std.Io compile error: group.async

Zig Version

0.16.0-dev.1399+7b325e08c

Steps to Reproduce and Observed Behavior

/home/yfr/.local/share/mise/installs/zig/master/lib/std/Io.zig:1041:17: error: error union is ignored
                @call(.auto, function, args_casted.*);
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/yfr/.local/share/mise/installs/zig/master/lib/std/Io.zig:1041:17: note: consider using 'try', 'catch', or 'if'

The line which the error refers to:

zig/lib/std/Io.zig

Line 1041 in 7b325e0

@call(.auto, function, args_casted.*);

Expected Behavior

zig should be able to compile the standard library

Simple fix

When the error union should be given back to the caller then this would be a possible fix:

pub fn async(g: *Group, io: Io, function: anytype, args: std.meta.ArgsTuple(@TypeOf(function))) !void {
        const Args = @TypeOf(args);
        const TypeErased = struct {
            fn start(group: *Group, context: *const anyopaque) void {
                _ = group;
                const args_casted: *const Args = @ptrCast(@alignCast(context));
                try @call(.auto, function, args_casted.*);
            }
        };
        io.vtable.groupAsync(io.userdata, g, @ptrCast(&args), .of(Args), TypeErased.start);
    }

You need also change fn start signature in std.Io.VTable to return !void, so you actually could use try inside. But that raises question about groupAsync comment, that says:

This mode does not support results, await, or cancel.

Yet, groupCancel exists.

@kristoff-it

I checked on this with @kristoff-it it totally makes sense that std.Io.Group.async/3 should be given a function which does not return an error union (which resolves the compile error).

Maybe we could improve the error message in this case?

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std.Io compile error: group.async #25995

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Steps to Reproduce and Observed Behavior

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Simple fix

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std.Io compile error: group.async #25995

Description

Zig Version

Steps to Reproduce and Observed Behavior

Expected Behavior

Simple fix

Activity

floatdrop commented on Nov 21, 2025

YannickFricke commented on Nov 21, 2025

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