Remove frame-procedure

* libguile/frames.h:
* libguile/frames.c (scm_frame_procedure): Remove.
* test-suite/tests/eval.test ("stacks"): Adapt test.
* NEWS: Add news item.
* doc/ref/api-debug.texi (Frames): Document frame-procedure-name instead
  of frame-procedure.

NEWS

@@ -6,7 +6,28 @@ Please send Guile bug reports to bug-guile@gnu.org.
 
 
 
-Changes in 2.1.1 (changes since the 2.0.x series):
+Changes in 2.1.2 (changes since the 2.1.1 alpha release):
+
+* Incompatible changes
+
+** Remove frame-procedure
+
+Several optimizations in Guile make `frame-procedure' an interface that
+we can no longer support.  For background, `frame-procedure' used to
+return the value at slot 0 in a frame, which usually corresponds to the
+SCM value of the procedure being applied.  However it could be that this
+slot is re-used for some other value, because the closure was not needed
+in the function.  Such a re-use might even be for an untagged value, in
+which case treating slot 0 as a SCM value is quite dangerous.  It's also
+possible that so-called "well-known" closures (closures whose callers
+are all known) are optimized in such a way that slot 0 is not a
+procedure but some optimized representation of the procedure's free
+variables.  Instead, developers building debugging tools that would like
+access to `frame-procedure' are invited to look at the source for the
+`(system vm frame)' for alternate interfaces.
+
+
+Changes in 2.1.x (changes since the 2.0.x series):
 
 * Notable changes
 

doc/ref/api-debug.texi

@@ -177,10 +177,10 @@ Return the previous frame of @var{frame}, or @code{#f} if
 @var{frame} is the first frame in its stack.
 @end deffn
 
-@deffn {Scheme Procedure} frame-procedure frame
-@deffnx {C Function} scm_frame_procedure (frame)
-Return the procedure for @var{frame}, or @code{#f} if no
-procedure is associated with @var{frame}.
+@deffn {Scheme Procedure} frame-procedure-name frame
+@deffnx {C Function} scm_frame_procedure_name (frame)
+Return the name of the procedure being applied in @var{frame}, as a
+symbol, or @code{#f} if the procedure has no name.
 @end deffn
 
 @deffn {Scheme Procedure} frame-arguments frame

libguile/frames.c

@@ -144,19 +144,6 @@ scm_c_frame_closure (enum scm_vm_frame_kind kind, const struct scm_frame *frame)
   return SCM_BOOL_F;
 }
 
-SCM_DEFINE (scm_frame_procedure, "frame-procedure", 1, 0, 0,
-	    (SCM frame),
-	    "")
-#define FUNC_NAME s_scm_frame_procedure
-{
-  SCM_VALIDATE_VM_FRAME (1, frame);
-
-  /* FIXME: Retrieve procedure from address?  */
-  return scm_c_frame_closure (SCM_VM_FRAME_KIND (frame),
-                              SCM_VM_FRAME_DATA (frame));
-}
-#undef FUNC_NAME
-
 static SCM frame_procedure_name_var;
 
 static void

libguile/frames.h

@@ -156,7 +156,6 @@ SCM_INTERNAL int scm_c_frame_previous (enum scm_vm_frame_kind kind,
 #endif
 
 SCM_API SCM scm_frame_p (SCM obj);
-SCM_API SCM scm_frame_procedure (SCM frame);
 SCM_API SCM scm_frame_procedure_name (SCM frame);
 SCM_API SCM scm_frame_call_representation (SCM frame);
 SCM_API SCM scm_frame_arguments (SCM frame);

test-suite/tests/eval.test

@@ -365,8 +365,8 @@
     ;; stack.
     (let* ((stack (make-tagged-trimmed-stack tag '(#t)))
            (frames (stack->frames stack))
-           (num (count (lambda (frame) (eq? (frame-procedure frame)
-                                       substring))
+           (num (count (lambda (frame) (eq? (frame-procedure-name frame)
+                                            'substring))
                        frames)))
       (= num 1)))