Feature #18242: Parser makes multiple assignment sad in confusing way

• Status: Open
• Assignee: -
• Target version: -

[danh337 (Dan H)]

Example:

a, b = 2, 1     if 1 < 2     # Works
a, b = [2, 1]   if 1 < 2     # Works
(a, b) = 2, 1   if 1 < 2     # Works
(a, b) = [2, 1] if 1 < 2     # Works
(a, b = [2, 1]) if 1 < 2     # Works
a, b = 2, 1     unless 2 < 1 # Works
a, b = [2, 1]   unless 2 < 1 # Works
(a, b) = 2, 1   unless 2 < 1 # Works
(a, b) = [2, 1] unless 2 < 1 # Works
(a, b = [2, 1]) unless 2 < 1 # Works
1 < 2   and a, b = 2, 1      # SyntaxError
1 < 2   and a, b = [2, 1]    # SyntaxError
1 < 2   and (a, b) = 2, 1    # SyntaxError
1 < 2   and (a, b) = [2, 1]  # SyntaxError
(1 < 2) and a, b = 2, 1      # SyntaxError
(1 < 2) and a, b = [2, 1]    # SyntaxError
(1 < 2) and (a, b) = 2, 1    # SyntaxError
(1 < 2) and (a, b) = [2, 1]  # SyntaxError
1 < 2   and (a, b = 2, 1)    # Works
1 < 2   and (a, b = [2, 1])  # Works
2 < 1   or a, b = 2, 1       # SyntaxError
2 < 1   or a, b = [2, 1]     # SyntaxError
2 < 1   or (a, b) = 2, 1     # SyntaxError
2 < 1   or (a, b) = [2, 1]   # SyntaxError
(2 < 1) or a, b = 2, 1       # SyntaxError
(2 < 1) or a, b = [2, 1]     # SyntaxError
(2 < 1) or (a, b) = 2, 1     # SyntaxError
(2 < 1) or (a, b) = [2, 1]   # SyntaxError
2 < 1   or (a, b = 2, 1)     # Works
2 < 1   or (a, b = [2, 1])   # Works

Based on the precedence rules I've been able to find, all of these should work.

Believe it or not, there are cases where using and or or in a stanza of lines is much more readable.

Should the parser allow all of these? See attached driver script to reproduce this output.

[jeremyevans0 (Jeremy Evans)]

• File and-or-masgn-18242.diff and-or-masgn-18242.diff added
• Tracker changed from Bug to Feature
• ruby -v deleted (ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-linux])
• Backport deleted (2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN)

The parser is currently not setup to handle this, so I don't think it is a bug. You would have to add new parser rules to allow it, so I would consider this a feature request and not a bug. Attached is a patch that implements the necessary parser rules, without causing any conflicts. However, the patch doesn't include the parts needed to make ripper work, as I couldn't figure that out. @nobu (Nobuyoshi Nakada), any chance you could add the necessary code to make ripper work?

[danh337 (Dan H)]

jeremyevans0 (Jeremy Evans) wrote in #note-1:

[...] Attached is a patch that implements the necessary parser rules, without causing any conflicts. However, the patch doesn't include the parts needed to make ripper work, as I couldn't figure that out. @nobu (Nobuyoshi Nakada), any chance you could add the necessary code to make ripper work?

@jeremyevans0 (Jeremy Evans) you rock. Thanks sir.

[nobu (Nobuyoshi Nakada)]

That patch seems not including 1 < 2 and a = 1, 2.

https://github.com/ruby/ruby/pull/4945

[danh337 (Dan H)]

nobu (Nobuyoshi Nakada) wrote in #note-3:

That patch seems not including 1 < 2 and a = 1, 2.

https://github.com/ruby/ruby/pull/4945

Thank you @nobu (Nobuyoshi Nakada) !

[danh337 (Dan H)]

@nobu (Nobuyoshi Nakada) I built your PR branch and confirmed that this new parsing works great with the driver.rb attached.

Will this patch have to wait for the 3.1.0 release? Sorry I'm not sure how the whole patching and backporting processes work. (But I'm pretty sure it can get complicated.) If these were syntax errors in the past, should the patch be safe for stable versions too?

[danh337 (Dan H)]

• File driver.rb driver.rb added

Attached is an improved driver. Again, every test case works with nobu's branch.

[nobu (Nobuyoshi Nakada)]

I agree with @jeremyevans0 (Jeremy Evans) on that this is not a bug.
Feature requests need the approval by Matz to merge.

[danh337 (Dan H)]

These and & or operators are good things. They are much more readable for one-liners in some cases.

@matz (Yukihiro Matsumoto) @nobu (Nobuyoshi Nakada) I know you are super busy, but is there any way to move this forward?