    if(NOT GIT_FOUND)
      message(FATAL_ERROR "CPM requires Git.")
    endif()
    if (NOT EXISTS ${CPM_DIR}/CPM.cmake)
      message(STATUS "Cloning repo (https://github.com/iauns/cpm)")
      execute_process(
        COMMAND "${GIT_EXECUTABLE}" clone https://github.com/iauns/cpm ${CPM_DIR}
        RESULT_VARIABLE error_code
        OUTPUT_QUIET ERROR_QUIET)
      if(error_code)
        message(FATAL_ERROR "CPM failed to get the hash for HEAD")
      endif()
    endif()
    include(${CPM_DIR}/CPM.cmake)
  endif()

  # Include CPM modules or externals here (with CPM_AddModule).

  CPM_InitModule(${CPM_MODULE_NAME})

Be sure to update the <name> at the beginning of the snippet. <name> is placed in the namespace preprocessor definition for your module. For example, if <name> is 'spire' then the preprocessor definition that will be added to your project will be CPM_SPIRE_NS. Use this definition as a wrapper around your code and namespaces. Don't worry about users using the same name in their call to CPM_AddModule as the name you choose in your call to CPM_InitModule. CPM will automatically handle this for you. Also use CPM_LIB_TARGET_NAME as the name of your library in add_library and include CPM_LIBRARIES in target_link_libraries for your static library. Example:

  # Our CPM module library
  add_library(${CPM_LIB_TARGET_NAME} ${Source})
  target_link_libraries(${CPM_LIB_TARGET_NAME} ${CPM_LIBRARIES})

Here is an example class that demonstrates the namespace wrapping:

  namespace CPM_SPIRE_NS {

  ... code here ...

  } // namespace CPM_SPIRE_NS

Library target name

If you used the code snippet above make sure that your generated library target name is ${CPM_LIB_TARGET_NAME}. This will ensure your library target name matches with what CPM is expecting. But, if you can't name your target ${CPM_LIB_TARGET_NAME} for any reason, use CPM_ExportAdditionalLibraryTarget instead in order name your target whatever you would like. See the function reference below.

Wrapping Namespace

CPM allows multiple different versions of the same module to be statically linked into the same target . As such, when you are building a module for CPM (not when you are using CPM modules!), you should either surround your top-level namespaces in CPM_[module name]_NS tags or use CPM_[module name]_NS as your top level namespace, like so:

  namespace CPM_[module name]_NS {

    ...  

  } // namespace CPM_[module name]_NS

The first argument given to CPM_InitModule becomes [module name] in your application.

Note that this is not required but it is heavily recommended when you are building CPM modules. You must include this if you want your users to be able to use multiple versions of your module within the same static linkage unit.

Directory Structure

In order to avoid header name conflicts CPM modules adhere to the directory following structure:

  Root of [module name]
    |-> CMakeLists.txt
    |-> test
    |-> [module name]
      |-> [public headers go here]  
      |-> src
        |-> [private headers and source code]

Using this structure users would include your public headers using:

  #include <[module name]/interface.h>

Exporting Build Info

Include Paths

By default, the root of your project is added to the include path. If you need to expose more directories to the consumer of your module use the CPM_ExportAdditionalIncludeDir function to add directories to the consumer's include path. The first and only argument to CPM_ExportAdditionalIncludeDir is the directory you want to add to the path. Be sure to clearly document any changes you make to the include path in your module's README.

Definitions

Just as with the include paths above you can set preprocessor definitions for the consumer. Use the function CPM_ExportAdditionalDefinition, like below:

  CPM_ExportAdditionalDefinition("-DMONGO_HAVE_STDINT")

Targets

If you have additional targets, or don't want to use the target name that CPM generates for you, you can use the CPM_ExportAdditionalLibraryTarget function that comes with CPM.

  CPM_ExportAdditionaLibraryTarget("MyTargetName")

This target will be added to the target_link_libraries call issued by the consumer of your module.

Registering Your Module

Once you have finished writing your module, add your repository to the ecosystem using the CPM website. A dependency graph will be automatically generated for your module, and you will be able to see others using your module.

