Move backtrace to ELisp using a new mapbacktrace primitive

* src/eval.c (get_backtrace_starting_at, backtrace_frame_apply)
(Fmapbacktrace, Fbacktrace_frame_internal): New functions.
(get_backtrace_frame, Fbacktrace_debug): Use `get_backtrace_starting_at'.

* lisp/subr.el (backtrace--print-frame): New function.
(backtrace): Reimplement using `backtrace--print-frame' and `mapbacktrace'.
(backtrace-frame): Reimplement using `backtrace-frame--internal'.

* lisp/emacs-lisp/debug.el (debugger-setup-buffer): Pass a base to
`mapbacktrace' instead of searching for "(debug" in the output of
`backtrace'.

* test/lisp/subr-tests.el (subr-test-backtrace-simple-tests)
(subr-test-backtrace-integration-test): New tests.

* doc/lispref/debugging.texi (Internals of Debugger): Document
`mapbacktrace' and missing argument BASE of `backtrace-frame'.

1 files changed, 22 insertions, 1 deletions

diff --git a/doc/lispref/debugging.texi b/doc/lispref/debugging.texi
index c80b0f95b37..8fb663d2aee 100644
--- a/doc/lispref/debugging.texi
+++ b/doc/lispref/debugging.texi
@@ -727,7 +727,7 @@ invocation.
 This variable is obsolete and will be removed in future versions.
 @end defvar
 
-@defun backtrace-frame frame-number
+@defun backtrace-frame frame-number &optional base
 The function @code{backtrace-frame} is intended for use in Lisp
 debuggers.  It returns information about what computation is happening
 in the stack frame @var{frame-number} levels down.
@@ -744,10 +744,31 @@ In the return value, @var{function} is whatever was supplied as the
 case of a macro call.  If the function has a @code{&rest} argument, that
 is represented as the tail of the list @var{arg-values}.
 
+If @var{base} is specified, @var{frame-number} counts relative to
+the topmost frame whose @var{function} is @var{base}.
+
 If @var{frame-number} is out of range, @code{backtrace-frame} returns
 @code{nil}.
 @end defun
 
+@defun mapbacktrace function &optional base
+The function @code{mapbacktrace} calls @var{function} once for each
+frame in the backtrace, starting at the first frame whose function is
+@var{base} (or from the top if @var{base} is omitted or @code{nil}).
+
+@var{function} is called with four arguments: @var{evald}, @var{func},
+@var{args}, and @var{flags}.
+
+If a frame has not evaluated its arguments yet or is a special form,
+@var{evald} is @code{nil} and @var{args} is a list of forms.
+
+If a frame has evaluated its arguments and called its function
+already, @var{evald} is @code{t} and @var{args} is a list of values.
+@var{flags} is a plist of properties of the current frame: currently,
+the only supported property is @code{:debug-on-exit}, which is
+@code{t} if the stack frame's @code{debug-on-exit} flag is set.
+@end defun
+
 @include edebug.texi
 
 @node Syntax Errors