ENH: Add policy CMP0005 to decide whether add_definitions should escape defs.

Source/cmMakefile.cxx

@@ -1023,14 +1023,11 @@ void cmMakefile::RemoveDefineFlag(const char* flag)
 bool cmMakefile::ParseDefineFlag(std::string const& def, bool remove)
 {
   // Create a regular expression to match valid definitions.
-  // Definitions with non-trivial values must not be matched because
-  // escaping them could break compatibility with escapes added by
-  // users.
   static cmsys::RegularExpression
-    regex("^[-/]D[A-Za-z_][A-Za-z0-9_]*(=[A-Za-z0-9_.]+)?$");
+    valid("^[-/]D[A-Za-z_][A-Za-z0-9_]*(=.*)$");
 
   // Make sure the definition matches.
-  if(!regex.find(def.c_str()))
+  if(!valid.find(def.c_str()))
     {
     return false;
     }
@@ -1043,6 +1040,37 @@ bool cmMakefile::ParseDefineFlag(std::string const& def, bool remove)
     return false;
     }
 
+  // Definitions with non-trivial values require a policy check.
+  static cmsys::RegularExpression
+    trivial("^[-/]D[A-Za-z_][A-Za-z0-9_]*(=[A-Za-z0-9_.]+)?$");
+  if(!trivial.find(def.c_str()))
+    {
+    // This definition has a non-trivial value.
+    switch(this->GetPolicyStatus(cmPolicies::CMP0005))
+      {
+      case cmPolicies::WARN:
+        this->IssueMessage(
+          cmake::AUTHOR_WARNING,
+          this->GetPolicies()->GetPolicyWarning(cmPolicies::CMP0005)
+          );
+      case cmPolicies::OLD:
+        // OLD behavior is to not escape the value.  We should not
+        // convert the definition to use the property.
+        return false;
+      case cmPolicies::REQUIRED_IF_USED:
+      case cmPolicies::REQUIRED_ALWAYS:
+        this->IssueMessage(
+          cmake::FATAL_ERROR,
+          this->GetPolicies()->GetRequiredPolicyError(cmPolicies::CMP0005)
+          );
+        return false;
+      case cmPolicies::NEW:
+        // NEW behavior is to escape the value.  Proceed to convert it
+        // to an entry in the property.
+        break;
+      }
+    }
+
   // Get the definition part after the flag.
   const char* define = def.c_str() + 2;
 

Source/cmPolicies.cxx

@@ -216,6 +216,27 @@ cmPolicies::cmPolicies()
     "that in effect when the target is created by an add_executable or "
     "add_library command.",
     2,6,0, cmPolicies::WARN);
+
+  this->DefinePolicy(
+    CMP0005, "CMP0005",
+    "Preprocessor definition values are now escaped automatically.",
+    "This policy determines whether or not CMake should generate escaped "
+    "preprocessor definition values added via add_definitions.  "
+    "CMake versions 2.4 and below assumed that only trivial values would "
+    "be given for macros in add_definitions calls.  "
+    "It did not attempt to escape non-trivial values such as string "
+    "literals in generated build rules.  "
+    "CMake versions 2.6 and above support escaping of most values, but "
+    "cannot assume the user has not added escapes already in an attempt to "
+    "work around limitations in earlier versions.\n"
+    "The OLD behavior for this policy is to place definition values given "
+    "to add_definitions directly in the generated build rules without "
+    "attempting to escape anything.  "
+    "The NEW behavior for this policy is to generate correct escapes "
+    "for all native build tools automatically.  "
+    "See documentation of the COMPILE_DEFINITIONS target property for "
+    "limitations of the escaping implementation.",
+    2,6,0, cmPolicies::WARN);
 }
 
 cmPolicies::~cmPolicies()

Source/cmPolicies.h

@@ -45,6 +45,7 @@ public:
     CMP0002, // Target names must be unique
     CMP0003, // Linking does not include extra -L paths
     CMP0004, // Libraries linked may not have leading or trailing whitespace
+    CMP0005, // Definition value escaping
 
     // Always the last entry.  Useful mostly to avoid adding a comma
     // the last policy when adding a new one.