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.

3 files changed, 54 insertions, 4 deletions

diff --git a/stdlib/with-resources.tl b/stdlib/with-resources.tl
index 9d4a89c9..e95ed4f9 100644
--- a/stdlib/with-resources.tl
+++ b/stdlib/with-resources.tl
@@ -30,8 +30,13 @@
      ^(let ((,sym ,init))
         (with-resources ,rest ,*body)))
     (((sym init . cleanup) . rest)
-     ^(let ((,sym ,init))
-        (when ,sym
+     (if (and (plusp sys:compat) (<= sys:compat 265))
+       ^(let ((,sym ,init))
+          (when ,sym
+            (unwind-protect
+              (with-resources ,rest ,*body)
+              ,*cleanup)))
+       ^(let ((,sym ,init))
           (unwind-protect
             (with-resources ,rest ,*body)
             ,*cleanup))))
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))
diff --git a/txr.1 b/txr.1
index 363fedf8..9d5ae2b1 100644
--- a/txr.1
+++ b/txr.1
@@ -47841,6 +47841,14 @@ if no
 .metn body-form s
 are present.
 
+.TP* Note:
+
+From its inception, until \*(TX 265,
+.code with-resources
+featured an undocumented behavior. Details are given in the
+COMPATIBILITY section's Compatibility Version Values subsection,
+in the notes for compatibility value 265.
+
 .TP* "Example:"
 
 The following expression opens a text file and reads a line from it,
@@ -47853,8 +47861,6 @@ immediately:
       (put-line l)))
 .brev
 
-
-
 .coNP Special variable @ *unhandled-hook*
 The
 .code *unhandled-hook*
@@ -82755,6 +82761,27 @@ of these version values, the described behaviors are provided if
 is given an argument which is equal or lower. For instance
 .code "-C 103"
 selects the behaviors described below for version 105, but not those for 102.
+.IP 265
+Until \*(TX 265, the
+.code with-resources
+macro exhibits an undocumented behavior: the three-element binding expression
+.mono
+.meti >> ( var < init << cleanup )
+.onom
+immediately causes the
+.code with-resources
+form to terminate with a return value of
+.code nil
+if the
+.meta init
+form returns
+.codn nil .
+Neither the
+.meta cleanup
+in the same expression, nor any subsequent binding expressions or the body
+of the construct, are evaluated. Prior cleanup forms are evaluated in
+reverse order, as documented. A compatibility value of 265 or less restores
+this behavior.
 .IP 262
 Selection 262 compatibility restores a wrong behavior which existed between
 versions 191 and 262 due to a regression. The wrong behavior is that the