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bug#37540: [PATCH] Wishlist: Allow edebug-specs to signal arbitrary erro
From: |
Alan Mackenzie |
Subject: |
bug#37540: [PATCH] Wishlist: Allow edebug-specs to signal arbitrary error strings on syntax errors in macros. |
Date: |
Sat, 28 Sep 2019 12:30:34 +0000 |
User-agent: |
Mutt/1.10.1 (2018-07-13) |
Hello, Emacs.
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)?
diff --git a/lisp/emacs-lisp/edebug.el b/lisp/emacs-lisp/edebug.el
index 717026995a..73257f1568 100644
--- a/lisp/emacs-lisp/edebug.el
+++ b/lisp/emacs-lisp/edebug.el
@@ -1683,6 +1683,7 @@ 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.
@@ -1816,6 +1817,14 @@ 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.
@@ -2185,6 +2194,8 @@ 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: [PATCH] Wishlist: Allow edebug-specs to signal arbitrary error strings on syntax errors in macros.,
Alan Mackenzie <=