printer: bug: fallback syms printed without prefix.

This is a basic read/print consistency problem.  When a symbol
is printed that is anywhere in the fallback list of the
current package, we are dumping it unqualified, even if
it is hidden by a same-named symbol in the current package
itself or such a symbol occurring earlier in the fallback
list.

* lib.c (symbol_needs_prefix): When the to-be-printed symbol
is found in the fallback list, re-scan the current package
for a symbol having the same name, as well as the preceding
nodes in the fallback list. If such a symbol is found, then
the to-be printed symbol must be package-qualified.

* tests/012/syms.expected: New file.

* tests/012/syms.tl: Likewise.

* tests/012/compile.tl: Pull syms into compile job.

* txr.1: Clarify text about this. The existing text's
only reasonable interpretation supports the behavior which
this patch ensures (which is needed on grounds of read/print
consistency) but the text lacks precision.

1 files changed, 10 insertions, 3 deletions

diff --git a/lib.c b/lib.c
index cf2d6cf8..6b13be82 100644
--- a/lib.c
+++ b/lib.c
@@ -7015,6 +7015,7 @@ val symbol_needs_prefix(val self, val package, val sym)
 
   {
     val fallback = get_hash_userdata(package->pk.symhash);
+    val rescanfb = fallback;
 
     for (; fallback; fallback = cdr(fallback)) {
       val fb_pkg = car(fallback);
@@ -7024,11 +7025,17 @@ val symbol_needs_prefix(val self, val package, val sym)
           val cell = gethash_e(self, fb_pkg->pk.symhash, name);
           if (cell) {
             int found_in_fallback = (eq(cdr(cell), sym) != nil);
-            if (found_in_fallback)
-              return nil;
-            break;
+            if (!found_in_fallback)
+              break;
           }
         }
+        if (gethash_e(self, package->pk.symhash, name))
+          return sym_pkg->pk.name;
+        for (; rescanfb != fallback && rescanfb; rescanfb = cdr(rescanfb)) {
+          val fb_pkg = car(rescanfb);
+          if (gethash_e(self, fb_pkg->pk.symhash, name))
+            return sym_pkg->pk.name;
+        }
         return nil;
       } else {
         if (gethash_e(self, fb_pkg->pk.symhash, name))