Note that this step is not mandatory. You can use your module without registering it by pointing CPM to the URL of your git repository. Module registration is recommended because it makes it easier for others to find.

Building Externals

If you are wrapping non-CPM code then you are likely building a CPM external. Building an external is just like building a module except for a call to:

  CPM_ForceOnlyOneModuleVersion()

somewhere in your module's CMakeLists.txt file. This function ensures exactly one (and only one) version of your module is ever statically linked.

In addition to this, you should reference the original repository in your cpm-modules JSON file by adding the 'externalURL' key/value pair. The key being 'externalURL' and the value being be a URL locating the repository for which you have created this external. Also set the 'external' key to 'true' in your JSON file so that the CPM website knows you have built an external. For an example see: CPM External for Google Test.

CPM Function Reference

All CMake functions that CPM exposes are listed below.

General Purpose

CPM_AddModule

Adds a CPM module to your project. All arguments except <name> are optional. Additionally, one of either the GIT_REPOSITORY or SOURCE_DIR arguments must be present in your call to CPM_AddModule. Should be called before either CPM_Finish or CPM_InitModule

  CPM_AddModule(<name>           # Required - Module target name. Used to generate your 
                                 # preprocessor definition.
    [GIT_REPOSITORY repo]        # Git repository that corresponds to a CPM module.
                                 # If this argument is not specfied, then SOURCE_DIR must be set.
    [GIT_TAG tag]                # Git tag to checkout. Tags, shas, and branches all work.
    [USE_EXISTING_VER truth]     # If set to true, and an existing version of this module is 
                                 # found then the existing version of this module is used
                                 # instead of the version indicated by GIT_TAG.
    [SOURCE_DIR dir]             # Uses 'dir' as the source directory instead of cloning
                                 # from a repo. If this is not specified, then 
                                 # GIT_REPOSITORY must be specified.
    [SOURCE_GHOST_GIT_REPO repo] # Ghost repository when using SOURCE_DIR.
                                 # Used to correctly correlate SOURCE_DIR modules with their 
                                 # correct upstream repository.
    [SOURCE_GHOST_GIT_TAG tag]   # Ghost git tag when using SOURCE_DIR.
    [EXPORT_MODULE truth]        # If true, then this module's (<name>) definitions and includes
                                 # will be exported to any consumer of your module.
    [FORWARD_DECLARATION truth]  # If true, then only the module's preprocessor definition 
                                 # (that the <name> argument above is used to generate) 
                                 # is exported to the consumer of the module. This is useful 
                                 # for situations where you only need to forward declare a 
                                 # module's classes in your interface classes and not actually 
                                 # include the target module's interface headers. This is 
                                 # preferred over EXPORT_MODULE.
    )

CPM_EnsureRepoIsCurrent

A utility function that allows you to download and ensure that some repository is up to date and present on the filesystem before proceeding forward with CMakeLists.txt processing. Useful for building CPM externals. You can use this function outside of any call to CPM_Finish or CPM_InitModule

  CPM_EnsureRepoIsCurrent(
    [TARGET_DIR dir]             # Required - Directory in which to place repository.
    [GIT_REPOSITORY repo]        # Git repository to clone and keep up to date.
    [GIT_TAG tag]                # Git tag to checkout.
    [SVN_REPOSITORY repo]        # SVN repository to checkout.
    [SVN_REVISION rev]           # SVN revision.
    [SVN_TRUST_CERT 1]           # Trust the Subversion server site certificate
    [USE_CACHING 1]              # Enables caching of repositories if the user 
                                 # has specified CPM_MODULE_CACHING_DIR.
                                 # Not enabled by default.
    )

CPM_Finish

This function is for the top-level application only. Call when you are finished issuing calls to CPM_AddModule.

CPM_Finish()

Modules Only

The functions listed in this section are used exclusively for constructing modules. If you use one of these functions in non-module code, a CMake warning will be generated and the function call will be ignored.

CPM_InitModule

This function is the module's counterpart to CPM_Finish. Call this to indicate to CPM that you have finished issuing calls to CPM_AddModule. The only argument indicates the name of the module. This name will only be used for generating the preprocessor definition you should use for your module.

