From 81715deb567a159997e3a774883f1910074ee0dc Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Sun, 17 Dec 2023 19:09:22 -0800
Subject: txr: bug in handling @{nil ...} variable match.

In March 2012, b7f1f4c5bbea86e288b6a4d68595c1d2d07217bd
introduced the feature that the @nil variable matches and
discards. This was incompletely implemented. Some cases
of a nil variable with modifiers fail to match.

* match.c (dest_bind): This function must correctly handle
the case when pattern is nil: it should just return bindings
without extending them. If the pattern is any nonbindable
symbol, it should indicate a failed match using t.
The logic has not been touched since 2009, at which time
an additional bogosity was introduced of calling
funcall(testfun, pattern, value) when pattern is a
non-bindable symbol. If value is a string, that could
never work. Possibly the idea is that the value could come
from a symbol-valued expression, such as one producing
a keyword symbol. We are not going to support that, unless
someone complains.

* tests/000/nilvar.txr, tests/000/nilvar.expected: New files,
providing a test case that fails without this commit.
---
 match.c                   | 4 +++-
 tests/000/nilvar.expected | 1 +
 tests/000/nilvar.txr      | 3 +++
 3 files changed, 7 insertions(+), 1 deletion(-)
 create mode 100644 tests/000/nilvar.expected
 create mode 100644 tests/000/nilvar.txr

diff --git a/match.c b/match.c
index 0bc40838..0f1583f1 100644
--- a/match.c
+++ b/match.c
@@ -381,8 +381,10 @@ static val dest_bind(val spec, val bindings, val pattern,
         return t;
       }
       return cons(cons(pattern, value), bindings);
+    } else if (pattern) {
+      return t;
     } else {
-      return funcall2(testfun, pattern, value) ? bindings : t;
+      return bindings;
     }
   } else if (consp(pattern)) {
     val piter = pattern, viter = value;
diff --git a/tests/000/nilvar.expected b/tests/000/nilvar.expected
new file mode 100644
index 00000000..70985094
--- /dev/null
+++ b/tests/000/nilvar.expected
@@ -0,0 +1 @@
+a:c
diff --git a/tests/000/nilvar.txr b/tests/000/nilvar.txr
new file mode 100644
index 00000000..a6d1391c
--- /dev/null
+++ b/tests/000/nilvar.txr
@@ -0,0 +1,3 @@
+@(next :string "a !b c")
+@(coll)@(cases)@{nil /!\S+/}@(or)@{var /\S+/}@(end)@(end)
+@(do (put-line (join-with ":" var)))
-- 
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