Possible method call error showing up on some simple code

[dmalyuta]

I am using:

• OS: Ubuntu 20.04.1 LTS
• Julia: 1.5.3
• StaticLint: [b3cc710f] StaticLint v7.0.0
• SymbolServer: [cf896787] SymbolServer v6.0.1

The following code seems problematic:

abstract type MyType end

mutable struct Bar<:MyType
    val::Integer
end

function multiply!(x::T, y::Integer)::Nothing where {T<:MyType}
    x.val *= y
    return nothing
end

z = Bar(2)
multiply!(z, 3)

println(z.val)

Here is what StaticLint shows:

It seems that StaticLint has a history of issues with this kind of error: here, here, and here

[pfitzseb]

I think there are two issues here:

1. function multiply!(x::T, y::Integer)::Nothing where {T<:MyType} (needs both the where clause and return type annotation) being treated as a call.
2. We can't infer the type of z.

So

function multiply!(x::T, y::Integer) where T <: MyType # no return type annotation
    x.val *= y
    return nothing
end

function f(z::Bar) # make sure we can figure out the type of z
    multiply!(z, 3)
end

works just fine.

[dmalyuta]

Just to be clear, your point 1 is a current issue with StaticLint? Do we agree that function multiply!(x::T, y::Integer)::Nothing where {T<:MyType} should be interpreted as a function signature? If I remove the ::Nothing, then the following code works without any errors reported by StaticLint:

abstract type MyType end

mutable struct Bar<:MyType
    val::Integer
end

function multiply!(x::T, y::Integer) where {T<:MyType}
    x.val *= y
    return nothing
end

z = Bar(2)
multiply!(z, 3)

println(z.val)

[ZacLN]

It's just a bug, I'll fix it

[dmalyuta]

Hmm I think that the fix by @ZacLN has the inadvertent side-effect of suppressing warnings such as An argument is included in a function signature but not used within its body. when the function signature contains the where {T<:...} syntax. For example, for the following function StaticLint does not show any warnings:

function multiply!(x::T, y::Integer, z::Integer)::Nothing where {T<:MyType}
    x.val *= y
    return nothing
end

On the other hand, the following function does show a warning that the z argument is not used within its body:

function multiply!(x::Bar, y::Integer, z::Integer)::Nothing
    x.val *= y
    return nothing
end