Avoid stacks in dynamically-bound values

* libguile/dynstack.h:
* libguile/dynstack.c (scm_dynstack_find_old_fluid_value): New
  function.
* libguile/fluids.c (saved_dynamic_state_ref): New helper.
  (scm_fluid_ref): Fix docstring.
  (scm_fluid_ref_star): New function allowing access to previous values
  for a fluid.
  (scm_dynamic_state_ref): New internal function.
* libguile/fluids.h: Add scm_fluid_ref_star and scm_dynamic_state_ref.
* libguile/stacks.c (scm_stack_id): Adapt to %stacks not being a chain.
* libguile/throw.c (catch, throw_without_pre_unwind): Adapt to
  %exception-handlers not being a chain.
* module/ice-9/boot-9.scm (catch, dispatch-exception): Instead of having
  %exception-handlers be a chain, use fluid-ref* to access the chain
  that is in place at the time the exception is thrown.  Prevents
  unintended undelimited capture of the current exception handler stack
  by a delimited "catch".
  (%start-stack): Similarly, don't be a chain.
* module/system/repl/debug.scm (frame->stack-vector):
* module/system/repl/error-handling.scm (call-with-error-handling):
* module/ice-9/save-stack.scm (save-stack): Adapt to %stacks not being a
  chain.
* test-suite/tests/exceptions.test ("delimited exception handlers"): Add
  tests.
* doc/ref/api-control.texi (Fluids and Dynamic States): Add docs.

1 files changed, 3 insertions, 0 deletions

diff --git a/libguile/dynstack.h b/libguile/dynstack.h
index 9d91fb667..7e191fc27 100644
--- a/libguile/dynstack.h
+++ b/libguile/dynstack.h
@@ -201,6 +201,9 @@ SCM_INTERNAL scm_t_bits* scm_dynstack_find_prompt (scm_t_dynstack *, SCM,
                                                    scm_t_uint32 **,
                                                    scm_i_jmp_buf **);
 
+SCM_INTERNAL SCM scm_dynstack_find_old_fluid_value (scm_t_dynstack *,
+                                                    SCM, size_t, SCM);
+
 SCM_INTERNAL void scm_dynstack_wind_prompt (scm_t_dynstack *, scm_t_bits *,
                                             scm_t_ptrdiff, scm_i_jmp_buf *);