GenEx: Add expressions to specify build- or install-only values

This is for specifying INCLUDE_DIRECTORIES relevant to the build-location
or the install location for example:

 set_property(TARGET foo PROPERTY
   INTERFACE_INCLUDE_DIRECTORIES
   "$<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR};${CMAKE_CURRENT_SOURCE_DIR}>"
   "$<INSTALL_INTERFACE:${CMAKE_INSTALL_PREFIX}/include>"
 )

A 'bar' target can then use:

 set_property(TARGET bar PROPERTY
   INCLUDE_DIRECTORIES
   "$<TARGET_PROPERTY:foo,INTERFACE_INCLUDE_DIRECTORIES>"
 )

and it will work whether foo is in the same project, or an imported target
from an installation location, or an imported target from a build location
generated by the export() command.

Because the generator expressions are only evaluated at build-time, these
new expressions are equivalent to the ZeroNode and OneNode.

The GeneratorExpression test is split into parts. Some shells can't run
the custom command as it is getting too long.

1 files changed, 3 insertions, 1 deletions

diff --git a/Source/cmGeneratorExpression.h b/Source/cmGeneratorExpression.h
index 15e637c..99056a5 100644
--- a/Source/cmGeneratorExpression.h
+++ b/Source/cmGeneratorExpression.h
@@ -51,7 +51,9 @@ public:
   cmsys::auto_ptr<cmCompiledGeneratorExpression> Parse(const char* input);
 
   enum PreprocessContext {
-    StripAllGeneratorExpressions
+    StripAllGeneratorExpressions,
+    BuildInterface,
+    InstallInterface
   };
 
   static std::string Preprocess(const std::string &input,