Create CMP0014 to require CMakeLists.txt files

Until now CMake accidentally accepted add_subdirectory() and subdirs()
calls referring to directories that do not contain a CMakeLists.txt
file.  We introduce CMake Policy CMP0014 to make this case an error.

Source/cmLocalGenerator.cxx

@@ -167,9 +167,49 @@ void cmLocalGenerator::ComputeObjectMaxPath()
 //----------------------------------------------------------------------------
 void cmLocalGenerator::ReadInputFile()
 {
+  // Look for the CMakeLists.txt file.
   std::string currentStart = this->Makefile->GetStartDirectory();
   currentStart += "/CMakeLists.txt";
-  this->Makefile->ReadListFile(currentStart.c_str());
+  if(cmSystemTools::FileExists(currentStart.c_str(), true))
+    {
+    this->Makefile->ReadListFile(currentStart.c_str());
+    return;
+    }
+
+  if(!this->Parent)
+    {
+    return;
+    }
+
+  // The file is missing.  Check policy CMP0014.
+  cmMakefile* mf = this->Parent->GetMakefile();
+  cmOStringStream e;
+  e << "The source directory\n"
+    << "  " << this->Makefile->GetStartDirectory() << "\n"
+    << "does not contain a CMakeLists.txt file.";
+  switch (mf->GetPolicyStatus(cmPolicies::CMP0014))
+    {
+    case cmPolicies::WARN:
+      // Print the warning.
+      e << "\n"
+        << "CMake does not support this case but it used "
+        << "to work accidentally and is being allowed for "
+        << "compatibility."
+        << "\n"
+        << mf->GetPolicies()->GetPolicyWarning(cmPolicies::CMP0014);
+      mf->IssueMessage(cmake::AUTHOR_WARNING, e.str());
+    case cmPolicies::OLD:
+      // OLD behavior does not warn.
+      return;
+    case cmPolicies::REQUIRED_IF_USED:
+    case cmPolicies::REQUIRED_ALWAYS:
+      e << "\n"
+        << mf->GetPolicies()->GetRequiredPolicyError(cmPolicies::CMP0014);
+    case cmPolicies::NEW:
+      // NEW behavior prints the error.
+      mf->IssueMessage(cmake::FATAL_ERROR, e.str());
+      break;
+    }
 }
 
 void cmLocalGenerator::SetupPathConversions()

Source/cmPolicies.cxx

@@ -387,6 +387,18 @@ cmPolicies::cmPolicies()
     "The NEW behavior for this policy is to disallow duplicate binary "
     "directories with an error.",
     2,6,5, cmPolicies::WARN);
+
+    this->DefinePolicy(
+    CMP0014, "CMP0014",
+    "Input directories must have CMakeLists.txt.",
+    "CMake versions before 2.8 silently ignored missing CMakeLists.txt "
+    "files in directories referenced by add_subdirectory() or subdirs(), "
+    "treating them as if present but empty.  "
+    "In CMake 2.8.0 and above this policy determines whether or not "
+    "the case is an error.  "
+    "The OLD behavior for this policy is to silently ignore the problem.  "
+    "The NEW behavior for this policy is to report an error.",
+    2,7,20090902, cmPolicies::WARN);
 }
 
 cmPolicies::~cmPolicies()

Source/cmPolicies.h

@@ -54,6 +54,7 @@ public:
     CMP0011, // Strong policy scope for include and find_package
     CMP0012, // Strong handling of boolean constants
     CMP0013, // Duplicate binary directories not allowed
+    CMP0014, // Input directories must have CMakeLists.txt
 
     // Always the last entry.  Useful mostly to avoid adding a comma
     // the last policy when adding a new one.