cmTarget: Deprecate the LOCATION target property with a policy.

The final location and name of a build-target is not determined
until generate-time. However, reading the LOCATION property from
a target is currently allowed at configure time. Apart from creating
possibly-erroneous results, this has an impact on the implementation
of cmake itself, and prevents some major cleanups from being made.

Disallow reading LOCATION from build-targets with a policy. Port some
existing uses of it in CMake itself to use the TARGET_FILE generator
expression.

4 files changed, 75 insertions, 0 deletions

diff --git a/Source/cmPolicies.cxx b/Source/cmPolicies.cxx
index 1d3469f..d07645c 100644
--- a/Source/cmPolicies.cxx
+++ b/Source/cmPolicies.cxx
@@ -637,6 +637,28 @@ cmPolicies::cmPolicies()
     "The OLD behavior for this policy is to use compiler id \"Clang\".  "
     "The NEW behavior for this policy is to use compiler id \"AppleClang\".",
     2,8,13,0, cmPolicies::WARN);
+
+  this->DefinePolicy(
+    CMP0026, "CMP0026",
+    "Disallow use of the LOCATION target property.",
+    "CMake 2.8.12 and lower allowed reading the LOCATION target property to "
+    "determine the eventual location of build targets.  This relies on the "
+    "assumption that all necessary information is available at "
+    "configure-time to determine the final location and filename of the "
+    "target.  However, this property is not fully determined until later at "
+    "generate-time.  At generate time, the $<TARGET_FILE> generator "
+    "expression can be used to determine the eventual LOCATION of a target "
+    "output."
+    "\n"
+    "Code which reads the LOCATION target property can be ported to use the "
+    "$<TARGET_FILE> generator expression together with the file(GENERATE) "
+    "subcommand to generate a file containing the target location."
+    "\n"
+    "The OLD behavior for this policy is to allow reading the LOCATION "
+    "property from build-targets.  "
+    "The NEW behavior for this policy is to not to allow reading the "
+    "LOCATION property from build-targets.",
+    2,8,13,0, cmPolicies::WARN);
 }
 
 cmPolicies::~cmPolicies()
diff --git a/Source/cmPolicies.h b/Source/cmPolicies.h
index ec8959d..e33171b 100644
--- a/Source/cmPolicies.h
+++ b/Source/cmPolicies.h
@@ -76,6 +76,7 @@ public:
     CMP0023, ///< Disallow mixing keyword and plain tll signatures
     CMP0024, ///< Disallow including export() result.
     CMP0025, ///< Compiler id for Apple Clang is now AppleClang
+    CMP0026, ///< Disallow use of the LOCATION target property.
 
     /** \brief Always the last entry.
      *
diff --git a/Source/cmTarget.cxx b/Source/cmTarget.cxx
index 1c04e4e..43d9ed1 100644
--- a/Source/cmTarget.cxx
+++ b/Source/cmTarget.cxx
@@ -4130,6 +4130,43 @@ const char *cmTarget::GetProperty(const char* prop)
 }
 
 //----------------------------------------------------------------------------
+bool cmTarget::HandleLocationPropertyPolicy()
+{
+  if (this->IsImported())
+    {
+    return true;
+    }
+  const char *modal = 0;
+  cmake::MessageType messageType = cmake::AUTHOR_WARNING;
+  switch (this->Makefile->GetPolicyStatus(cmPolicies::CMP0026))
+    {
+    case cmPolicies::WARN:
+      modal = "should";
+    case cmPolicies::OLD:
+      break;
+    case cmPolicies::REQUIRED_ALWAYS:
+    case cmPolicies::REQUIRED_IF_USED:
+    case cmPolicies::NEW:
+      modal = "may";
+      messageType = cmake::FATAL_ERROR;
+    }
+
+  if (modal)
+    {
+    cmOStringStream e;
+    e << (this->Makefile->GetPolicies()
+          ->GetPolicyWarning(cmPolicies::CMP0026)) << "\n";
+    e << "The LOCATION property " << modal << " not be read from target \""
+      << this->GetName() << "\".  Use the target name directly with "
+      "add_custom_command, or use the generator expression $<TARGET_FILE>, "
+      "as appropriate.\n";
+    this->Makefile->IssueMessage(messageType, e.str().c_str());
+    }
+
+  return messageType != cmake::FATAL_ERROR;
+}
+
+//----------------------------------------------------------------------------
 const char *cmTarget::GetProperty(const char* prop,
                                   cmProperty::ScopeType scope)
 {
@@ -4154,6 +4191,11 @@ const char *cmTarget::GetProperty(const char* prop,
     {
     if(strcmp(prop,"LOCATION") == 0)
       {
+      if (!this->HandleLocationPropertyPolicy())
+        {
+        return 0;
+        }
+
       // Set the LOCATION property of the target.
       //
       // For an imported target this is the location of an arbitrary
@@ -4169,6 +4211,10 @@ const char *cmTarget::GetProperty(const char* prop,
     // Support "LOCATION_<CONFIG>".
     if(strncmp(prop, "LOCATION_", 9) == 0)
       {
+      if (!this->HandleLocationPropertyPolicy())
+        {
+        return 0;
+        }
       std::string configName = prop+9;
       this->SetProperty(prop, this->GetLocation(configName.c_str()));
       }
@@ -4181,6 +4227,10 @@ const char *cmTarget::GetProperty(const char* prop,
         std::string configName(prop, len-9);
         if(configName != "IMPORTED")
           {
+          if (!this->HandleLocationPropertyPolicy())
+            {
+            return 0;
+            }
           this->SetProperty(prop, this->GetLocation(configName.c_str()));
           }
         }
diff --git a/Source/cmTarget.h b/Source/cmTarget.h
index a88c5ec..3c36da7 100644
--- a/Source/cmTarget.h
+++ b/Source/cmTarget.h
@@ -554,6 +554,8 @@ public:
   { return this->TargetTypeValue == STATIC_LIBRARY; }
 
 private:
+  bool HandleLocationPropertyPolicy();
+
   // The set of include directories that are marked as system include
   // directories.
   std::set<cmStdString> SystemIncludeDirectories;