Re: [TCLCORE] [Ext] Re: TIP 672 Implementation Complete - Ready for Sponsorship

[Phillip B. <phi...@um...>]

I have an update concerning one behavior and the viability of $(( ... )) as
the expr shorthand syntax - one thing that Eric and I discovered in trying
different testcases is that Tcl 8.6 and Tcl 9.0 differ in how they handle
this Tcl code:

array set {} { (index 99 }

puts $((index)


Tcl 8.6 treats an unescaped (index string as an index value and prints the
value 99.

Tcl 9.0 treats $((index) as an invalid input:

invalid character in array index

    while executing

"puts $("

    (file "t.tcl" line 4)


In order to extract the expected value from Tcl 9, the '(' character must
be escaped:


% puts $(\(index)

99


Note also that the trailing ')' character is invalid in both 8.6 and 9.0
where both produce this output:


% array set {} { index) 99 }

% puts $(index))

can't read "(index)": no such element in array

% puts $(index\))

99


While both treat (index) as an invalid index, they produce different error
messages:


8.6:

can't read "((index)": no such element in array


9.0:

invalid character in array index



I ran this through fossil bisect, and found that the change came with this
commit:


% fossil info 378e95c3827e07e7

hash:         378e95c3827e07e77edb1ff47768a8b89b79005d 2022-10-04 16:04:29
UTC

parent:       e89e02bd39217e034402a429b9241f848b00e674 2022-10-04 15:57:51
UTC

merged-from:  102677d930e6206eaa65329fa6d623eaef009b2b 2022-09-29 19:17:10
UTC

child:        2e1f06b6e01e758aaffbfa9a399eec16e7688c74 2022-10-04 18:25:18
UTC

merged-into:  e34bd0f05fa79d65542e0fe45ec3a52df09453e3 2022-10-04 16:06:01
UTC

tags:         trunk, main

comment:      TIP #465: Change Rule 8 of the Dodekalogue to Cut Some Corner
Cases (user: jan.nijtmans)


Jan,  Can you confirm whether the current behavior here is correct for 9.0
- or is it a bug?  If it is correct behavior, then it seems that the $((
expression )) syntax is currently guarded from being recognized as valid
syntax at least in this context.


If it is a bug, can you explain the intent of the change?


Fossil bisect shows this set of results going from core-8-6-branch to main
with good marking 8.6 behavior and bad marking 9.0 behavior:


% fossil bisect bad

bisect complete

  1 BAD     2025-10-23 13:29:59 fe5a2b815496eee4

  2 GOOD    2025-10-01 09:34:18 6f4ed276049067f2

  4 BAD     2023-04-12 18:19:37 0d197907c6441328

  7 BAD     2022-12-16 10:25:02 67c049ff94ddd48f

  8 BAD     2022-11-01 16:13:26 05e443d1725ae9ae

  9 BAD     2022-10-11 15:55:06 0cd124939e1894c0

 11 BAD     2022-10-08 15:43:40 58f6cbaca1610f18

 12 BAD     2022-10-06 10:15:49 ed075af7b197faa6

 13 BAD     2022-10-04 22:05:19 5a5bf81d4c384f25

 14 BAD     2022-10-04 18:25:18 2e1f06b6e01e758a

 15 BAD     2022-10-04 16:04:29 378e95c3827e07e7 CURRENT

 10 GOOD    2022-10-04 15:57:51 e89e02bd39217e03

  6 GOOD    2022-09-19 14:06:59 0b9810772d261993

  5 GOOD    2021-07-23 10:08:35 2e62fe9b610ddccd

  3 GOOD    2019-06-28 22:43:10 309d50a740952c04


Phil