Switch statement type inference issues with !?<type>

[ntgraff]

In the following code, notNull is always null:

const std = @import("std");

fn maybe2(num: u32) anyerror!?u32 {
    return num;
}

fn maybe(should: enum{Yes, No}, num: u32) anyerror!?u32 {
    return switch (should) {
        .Yes => maybe2(num),
        else => null,
    };
}

test "incorrect return" {
    const notNull = maybe(.Yes, 12) catch unreachable;
    // error: attempt to unwrap null
    std.testing.expect(notNull.? == 12);
}

The following cases work as expected:

const std = @import("std");

fn maybe2(num: u32) ?u32 {
    return num;
}

fn maybe(should: enum{Yes, No}, num: u32) ?u32 {
    return switch (should) {
        .Yes => maybe2(num),
        else => null,
    };
}

test "incorrect return" {
    const notNull = maybe(.Yes, 12);
    std.testing.expect(notNull.? == 12);
}

const std = @import("std");
fn maybe(should: enum{Yes, No}, num: u32) anyerror!?u32 {
    return switch (should) {
        .Yes => num,
        else => null,
    };
}

test "incorrect return" {
    const notNull = maybe(.Yes, 12) catch unreachable;
    std.testing.expect(notNull.? == 12);
}

const std = @import("std");

fn maybe2(num: u32) ?u32 {
    return num;
}

fn maybe(should: enum{Yes, No}, num: u32) anyerror!?u32 {
    return switch (should) {
        .Yes => maybe2(num),
        .No => null,
    };
}

test "incorrect return" {
    const notNull = maybe(.Yes, 12) catch unreachable;
    std.testing.expect(notNull.? == 12);
}

In the first example, replacing else with .No, you get error: expected type 'u32', found '(null)' when compiling. Zig version is 0.4.0+7d9ee5d6d