CPM_InitModule("my_module")

CPM_ExportAdditionalDefinition

When building modules, this exports an additional definition in the module consumer's scope. Use sparingly. Primarily used to expose mandatory external project definitions.

CPM_ExportAdditionalDefinition("-DMY_DEFINITION=42")

CPM_ExportAdditionalIncludeDir

Exposes an additional include directory to the consumer of a module. Use sparingly. Primarily used to expose external project directories to module consumers.

CPM_ExportAdditionalIncludeDir("./foo/bar")

Note, for this function, do not quote lists of include directories. Pass the list in as-is.

CPM_ExportAdditionalLibraryTarget

This function is mostly used to avoid having to name targets per the ${CPM_TARGET_NAME} convention in CPM. For an example of its use see http://github.com/iauns/cpm-google-test. Google test itself generates its own target name when included as a subdirectory so we must use that name.

CPM_ExportAdditionalLibraryTarget("my_target")

Miscellaneous Issues and Questions

Below are some common issues users encounter and solutions to them.

When are modules downloaded and updated?

During the CMake configure step. No repository cloning or fetching occurs during the build step.

Exposing foreign module interfaces

Some modules require the ability to expose classes from other modules through public headers. This is allowed by tagging the module that you plan on exporting with EXPORT_MODULE TRUE just like:

  CPM_AddModule("GLM"
    GIT_REPOSITORY "https://github.com/iauns/cpm-glm"
    GIT_TAG "origin/master"
    USE_EXISTING_VER TRUE
    EXPORT_MODULE TRUE    # Use EXPORT_MODULE sparingly. We expose GLM's interface
    )                     # through our own interface hence why we export it.

In this case, GLM's definitions and include paths will be exported to the direct consumer of your module. It will not export this module to any parents of your consumer.

Using an existing module version

CPM allows you the flexibility of selecting the most recently used version of a particular module instead of the version you requested. This is useful when you are working with externals or modules that require you to only use one version. Simply add USE_EXISTING_VER TRUE in your call to CPM_AddModule. An example of this is given above in the section on exposing foreign module interfaces.

For example, if a module you added (lets call this module B) requested version v0.9.5 of module A, and you subsequently requested v0.9.1 of module A, then your version would be upgraded to v0.9.5 to comply with the pre-existing version of the module if you specified USE_EXISTING_VER TRUE when adding module A. It is considered best practice to set USE_EXSTING_VER to TRUE when adding externals (not regular modules) to your project. Especially when building modules for others to use. But also be aware that your version can be downgraded in the same manner. You can generally avoid being downgraded by re-arranging the order of your calls to CPM_AddModule.

When adding regular non-external modules, you may consider using this option to reduce the size of your executable if multiple different versions of the same module are being used. Just be weary of compiler errors due to version conflicts. In most cases, this option should be avoided when using regular, non-external, CPM modules.

Force only one module version

As pointed out in the externals section you may force all consumers, indirect or direct, of your module to use only one version. Most module creators won't need to worry about this corner case, but it is required that all externals use this. Include a call to CPM_ForceOnlyOneModuleVersion anywhere in your module's CMakeLists.txt file to enforce this. Usually this call is made directly before calling CPM_InitModule.

If you do this, you should indicate that your module is an 'external' in your module's JSON file. Even if you don't use any external code. It is important to separate these modules from 'regular' modules, and the nomenclature we have chosen for these types of modules are 'externals'.

Downloading repos without external projects

CPM provides a utility function that allows you to download repositories at configuration time. This function is: CPM_EnsureRepoIsCurrent. This function will also ensure the tag you specify is up to date and the repo is present before continuing execution of CMakeLists.txt. You can download both git repositories and SVN repositories using this function. For a reference regarding the function's parameters, see the comments at the top of CPM.cmake.

For examples of using this function, see the google test CPM external.

How do I cache modules?

CPM supports cached repositories and modules by setting either the CPM_MODULE_CACHE_DIR CMake variable or the CPM_CACHE_DIR environment variable to an appropriate cache directory (such as ~/.cpm_cache). When set, a search will be performed in the cache directory for all modules that don't already exist in your project's build directory. If the module is not found in the cache directory, CPM will download the module into the cache directory. This is useful if you find yourself with no or limited internet access from time to time as your cache directory will be searched before attempting to download the repository from the internet.

