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, 29 insertions, 1 deletions

diff --git a/test-suite/tests/exceptions.test b/test-suite/tests/exceptions.test
index a839b68de..391a19dca 100644
--- a/test-suite/tests/exceptions.test
+++ b/test-suite/tests/exceptions.test
@@ -16,7 +16,8 @@
 ;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 
 
-(use-modules (test-suite lib))
+(define-module (test-suite exceptions)
+  #:use-module (test-suite lib))
 
 (define-syntax-parameter push
   (lambda (stx)
@@ -365,3 +366,30 @@
   ;;     (not (eval `(,false-if-exception (,error "xxx"))
   ;;                empty-environment))))
   )
+
+(with-test-prefix "delimited exception handlers"
+  (define (catch* key thunk)
+    (let ((tag (make-prompt-tag)))
+      (call-with-prompt tag
+        (lambda ()
+          (catch key
+            (lambda ()
+              (abort-to-prompt tag)
+              (thunk))
+            (lambda args args)))
+        (lambda (k) k))))
+  (pass-if-equal '(foo)
+      (let ((thunk (catch* 'foo (lambda () (throw 'foo)))))
+        (thunk)))
+  (pass-if-equal '(foo)
+      (let* ((thunk1 (catch* 'foo (lambda () (throw 'foo))))
+             (thunk2 (catch* 'bar (lambda () (thunk1)))))
+        (thunk1)))
+  (pass-if-equal '(foo)
+      (let* ((thunk1 (catch* 'foo (lambda () (throw 'foo))))
+             (thunk2 (catch* 'bar (lambda () (thunk1)))))
+        (thunk2)))
+  (pass-if-equal '(bar)
+      (let* ((thunk1 (catch* 'foo (lambda () (throw 'bar))))
+             (thunk2 (catch* 'bar (lambda () (thunk1)))))
+        (thunk2))))