Fix custom marshalization with symbolize_names: true

[casperisfine]

Reported to me by @peterthesling.

Repo script

require 'psych'
class Foo
  def initialize(bar)
    @bar = bar
  end
  def init_with(coder)
    @bar = coder["bar"]
  end
  def encode_with(coder)
    coder["bar"] = @bar
  end
end
p Psych.load(Psych.dump(Foo.new(42))) # => #<Foo:0x00007fea51a63d88 @bar=42>
p Psych.load(Psych.dump(Foo.new(42)), symbolize_names: true) # => #<Foo:0x00007fea51a625a0 @bar=nil>

What happens is that the Hash built to be passed to init_with get its keys symbolized, which breaks the init_with.

cc @tenderlove

[casperisfine]

jruby failures seem unrelated.

[peterthesling]

Thanks for the fast response!

[whitehat101]

force_string_keys is a misleading name. If you have a YAML doc that has Symbols, Numerics, Booleans, etc, as keys then setting force_string_keys = true passes those through without modification, it doesn't force them to be strings, it just skips the #to_sym call.

[casperisfine]

Yes, I wasn't very insprired at that time, I think I'll rename it to tagged or something.

[whitehat101]

What's the use case for combining custom init_with and encode_with with Psych.load(..., symbolize_names: true)?

If you have an untyped/untagged document, and you're using YAML as a JSON replacement, symbolize_names: true makes sense since it's mimicking the JSON.load API, and lets you get symbols without any customization.

But if you do have custom init_with and encode_with, that's because you want fine control over how your object is (un)marshaled. If your object has an init_with, are we expecting symbolize_names: true is ignored? Or are we expecting that symbolize_names: true only applies to untagged mappings?

Behavior like this?:

doc = <<~YAML
---
baz: !ruby/object:Foo
  bar: 42
YAML

p Psych.load(doc)
# {"baz"=>#<Foo:0x000056141892d218 @bar=42>}
p Psych.load(doc, symbolize_names: true)
# {:baz=>#<Foo:0x0000561418cefe00 @bar=42>}

Using symbolize_names because you can't or don't want to use symbols in the dumped document?

doc = <<~YAML
---
:baz: !ruby/object:Foo
  bar: 42
YAML
p Psych.load(doc)
# {:baz=>#<Foo:0x0000561418cefe00 @bar=42>}

[casperisfine]

Or are we expecting that symbolize_names: true only applies to untagged mappings?

Yes, and that was the behavior up to Psych 3.1.0, this PR fixes a regression.