Resurrect edebug-set-initial-mode, repurposing it to set the global mode.

lisp/emacs-lisp/edebug.el (edebug-initial-mode-alist): Uncomment, and
amend to match current modes and functions.
(edebug-set-initial-mode): Uncomment and change from setting a defun's
`edebug-initial-mode''s property to setting the variable
`edebug-initial-mode'.
(top level): Create new binding C-x C-a C-m for
`edebug-set-initial-mode'.

doc/lispref/edebug.texi (Edebug Execution Modes): document
`edebug-set-initial-mode' and its new key binding.
(Edebug Options): Mention the new command in the pertinent place.

etc/NEWS: Write entry for this change.

doc/lispref/edebug.texi

@@ -285,10 +285,21 @@ When you enter a new Edebug level, Edebug will normally stop at the
 first instrumented function it encounters.  If you prefer to stop only
 at a break point, or not at all (for example, when gathering coverage
 data), change the value of @code{edebug-initial-mode} from its default
-@code{step} to @code{go} or @code{Go-nonstop}, or one of its other
-values (@pxref{Edebug Options}).  Note that you may reenter the same
-Edebug level several times if, for example, an instrumented function
-is called several times from one command.
+@code{step} to @code{go}, or @code{Go-nonstop}, or one of its other
+values (@pxref{Edebug Options}).  You can do this readily with
+@kbd{C-x C-a C-m} (@code{edebug-set-initial-mode}):
+
+@deffn Command edebug-set-initial-mode
+@kindex C-x C-a C-m
+This command, bound to @kbd{C-x C-a C-m}, sets
+@code{edebug-initial-mode}.  It prompts you for a key to indicate the
+mode.  You should enter one of the eight keys listed above, which sets
+the corresponding mode.
+@end deffn
+
+Note that you may reenter the same Edebug level several times if, for
+example, an instrumented function is called several times from one
+command.
 
 While executing or tracing, you can interrupt the execution by typing
 any Edebug command.  Edebug stops the program at the next stop point and
@@ -1565,7 +1576,8 @@ mode for Edebug when it is first activated.  Possible values are
 @code{step}, @code{next}, @code{go}, @code{Go-nonstop}, @code{trace},
 @code{Trace-fast}, @code{continue}, and @code{Continue-fast}.
 
-The default value is @code{step}.
+The default value is @code{step}.  This variable can be set
+interactively with @kbd{C-x C-a C-m} (@code{edebug-set-initial-mode}).
 @xref{Edebug Execution Modes}.
 @end defopt
 

etc/NEWS

@@ -460,6 +460,11 @@ typing RET.
 *** If `quick-calc' is called with a prefix argument, insert the
 result of the calculation into the current buffer.
 
++++
+** In Edebug, you can now set the initial mode with C-x C-a C-m.  With
+this you can tell Edebug not to stop at the start of the first
+instrumented function.
+
 ** ElDoc
 *** New minor mode `global-eldoc-mode'
 *** `eldoc-documentation-function' now defaults to `ignore'

lisp/emacs-lisp/edebug.el

@@ -3216,57 +3216,45 @@ This is useful for exiting even if `unwind-protect' code may be executed."
   (setq edebug-execution-mode 'Go-nonstop)
   (top-level))
 
-
 ;;(defun edebug-exit-out ()
 ;;  "Go until the current function exits."
 ;;  (interactive)
 ;;  (edebug-set-mode 'exiting "Exit..."))
 
-
-;;; The following initial mode setting definitions are not used yet.
-
-'(defconst edebug-initial-mode-alist
-  '((edebug-Continue-fast . Continue-fast)
-    (edebug-Trace-fast . Trace-fast)
-    (edebug-continue . continue)
-    (edebug-trace . trace)
-    (edebug-go . go)
-    (edebug-step-through . step)
-    (edebug-Go-nonstop . Go-nonstop)
-    )
+(defconst edebug-initial-mode-alist
+  '((edebug-step-mode . step)
+    (edebug-next-mode . next)
+    (edebug-trace-mode . trace)
+    (edebug-Trace-fast-mode . Trace-fast)
+    (edebug-go-mode . go)
+    (edebug-continue-mode . continue)
+    (edebug-Continue-fast-mode . Continue-fast)
+    (edebug-Go-nonstop-mode . Go-nonstop))
   "Association list between commands and the modes they set.")
 
+(defvar edebug-mode-map)		; will be defined fully later.
 
-'(defun edebug-set-initial-mode ()
-  "Ask for the initial mode of the enclosing function.
+(defun edebug-set-initial-mode ()
+  "Set the initial execution mode of Edebug.
 The mode is requested via the key that would be used to set the mode in
 edebug-mode."
   (interactive)
-  (let* ((this-function (edebug-which-function))
-	 (keymap (if (eq edebug-mode-map (current-local-map))
-		     edebug-mode-map))
-	 (old-mode (or (get this-function 'edebug-initial-mode)
-		       edebug-initial-mode))
+  (let* ((old-mode edebug-initial-mode)
 	 (key (read-key-sequence
 	       (format
-		"Change initial edebug mode for %s from %s (%s) to (enter key): "
-		       this-function
-		       old-mode
-		       (where-is-internal
-			(car (rassq old-mode edebug-initial-mode-alist))
-			keymap 'firstonly
-			))))
-	 (mode (cdr (assq (key-binding key) edebug-initial-mode-alist)))
-	 )
-    (if (and mode
-	     (or (get this-function 'edebug-initial-mode)
-		 (not (eq mode edebug-initial-mode))))
+		"Change initial edebug mode from %s (%c) to (enter key): "
+		old-mode
+		(aref (where-is-internal
+		       (car (rassq old-mode edebug-initial-mode-alist))
+		       edebug-mode-map 'firstonly)
+		      0))))
+	 (mode (cdr (assq (lookup-key edebug-mode-map key)
+			  edebug-initial-mode-alist))))
+    (if mode
 	(progn
-	  (put this-function 'edebug-initial-mode mode)
-	  (message "Initial mode for %s is now: %s"
-		   this-function mode))
-      (error "Key must map to one of the mode changing commands")
-      )))
+	  (setq edebug-initial-mode mode)
+	  (message "Edebug's initial mode is now: %s" mode))
+      (error "Key must map to one of the mode changing commands"))))
 
 ;;; Evaluation of expressions
 
@@ -3425,7 +3413,9 @@ be installed in `emacs-lisp-mode-map'.")
   (define-key emacs-lisp-mode-map "\C-x\C-a\C-s" 'edebug-step-mode)
   (define-key emacs-lisp-mode-map "\C-x\C-a\C-n" 'edebug-next-mode)
   (define-key emacs-lisp-mode-map "\C-x\C-a\C-c" 'edebug-go-mode)
-  (define-key emacs-lisp-mode-map "\C-x\C-a\C-l" 'edebug-where))
+  (define-key emacs-lisp-mode-map "\C-x\C-a\C-l" 'edebug-where)
+  ;; The following isn't a GUD binding.
+  (define-key emacs-lisp-mode-map "\C-x\C-a\C-m" 'edebug-set-initial-mode))
 
 (defvar edebug-mode-map
   (let ((map (copy-keymap emacs-lisp-mode-map)))