with-resources: undocumented nil skip behavior.

Paul A. Patience discovered the hidden "feature" of
with-resourcers, that the three-argument form of the binding
(var init cleanup) causes the with-resources form to terminate
if init returns nil. The (var init) syntax doesn't generate
this logic.

* stdlib/with-resources.tl (with-resources): Do not emit the
when form unless <= 265 compatibility is in effect.

* tests/012/oop-mac.tl: New file.

* txr.1: Compat note added.

1 files changed, 18 insertions, 0 deletions

diff --git a/tests/012/oop-mac.tl b/tests/012/oop-mac.tl
new file mode 100644
index 00000000..d3c3e480
--- /dev/null
+++ b/tests/012/oop-mac.tl
@@ -0,0 +1,18 @@
+(load "../common")
+
+(test (with-resources ((a nil (list a))
+                       (b nil)
+                       (c nil (list c)))
+        (list a b c))
+      (nil nil nil))
+
+(test (build
+        (catch
+          (with-resources ((a 1 (add a))
+                           (x nil)
+                           (b 2 (add b))
+                           (y (throw 'out))
+                           (z nil t)
+                           (c 3 (add c))))
+          (out () (add 4))))
+      (2 1 4))