unuse-sym: fix in face of use-sym-as.

* lib.c (unuse_sym): A used symbol may now appear in a package
under a different name. So if we don't find a symbol under
the symbol's name, or find a different symbol, we must try
a reverse hash search before giving up.

* txr.1: Add notes to use-sym-as that unuse-sym must be
used to undo its effect. Add notes to unuse-sym discussing
similarities and differences versus unintern.

* tests/012/use-as.tl: New test cases.

3 files changed, 60 insertions, 0 deletions

diff --git a/lib.c b/lib.c
index d7a7ce66..e5d01387 100644
--- a/lib.c
+++ b/lib.c
@@ -7359,6 +7359,16 @@ val unuse_sym(val symbol, val package_in)
   val visible = cdr(found_visible);
   val hidden = cdr(found_hidden);
 
+  if (!found_visible || visible != symbol) {
+    name = hash_revget(package->pk.symhash, symbol, eq_f, identity_f);
+    if (name) {
+      found_visible = gethash_e(self, package->pk.symhash, name);
+      found_hidden = gethash_e(self, package->pk.hidhash, name);
+      visible = cdr(found_visible);
+      hidden = cdr(found_hidden);
+    }
+  }
+
   if (!found_visible || visible != symbol)
     return nil;
 
diff --git a/tests/012/use-as.tl b/tests/012/use-as.tl
index 681a968d..eb736d9d 100644
--- a/tests/012/use-as.tl
+++ b/tests/012/use-as.tl
@@ -29,3 +29,11 @@
   (use-sym-as 3 '#:foo) :error
   (use-sym-as 'ldraw 3) :error
   (use-sym-as 'x 'x) x)
+
+(mtest
+  (find-symbol "ldraw") lottery:draw
+  (find-symbol "gdraw") graphics:draw
+  (unuse-sym 'ldraw) lottery:draw
+  (unuse-sym 'gdraw) graphics:draw
+  (find-symbol "ldraw") nil
+  (find-symbol "gdraw") nil)
diff --git a/txr.1 b/txr.1
index 9a7f8886..61355fff 100644
--- a/txr.1
+++ b/txr.1
@@ -67308,6 +67308,15 @@ clauses
 and
 .codn :use-syms-as .
 
+Note:
+if
+.code use-sym-as
+is used to introduce a foreign symbol into a package under a different
+name, that symbol cannot be removed with
+.codn unintern .
+It can only be removed using
+.codn unuse-sym .
+
 .coNP Function @ unuse-sym
 .synb
 .mets (unuse-sym < symbol <> [ package ])
@@ -67355,6 +67364,39 @@ then
 .meta symbol
 itself is returned.
 
+There are close similarities between the function
+.code unintern
+and
+.codn unuse-sym ,
+but the two are significantly different.
+
+Firstly,
+.code unuse-sym
+cannot be used to remove a symbol from its home package. As noted
+above, this requires
+.codn unintern .
+
+Secondly,
+.code unuse-sym
+can be used to undo the effect of
+.code use-sym-as
+whereby a foreign symbol is introduced into a package under a
+different name. If
+.meta symbol
+is not found under its name,
+.code unuse-sym
+will search the package for that symbol to discover whether it is
+present under a different name, and proceed with the removal
+using that name. The
+.code unintern
+function performs no such secondary check; if
+.meta symbol
+is not found in the package under its own name, the operation fails,
+and so
+.code unintern
+cannot be used for undoing the effect of
+.codn use-sym-as .
+
 .coNP Functions @ use-package and @ unuse-package
 .synb
 .mets (use-package < package-list <> [ package ])