Compile error on errorset inference involving async functions

[adrusi]

The 0.4.0 compiler fails an assertion for the following code:

const std = @import("std");

async fn a() !void {
    return error.Example;
}

const Error = @typeInfo(@typeInfo(@typeOf(a)).Fn.return_type.?).ErrorUnion.error_set;
// const Error = anyerror;

async fn b(err1: *?Error) void {
    const p = async<std.debug.global_allocator> a() catch {
        @panic("failed to start coroutine");
    };
    await p catch |err| {
        err1.* = err;
    };
}

fn c() !void {
    var err1: ?Error = null;
    const p = try async<std.debug.global_allocator> b(&err1);

    if (err1) |err| {
        return err;
    }
}
    
test "make compile fail" {
    try c();
}

Compiler output:

$ zig test bug.zig
zig: /build/zig/src/zig-0.4.0/src/analyze.cpp:3581: void define_local_param_variables(CodeGen*, ZigFn*): Assertion `!fn_type->data.fn.is_generic' failed.

Defining Error to be anyerror makes it compile and run as expected.

[andrewrk]

Updated test case after the async/await rewrite:

const std = @import("std");

async fn a() !void {
    return error.Example;
}

const Error = @typeInfo(@typeInfo(@typeOf(a)).Fn.return_type.?).ErrorUnion.error_set;
// const Error = anyerror;

async fn b(err1: *?Error) void {
    var f = async a();
    await f catch |err| {
        err1.* = err;
    };
}

fn c() !void {
    var err1: ?Error = null;
    const p = async b(&err1);

    if (err1) |err| {
        return err;
    }
}

test "make compile fail" {
    try c();
}

output for me:

1/1 test "make compile fail"...error: Example
/home/andy/dev/zig/build/test.zig:22:9: 0x20578d in c (test)
        return err;
        ^
/home/andy/dev/zig/build/test.zig:27:5: 0x2055bc in test "make compile fail" (test)
    try c();
    ^
/home/andy/dev/zig/build/lib/zig/std/special/test_runner.zig:21:21: 0x227bb9 in std.special.main (test)
            else => return err,
                    ^

I believe this is resolved.