Compiler error when subclassing HTTP::Handler with a generic class

[porras]

Hi, I think I hit a weird one 😁

There is a very specific combination of things that I need to do to trigger this bug. I think this is the minimal code that reproduces the bug, at least anything that I remove from it fixes the issue:

require "http/server"

class MyGenericHandler(T) < HTTP::Handler
  def call(context)
    call_next(context)
  end
end

class MyNormalHandler < HTTP::Handler
  def call(context)
  end
end

my = MyNormalHandler.new

p my

server = HTTP::Server.new("0.0.0.0", "3000", [
  HTTP::ErrorHandler.new,
  MyGenericHandler(String).new,
  my,
])

Output on current master (cf019e2):

$ ../crystal/bin/crystal build bug.cr
Using compiled compiler at .build/crystal
Bug: MyGenericHandler(String) doesn't implement add_def
[4315258786] *CallStack::unwind:Array(Pointer(Void)) +82
[4315258689] *CallStack#initialize<CallStack>:Array(Pointer(Void)) +17
[4315258648] *CallStack::new:CallStack +40
[4315262321] *Exception#initialize<Exception, String, Nil>:CallStack +33
[4315262252] *Exception::new<String>:Exception +92
[4315101497] *raise<String>:NoReturn +9
[4316424383] *Crystal::Type+@Crystal::Type#add_def<Crystal::Type+, Crystal::Def>:NoReturn +79
[4316686014] *Crystal::VirtualType@Crystal::VirtualTypeLookup#lookup_matches<Crystal::VirtualType, Crystal::CallSignature, Crystal::VirtualType, Crystal::VirtualType>:Crystal::Matches +13166
[4316672732] *Crystal::VirtualType@Crystal::VirtualTypeLookup#lookup_matches<Crystal::VirtualType, Crystal::CallSignature>:Crystal::Matches +108
[4319476613] *Crystal::Call#lookup_matches_with_signature<Crystal::Call, Crystal::Type+, Crystal::CallSignature, Bool>:Crystal::Matches +389
[4319474882] *Crystal::Call#lookup_matches_checking_expansion<Crystal::Call, Crystal::Type+, Crystal::CallSignature, Bool>:Crystal::Matches +9570
[4319443184] *Crystal::Call#lookup_matches_in_type<Crystal::Call, Crystal::Type+, Array(Crystal::Type+), Nil, String, Bool>:Array(Crystal::Def+) +624
[4319442544] *Crystal::Call#lookup_matches_in<Crystal::Call, Crystal::Type+, Array(Crystal::Type+), Nil, String, Bool>:Array(Crystal::Def+) +16
[4319442508] *Crystal::Call#lookup_matches_in:search_in_parents<Crystal::Call, Crystal::Type+, Array(Crystal::Type+), Bool>:Array(Crystal::Def+) +508
[4319310501] *Crystal::Call#lookup_matches_in<Crystal::Call, Crystal::UnionType+, Array(Crystal::Type+), Nil, String, Bool>:Array(Crystal::Def+) +581
[4319533601] *Crystal::Call#lookup_matches_in<Crystal::Call, Crystal::UnionType+, Array(Crystal::Type+)>:Array(Crystal::Def+) +65
[4319308375] *Crystal::Call#lookup_matches_without_splat<Crystal::Call, Array(Crystal::Type+)>:Array(Crystal::Def+) +199
[4319307700] *Crystal::Call#lookup_matches<Crystal::Call>:Array(Crystal::Def+) +420
[4319203854] *Crystal::Call#recalculate<Crystal::Call>:Array(Crystal::Def+)? +1534
[4324645970] *Crystal::TypeVisitor#visit<Crystal::TypeVisitor, Crystal::Call>:Bool +2322
[4315519909] *Crystal::ASTNode+@Crystal::ASTNode#accept<Crystal::ASTNode+, Crystal::TypeVisitor>:Nil +1589
[4318904672] *Crystal::Expressions#accept_children<Crystal::Expressions, Crystal::TypeVisitor>:Array(Crystal::ASTNode+) +96
[4315527441] *Crystal::ASTNode+@Crystal::ASTNode#accept<Crystal::ASTNode+, Crystal::TypeVisitor>:Nil +9121
[4324671985] *Crystal::TypeVisitor#visit<Crystal::TypeVisitor, Crystal::Block>:(Nil | Bool) +1953
[4319628928] *Crystal::Block@Crystal::ASTNode#accept<Crystal::Block, Crystal::TypeVisitor>:Nil +48
[4324642119] *Crystal::TypeVisitor#visit<Crystal::TypeVisitor, Crystal::Yield>:Bool +4215
[4315519545] *Crystal::ASTNode+@Crystal::ASTNode#accept<Crystal::ASTNode+, Crystal::TypeVisitor>:Nil +1225
[4324630920] *Crystal::TypeVisitor#type_assign<Crystal::TypeVisitor, Crystal::Var+, Crystal::ASTNode+, Crystal::Assign>:Crystal::MetaVar? +40
[4324629997] *Crystal::TypeVisitor#visit<Crystal::TypeVisitor, Crystal::Assign>:Bool +109
[4315519282] *Crystal::ASTNode+@Crystal::ASTNode#accept<Crystal::ASTNode+, Crystal::TypeVisitor>:Nil +962
[4318904672] *Crystal::Expressions#accept_children<Crystal::Expressions, Crystal::TypeVisitor>:Array(Crystal::ASTNode+) +96
[4315527441] *Crystal::ASTNode+@Crystal::ASTNode#accept<Crystal::ASTNode+, Crystal::TypeVisitor>:Nil +9121
[4324695405] *Crystal::TypeVisitor#visit<Crystal::TypeVisitor, Crystal::If>:Bool +1021
[4315521413] *Crystal::ASTNode+@Crystal::ASTNode#accept<Crystal::ASTNode+, Crystal::TypeVisitor>:Nil +3093
[4318904672] *Crystal::Expressions#accept_children<Crystal::Expressions, Crystal::TypeVisitor>:Array(Crystal::ASTNode+) +96
