IECore module : Add DLL directory for DLL dependencies

This fixes `scons testCorePython` and provides a mechanism for folks to fix
imports in their own environments.

At first I tried to just hardcode the directory to match the directory
layout used by Gaffer, using a path relative to `__file__`. But that didn't
work, because when we run `scons testCorePython`, we haven't installed the IECore
module yet (we test it in place in the local dir). The `IECORE_DLL_DIRECTORIES`
environment variable was the only other option I could see, and I suppose it
at least gives folks a hand if they have their own installation layouts.

Author: johnhaddon

SConstruct

@@ -1496,6 +1496,7 @@ if testEnv["PLATFORM"] == "darwin" :
 testEnv["ENV"][testEnv["TEST_LIBRARY_PATH_ENV_VAR"]] = os.pathsep.join( [ testEnv["ENV"].get(testEnv["TEST_LIBRARY_PATH_ENV_VAR"], ""), testEnvLibPath ] )
 if testEnv["TEST_LIBRARY_PATH_ENV_VAR"] != libraryPathEnvVar :
 	testEnv["ENV"][libraryPathEnvVar] = os.pathsep.join( [ testEnv["ENV"].get(libraryPathEnvVar, ""), testEnvLibPath ] )
+testEnv["ENV"]["IECORE_DLL_DIRECTORIES"] = testEnv["ENV"][libraryPathEnvVar]
 testEnv["ENV"]["IECORE_OP_PATHS"] = os.path.join( "test", "IECore", "ops" )
 
 c = configureSharedLibrary( testEnv )

python/IECore/__init__.py

@@ -38,7 +38,7 @@
 #
 # Some parts of the IECore library are defined purely in Python. These are shown below.
 
-import os, sys, ctypes
+import os, sys, ctypes, pathlib
 if os.name == "posix" and os.environ.get( "IECORE_RTLD_GLOBAL", "1" ) == "1" :
 	# Historically, we had problems with cross-module RTTI on Linux, whereby
 	# different Python modules and/or libraries could end up with their own
@@ -56,8 +56,15 @@
 		sys.getdlopenflags() | ctypes.RTLD_GLOBAL
 	)
 
+if hasattr( os, "add_dll_directory" ) and "IECORE_DLL_DIRECTORIES" in os.environ :
+	for directory in os.environ.get( "IECORE_DLL_DIRECTORIES" ).split( os.pathsep ) :
+		directory = pathlib.Path( directory ).resolve()
+		if directory.is_dir() :
+			os.add_dll_directory( directory )
+	del directory
+
 # Remove pollution of IECore namespace
-del os, sys, ctypes
+del os, sys, ctypes, pathlib
 
 __import__( "imath" )