Bug #20790: Syntax acceptance of `*x = p rescue p 1` is different between parse.y and prism

• Status: Open
• Assignee: -
• Target version: -
• ruby -v: ruby 3.4.0dev (2024-10-09T03:27:05Z master ed11a244dd) +PRISM [x86_64-linux]
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN

[tompng (tomoya ishida)]

*x = p rescue p 1 # syntax error in prism
*x = p 1 rescue p 1 # both syntax ok
x = p rescue p 1 # both syntax error
x = p 1 rescue p 1 # both syntax ok

Which is correct? If *x = p rescue p 1 is syntax valid, should x = p rescue p 1 also be syntax valid?

[mame (Yusuke Endoh)]

• Related to Bug #8279: Single-line rescue parsing added

[mame (Yusuke Endoh)]

Discussed at the dev meeting. Here is matz's preference.

                    # current parse.y behavior   # matz's preference
*x = p rescue p 1   # (*x = p) rescue (p 1)      # *x = (p rescue (p 1))
*x = p 1 rescue p 1 # (*x = p 1) rescue (p 1)    # *x = ((p 1) rescue (p 1))
a, b = p rescue p   # a, b = (p rescue p)        # as is
x = p rescue p      # x = (p rescue p)           # as is
x = p rescue p 1    # x = (p rescue p) 1 (ERROR) # x = (p rescue p 1)
x = p 1 rescue p 1  # x = ((p 1) rescue (p 1))   # as is

@yui-knk (Kaneko Yuichiro) @kddnewton (Kevin Newton) What do you think?

[kddnewton (Kevin Newton)]

That makes sense to me, we can make that work.

[ydah (Yudai Takada)]

I checked if it is feasible with parse.y: https://github.com/ydah/ruby/commit/50100c136ac4bbe379b2c360994b739227610e17

I have been able to confirm that the following are feasible with the modifications shown above.

                    # current parse.y behavior   # matz's preference
*x = p rescue p 1   # (*x = p) rescue (p 1)      # *x = (p rescue (p 1))
*x = p 1 rescue p 1 # (*x = p 1) rescue (p 1)    # *x = ((p 1) rescue (p 1))
a, b = p rescue p   # a, b = (p rescue p)        # as is
x = p rescue p      # x = (p rescue p)           # as is
x = p 1 rescue p 1  # x = ((p 1) rescue (p 1))   # as is

The following are still under investigation for feasibility.

                    # current parse.y behavior   # matz's preference
x = p rescue p 1    # x = (p rescue p) 1 (ERROR) # x = (p rescue p 1)