Support is added for all of the non-type expression contexts where we currently accept built-in conversions, such as reordering the fields in a struct.
- Makes `Self` a keyword
- Inside `class Foo { `... `}`, `Self` means `Foo`
- Inside `class Foo(T:! Type, U:! Type) {` ...` }`, `Self` means `Foo(T, U)`
- `impl as Bar` means `impl Self as Bar`
- Inside `external impl Foo as Bar {`...`}`, not in a scope already defining `Self`, `Self` means `Foo`
Implemented by introducing a new kind of declaration, a `SelfDeclaration`, that is automatically added to class and impl declarations.
Co-authored-by: Jon Meow <jperkins@google.com>
Use FileCheck's `[[@LINE+n]]` mechanism to refer to the next line.
This is made awkward by a couple of things:
* We want to keep the `CHECK` lines in the original order.
* Errors are sometimes more than one line long.
The approach we use is to interleave the original lines and the check lines, putting each check line as early as possible subject to two rules:
1) Check lines never precede the 'AUTOUPDATE' line
2) Except when required by rule (1), a check line that refers to a source line by line number is never placed earlier than a source line that precedes that source line.
The actual `[[@LINE+n]]` annotations are created in a second pass after we've interleaved the lines so that we can work out the correct offsets.
Co-authored-by: Jon Meow <jperkins@google.com>