Merge topic 'find-package-prefer-config'

26a99da206 find_package: Add option to prefer Config mode
c365243a3a find_package: Factor out module and config find_package methods

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Ruslan Baratov <ruslan_baratov@yahoo.com>
Merge-request: !3339

10 files changed, 155 insertions, 51 deletions

diff --git a/Help/command/find_package.rst b/Help/command/find_package.rst
index eb44eb2..e5e5b2c 100644
--- a/Help/command/find_package.rst
+++ b/Help/command/find_package.rst
@@ -59,6 +59,13 @@ for finding the package, checking the version, and producing any needed
 messages.  Some find-modules provide limited or no support for versioning;
 check the module documentation.
 
+If the ``MODULE`` option is not specfied in the above signature,
+CMake first searches for the package using Module mode. Then, if the
+package is not found, it searches again using Config mode. A user
+may set the variable :variable:`CMAKE_FIND_PACKAGE_PREFER_CONFIG` to
+``TRUE`` to direct CMake first search using Config mode before falling
+back to Module mode.
+
 Full Signature and Config Mode
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/Help/manual/cmake-variables.7.rst b/Help/manual/cmake-variables.7.rst
index fd5e28f..1011ed2 100644
--- a/Help/manual/cmake-variables.7.rst
+++ b/Help/manual/cmake-variables.7.rst
@@ -172,6 +172,7 @@ Variables that Change Behavior
    /variable/CMAKE_FIND_NO_INSTALL_PREFIX
    /variable/CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY
    /variable/CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY
+   /variable/CMAKE_FIND_PACKAGE_PREFER_CONFIG
    /variable/CMAKE_FIND_PACKAGE_RESOLVE_SYMLINKS
    /variable/CMAKE_FIND_PACKAGE_WARN_NO_MODULE
    /variable/CMAKE_FIND_ROOT_PATH
diff --git a/Help/release/dev/find-package-prefer-config.rst b/Help/release/dev/find-package-prefer-config.rst
new file mode 100644
index 0000000..377e8c5
--- /dev/null
+++ b/Help/release/dev/find-package-prefer-config.rst
@@ -0,0 +1,6 @@
+find-package-prefer-config
+--------------------------
+
+* Variable :variable:`CMAKE_FIND_PACKAGE_PREFER_CONFIG` was added to tell
+  :command:`find_package` calls to look for a package configuration
+  file first even if a find module is available.
diff --git a/Help/variable/CMAKE_FIND_PACKAGE_PREFER_CONFIG.rst b/Help/variable/CMAKE_FIND_PACKAGE_PREFER_CONFIG.rst
new file mode 100644
index 0000000..db658a1
--- /dev/null
+++ b/Help/variable/CMAKE_FIND_PACKAGE_PREFER_CONFIG.rst
@@ -0,0 +1,27 @@
+CMAKE_FIND_PACKAGE_PREFER_CONFIG
+---------------------------------
+
+Tell :command:`find_package` to try "Config" mode before "Module" mode if no
+mode was specified.
+
+The command :command:`find_package` operates without an explicit mode when
+the reduced signature is used without the ``MODULE`` option. In this case,
+by default, CMake first tries Module mode by searching for a
+``Find<pkg>.cmake`` module.  If it fails, CMake then searches for the package
+using Config mode.
+
+Set ``CMAKE_FIND_PACKAGE_PREFER_CONFIG`` to ``TRUE`` to tell
+:command:`find_package` to first search using Config mode before falling back
+to Module mode.
+
+This variable may be useful when a developer has compiled a custom version of
+a common library and wishes to link it to a dependent project.  If this
+variable is set to ``TRUE``, it would prevent a dependent project's call
+to :command:`find_package` from selecting the default library located by the
+system's ``Find<pkg>.cmake`` module before finding the developer's custom
+built library.
+
+Once this variable is set, it is the responsibility of the exported
+``<pkg>Config.cmake`` files to provide the same result variables as the
+``Find<pkg>.cmake`` modules so that dependent projects can use them
+interchangeably.
diff --git a/Help/variable/CMAKE_FIND_PACKAGE_WARN_NO_MODULE.rst b/Help/variable/CMAKE_FIND_PACKAGE_WARN_NO_MODULE.rst
index f1116bb..5c4f23a 100644
--- a/Help/variable/CMAKE_FIND_PACKAGE_WARN_NO_MODULE.rst
+++ b/Help/variable/CMAKE_FIND_PACKAGE_WARN_NO_MODULE.rst
@@ -17,3 +17,6 @@ Set ``CMAKE_FIND_PACKAGE_WARN_NO_MODULE`` to ``TRUE`` to tell
 :command:`find_package` to warn when it implicitly assumes Config mode.  This
 helps developers enforce use of an explicit mode in all calls to
 :command:`find_package` within a project.
+
+This variable has no effect if :variable:`CMAKE_FIND_PACKAGE_PREFER_CONFIG` is
+set to ``TRUE``.
diff --git a/Source/cmFindPackageCommand.cxx b/Source/cmFindPackageCommand.cxx
index 7ebd211..8eefaa7 100644
--- a/Source/cmFindPackageCommand.cxx
+++ b/Source/cmFindPackageCommand.cxx
@@ -498,57 +498,80 @@ bool cmFindPackageCommand::InitialPass(std::vector<std::string> const& args,
   this->SetModuleVariables(components);
 
