bug in method signatures with nested where inside variable bounds
#31542
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bug
Indicates an unexpected problem or unintended behavior
compiler:lowering
Syntax lowering (compiler front end, 2nd stage)
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JeffBezanson
added
bug
vtjnash
added a commit
that referenced
this issue
Feb 9, 2025
Deferring this part of defining the ctor code allows it to do some
value-based optimizations, without the awkwardness previously of needing
to do conditional lowering of all of the possible versions that might be
useful just from syntax transforms. This feels very like a generated
function: how it expands just the function body, except it is flipped so
that then we wrap the result in a single Method instead of being created
from a Method!
Avoids lowering inaccuracies where a variable appears but is not used:
```julia
julia> struct Foo{T}
x::(T; Any)
end
WARNING: method definition for Foo at REPL[1]:2 declares type variable T but does not use it.
julia> struct Foo{T}
x::Union{Any, T}
end
WARNING: method definition for Foo at REPL[1]:2 declares type variable T but does not use it.
```
Avoids hitting #31542:
```julia
julia> struct Foo{T}
x::(Val{T} where T)
end
ERROR: syntax: invalid variable expression in "where" around REPL[1]:2
```
Avoids generating a `convert` call when the user declares explicit
`::Any` declarations, the same as if the user didn't annotate the field:
```julia
julia> struct Foo
x::Any
y::Int
end
julia> code_lowered(Foo)[2]
CodeInfo(
@ REPL[1]:2 within `unknown scope`
1 ─ %1 = builtin Core.fieldtype(#ctor-self#, 2)
│ %2 = y
│ @_4 = %2
│ %4 = builtin @_4 isa %1
└── goto #3 if not %4
2 ─ goto #4
3 ─ @_4 = Base.convert(%1, @_4)
4 ┄ %8 = @_4
│ %9 = %new(#ctor-self#, x, %8)
└── return %9
)
```
vtjnash
added a commit
that referenced
this issue
Feb 9, 2025
Deferring this part of defining the ctor code allows it to do some
value-based optimizations, without the awkwardness previously of needing
to do conditional lowering of all of the possible versions that might be
useful just from syntax transforms. This feels very like a generated
function: how it expands just the function body, except it is flipped so
that then we wrap the result in a single Method instead of being created
from a Method!
Avoids lowering inaccuracies where a variable appears but is not used.
These warnings are now prevented:
```julia
julia> struct Foo{T}
x::(T; Any)
end
WARNING: method definition for Foo at REPL[1]:2 declares type variable T but does not use it.
julia> struct Foo{T}
x::Union{Any, T}
end
WARNING: method definition for Foo at REPL[1]:2 declares type variable T but does not use it.
```
Avoids hitting #31542.
This lowering mistake is now avoided:
```julia
julia> struct Foo{T}
x::(Val{T} where T)
end
ERROR: syntax: invalid variable expression in "where" around REPL[1]:2
```
As a minor optimization, this avoids generating a `convert` call when
the user declares explicit `::Any` declarations, the same as if the user
didn't annotate the field type:
```julia
julia> struct Foo
x::Any
y::Int
z
end
julia> code_lowered(Foo)[2]
CodeInfo(
@ REPL[1]:2 within `unknown scope`
1 ─ %1 = builtin Core.fieldtype(#ctor-self#, 2)
│ %2 = y
│ @_4 = %2
│ %4 = builtin @_4 isa %1
└── goto #3 if not %4
2 ─ goto #4
3 ─ @_4 = Base.convert(%1, @_4)
4 ┄ %8 = @_4
│ %9 = %new(#ctor-self#, x, %8, z)
└── return %9
)
```
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This happens because of the odd way method signatures are lowered and the name collision with the inner and outer
A; it's not a problem forwhereexpressions generally:The text was updated successfully, but these errors were encountered: