trace: implement redefinition checks.

The tracing module should warn when traced functions or
methods are being redefined, and stop tracing the original
methods.

* eval.c (trace_check): New function. Calls
sys:trace-redefined-check if the trace module has been
loaded, otherwise does nothing.
(op_defun, op_defmacro): Call trace_check to have a warning
issued for a redefined traced function or macro.

* eval.h (trace_check): Declared.

* lisplib.c (trace_loaded): New global variable.
(trace_instantiate): Flip trace_loaded to t.

* lisplib.h (trace_loaded): Declared.

* share/txr/stdlib/trace.tl (sys:trace-redefine-check): New
function. Checks two situations: traced function or method
is redefined (neither old nor new is traced any longer),
and traced method is overridden (base method continues to be
traced, override is not traced).

* struct.c (static_slot_ensure): Do a trace check here,
taking care of defmeth.

1 files changed, 15 insertions, 0 deletions

diff --git a/share/txr/stdlib/trace.tl b/share/txr/stdlib/trace.tl
index a184dbc8..940425c2 100644
--- a/share/txr/stdlib/trace.tl
+++ b/share/txr/stdlib/trace.tl
@@ -67,6 +67,21 @@
       (dohash (n v sys:*trace-hash*)
         (disable n n)))))
 
+(defun sys:trace-redefine-check (orig-name)
+  (let ((name (sys:trace-canonicalize-name orig-name)))
+    (when [sys:*trace-hash* name]
+      (catch
+        (cond
+          ((neq name orig-name)
+             (throwf 'warning "~!~s won't be traced, though it overrides\n\
+                               ~s which is currently traced"
+                      name orig-name))
+          (t (throwf 'warning "previously traced ~s is redefined and no\ \
+                               longer traced"
+                      name)
+             (sys:untrace (list name))))
+        (continue ())))))
+
 (defmacro trace (. names)
   ^(sys:trace ',names))