Bug #17719: Irregular evaluation order in hash literals

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN

[nobu (Nobuyoshi Nakada)]

@mame (Yusuke Endoh) pointed out an irregular evaluation order example.

$ ruby -e '{foo:p(1), bar:p(2), foo:p(3)}'
-e:1: warning: key :foo is duplicated and overwritten on line 1
1
3
2

It feels like a bug.
https://github.com/nobu/ruby/tree/duplicated-keys-order

Or, probably it would be better to turn into an error?

[xtkoba (Tee KOBAYASHI)]

To me the evaluation order of 1->3->2 is a bit unexpected, but it might be OK unless specified otherwise.

IMO, duplicate keys in hash literals should be allowed in a scripting language like Ruby. For example, they are explicitly allowed in another scripting language named Python [1]. On the other hand, compiled languages should disallow them.

[1] https://mail.python.org/pipermail/python-ideas/2019-March/055726.html

[nobu (Nobuyoshi Nakada)]

I think it can be fixed by removing the optimization in the parser and leaving it to the compiler.

[jeremyevans0 (Jeremy Evans)]

nobu (Nobuyoshi Nakada) wrote in #note-2:

I think it can be fixed by removing the optimization in the parser and leaving it to the compiler.

I tried the approach of removing the optimization from the parser completely (https://github.com/jeremyevans/ruby/commit/bead10831e4f7ea6fc517fe66796f12579915fb3), but it doesn't handle duplicate keys in keyword arguments, resulting in incorrect unknown keyword errors: https://github.com/jeremyevans/ruby/runs/3900240357#step:15:168

I also tried rebasing your duplicated-keys-order branch against master, and that appears to fix the issue. I submitted a pull request for that: https://github.com/ruby/ruby/pull/4969

• Status changed from Open to Closed

Applied in changeset git|fac2c0f73cafb5d65bfbba7aa8018fa427972d71.

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Fix evaluation order of hash values for duplicate keys

Fixes [Bug #17719]

Co-authored-by: Nobuyoshi Nakada [e-mail]
Co-authored-by: Ivo Anjo [e-mail]