[4315527441] *Crystal::ASTNode+@Crystal::ASTNode#accept<Crystal::ASTNode+, Crystal::TypeVisitor>:Nil +9121
[4319532159] *Crystal::Call#instantiate<Crystal::Call, Crystal::Matches, Crystal::Type+, Nil>:Array(Crystal::Def+) +9375
[4319462508] *Crystal::Call#lookup_matches_in_type<Crystal::Call, Crystal::Type+, Array(Crystal::Type+), Nil, String, Bool>:Array(Crystal::Def+) +19948
[4319442544] *Crystal::Call#lookup_matches_in<Crystal::Call, Crystal::Type+, Array(Crystal::Type+), Nil, String, Bool>:Array(Crystal::Def+) +16
[4319534705] *Crystal::Call#lookup_matches_in<Crystal::Call, Crystal::Type+, Array(Crystal::Type+)>:Array(Crystal::Def+) +513
[4319309197] *Crystal::Call#lookup_matches_without_splat<Crystal::Call, Array(Crystal::Type+)>:Array(Crystal::Def+) +1021
[4319307700] *Crystal::Call#lookup_matches<Crystal::Call>:Array(Crystal::Def+) +420
[4319203854] *Crystal::Call#recalculate<Crystal::Call>:Array(Crystal::Def+)? +1534
[4324645970] *Crystal::TypeVisitor#visit<Crystal::TypeVisitor, Crystal::Call>:Bool +2322
[4315519909] *Crystal::ASTNode+@Crystal::ASTNode#accept<Crystal::ASTNode+, Crystal::TypeVisitor>:Nil +1589
[4324630920] *Crystal::TypeVisitor#type_assign<Crystal::TypeVisitor, Crystal::Var+, Crystal::ASTNode+, Crystal::Assign>:Crystal::MetaVar? +40
[4324629997] *Crystal::TypeVisitor#visit<Crystal::TypeVisitor, Crystal::Assign>:Bool +109
[4315519282] *Crystal::ASTNode+@Crystal::ASTNode#accept<Crystal::ASTNode+, Crystal::TypeVisitor>:Nil +962
[4318904672] *Crystal::Expressions#accept_children<Crystal::Expressions, Crystal::TypeVisitor>:Array(Crystal::ASTNode+) +96
[4315527441] *Crystal::ASTNode+@Crystal::ASTNode#accept<Crystal::ASTNode+, Crystal::TypeVisitor>:Nil +9121
[4316098524] *Crystal::Program#expand_macro_def<Crystal::Program, Crystal::Def+>:Nil +2252
[4316096253] *Crystal::Program#expand_macro_defs<Crystal::Program>:Nil +77
[4316096096] *Crystal::Program#infer_type_intermediate<Crystal::Program, Crystal::Expressions>:Crystal::Expressions +80
[4316095867] *Crystal::Program#infer_type<Crystal::Program, Crystal::Expressions>:Crystal::Expressions +59
[4325162883] *Crystal::Compiler#infer_type<Crystal::Compiler, Crystal::Program, Crystal::Expressions>:Crystal::Expressions +211
[4325159432] *Crystal::Compiler#compile<Crystal::Compiler, Array(Crystal::Compiler::Source), String>:Crystal::Compiler::Result +456
[4326310684] *Crystal::Command::CompilerConfig#compile<Crystal::Command::CompilerConfig, String>:Crystal::Compiler::Result +92
[4326277855] *Crystal::Command#run_command<Crystal::Command>:Nil +399
[4326267394] *Crystal::Command#run<Crystal::Command>:(Nil | Bool | Array(String) | IO::FileDescriptor+ | Crystal::Compiler::Result | Array(Crystal::ImplementationTrace) | Array(Crystal::Init::View+:Class)) +1586
[4326265500] *Crystal::Command::run<Array(String)>:(Nil | Bool | Array(String) | IO::FileDescriptor+ | Crystal::Compiler::Result | Array(Crystal::ImplementationTrace) | Array(Crystal::Init::View+:Class)) +44
[4326265373] *Crystal::Command::run:(Nil | Bool | Array(String) | IO::FileDescriptor+ | Crystal::Compiler::Result | Array(Crystal::ImplementationTrace) | Array(Crystal::Init::View+:Class)) +45
[4315101006] __crystal_main +56734
[4315132063] main +47

Error: you've found a bug in the Crystal compiler. Please open an issue, including source code that will allow us to reproduce the bug: https://github.com/manastech/crystal/issues

Note that I don't need to call server.listen for the issue to appear (but doing it doesn't fix it).

When I say “anything that I remove from it fixes the issue” I specifically include:

• Removing the type parameter on the handler subclass
• Removing the generic handler from the handlers chain
• Removing the normal handler from the handlers chain
• Removing the error handler from the handlers chain (other builtin handlers such as the log handler didn't cause the issue)
• And, in case some of those are not weird enough, here comes the weirdest: removing the inspection of the handler instance. Note that I'm not inspecting the potentially problematic one with the type parameter, but the other one 😮

When I start the server with any of those fixes applied, it works perfectly fine. I'm on a Mac with Yosemite, in case that's relevant.

I wasn't sure whether subclassing a non-generic class adding a type parameter was supported but it seems to work fine everywhere else (and in fact here unless this specific combination of things are present).

[asterite]

Seems like a duplicate of #846, but I'm not sure. Now that there's a first pass that defines classes and methods this might be easier to solve.

[asterite]

Closed in favor of #2665