fix field alignment kludge by implementing lazy values #3115
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This breaks behavior tests as well as compile error notes for generic function calls. However it introduces better circular dependency compile errors. The next step is to add Lazy Values to fix the regressions.
this case now works:
```zig
const Node = struct {
field: fn (*Node) *Node,
};
```
this case now works:
```zig
const A = struct {
b: B,
};
const B = fn (A) void;
```
this case works now:
```zig
const A = struct {
b_list_pointer: *const []B,
};
const B = struct {
a_pointer: *const A,
};
const b_list: []B = [_]B{};
const a = A{ .b_list_pointer = &b_list };
const obj = B{ .a_pointer = &a };
```
this case works now:
```zig
const Node = struct {
node: ?*Node,
};
```
this case regressed and now fixed: ```zig const a: ?*i32 = undefined; const b: ?*f32 = @ptrCast(?*f32, a); ```
this case works now:
```zig
const Expr = union(enum) {
Literal: u8,
Question: *Expr,
};
```
this case works now:
```zig
const Foo = struct {
field: @typeof(func).ReturnType,
};
fn func(self: *Foo) void {}
```
this case works now:
```zig
const Foo = struct {
field: Bar(@Alignof(*Foo)),
};
fn Bar(comptime alignment: u29) type {
return struct {
field: *align(alignment) Foo,
};
}
```
...with optional unwrapping with var initialized to undefined
and add check for alignment specified on enum fields
This was referenced Aug 27, 2019
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This is an implementation of lazy values (#2174) which is required to fix many false positive circular dependency bugs, as well as field alignment bugs. It also implements ability to set alignment of struct and union fields (#1512). It also improves the error notes for "unable to evaluate constant expression" (#1732).
Checklist:
resolve_struct_typethat calculates field offsets needs to have the logic fromget_struct_type