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, 20 insertions, 0 deletions

diff --git a/Source/cmPolicies.cxx b/Source/cmPolicies.cxx
index be546f8..169814a 100644
--- a/Source/cmPolicies.cxx
+++ b/Source/cmPolicies.cxx
@@ -335,6 +335,26 @@ cmPolicies::cmPolicies()
     "the string untouched, and continue. "
     "The NEW behavior for this policy is to report an error.",
     2,6,3, cmPolicies::WARN);
+
+  this->DefinePolicy(
+    CMP0011, "CMP0011",
+    "Included scripts do automatic cmake_policy PUSH and POP.",
+    "In CMake 2.6.2 and below, CMake Policy settings in scripts loaded by "
+    "the include() and find_package() commands would affect the includer.  "
+    "Explicit invocations of cmake_policy(PUSH) and cmake_policy(POP) were "
+    "required to isolate policy changes and protect the includer.  "
+    "While some scripts intend to affect the policies of their includer, "
+    "most do not.  "
+    "In CMake 2.6.3 and above, include() and find_package() by default PUSH "
+    "and POP an entry on the policy stack around an included script, "
+    "but provide a NO_POLICY_SCOPE option to disable it.  "
+    "This policy determines whether or not to imply NO_POLICY_SCOPE for "
+    "compatibility.  "
+    "The OLD behavior for this policy is to imply NO_POLICY_SCOPE for "
+    "include() and find_package() commands.  "
+    "The NEW behavior for this policy is to allow the commands to do their "
+    "default cmake_policy PUSH and POP.",
+    2,6,3, cmPolicies::WARN);
 }
 
 cmPolicies::~cmPolicies()