Here's a quick example of using this variable from the command line:

  cmake -DCPM_MODULE_CACHE_DIR=~/.cpm_cache ...

The cache directory is searched only when a module is not found in your project's build directory. If the module is then found in the cache directory, the cache directory will be updated using the appropriate SCM and its directory contents will be copied into your project's build directory. Any subsequent invokation of CMake will find the module in your project's build directory and will not search in the cache directory. Unless you have cleaned the project or removed the build directory's modules.

How do I cache CPM itself?

Use the following code snippet instead of the one given above. This snippet checks to see if CPM exists in the cache directory before attempting to download it.

#------------------------------------------------------------------------------
# Required CPM Setup - See: http://github.com/iauns/cpm
#------------------------------------------------------------------------------
set(CPM_DIR "${CMAKE_CURRENT_BINARY_DIR}/cpm-packages" CACHE TYPE STRING)
find_package(Git)
if(NOT GIT_FOUND)
  message(FATAL_ERROR "CPM requires Git.")
endif()
if ((NOT DEFINED CPM_MODULE_CACHE_DIR) AND (NOT "$ENV{CPM_CACHE_DIR}" STREQUAL ""))
  set(CPM_MODULE_CACHE_DIR "$ENV{CPM_CACHE_DIR}")
endif()
if ((NOT EXISTS ${CPM_DIR}/CPM.cmake) AND (DEFINED CPM_MODULE_CACHE_DIR))
  if (EXISTS "${CPM_MODULE_CACHE_DIR}/github_iauns_cpm")
    message(STATUS "Found cached version of CPM.")
    file(COPY "${CPM_MODULE_CACHE_DIR}/github_iauns_cpm/" DESTINATION ${CPM_DIR})
  endif()
endif()
if (NOT EXISTS ${CPM_DIR}/CPM.cmake)
  message(STATUS "Cloning repo (https://github.com/iauns/cpm)")
  execute_process(
    COMMAND "${GIT_EXECUTABLE}" clone https://github.com/iauns/cpm ${CPM_DIR}
    RESULT_VARIABLE error_code
    OUTPUT_QUIET ERROR_QUIET)
  if(error_code)
    message(FATAL_ERROR "CPM failed to get the hash for HEAD")
  endif()
endif()
include(${CPM_DIR}/CPM.cmake)

# Modules go here...

CPM_Finish()

How do I see the module dependency hierarchy?

When building your project define: CPM_SHOW_HIERARCHY=TRUE.

On the command line this would look something like

  cmake -DCPM_SHOW_HIERARCHY=TRUE ...

It is best to run this command after you have successfully built your project so the output is not muddied by status messages.

I get errors regarding reused binary directories

If you get errors similar to:

  The binary directory

    /Users/jhughes/me/cpp/cpm/modules/ ... /bin

  is already used to build a source directory.  It cannot be used to build
  source directory.

This means that there exists a circular module reference which is not allowed in CPM. The module graph must not contain cycles. For example, if Module A adds Module B, and Module B adds Module A, you will get this error.

How do I Manage CPM Namespaces?

There are a number of options here. You could rename the CPM_<NAME>_NS at the top of your implementation files:

namespace Spire = CPM_SPIRE_NS;

Or you can build a header that renames all of the module namespaces for you. Something akin to the following:

  #ifndef __MY_NAMESPACES_H
  #define __MY_NAMESPACES_H

  // 'Forward declaration' of CPM module namespaces.
  namespace CPM_SPIRE_NS {}
  namespace CPM_SPIRE_SCIRUN_NS {}
  ... (more forward declarations) ...

  // Renaming the namespaces in our top level namespace.
  namespace my_namespace {
    namespace Spire     = CPM_SPIRE_NS;
    namespace SpireSR   = CPM_SPIRE_SCIRUN_NS;
  }

  #endif

Be careful with the latter header based approach since there are some pitfalls. For example, the increased possibility of header guard confilcts and namespace conflicts. In general, renaming the namespace at the source level is the recommended way to go.