From 9d7587940d3d43d0d88bb12b26a24ce688ec7a71 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Wed, 28 Apr 2021 20:41:22 -0700
Subject: macros: lexical-var-p: don't report t for specials.

The lexical-var-p function wrongly reports true for locally
rebound special variables, which are not lexical.

* eval.c (special_var_p): Static function moved to avoid
forward declaration.
(lexical_var_p): Bail if sym satisfies special_var_p.
(old_lexical_var_p): New function, copy of old lexical_var_p
before this bugfix.
(eval_init): Conditionally register lexical-var-p as either
lexical_var_p or old_lexical_var_p depending on the compat
value.

* txr.1: Update documentation for lexical-var-p to clarify
that it doesn't report true for specials. Also make note that
it doesn't report true for global lexicals, and likewise that
lexical-fun-p doesn't report global functions.
Added compat note.
---
 eval.c | 38 ++++++++++++++++++++++++++++++--------
 txr.1  | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 82 insertions(+), 12 deletions(-)

diff --git a/eval.c b/eval.c
index 5983f2cd..b2e0605a 100644
--- a/eval.c
+++ b/eval.c
@@ -715,10 +715,19 @@ static val reparent_env(val child, val parent)
   return child;
 }
 
+static val special_var_p(val sym)
+{
+  uses_or2;
+  return or2(gethash(special, sym),
+             if2(lisplib_try_load(sym), gethash(special, sym)));
+}
+
 static val lexical_var_p(val menv, val sym)
 {
   if (nilp(menv)) {
     return nil;
+  } else if (special_var_p(sym)) {
+    return nil;
   } else {
     type_check(lit("lexical-var-p"), menv, ENV);
 
@@ -732,6 +741,23 @@ static val lexical_var_p(val menv, val sym)
   }
 }
 
+static val old_lexical_var_p(val menv, val sym)
+{
+  if (nilp(menv)) {
+    return nil;
+  } else {
+    type_check(lit("lexical-var-p"), menv, ENV);
+
+    {
+      val binding = assoc(sym, menv->e.vbindings);
+
+      if (binding)
+        return tnil(cdr(binding) == special_s);
+      return lexical_var_p(menv->e.up_env, sym);
+    }
+  }
+}
+
 static val lexical_fun_p(val menv, val sym)
 {
   if (nilp(menv)) {
@@ -780,13 +806,6 @@ static val mark_special(val sym)
   return sethash(special, sym, t);
 }
 
-static val special_var_p(val sym)
-{
-  uses_or2;
-  return or2(gethash(special, sym),
-             if2(lisplib_try_load(sym), gethash(special, sym)));
-}
-
 static void copy_env_handler(mem_t *ptr)
 {
   val *penv = coerce(val *, ptr);
@@ -6793,7 +6812,10 @@ void eval_init(void)
   reg_fun(intern(lit("env-vbindings"), user_package), func_n1(env_vbindings));
   reg_fun(intern(lit("env-fbindings"), user_package), func_n1(env_fbindings));
   reg_fun(intern(lit("env-next"), user_package), func_n1(env_next));
-  reg_fun(intern(lit("lexical-var-p"), user_package), func_n2(lexical_var_p));
+  reg_fun(intern(lit("lexical-var-p"), user_package),
+          func_n2(if3(opt_compat && opt_compat <= 257,
+                      old_lexical_var_p,
+                      lexical_var_p)));
   reg_fun(intern(lit("lexical-fun-p"), user_package), func_n2(lexical_fun_p));
   reg_fun(intern(lit("lexical-lisp1-binding"), user_package),
           func_n2(lexical_lisp1_binding));
diff --git a/txr.1 b/txr.1
index c3524bfa..ddf1f105 100644
--- a/txr.1
+++ b/txr.1
@@ -36785,11 +36785,45 @@ parameter. Using these functions, a macro can enquire whether
 a given
 .meta form
 is a symbol which has a variable binding or a function binding
-in the lexical environment.
+in the local lexical environment.
 This information is known during macro expansion. The macro expander
 recognizes lexical function and variable bindings, because these
 bindings can shadow macros.
 
+Special variables are not lexical. The function
+.code lexical-var-p
+returns
+.code nil
+if
+.meta form
+satisfies
+.code special-var-p
+function, indicating that it is the name of a special variable.
+
+The
+.code lexical-var-p
+function also returns
+.code nil
+for global lexical variables. If
+.meta form
+is a symbol for which only a global lexical variable binding is apparent,
+.code lexical-var-p
+returns
+.codn nil .
+Testing for the existence for a global variable can be done using
+.codn boundp ;
+if a symbol is
+.code boundp
+but not
+.codn special-var-p ,
+then it is a global lexical variable.
+
+Similarly,
+.code lexical-fun-p
+returns
+.code nil
+for global functions.
+
 .TP* Example:
 
 .verb
@@ -36806,14 +36840,20 @@ bindings can shadow macros.
       (t :not-lex-fun-var)))
 
   ;;
-  ;; This returns:
-  ;;
-  ;;   (:lexical-var :not-lex-fun-var :lexical-fun)
+  ;; Use classify macro above to report classification
+  ;; of the x, y and f symbols in the given scope
   ;;
   (let ((x 1) (y 2))
     (symacrolet ((y x))
       (flet ((f () (+ 2 2)))
         (list (classify x) (classify y) (classify f)))))
+  --> (:lexical-var :not-lex-fun-var :lexical-fun)
+
+  ;; Locally bound specials are not lexical
+
+  (let ((*stdout* *stdnull*))
+    (classify *stdout*))
+  --> :not-lex-fun-var
 .brev
 
 .TP* Note:
@@ -79273,6 +79313,14 @@ A compatibility value of 248 or lower restores the above old behaviors of
 .code @
 and
 .codn hash-revget .
+.IP 257
+Until \*(TX 257, the function
+.code lexical-var-p
+returned
+.code t
+for not only lexical variables, but also for locally bound special variables,
+which are not lexical. The behavior is restored if 257 or older compatibility
+is selected.
 .IP 244
 Until \*(TX 244, the
 .code env-hash
-- 
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