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bug#37540: Bug 37540: [PATCH] Wishlist: Allow edebug-specs to signal arb
From: |
Alan Mackenzie |
Subject: |
bug#37540: Bug 37540: [PATCH] Wishlist: Allow edebug-specs to signal arbitrary error strings on syntax errors in macros. |
Date: |
Tue, 14 Jan 2020 20:14:13 +0000 |
User-agent: |
Mutt/1.10.1 (2018-07-13) |
Hello Emacs and Eli.
On Sat, Sep 28, 2019 at 12:30:34 +0000, Alan Mackenzie wrote:
> I think it would be a good idea to allow edebug-specs to signal syntax
> errors with arbitrary strings, like:
> ("`" &error "Too deeply nested backquotes")
> . The motivation is to complete the correction in bug #31090, which
> fixed edebug's handling of nested backquotes in macros.
> The problem with that fix is it doesn't handle triply nested backquotes
> (without , or ,@ between them) at all well. There is a fundamental
> structure clash between backquote's nesting and Lisp's nesting of
> parentheses.
> The pragmatic solution is simply to ban triply nested backquotes (i.e.
> three `s without ,s or ,@s between them) from edebug instrumentation.
> However, this really needs a mechanism to output an error message
> string. There is currently no such mecahanism in edebug.
> The following patch implements an &error mechanism in edebug.el, and
> illustrates its use in the case which motivated it.
> Any objections to committing this patch (together with the needed
> amendments to documentation and NEWS)?
, to which Eli's response was to request me to wait until the emacs-27
release branch had been cut. That has now happened.
So, are there any objections to me now committing this patch (current
version below, including a documentation amendment), plus a NEWS item,
to the master branch?
diff --git a/doc/lispref/edebug.texi b/doc/lispref/edebug.texi
index 8be8307c75..cfef5c12d1 100644
--- a/doc/lispref/edebug.texi
+++ b/doc/lispref/edebug.texi
@@ -1362,6 +1362,11 @@ Specification List
is primarily used to generate more specific syntax error messages. See
@ref{Backtracking}, for more details. Also see the @code{let} example.
+@item &error
+@code{&error} should be followed by a string, an error message, in the
+edebug-spec; it aborts the instrumentation, displaying the message in
+the minibuffer.
+
@item @var{other-symbol}
@cindex indirect specifications
Any other symbol in a specification list may be a predicate or an
diff --git a/lisp/emacs-lisp/edebug.el b/lisp/emacs-lisp/edebug.el
index b8d2fb5beb..a57c48f1f9 100644
--- a/lisp/emacs-lisp/edebug.el
+++ b/lisp/emacs-lisp/edebug.el
@@ -1714,6 +1714,7 @@ edebug-match-specs
(cl-macrolet-body . edebug-match-cl-macrolet-body)
(¬ . edebug-match-¬)
(&key . edebug-match-&key)
+ (&error . edebug-match-&error)
(place . edebug-match-place)
(gate . edebug-match-gate)
;; (nil . edebug-match-nil) not this one - special case it.
@@ -1847,6 +1848,14 @@ edebug-match-&key
(car (cdr pair))))
specs))))
+(defun edebug-match-&error (cursor specs)
+ ;; Signal an error, using the following string in the spec as argument.
+ (setq edebug-gate t)
+ (let* ((error-string (car specs)))
+ (if (stringp error-string)
+ (edebug-no-match cursor error-string)
+ (error "String expected after &error in edebug-spec"))))
+
(defun edebug-match-gate (_cursor)
;; Simply set the gate to prevent backtracking at this level.
@@ -2216,6 +2225,8 @@ backquote-form
(def-edebug-spec nested-backquote-form
(&or
+ ("`" &error "Triply nested backquotes (without commas \"between\" them) \
+are too difficult to instrument")
;; Allow instrumentation of any , or ,@ contained within the (\, ...) or
;; (\,@ ...) matched on the next line.
([&or "," ",@"] backquote-form)
--
Alan Mackenzie (Nuremberg, Germany).
- bug#37540: Bug 37540: [PATCH] Wishlist: Allow edebug-specs to signal arbitrary error strings on syntax errors in macros.,
Alan Mackenzie <=