[Playground] You've reached a bug in the playground

[Vici37]

I think I found a possible infinite loop in the standard library when implementing a new Int type, and while trying to minimally reproduce it, triggered a bug in the playground.

Code:

struct MyInt < Int
  def popcount; end
  def trailing_zeros_count; end
end

three = MyInt.new

Exception:

error in line 7
Error: instantiating 'Crystal::Playground::Agent#i(Int32)'


In /usr/share/crystal/src/compiler/crystal/tools/playground/agent.cr:25:5

 25 | send "value" do |json|
      ^---
Error: instantiating 'send(String)'


In /usr/share/crystal/src/compiler/crystal/tools/playground/agent.cr:62:20

 62 | message = JSON.build do |json|
                     ^----
Error: instantiating 'JSON:Module#build()'


In /usr/share/crystal/src/json/builder.cr:404:12

 404 | String.build do |str|
              ^----
Error: instantiating 'String.class#build()'


In /usr/share/crystal/src/string.cr:286:21

 286 | String::Builder.build(capacity) do |builder|
                       ^----
Error: instantiating 'String::Builder.class#build(Int32)'


In /usr/share/crystal/src/string.cr:286:21

 286 | String::Builder.build(capacity) do |builder|
                       ^----
Error: instantiating 'String::Builder.class#build(Int32)'


In /usr/share/crystal/src/json/builder.cr:404:12

 404 | String.build do |str|
              ^----
Error: instantiating 'String.class#build()'


In /usr/share/crystal/src/json/builder.cr:405:7

 405 | build(str, indent) do |json|
       ^----
Error: instantiating 'build(String::Builder, Nil)'


In /usr/share/crystal/src/json/builder.cr:415:13

 415 | builder.document do
               ^-------
Error: instantiating 'JSON::Builder#document()'


In /usr/share/crystal/src/json/builder.cr:415:13

 415 | builder.document do
               ^-------
Error: instantiating 'JSON::Builder#document()'


In /usr/share/crystal/src/json/builder.cr:405:7

 405 | build(str, indent) do |json|
       ^----
Error: instantiating 'build(String::Builder, Nil)'


In /usr/share/crystal/src/compiler/crystal/tools/playground/agent.cr:62:20

 62 | message = JSON.build do |json|
                     ^----
Error: instantiating 'JSON:Module#build()'


In /usr/share/crystal/src/compiler/crystal/tools/playground/agent.cr:63:12

 63 | json.object do
           ^-----
Error: instantiating 'JSON::Builder#object()'


In /usr/share/crystal/src/compiler/crystal/tools/playground/agent.cr:63:12

 63 | json.object do
           ^-----
Error: instantiating 'JSON::Builder#object()'


In /usr/share/crystal/src/compiler/crystal/tools/playground/agent.cr:25:5

 25 | send "value" do |json|
      ^---
Error: instantiating 'send(String)'


In /usr/share/crystal/src/compiler/crystal/tools/playground/agent.cr:27:27

 27 | json.field "value", safe_to_value(value)
                          ^------------
Error: instantiating 'safe_to_value(MyInt)'


In /usr/share/crystal/src/compiler/crystal/tools/playground/agent.cr:46:5

 46 | to_value(value) rescue "(error)"
      ^-------
Error: instantiating 'to_value(MyInt)'


In /usr/share/crystal/src/compiler/crystal/tools/playground/agent.cr:54:11

 54 | value.inspect
            ^------
Error: instantiating 'MyInt#inspect()'


In /usr/share/crystal/src/object.cr:129:12

 129 | String.build do |io|
              ^----
Error: instantiating 'String.class#build()'


In /usr/share/crystal/src/string.cr:286:21

 286 | String::Builder.build(capacity) do |builder|
                       ^----
Error: instantiating 'String::Builder.class#build(Int32)'


In /usr/share/crystal/src/string.cr:286:21

 286 | String::Builder.build(capacity) do |builder|
                       ^----
Error: instantiating 'String::Builder.class#build(Int32)'


In /usr/share/crystal/src/object.cr:129:12

 129 | String.build do |io|
              ^----
Error: instantiating 'String.class#build()'


In /usr/share/crystal/src/object.cr:130:7

 130 | inspect io
       ^------
Error: instantiating 'inspect(String::Builder)'


In /usr/share/crystal/src/object.cr:148:5

 148 | to_s io
       ^---
Error: instantiating 'to_s(String::Builder)'


In /usr/share/crystal/src/int.cr:737:7

 737 | internal_to_s(base, precision, upcase) do |ptr, count, negative|
       ^------------
Error: instantiating 'internal_to_s(Int32, Int32, Bool)'


In /usr/share/crystal/src/int.cr:762:30

 762 | ptr.value = digits[num.remainder(base).abs]
                              ^--------
Error: instantiating 'MyInt#remainder(Int32)'


In /usr/share/crystal/src/int.cr:185:5

 185 | {% begin %}
       ^
Error: expanding macro


There was a problem expanding macro 'macro_139643677739200'

Called macro defined in /usr/share/crystal/src/int.cr:185:5

 185 | {% begin %}

Which expanded to:

    1 | 
    2 |       if other == 0
    3 |         raise DivisionByZeroError.new
 >  4 |       elsif self < 0 && self == MyInt::MIN && other == -1
    5 |         self.class.new(0)
    6 |       else
    7 |         unsafe_mod other
    8 |       end
    9 |     
Error: undefined constant MyInt::MIN

The underlying error looks to be a compiler error due to macro expansion (trying to use the non-existent MIN constant on MyInt). This seems minor as the "bug in the playground" looks more like a bug in my code that the playground couldn't correctly parse.

[Blacksmoke16]

Pretty sure it's not really a good idea to extend stdlib types. But either way, somewhat interesting it doesn't error when not using the playground.

EDIT: This isn't really specific to the playground, so what is the actual bug here?

[Vici37]

Generally agreed :D I'm playing around implementing my own arbitrary arithmetic library written in native crystal (starting with essentially the same interface / specs as BigInt).

I think the above does error when not using the playground, I'm creating this issue as the popup appears in the playground requesting that an issue gets made for it:

[Vici37]

Regardless if it's not a bug in the playground (the bug is in my code for sure), there's another bug where the playground think this is it's bug.

[HertzDevil]

BigInt < Int, so this use case is anticipated, unlike e.g. inheriting from Array. (The compiler does not declare BigInt as a built-in type using Crystal::Program.)

[HertzDevil]

In general I don't think implementations for Int::Primitive should reside in Int itself. However Int::Primitive is a union so we have to either invent a new module or inline the defs in the individual integer types themselves.