Generate an early-return guard in target Export files.

Previously it was necessary for writers of Config files
which incude exported target files to write the guard themselves, but
this was not immediately obvious or documented. Options for them
would be to use a variable, or an INHERITED directory property in an
effort to avoid accidental name clashes in all contexts in
which find_package can be used.

Getting this right requires boiler plate code, so generate a simpler
check automatically instead.

4 files changed, 61 insertions, 0 deletions

diff --git a/Source/cmExportBuildFileGenerator.cxx b/Source/cmExportBuildFileGenerator.cxx
index fb3f39f..cd6a7ab 100644
--- a/Source/cmExportBuildFileGenerator.cxx
+++ b/Source/cmExportBuildFileGenerator.cxx
@@ -22,6 +22,20 @@ cmExportBuildFileGenerator::cmExportBuildFileGenerator()
 //----------------------------------------------------------------------------
 bool cmExportBuildFileGenerator::GenerateMainFile(std::ostream& os)
 {
+  {
+  std::string expectedTargets;
+  std::string sep;
+  for(std::vector<cmTarget*>::const_iterator
+        tei = this->Exports->begin();
+      tei != this->Exports->end(); ++tei)
+    {
+    expectedTargets += sep + this->Namespace + (*tei)->GetName();
+    sep = " ";
+    }
+
+  this->GenerateExpectedTargetsCode(os, expectedTargets);
+  }
+
   // Create all the imported targets.
   for(std::vector<cmTarget*>::const_iterator
         tei = this->Exports->begin();
diff --git a/Source/cmExportFileGenerator.cxx b/Source/cmExportFileGenerator.cxx
index 8dffae4..3f738cc 100644
--- a/Source/cmExportFileGenerator.cxx
+++ b/Source/cmExportFileGenerator.cxx
@@ -287,6 +287,37 @@ void cmExportFileGenerator::GenerateImportVersionCode(std::ostream& os)
 }
 
 //----------------------------------------------------------------------------
+void cmExportFileGenerator::GenerateExpectedTargetsCode(std::ostream& os,
+                                            const std::string &expectedTargets)
+{
+  os << "SET(_targetsDefined)\n"
+        "SET(_targetsNotDefined)\n"
+        "SET(_expectedTargets)\n"
+        "FOREACH(_expectedTarget " << expectedTargets << ")\n"
+        "  LIST(APPEND _expectedTargets ${_expectedTarget})\n"
+        "  IF(NOT TARGET ${_expectedTarget})\n"
+        "    LIST(APPEND _targetsNotDefined ${_expectedTarget})\n"
+        "  ENDIF(NOT TARGET ${_expectedTarget})\n"
+        "  IF(TARGET ${_expectedTarget})\n"
+        "    LIST(APPEND _targetsDefined ${_expectedTarget})\n"
+        "  ENDIF(TARGET ${_expectedTarget})\n"
+        "ENDFOREACH(_expectedTarget)\n"
+        "IF(\"${_targetsDefined}\" STREQUAL \"${_expectedTargets}\")\n"
+        "  SET(CMAKE_IMPORT_FILE_VERSION)\n"
+        "  CMAKE_POLICY(POP)\n"
+        "  RETURN()\n"
+        "ENDIF(\"${_targetsDefined}\" STREQUAL \"${_expectedTargets}\")\n"
+        "IF(NOT \"${_targetsDefined}\" STREQUAL \"\")\n"
+        "  MESSAGE(FATAL_ERROR \"Some (but not all) targets in this export "
+        "set were already defined.\\nTargets Defined: ${_targetsDefined}\\n"
+        "Targets not yet defined: ${_targetsNotDefined}\\n\")\n"
+        "ENDIF(NOT \"${_targetsDefined}\" STREQUAL \"\")\n"
+        "UNSET(_targetsDefined)\n"
+        "UNSET(_targetsNotDefined)\n"
+        "UNSET(_expectedTargets)\n"
+        "\n\n";
+}
+//----------------------------------------------------------------------------
 void
 cmExportFileGenerator
 ::GenerateImportTargetCode(std::ostream& os, cmTarget* target)
diff --git a/Source/cmExportFileGenerator.h b/Source/cmExportFileGenerator.h
index 70bc65d..4a75c52 100644
--- a/Source/cmExportFileGenerator.h
+++ b/Source/cmExportFileGenerator.h
@@ -63,6 +63,8 @@ protected:
   void GenerateMissingTargetsCheckCode(std::ostream& os,
                                const std::vector<std::string>& missingTargets);
 
+  void GenerateExpectedTargetsCode(std::ostream& os,
+                                          const std::string &expectedTargets);
 
   // Collect properties with detailed information about targets beyond
   // their location on disk.
diff --git a/Source/cmExportInstallFileGenerator.cxx b/Source/cmExportInstallFileGenerator.cxx
index 7841731..6ba7d9f 100644
--- a/Source/cmExportInstallFileGenerator.cxx
+++ b/Source/cmExportInstallFileGenerator.cxx
@@ -39,6 +39,20 @@ std::string cmExportInstallFileGenerator::GetConfigImportFileGlob()
 //----------------------------------------------------------------------------
 bool cmExportInstallFileGenerator::GenerateMainFile(std::ostream& os)
 {
+  {
+  std::string expectedTargets;
+  std::string sep;
+  for(std::vector<cmTargetExport*>::const_iterator
+        tei = this->IEGen->GetExportSet()->GetTargetExports()->begin();
+      tei != this->IEGen->GetExportSet()->GetTargetExports()->end(); ++tei)
+    {
+    expectedTargets += sep + this->Namespace + (*tei)->Target->GetName();
+    sep = " ";
+    }
+
+  this->GenerateExpectedTargetsCode(os, expectedTargets);
+  }
+
   // Create all the imported targets.
   for(std::vector<cmTargetExport*>::const_iterator
         tei = this->IEGen->GetExportSet()->GetTargetExports()->begin();