   // See if there is a Find<PackageName>.cmake module.
-  if (this->UseFindModules) {
-    bool foundModule = false;
-    if (!this->FindModule(foundModule)) {
-      this->AppendSuccessInformation();
-      return false;
+  bool loadedPackage = false;
+  if (this->Makefile->IsOn("CMAKE_FIND_PACKAGE_PREFER_CONFIG")) {
+    if (this->UseConfigFiles && this->FindPackageUsingConfigMode()) {
+      loadedPackage = true;
+    } else if (this->FindPackageUsingModuleMode()) {
+      loadedPackage = true;
     }
-    if (foundModule) {
-      this->AppendSuccessInformation();
-      return true;
+  } else {
+    if (this->UseFindModules && this->FindPackageUsingModuleMode()) {
+      loadedPackage = true;
+    } else {
+      // Handle CMAKE_FIND_PACKAGE_WARN_NO_MODULE (warn when CONFIG mode is
+      // implicitly assumed)
+      if (this->UseFindModules && this->UseConfigFiles &&
+          this->Makefile->IsOn("CMAKE_FIND_PACKAGE_WARN_NO_MODULE")) {
+        std::ostringstream aw;
+        if (this->RequiredCMakeVersion >= CMake_VERSION_ENCODE(2, 8, 8)) {
+          aw << "find_package called without either MODULE or CONFIG option "
+                "and "
+                "no Find"
+             << this->Name
+             << ".cmake module is in CMAKE_MODULE_PATH.  "
+                "Add MODULE to exclusively request Module mode and fail if "
+                "Find"
+             << this->Name
+             << ".cmake is missing.  "
+                "Add CONFIG to exclusively request Config mode and search for "
+                "a "
+                "package configuration file provided by "
+             << this->Name << " (" << this->Name << "Config.cmake or "
+             << cmSystemTools::LowerCase(this->Name) << "-config.cmake).  ";
+        } else {
+          aw << "find_package called without NO_MODULE option and no "
+                "Find"
+             << this->Name
+             << ".cmake module is in CMAKE_MODULE_PATH.  "
+                "Add NO_MODULE to exclusively request Config mode and search "
+                "for a "
+                "package configuration file provided by "
+             << this->Name << " (" << this->Name << "Config.cmake or "
+             << cmSystemTools::LowerCase(this->Name)
+             << "-config.cmake).  "
+                "Otherwise make Find"
+             << this->Name
+             << ".cmake available in "
+                "CMAKE_MODULE_PATH.";
+        }
+        aw << "\n"
+              "(Variable CMAKE_FIND_PACKAGE_WARN_NO_MODULE enabled this "
+              "warning.)";
+        this->Makefile->IssueMessage(MessageType::AUTHOR_WARNING, aw.str());
+      }
+
+      if (this->FindPackageUsingConfigMode()) {
+        loadedPackage = true;
+      }
     }
   }
 
-  if (this->UseFindModules && this->UseConfigFiles &&
-      this->Makefile->IsOn("CMAKE_FIND_PACKAGE_WARN_NO_MODULE")) {
-    std::ostringstream aw;
-    if (this->RequiredCMakeVersion >= CMake_VERSION_ENCODE(2, 8, 8)) {
-      aw << "find_package called without either MODULE or CONFIG option and "
-            "no Find"
-         << this->Name
-         << ".cmake module is in CMAKE_MODULE_PATH.  "
-            "Add MODULE to exclusively request Module mode and fail if "
-            "Find"
-         << this->Name
-         << ".cmake is missing.  "
-            "Add CONFIG to exclusively request Config mode and search for a "
-            "package configuration file provided by "
-         << this->Name << " (" << this->Name << "Config.cmake or "
-         << cmSystemTools::LowerCase(this->Name) << "-config.cmake).  ";
-    } else {
-      aw
-        << "find_package called without NO_MODULE option and no "
-           "Find"
-        << this->Name
-        << ".cmake module is in CMAKE_MODULE_PATH.  "
-           "Add NO_MODULE to exclusively request Config mode and search for a "
-           "package configuration file provided by "
-        << this->Name << " (" << this->Name << "Config.cmake or "
-        << cmSystemTools::LowerCase(this->Name)
-        << "-config.cmake).  "
-           "Otherwise make Find"
-        << this->Name
-        << ".cmake available in "
-           "CMAKE_MODULE_PATH.";
-    }
-    aw << "\n"
-          "(Variable CMAKE_FIND_PACKAGE_WARN_NO_MODULE enabled this warning.)";
-    this->Makefile->IssueMessage(MessageType::AUTHOR_WARNING, aw.str());
-  }
-
-  // No find module.  Assume the project has a CMake config file.  Use
-  // a <PackageName>_DIR cache variable to locate it.
+  this->AppendSuccessInformation();
+  return loadedPackage;
+}
+
+bool cmFindPackageCommand::FindPackageUsingModuleMode()
+{
+  bool foundModule = false;
+  if (!this->FindModule(foundModule)) {
+    return false;
+  }
+  return foundModule;
+}
+
+bool cmFindPackageCommand::FindPackageUsingConfigMode()
+{
   this->Variable = this->Name;
   this->Variable += "_DIR";
 
