# stage2: remove AstGen none_or_ref · gitcafe/zig

[View on GitCafe](https://git.cafe/gitcafe/zig/commit/b65582e834de34f2351fa04a47f20e7f9c16a47c)

Repository: [gitcafe/zig](https://git.cafe/gitcafe/zig)

Visibility: public

Requested revision: b65582e834de34f2351fa04a47f20e7f9c16a47c

Requested commit: b65582e834de34f2351fa04a47f20e7f9c16a47c

Commit: b65582e834de34f2351fa04a47f20e7f9c16a47c

Tree: 903977d19050915584c568b9a6b04b57e0996d59

Author: Robin Voetter

Committer: Robin Voetter

## Message

````
stage2: remove AstGen none_or_ref

The remaining uses of this result location were causing a bunch of errors
problems where the pointers returned from rvalue and lvalue expressions
would be confused, allowing for extra pointers on rvalue expressions.
For example:
```zig
const X = struct {a: i32};
var x: X = .{.a = 1};
var ptr = &x;
_ = x.a;
```
In the last line, the lookup of x with result location .none_or_ref would
return a double pointer (**X). This would be dereferenced one, after which
a relative pointer to `a` would be fetched and derefenced to get the final
result.

However, this also allows us to manually construct a double pointer, and
fetch the field of the inner type of that:
```zig
_ = &(&(x)).a;
```

This problem also manifests itself with element access. There are two obvious
ways to fix the problem, both of which include replacing the usage of
.none_or_ref for field- and element accesses with something which
deterministically produce either a pointer or value: either result location
.ref or .none. In the former case, this would be paired with .elem_ptr, and
in the latter case with .elem_val.

Note that the stage 1 compiler does not have this problem, because there is
no equivalent of .elem_val and .field_val. In this way it is equivalent to
using the result location .ref for field- and element accesses.

In this case i have used .none, as this matches language behaviour more
closely.

````

## Parents

- [bfedf40c9267367d6ffdad54050dcbd451136b58](https://git.cafe/gitcafe/zig/commit/bfedf40c9267367d6ffdad54050dcbd451136b58?format=markdown)

[Source at this commit](https://git.cafe/gitcafe/zig/tree/b65582e834de34f2351fa04a47f20e7f9c16a47c?format=markdown)