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Generate non-frozen strings on TruffleRuby for consistency #963

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Merged
byroot merged 1 commit into from
Mar 26, 2026
+23 −5
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Generate non-frozen strings on TruffleRuby for consistency #963

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10 changes: 5 additions & 5 deletions lib/json/truffle_ruby/generator.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -517,7 +517,7 @@ def json_transform(state)

if empty?
state.depth -= 1
return '{}'
return +'{}'
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@eregon eregon Mar 26, 2026

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It would be faster to do the +/.dup in .dump vs in every "empty case" as most of these do not need to be mutable.
Probably just .dup here would be enough:
https://github.com/rwstauner/json/blob/cd2f0195a2824bcb88e2173f1f4ecf7ec68528cc/lib/json/truffle_ruby/generator.rb#L352
I'll try it.

Though that wouldn't work if people expect obj.to_json to return a mutable String, but not sure there is such an expectation. Notably true.to_s is already frozen?, even on CRuby.

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@byroot byroot Mar 26, 2026

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Though that wouldn't work if people expect obj.to_json to return a mutable String, but not sure there is such an expectation.

It's best to stay consistent with the C version that is largely used, and it does always return a mutable string.

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@eregon eregon Mar 26, 2026

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#964

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@eregon eregon Mar 26, 2026

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Mmh, OTOH it's natural to have frozen strings when implementing in Ruby and rather unusual to have frozen strings in C, so I wonder if the semantics here are more influenced by that than intentional. We have some differences in core classes in TruffleRuby like frozen exception messages and we made the choice to mostly keep them frozen.

I think it's worth doing #964, but if you disagree let me know and I'll just drop the first commit.
The second commit is safe regardless.

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@byroot byroot Mar 26, 2026

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so I wonder if the semantics here are more influenced by that than intentional.

Of course, but my point is that regardless of the intent, it has been this way for a long time and may cause a compatibility issue.

Which is worse because it means to_json would sometimes return frozen string sometimes mutable ones, meaning it's very easy to miss that case when testing. So I'm not in favor of method returning either, it has to be consistent.

It's not that rare to have code such as object.to_json << "\n".

end

delim = ",#{state.object_nl}"
Expand Down Expand Up @@ -609,7 +609,7 @@ def json_transform(state)

if empty?
state.depth -= 1
return '[]'
return +'[]'
end

result = '['.dup
Expand Down Expand Up @@ -734,17 +734,17 @@ def to_json(state = nil, *args)

module TrueClass
# Returns a JSON string for true: 'true'.
def to_json(*) 'true' end
def to_json(*) +'true' end
end

module FalseClass
# Returns a JSON string for false: 'false'.
def to_json(*) 'false' end
def to_json(*) +'false' end
end

module NilClass
# Returns a JSON string for nil: 'null'.
def to_json(*) 'null' end
def to_json(*) +'null' end
end
end
end
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18 changes: 18 additions & 0 deletions test/json/json_generator_test.rb
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Expand Up @@ -84,6 +84,24 @@ def test_dump_strict
assert_equal '"World"', "World".to_json(strict: true)
end

def test_not_frozen
[
[[], '[]'],
[{}, '{}'],
["string", '"string"'],
[:sym, '"sym"'],
[1, '1'],
[1.0, '1.0'],
[true, 'true'],
[false, 'false'],
[nil, 'null'],
].each do |(obj, exp)|
dumped = dump(obj, strict: true)
assert_equal exp, dumped
refute_predicate dumped, :frozen?
end
end

def test_state_depth_to_json
depth = Object.new
def depth.to_json(state)
Expand Down