From 68f4e80e2cc1fe379d1bdf415fd7120825434916 Mon Sep 17 00:00:00 2001
From: Geoffrey Gunter <12984092+gmgunter@users.noreply.github.com>
Date: Thu, 13 Jan 2022 23:38:37 -0800
Subject: [PATCH] Fix CMake package config file (#3068)

* Fix CMake package config file

There are currently a few issues with how the COIN-OR dependencies are
resolved when using `find_package(ortools CONFIG)` to add or-tools to
an external CMake project.

* With CMake >=3.9.6, we try to find the Clp and Cbc packages using the
  CONFIG mode of `find_package`. This always fails since neither
  library provides a CMake config file.

* If we address the above issue by instead using the MODULE mode of
  `find_package`, then we need to add `FindCbc.cmake` and
  `FindCpl.cmake` scripts to the CMAKE_MODULE_PATH in order to teach
  CMake how to find these dependencies. I propose that or-tools should
  install these scripts alongside its config file so that they're
  available to external CMake projects.

* Finally, the `FindCbc.cmake` script included with or-tools defines the
  variable `CBC_FOUND` when it's successful, rather than `Cbc_FOUND` as
  expected (CMake variables are case-sensitive). The `FindCpl.cmake`
  script has a similar issue. As a result, even when the above two
  points are addressed, `find_package(ortools CONFIG)` will still fail
  because CMake erroneously thinks that these two dependencies weren't
  succesfully found.

This commit attempts to address the above issues with the following
changes:

* The or-tools CMake config file is modified to allow searching for Cbc
  and Cpl using the MODULE mode of `find_package`.

* `FindCbc.cmake` and `FindCpl.cmake` are installed with the CMake
  package config files and are added to the CMAKE_MODULE_PATH if
  `USE_COINOR` was truthy.

* The `FindCbc.cmake` and `FindCpl.cmake` files are modified to change
  the case of variables they export.

* Only install FindXXX.cmake modules if COIN-OR support was enabled
---
 cmake/FindCbc.cmake          | 6 +++---
 cmake/FindClp.cmake          | 6 +++---
 cmake/cpp.cmake              | 8 ++++++++
 cmake/ortoolsConfig.cmake.in | 6 ++++--
 4 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/cmake/FindCbc.cmake b/cmake/FindCbc.cmake
index 3870a88989..c0d4407062 100644
--- a/cmake/FindCbc.cmake
+++ b/cmake/FindCbc.cmake
@@ -22,9 +22,9 @@ Cbc_FOUND          - True if Cbc found.
 #]=======================================================================]
 find_package(PkgConfig REQUIRED)
 
-pkg_check_modules(CBC REQUIRED cbc IMPORTED_TARGET GLOBAL)
-add_library(Coin::Cbc ALIAS PkgConfig::CBC)
-add_library(Coin::CbcSolver ALIAS PkgConfig::CBC)
+pkg_check_modules(Cbc REQUIRED cbc IMPORTED_TARGET GLOBAL)
+add_library(Coin::Cbc ALIAS PkgConfig::Cbc)
+add_library(Coin::CbcSolver ALIAS PkgConfig::Cbc)
 
 pkg_check_modules(OSI_CBC REQUIRED osi-cbc IMPORTED_TARGET GLOBAL)
 add_library(Coin::OsiCbc ALIAS PkgConfig::OSI_CBC)
diff --git a/cmake/FindClp.cmake b/cmake/FindClp.cmake
index 99b98e52e8..a89a12d67b 100644
--- a/cmake/FindClp.cmake
+++ b/cmake/FindClp.cmake
@@ -22,9 +22,9 @@ Clp_FOUND          - True if Clp found.
 #]=======================================================================]
 find_package(PkgConfig REQUIRED)
 
-pkg_check_modules(CLP REQUIRED clp IMPORTED_TARGET GLOBAL)
-add_library(Coin::Clp ALIAS PkgConfig::CLP)
-add_library(Coin::ClpSolver ALIAS PkgConfig::CLP)
+pkg_check_modules(Clp REQUIRED clp IMPORTED_TARGET GLOBAL)
+add_library(Coin::Clp ALIAS PkgConfig::Clp)
+add_library(Coin::ClpSolver ALIAS PkgConfig::Clp)
 
 pkg_check_modules(OSI_CLP REQUIRED osi-clp IMPORTED_TARGET GLOBAL)
 add_library(Coin::OsiClp ALIAS PkgConfig::OSI_CLP)
diff --git a/cmake/cpp.cmake b/cmake/cpp.cmake
index 8fad35ce01..395b870b8e 100644
--- a/cmake/cpp.cmake
+++ b/cmake/cpp.cmake
@@ -279,6 +279,14 @@ install(
   "${PROJECT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake"
   DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}"
   COMPONENT Devel)
+if(USE_COINOR)
+  install(
+    FILES
+    "${PROJECT_SOURCE_DIR}/cmake/FindCbc.cmake"
+    "${PROJECT_SOURCE_DIR}/cmake/FindClp.cmake"
+    DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}/modules"
+    COMPONENT Devel)
+endif()
 
 # add_cxx_sample()
 # CMake function to generate and build C++ sample.
diff --git a/cmake/ortoolsConfig.cmake.in b/cmake/ortoolsConfig.cmake.in
index e6475b4f3f..3c05af3b53 100644
--- a/cmake/ortoolsConfig.cmake.in
+++ b/cmake/ortoolsConfig.cmake.in
@@ -29,11 +29,13 @@ if(@BUILD_LP_PARSER@)
 endif()
 
 if(@USE_COINOR@)
+  # COIN-OR packages don't provide CMake config files
+  list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/modules")
   if(NOT Clp_FOUND AND NOT TARGET Coin::ClpSolver)
-    find_dependency(Clp REQUIRED ${CONFIG_FLAG})
+    find_dependency(Clp REQUIRED)
   endif()
   if(NOT Cbc_FOUND AND NOT TARGET Coin::CbcSolver)
-    find_dependency(Cbc REQUIRED ${CONFIG_FLAG})
+    find_dependency(Cbc REQUIRED)
   endif()
 endif()