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bug#24542: 25.1.50; The symbol `@' and sexp scanning
From: |
npostavs |
Subject: |
bug#24542: 25.1.50; The symbol `@' and sexp scanning |
Date: |
Mon, 02 Jan 2017 15:37:28 -0500 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) |
Michael Heerdegen <michael_heerdegen@web.de> writes:
> Michael Heerdegen <michael_heerdegen@web.de> writes:
>
>> insert
>>
>> (eq element '@)
>>
>> in an elisp mode buffer (e.g. scratch). Put point at the quote or the
>> "@". Eval
>>
>> (goto-char (scan-sexps (point) 1))
>>
>> and you get an error like:
>>
>>
>> Debugger entered--Lisp error: (scan-error "Containing expression ends
>> prematurely" 15 16)
>
> It seems that you can replace the symbol `@' in this recipe with any
> symbol whose name has the form "@+", i.e. `@@' or `@@@' or... When the
> symbol contains only one character different from "@", it doesn't seem
> to happen.
`@' has the prefix syntax flag, the elisp manual says `(elisp) Syntax Flags':
* `p' identifies an additional prefix character for Lisp syntax.
These characters are treated as whitespace when they appear between
^^^^^^^^^^^^^^^^^^^^^
expressions. When they appear within an expression, they are
handled according to their usual syntax classes.
So (eq element '@) acts the same as (eq element ' ). This could be
changed with something the following patch, but I'm not sure if it's the
right thing for non-Lisp languages...
diff --git i/src/syntax.c w/src/syntax.c
index 0ee1c74..253d3fb 100644
--- i/src/syntax.c
+++ w/src/syntax.c
@@ -2681,7 +2681,16 @@ scan_lists (EMACS_INT from, EMACS_INT count, EMACS_INT
depth, bool sexpflag)
}
if (prefix)
- continue;
+ {
+ int next_c = FETCH_CHAR_AS_MULTIBYTE (from_byte);
+ int next_syntax = SYNTAX_WITH_FLAGS (next_c);
+ bool next_prefix = SYNTAX_FLAGS_PREFIX (next_syntax);
+ enum syntaxcode next_code = syntax_multibyte (next_c,
multibyte_symbol_p);
+ if (next_prefix
+ || next_code == Ssymbol
+ || next_code == Sword)
+ continue;
+ }
switch (code)
{