bug#23949: 25.0.95; Regression in handling error caused by (string-match-p "." nil)

[Kaushal Modi]

Some interesting discovery .. hope this helps debug this:

Searched the whole emacs source and my ~/.emacs.d for 'is relative, it is com'. And the only place I found it was in lisp/progmodes/compile.el, line 2679:

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km²~/downloads/:git/emacs> ag 'is relative, it is com'     

lisp/progmodes/compile.el

2679:If DIRECTORY is relative, it is combined with `default-directory'.

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Somehow "(nil" replaced "If DIRECT", the whole thing got lower-cased, string after "com" in "combined" got truncated, and we got:

"(nilory is relative, it is com"

On Tue, Jul 12, 2016 at 9:33 AM Kaushal Modi <kaushal.modi@gmail.com> wrote:

Hi Eli,

This is what I get (obviously odd-looking string):

(gdb) frame 9

#9  0x0000000000624397 in Fread_from_string (string=54138084, start=0, end=0) at lread.c:2075

2075      ret = read_internal_start (string, start, end);

(gdb) p string

$15 = 54138084

(gdb) xstring

$16 = (struct Lisp_String *) 0x33a14e0

"(nilory is relative, it is com"

Looks like the 'nil' argument in '(string-match-p "." nil)' somehow did this?

(BTW this debug session is on the 2f67f8a commit of master (very recent, today). But the bug is present on emacs-25 too.)

On Tue, Jul 12, 2016 at 9:14 AM Eli Zaretskii <eliz@gnu.org> wrote:

In this frame, please show the value of 'string', like this:

 (gdb) frame 9
 (gdb) p string
 (gdb) xstring 

Kaushal Modi

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Kaushal Modi