Bug #20468: Segfault on safe navigation in for target

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 3.1: REQUIRED, 3.2: REQUIRED, 3.3: REQUIRED

[kddnewton (Kevin Newton)]

for foo&.bar in []; end

[nobu (Nobuyoshi Nakada)]

I can't imagine what it should do when foo == nil.
Should be a syntax error probably?

[nobu (Nobuyoshi Nakada)]

Hmmm, may be possible to interpret that code like as foo&.then {|recv| for recv.bar in []; end}.
Just an idea.

[nobu (Nobuyoshi Nakada)]

• Assignee set to matz (Yukihiro Matsumoto)

[nobu (Nobuyoshi Nakada)]

• Assignee deleted (matz (Yukihiro Matsumoto))

I found that a for loop variable is looser than I expected.
Not only a safe navigation call, even a constant can be used.
I don't think a constant is useful as a loop variable that is expected to be re-assigned.

https://github.com/ruby/ruby/pull/10723

[Eregon (Benoit Daloze)]

Given for foo.bar in []; end is valid and does for.bar = element,
I think for foo&.bar in []; end could simply do for&.bar = element which is the same as for.bar = element unless foo.nil? (NIL_P(foo) to be precise).

Changing the syntax for for variables sounds more risky and likely to unexpectedly disallow some new lhs forms when the lhs rule is updated, and the for_var rule is forgotten to be updated too.

[Eregon (Benoit Daloze)]

IOW I think the segfault could be fixed here without changing what is valid syntax.
And given this segfault probably affects older versions too there it seems better to fix the segfault than to change syntax.

[zverok (Victor Shepelev)]

Agree with @Eregon (Benoit Daloze). The code should be more or less equivalent to:

for temp in [1, 2, 3]
  foo&.bar = temp
end

...which is totally valid and foo&.bar = is a no-op (semantically).

[kddnewton (Kevin Newton)]

@nobu (Nobuyoshi Nakada) it's the same possibilities in for, rescue, and multi-write. As in:

for (foo, @foo, @@foo, $foo, Foo, Foo::Foo, foo.foo, foo[foo]) in bar; end

begin; rescue => foo; end
begin; rescue => @foo; end
begin; rescue => @@foo; end
begin; rescue => $foo; end
begin; rescue => Foo; end
begin; rescue => Foo::Foo; end
begin; rescue => foo.foo; end
begin; rescue => foo[foo]; end

(foo, @foo, @@foo, $foo, Foo, Foo::Foo, foo.foo, foo[foo]) = bar

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset git|2dd46bb82ffc4dff01d7ea70922f0e407acafb4e.

---

[Bug #20468] Fix safe navigation in for variable

[nobu (Nobuyoshi Nakada)]

• Has duplicate Bug #20561: Segfault with attr_writer, safe navigation and an "in" loop added

[Eregon (Benoit Daloze)]

• Backport changed from 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN to 3.1: REQUIRED, 3.2: REQUIRED, 3.3: REQUIRED