GNU bug report logs - #38892
28.0.50: Hash table printing oddities

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Pip Cet <pipcet <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 28.0.50: Hash table printing oddities
Date: Fri, 3 Jan 2020 12:13:28 +0000

[Message part 1 (text/plain, inline)]

The hash table printing code has some oddities: it will print extra
spaces sometimes, won't print as many elements as requested under all
circumstances, and behave oddly for empty hash tables when
print-length is 0.

Currently, this code will result in extra spaces in the hash table output:

(let ((h (make-hash-table)))
  (puthash 1 2 h)
  (puthash 2 3 h)
  (remhash 1 h)
  (format "%S" h))

(let ((h (make-hash-table)))
  (let ((print-length 0))
    (format "%S" h)))

In the latter case, the output actually includes "data ( ...)", though
"data ()" would be shorter and more accurate.

Also, the current code contains an oddity that would make it print
fewer than print-length hash cells in the data list:

(let ((h (make-hash-table)))
  (dotimes (i 100)
    (puthash i i h))
  (dotimes (i 99)
    (remhash i h))
  (let ((print-length 1))
    (format "%S" h)))

will produce "data ( ...)", when it should produce "data (99 99)".

Proposed patch attached.

[0001-Fix-hash-table-printing.patch (text/x-patch, attachment)]

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