ENH: Isolate policy changes in included scripts

Isolation of policy changes inside scripts is important for protecting
the including context.  This teaches include() and find_package() to
imply a cmake_policy(PUSH) and cmake_policy(POP) around the scripts they
load, with a NO_POLICY_SCOPE option to disable the behavior.  This also
creates CMake Policy CMP0011 to provide compatibility.  See issue #8192.

1 files changed, 23 insertions, 7 deletions

diff --git a/Source/cmFindPackageCommand.cxx b/Source/cmFindPackageCommand.cxx
index a57a4f1..5b61180 100644
--- a/Source/cmFindPackageCommand.cxx
+++ b/Source/cmFindPackageCommand.cxx
@@ -64,6 +64,7 @@ cmFindPackageCommand::cmFindPackageCommand()
   this->NoModule = false;
   this->DebugMode = false;
   this->UseLib64Paths = false;
+  this->PolicyScope = true;
   this->VersionMajor = 0;
   this->VersionMinor = 0;
   this->VersionPatch = 0;
@@ -77,7 +78,8 @@ cmFindPackageCommand::cmFindPackageCommand()
   this->VersionFoundCount = 0;
   this->CommandDocumentation =
     "  find_package(<package> [version] [EXACT] [QUIET]\n"
-    "               [[REQUIRED|COMPONENTS] [components...]])\n"
+    "               [[REQUIRED|COMPONENTS] [components...]]\n"
+    "               [NO_POLICY_SCOPE])\n"
     "Finds and loads settings from an external project.  "
     "<package>_FOUND will be set to indicate whether the package was found.  "
     "When the package is found package-specific information is provided "
@@ -116,6 +118,7 @@ cmFindPackageCommand::cmFindPackageCommand()
     "The complete Config mode command signature is:\n"
     "  find_package(<package> [version] [EXACT] [QUIET]\n"
     "               [[REQUIRED|COMPONENTS] [components...]] [NO_MODULE]\n"
+    "               [NO_POLICY_SCOPE]\n"
     "               [NAMES name1 [name2 ...]]\n"
     "               [CONFIGS config1 [config2 ...]]\n"
     "               [HINTS path1 [path2 ... ]]\n"
@@ -290,6 +293,11 @@ cmFindPackageCommand::cmFindPackageCommand()
   this->CommandDocumentation += this->GenericDocumentationMacPolicy;
   this->CommandDocumentation += this->GenericDocumentationRootPath;
   this->CommandDocumentation += this->GenericDocumentationPathsOrder;
+  this->CommandDocumentation +=
+    "\n"
+    "See the cmake_policy() command documentation for discussion of the "
+    "NO_POLICY_SCOPE option."
+    ;
 }
 
 //----------------------------------------------------------------------------
@@ -406,6 +414,12 @@ bool cmFindPackageCommand
       this->Compatibility_1_6 = false;
       doing = DoingConfigs;
       }
+    else if(args[i] == "NO_POLICY_SCOPE")
+      {
+      this->PolicyScope = false;
+      this->Compatibility_1_6 = false;
+      doing = DoingNone;
+      }
     else if(args[i] == "NO_CMAKE_BUILDS_PATH")
       {
       this->NoBuilds = true;
@@ -675,7 +689,7 @@ bool cmFindPackageCommand::FindModule(bool& found)
     std::string var = this->Name;
     var += "_FIND_MODULE";
     this->Makefile->AddDefinition(var.c_str(), "1");
-    bool result = this->ReadListFile(mfile.c_str());
+    bool result = this->ReadListFile(mfile.c_str(), DoPolicyScope);
     this->Makefile->RemoveDefinition(var.c_str());
     return result;
     }
@@ -753,7 +767,7 @@ bool cmFindPackageCommand::HandlePackageMode()
     this->StoreVersionFound();
 
     // Parse the configuration file.
-    if(this->ReadListFile(this->FileFound.c_str()))
+    if(this->ReadListFile(this->FileFound.c_str(), DoPolicyScope))
       {
       // The package has been found.
       found = true;
@@ -963,9 +977,10 @@ bool cmFindPackageCommand::FindAppBundleConfig()
 }
 
 //----------------------------------------------------------------------------
-bool cmFindPackageCommand::ReadListFile(const char* f)
+bool cmFindPackageCommand::ReadListFile(const char* f, PolicyScopeRule psr)
 {
-  if(this->Makefile->ReadListFile(this->Makefile->GetCurrentListFile(),f))
+  if(this->Makefile->ReadListFile(this->Makefile->GetCurrentListFile(), f, 0,
+                                  !this->PolicyScope || psr == NoPolicyScope))
     {
     return true;
     }
@@ -1304,9 +1319,10 @@ bool cmFindPackageCommand::CheckVersionFile(std::string const& version_file)
   sprintf(buf, "%u", this->VersionCount);
   this->Makefile->AddDefinition("PACKAGE_FIND_VERSION_COUNT", buf);
 
-  // Load the version check file.
+  // Load the version check file.  Pass NoPolicyScope because we do
+  // our own policy push/pop independent of CMP0011.
   bool suitable = false;
-  if(this->ReadListFile(version_file.c_str()))
+  if(this->ReadListFile(version_file.c_str(), NoPolicyScope))
     {
     // Check the output variables.
     bool okay = this->Makefile->IsOn("PACKAGE_VERSION_EXACT");