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Known Issues

This page tries to collate a list of things that are known to be broken or otherwise unexpected.

Importing operators

The following syntax

import Base: :+

is valid on Julia 1.10 and 1.11, but not on Julia 1.9 or 1.12 (the removal of this syntax in Julia 1.12 is a bugfix in Julia, i.e., an intentional change). JuliaFormatter will refuse to format this code (because JuliaSyntax.jl doesn't parse it).

You should change your code to either of the following, which both format fine:

import Base: +
import Base: (+)

Insertion of return

When using always_use_return = true (or any style that sets that, e.g. BlueStyle), JuliaFormatter will add return statements to things that aren't really a meaningful return value:

using JuliaFormatter: format_text

s = """
function foo()
    error("oops")
end
"""

format_text(s; always_use_return = true) |> println
function foo()
    return error("oops")
end
throw

Currently, JuliaFormatter special-cases throw(...) in that a return is not inserted before it. I personally dislike this heuristic because it's not provably correct: the cases that are special-cased are not the same as the cases that do not return. I intend to remove it in v3.

This is intentional and doesn't change any semantics (note that even though error(...) doesn't evaluate to an actual value, it is still an expression and has a type of Union{}, which is the bottom type). If you want to avoid this, you can insert a return nothing statement at the end of your function:

s2 = """
function foo()
    error("oops")
    return nothing  # unreachable
end
"""

format_text(s2; always_use_return = true) |> println
function foo()
    error("oops")
    return nothing  # unreachable
end

Inline comments

JuliaFormatter is quite buggy with inline comments of the form #= ... =#, especially because they aren't thoroughly tested. For example, sometimes they get inadvertently deleted, or formatting can be non-idempotent when they are present.

If you come across such problems please don't hesitate to open an issue, but I wanted to document this because it is specifically known to be a bit of a pain point. # ... comments are likely to be much more reliable.