cmake_policy: Add undocumented GET_WARNING command

This command is intended for modules that issue policy warnings so
they can get the warning string from CMake in a uniform manner,
rather than duplicating the string. Several modules been updated
to include an example of the usage of this new command.

Modules/BundleUtilities.cmake

@@ -230,11 +230,8 @@ if(DEFINED CMAKE_GENERATOR)
   if(_BundleUtilities_CMP0080 STREQUAL "NEW")
     message(FATAL_ERROR "BundleUtilities cannot be included at configure time!")
   elseif(NOT _BundleUtilities_CMP0080 STREQUAL "OLD")
-    message(AUTHOR_WARNING
+    cmake_policy(GET_WARNING CMP0080 _cmp0080_warning)
-      "Policy CMP0080 is not set: BundleUtilities prefers not to be included at configure time. "
+    message(AUTHOR_WARNING "${_cmp0080_warning}\n")
-      "Run \"cmake --help-policy CMP0080\" for policy details. "
-      "Use the cmake_policy command to set the policy and suppress this warning."
-      )
   endif()
 endif()
 

Modules/FindOpenGL.cmake

@@ -268,11 +268,9 @@ else()
   endif()
 
   if(_OpenGL_GL_POLICY_WARN AND OPENGL_gl_LIBRARY AND OPENGL_opengl_LIBRARY AND OPENGL_glx_LIBRARY)
+    cmake_policy(GET_WARNING CMP0072 _cmp0072_warning)
     message(AUTHOR_WARNING
-      "Policy CMP0072 is not set: FindOpenGL prefers GLVND by default when available.  "
+      "${_cmp0072_warning}\n"
-      "Run \"cmake --help-policy CMP0072\" for policy details.  "
-      "Use the cmake_policy command to set the policy and suppress this warning."
-      "\n"
       "FindOpenGL found both a legacy GL library:\n"
       "  OPENGL_gl_LIBRARY: ${OPENGL_gl_LIBRARY}\n"
       "and GLVND libraries for OpenGL and GLX:\n"

Modules/UseSWIG.cmake

@@ -554,11 +554,8 @@ function(SWIG_ADD_LIBRARY name)
     set (UseSWIG_TARGET_NAME_PREFERENCE STANDARD)
   else()
     if (NOT target_name_policy)
-      message(AUTHOR_WARNING
+      cmake_policy(GET_WARNING CMP0078 _cmp0078_warning)
-        "Policy CMP0078 is not set.  "
+      message(AUTHOR_WARNING "${_cmp0078_warning}\n")
-        "Run \"cmake --help-policy CMP0078\" for policy details.  "
-        "Use the cmake_policy command to set the policy and suppress this warning."
-        )
     endif()
     if (NOT DEFINED UseSWIG_TARGET_NAME_PREFERENCE)
       set (UseSWIG_TARGET_NAME_PREFERENCE LEGACY)

Source/cmCMakePolicyCommand.cxx

@@ -46,6 +46,9 @@ bool cmCMakePolicyCommand::InitialPass(std::vector<std::string> const& args,
   if (args[0] == "VERSION") {
     return this->HandleVersionMode(args);
   }
+  if (args[0] == "GET_WARNING") {
+    return this->HandleGetWarningMode(args);
+  }
 
   std::ostringstream e;
   e << "given unknown first argument \"" << args[0] << "\"";
@@ -181,3 +184,33 @@ bool cmCMakePolicyCommand::HandleVersionMode(
   this->Makefile->SetPolicyVersion(version_min, version_max);
   return true;
 }
+
+bool cmCMakePolicyCommand::HandleGetWarningMode(
+  std::vector<std::string> const& args)
+{
+  if (args.size() != 3) {
+    this->SetError(
+      "GET_WARNING must be given exactly 2 additional arguments.");
+    return false;
+  }
+
+  // Get arguments.
+  std::string const& id = args[1];
+  std::string const& var = args[2];
+
+  // Lookup the policy number.
+  cmPolicies::PolicyID pid;
+  if (!cmPolicies::GetPolicyID(id.c_str(), pid)) {
+    std::ostringstream e;
+    e << "GET_WARNING given policy \"" << id
+      << "\" which is not known to this version of CMake.";
+    this->SetError(e.str());
+    return false;
+  }
+
+  // Lookup the policy warning.
+  this->Makefile->AddDefinition(var,
+                                cmPolicies::GetPolicyWarning(pid).c_str());
+
+  return true;
+}

Source/cmCMakePolicyCommand.h

@@ -37,6 +37,7 @@ private:
   bool HandleSetMode(std::vector<std::string> const& args);
   bool HandleGetMode(std::vector<std::string> const& args);
   bool HandleVersionMode(std::vector<std::string> const& args);
+  bool HandleGetWarningMode(std::vector<std::string> const& args);
 };
 
 #endif

Source/cmPolicies.h

@@ -236,7 +236,7 @@ class cmMakefile;
     "target_link_libraries allows use with targets in other directories.", 3, \
     13, 0, cmPolicies::WARN)                                                  \
   SELECT(POLICY, CMP0080,                                                     \
-         "BundleUtilities cannot be included at configure time", 3, 13, 0,    \
+         "BundleUtilities cannot be included at configure time.", 3, 13, 0,   \
          cmPolicies::WARN)                                                    \
   SELECT(POLICY, CMP0081,                                                     \
          "Relative paths not allowed in LINK_DIRECTORIES target property.",   \

Tests/RunCMake/BundleUtilities/CMP0080-WARN-stderr.txt

@@ -1,4 +1,9 @@
 CMake Warning \(dev\) at .*/Modules/BundleUtilities\.cmake:[0-9]+ \(message\):
-  Policy CMP0080 is not set: BundleUtilities prefers not to be included at
+  Policy CMP0080 is not set: BundleUtilities cannot be included at configure
-  configure time\.  Run "cmake --help-policy CMP0080" for policy details\.  Use
+  time\.  Run "cmake --help-policy CMP0080" for policy details\.  Use the
-  the cmake_policy command to set the policy and suppress this warning\.
+  cmake_policy command to set the policy and suppress this warning\.
+
+Call Stack \(most recent call first\):
+  CMP0080-WARN\.cmake:[0-9]+ \(include\)
+  CMakeLists\.txt:[0-9]+ \(include\)
+This warning is for project developers\.  Use -Wno-dev to suppress it\.

Tests/RunCMake/UseSWIG/CMP0078-WARN-stderr.txt

@@ -1,9 +1,10 @@
-CMake Warning \(dev\) at .*/Modules/UseSWIG.cmake:[0-9]+ \(message\):
+CMake Warning \(dev\) at .*/Modules/UseSWIG\.cmake:[0-9]+ \(message\):
-  Policy CMP0078 is not set.  Run "cmake --help-policy CMP0078" for policy
+  Policy CMP0078 is not set: UseSWIG generates standard target names\.  Run
-  details.  Use the cmake_policy command to set the policy and suppress this
+  "cmake --help-policy CMP0078" for policy details\.  Use the cmake_policy
-  warning.
+  command to set the policy and suppress this warning\.
+
 Call Stack \(most recent call first\):
-  CMP0078-common.cmake:6 \(swig_add_library\)
+  CMP0078-common\.cmake:6 \(swig_add_library\)
-  CMP0078-WARN.cmake:1 \(include\)
+  CMP0078-WARN\.cmake:1 \(include\)
-  CMakeLists.txt:3 \(include\)
+  CMakeLists\.txt:3 \(include\)
 This warning is for project developers.  Use -Wno-dev to suppress it.$