matcher: fix backreferencing in predicate.

* share/txr/stdlib/match.tl (compile-predicate-match): Always
allocate res-var as a gensym; do not use resvar. Otherwise we
will freshly bind resvar as a local, failing to back-reference.

* tests/011/patmatch.tl: Add test cases, the second of which
fails before this change.

2 files changed, 7 insertions, 1 deletions

diff --git a/share/txr/stdlib/match.tl b/share/txr/stdlib/match.tl
index 0aea24b2..a1222c5a 100644
--- a/share/txr/stdlib/match.tl
+++ b/share/txr/stdlib/match.tl
@@ -288,7 +288,7 @@
                      (let ((sym (cadr vm)))
                        (set args (append (ldiff args vm) sym))
                        sym))))
-                (res-var (if rvar rvar (gensym "res-")))
+                (res-var (gensym "res-"))
                 (arg-var (if avar avar (gensym "obj-"))))
            (unless avar
              (set args (append args (list arg-var))))
diff --git a/tests/011/patmatch.tl b/tests/011/patmatch.tl
index a616b9d2..f49b115d 100644
--- a/tests/011/patmatch.tl
+++ b/tests/011/patmatch.tl
@@ -94,6 +94,12 @@
       (t (1 2 3)))
 (test (when-match @(@x (< . @sym)) '(3 2 1) (list x sym))
       nil)
+(test (let ((x t))
+        (when-match @(@x (< . @sym)) '(1 2 3) (list x sym)))
+      (t (1 2 3)))
+(test (let ((x nil))
+        (when-match @(@x (< . @sym)) '(1 2 3) (list x sym)))
+      nil)
 
 (test (if-match (@(or @a) @a) '(1 2) a :no) :no)
 (test (if-match (@(and @a) @a) '(1 2) a :no) :no)