Parsing breakage for anonymous function body starting with parenthesis

[yuyichao]

On current master, if an anonymous function's body starts with parenthesis, then parsing treats the parenthesis body as a function argument and treats the actual argument list as (invalid) function name.

julia> function(a)
           (a)
       end
ERROR: ParseError:
# Error @ REPL[1]:1:9
function(a)
#       └─┘ ── Invalid signature in function definition
Stacktrace:
 [1] top-level scope
   @ REPL:1

This used to work just fine on older versions.

Note that this parsing was and is still new-line sensitive,

Old:

julia> function (a)(a)
       end
a (generic function with 1 method)

julia> function (a::Int)(a)
       end
ERROR: syntax: function argument name not unique: "a" around REPL[1]:1
Stacktrace:
 [1] top-level scope
   @ REPL[1]:1

julia> function (a)
           (a)
       end
#5 (generic function with 1 method)

julia> function (a::Int)
           (a)
       end
#8 (generic function with 1 method)

New:

julia> function (a)(a)
       end
a (generic function with 1 method)

julia> function (a::Int)(a)
       end
ERROR: syntax: function argument name not unique: "a" around REPL[4]:1
Stacktrace:
 [1] top-level scope
   @ REPL[4]:1

julia> function (a)
           (a)
       end
ERROR: ParseError:
# Error @ REPL[5]:1:10
function (a)
#        └─┘ ── Invalid signature in function definition
Stacktrace:
 [1] top-level scope
   @ REPL:1

julia> function (a::Int)
           (a)
       end
ERROR: ParseError:
# Error @ REPL[6]:1:10
function (a::Int)
#        └──────┘ ── Invalid signature in function definition
Stacktrace:
 [1] top-level scope
   @ REPL:1

This works on f5f4c01 but stops working on b9f40be so I assume it's caused by #59870 .

Not sure if the change was intentional but it does break a few packages.

https://github.com/bramtayl/Unzip.jl/blob/c239114b4b7faf71dab924c1832a11eaa0312d22/src/Unzip.jl#L144
https://github.com/FluxML/Zygote.jl/blob/35acbf3ef2b3ab7fbc5ba41cac04eab26ffe1759/src/lib/array.jl#L609
https://github.com/QuantumBFS/Yao.jl/blob/1f35b0320c2c6b4dd4d7e1343f94704486877e54/lib/YaoBlocks/src/autodiff/chainrules_patch.jl#L81
https://github.com/JuliaImages/ImageSegmentation.jl/blob/c6ba02673db9f29095d2d9915f21566d2d9f9830/src/core.jl#L352

[yuyichao]

Actually it's not mistaking the first line as the function name since providing a function name there doesn't work either

julia> function a
           (a)
       end
ERROR: ParseError:
# Error @ REPL[8]:1:10
function a
#        ╙ ── Invalid signature in function definition
Stacktrace:
 [1] top-level scope
   @ REPL:1

And in this case it is exactly the same error on the old version. So it is correctly identifying the (a) as the signature part of the function but just refuse to accept an anonymous one....

[yuyichao]

Oh, yeah, forgot to show that if the body of the function starts with anything else it works just fine.

julia> function (a)
           return (a)
       end
#2 (generic function with 1 method)

[KristofferC]

Same as #60202?

[yuyichao]

Yes! I was searching with the parser tag and didn't find it..