Union with type that has optional field causes segfault in compiler

[ghost]

If an union has a type with an optional type then the compiler with crash with segfault.
Example code (stripped down from larger project):

const LhsExpr = struct {
    rhsExpr: ?AstObject
};

const AstObject = union {
    lhsExpr: LhsExpr
};

test "crash" {
    const lhsExpr = LhsExpr {
        .rhsExpr = null
    };

    const obj = AstObject {
        .lhsExpr = lhsExpr
    };
}

The compiler crashes because it fails to allocate at src/analyze.cpp:2293 (resolve_union_type) because union_type->data.unionation.gen_field_count is 0

[andrewrk]

Thanks for the stripped down example.

[ghost]

I see now that it's not supposed to work (but still not supposed to crash of course) because there is a recursive dependency (LhsExpr depends on a non-pointer type of AstObject and AstObject depends on a non-pointer type of LhsExpr).
So this works and doesn't crash:

const std = @import("std");

pub const LhsExpr = struct {
    rhsExpr: ?AstObject
};

pub const AstObject = union {
    lhsExpr: *LhsExpr
};

test "crash" {
    var lhsExpr = try std.debug.global_allocator.create(LhsExpr);
    const astObj = AstObject {
        .lhsExpr = lhsExpr
    };
}

however this does crash:

const std = @import("std");

pub const LhsExpr = struct {
    rhsExpr: ?AstObject
};

pub const AstObject = union {
    lhsExpr: *LhsExpr
};

test "crash" {
    const alignment = @alignOf(AstObject);
}

on the other hand @alignOf(LhsExpr) doesn't crash

[daurnimator]

I think this might be a dupe of #1735

[andrewrk]

Proposal to fix this: #2174

[andrewrk]

Now it gives this:

/home/andy/dev/zig/build/test.zig:1:17: error: struct 'LhsExpr' depends on itself
const LhsExpr = struct {
                ^
/home/andy/dev/zig/build/test.zig:5:5: note: while checking this field
    lhsExpr: LhsExpr,
    ^
/home/andy/dev/zig/build/test.zig:2:5: note: while checking this field
    rhsExpr: ?AstObject,
    ^
/home/andy/dev/zig/build/test.zig:8:30: note: referenced here
    const lhsExpr = LhsExpr{ .rhsExpr = null };
                             ^