Bug #20478: Circular parameter syntax error rules

• Status: Open
• Assignee: -
• Target version: -
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN

[kddnewton (Kevin Newton)]

I would like to revisit https://bugs.ruby-lang.org/issues/16343.

These cases are syntax errors:

def foo(bar = -> { bar }) end       # no lambda parameters
def foo(bar = ->() { bar }) end     # no lambda parameters
def foo(bar = baz { bar }) end      # no block parameters
def foo(bar = baz { _1 + bar }) end # parameters, but no pipes
def foo(bar = baz { it + bar }) end # parameters, but no pipes

These cases are not syntax errors:

def foo(bar = ->(baz) { bar }) end   # lambda parameters
def foo(bar = baz { || bar }) end    # no block parameters but empty pipes
def foo(bar = baz { |qux| bar }) end # block parameters

I don't think these rules are very intuitive, and they feel somewhat arbitrary. I would like to suggest we change them to be either:

• Syntax error is raised if the parameter is ever read in its default value at any scope depth
• Syntax error is raised if the parameter is ever read in its default value at depth 0

Either one is fine by me, but gating the syntax error based on the presence of pipes is really confusing.

[nobu (Nobuyoshi Nakada)]

Given that these Procs are only created if the argument bar is not assigned, should they all be syntax errors?

[kddnewton (Kevin Newton)]

Yes, I very much think they should all be syntax errors.

[nobu (Nobuyoshi Nakada)]

Even this should be a syntax error?

def foo(bar = ->(baz = bar) {}) end

That means it needs to manage the list of yet-unusable variables, not only tracking single variable.

[kddnewton (Kevin Newton)]

I figured that was already happening for the "unused" warning.

[byroot (Jean Boussier)]

• Related to Bug #16343: Inconsistent behavior of 'circular argument reference' error added