Bug: Anonymous enums can't be used with return type type

[MasterQ32]

Okay, this is a weird one. Somehow zig messes up enum literals when the type is declared local as a function parameter instead of "standalone" type. This also only happens when the return type is type, other types seem to work well (i32, void, []const u8):

const RetType = type; // replace with "void" and it compiles

pub fn foo(a: enum{a,b}) RetType { unreachable; }

pub fn main() void {
    foo(.a);
}

/tmp/fail.zig:7:9: error: expected type 'enum:4:15', found 'enum:4:15'
    foo(.a);
        ^
/tmp/fail.zig:4:15: note: enum:4:15 declared here
pub fn foo(a: enum{a,b}) RetType { unreachable; }
              ^
/tmp/fail.zig:4:15: note: enum:4:15 declared here
pub fn foo(a: enum{a,b}) RetType { unreachable; }
              ^
/tmp/fail.zig:7:8: note: referenced here
    foo(.a);

Zig Version: 0.5.0+a11da3773

[mikdusan]

This also only happens when the return type is type

It seems making the fn comptime is the confounder:

fn foo(comptime a: enum{a,b}) void { unreachable; }

pub fn main() void {
    foo(.a);
}

[MasterQ32]

This bug still persists, but i could narrow it down a bit:

// making the parameter comptime enforces the error,
// making it runtime removes it.
pub fn foo(comptime a: enum{a,b}) void { unreachable; }

pub fn main() void {
    foo(.a);
}

Looks like the bug is somewhere in the comptime resolution of enum literals to enum type

[andrewrk]

I believe the solution to this is going to be auditing how the comptime evaluation of parameter types are cached. This is related to #846. I want anonymous enums to also work in generic functions, after a comptime parameter. So this will require examining what "dependencies" from comptime parameters are used, and using only those as the cache key. That makes #846 a prerequisite to solving this bug. It also means that @typeInfo on generic function parameters and return type will get more useful.

[Rocknest]

export fn entry() void {
    repro(.a, 1);
}

fn repro(msg: enum {a, b}, comptime here_a_bug: u8) void {
    switch (msg) {
        .a => {},
        .b => {},
    }
}

[Vexu]

This will work with in the self-hosted compiler which is expected to ship with 0.9.0. In the meanwhile you should be able to workaround this by putting the enum in a separate declaration instead of having it as the parameter type.

[Vexu]

This worked earlier already but 2cfa716 added a similar enough test.