fix bug that was making hancho tutorial build dirs collide

hancho.py

@@ -248,7 +248,8 @@ class Config:
 
     def __init__(self, *args, **kwargs):
         for arg in args:
-            self.__dict__.update(arg.__dict__ if isinstance(arg, Config) else arg)
+            if arg is not None:
+                self.__dict__.update(arg.__dict__ if isinstance(arg, Config) else arg)
         self.__dict__.update(kwargs)
 
     def __getitem__(self, key):
@@ -275,7 +276,7 @@ def __call__(self, source_files, build_files = None, *, config = None):
             kwargs['source_files'] = source_files
         if build_files is not None:
             kwargs['build_files'] = build_files
-        return Task(self, kwargs)
+        return Task(self, config, kwargs)
 
     def expand(self, variant):
         return expand(self, variant)

tutorial/build.hancho

@@ -11,19 +11,19 @@ test_build = hancho.Config(
   build_files = "{swap_ext(source_files, '.pass')}",
 )
 
-test_build(source_files = "tut00.hancho")
-test_build(source_files = "tut01.hancho")
-test_build(source_files = "tut02.hancho")
-test_build(source_files = "tut03.hancho")
-test_build(source_files = "tut04.hancho")
+test_build("tut00.hancho")
+test_build("tut01.hancho")
+test_build("tut02.hancho")
+test_build("tut03.hancho")
+test_build("tut04.hancho")
 
-test_build(source_files = "tut10.hancho")
-test_build(source_files = "tut11.hancho")
-test_build(source_files = "tut12.hancho")
-test_build(source_files = "tut13.hancho")
-test_build(source_files = "tut14.hancho")
-test_build(source_files = "tut15.hancho")
-test_build(source_files = "tut16.hancho")
+test_build("tut10.hancho")
+test_build("tut11.hancho")
+test_build("tut12.hancho")
+test_build("tut13.hancho")
+test_build("tut14.hancho")
+test_build("tut15.hancho")
+test_build("tut16.hancho")
 
 test_build("tut20.hancho")
 test_build("tut30.hancho")

tutorial/tut40_rules.hancho

@@ -14,8 +14,5 @@ link = hancho.Config(
 )
 
 def c_binary(source_files, build_files, *, config = None):
-  objs = [
-    compile(file, config = config)
-    for file in source_files
-  ]
+  objs = [compile(file, config = config) for file in source_files]
   return link(objs, build_files, config = config)