@@ -580,9 +603,7 @@ bool cmFindPackageCommand::InitialPass(std::vector<std::string> const& args,
   this->IgnoredPaths.insert(ignored.begin(), ignored.end());
 
   // Find and load the package.
-  bool result = this->HandlePackageMode();
-  this->AppendSuccessInformation();
-  return result;
+  return this->HandlePackageMode();
 }
 
 void cmFindPackageCommand::SetModuleVariables(const std::string& components)
diff --git a/Source/cmFindPackageCommand.h b/Source/cmFindPackageCommand.h
index a11d253..4f6d97c 100644
--- a/Source/cmFindPackageCommand.h
+++ b/Source/cmFindPackageCommand.h
@@ -90,6 +90,9 @@ private:
     static PathLabel SystemRegistry;
   };
 
+  bool FindPackageUsingModuleMode();
+  bool FindPackageUsingConfigMode();
+
   // Add additional search path labels and groups not present in the
   // parent class
   void AppendSearchPathGroups();
diff --git a/Tests/FindPackageTest/CMakeLists.txt b/Tests/FindPackageTest/CMakeLists.txt
index 6c876a7..8802b73 100644
--- a/Tests/FindPackageTest/CMakeLists.txt
+++ b/Tests/FindPackageTest/CMakeLists.txt
@@ -541,7 +541,41 @@ endif()
 set(SortLib_DIR "" CACHE FILEPATH "Wipe out find results for testing." FORCE)
 unset(SortLib_VERSION)
 
-
 unset(CMAKE_FIND_PACKAGE_SORT_ORDER)
 unset(CMAKE_FIND_PACKAGE_SORT_DIRECTION)
 set(CMAKE_PREFIX_PATH )
+
+############################################################################
+##Test FIND_PACKAGE CMAKE_FIND_PACKAGE_PREFER_CONFIG
+
+set(CMAKE_PREFIX_PATH ${CMAKE_CURRENT_SOURCE_DIR}/PreferConfig)
+set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/PreferConfig)
+
+# prefer module mode
+set(CMAKE_FIND_PACKAGE_PREFER_CONFIG OFF)
+unset(ABC_FOUND)
+unset(ABC_CONFIG)
+
+find_package(ABC)
+if(NOT ABC_FOUND)
+    message(SEND_ERROR "Did not find ABC package")
+endif()
+if(ABC_CONFIG)
+    message(SEND_ERROR "Incorrectly found ABC in CONFIG mode, expected to find it with MODULE mode")
+endif()
+
+# Now prefer config mode
+set(CMAKE_FIND_PACKAGE_PREFER_CONFIG ON)
+unset(ABC_FOUND)
+unset(ABC_CONFIG)
+
+find_package(ABC)
+if(NOT ABC_FOUND)
+    message(SEND_ERROR "Did not find ABC package")
+endif()
+if(NOT ABC_CONFIG)
+    message(SEND_ERROR "Incorrectly found ABC in MODULE mode, expected to find it with CONFIG mode")
+endif()
+
+set(CMAKE_FIND_PACKAGE_PREFER_CONFIG OFF)
+set(CMAKE_PREFIX_PATH)
diff --git a/Tests/FindPackageTest/PreferConfig/ABCConfig.cmake b/Tests/FindPackageTest/PreferConfig/ABCConfig.cmake
new file mode 100644
index 0000000..281a5cd
--- /dev/null
+++ b/Tests/FindPackageTest/PreferConfig/ABCConfig.cmake
@@ -0,0 +1 @@
+set(ABC_FOUND TRUE)
diff --git a/Tests/FindPackageTest/PreferConfig/FindABC.cmake b/Tests/FindPackageTest/PreferConfig/FindABC.cmake
new file mode 100644
index 0000000..281a5cd
--- /dev/null
+++ b/Tests/FindPackageTest/PreferConfig/FindABC.cmake
@@ -0,0 +1 @@
+set(ABC_FOUND TRUE)