I'd split out the decl-specific handlers so that import_ref.cpp could
also call them. However, with the current model for imports and
constants, we shouldn't use them there. As a consequence, merge them
back into individual files for greater consistency with other helper
functions (and better visibility when making related code changes).
This addresses the const reliance of ResolvePrevInstForMerge by checking
the imported instruction, testing with `alias` name conflicts. Given the
need to examine structure, the helper function feels like it now gets in
the way, so I'm just removing it.
---------
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
This was to track use of a declaration after import, prior to a
redeclaration. Per [discussion on
Discord](https://discord.com/channels/655572317891461132/1217182321933815820/1236016521059237962),
we likely don't need this check due to the change in behavior of
`extern`.
Rather than potentially getting one of many `extern` decls and depending
on it by accident, it is now planned to be _required_ to be imported,
and the library doing a non-`extern` decl must _know_ it's importing the
`extern` decl. The stricter requirement on the library means it now
seems more reasonable to use the `extern` decl.
So kind of rolling back #3831, though keeping `ImportIRInstId` (at least
for now) and keeping `Loaded`/`Unloaded` terminology (seems a nicer
fit).
This doesn't actually track whether a declaration is `extern`. It does,
however:
- Factor out and expand merge support for classes, sharing handling with
functions.
- This makes the ClassRedefinition diagnostic redundant, as the
redeclaration checking overlaps.
- Add partial `extern` handling to class handling; just some
verifications of correct use.
- Factor out `extern` on member handling for sharing with `fn`.
- Fixes a bug in import_ref where a class's definition_id wasn't
assigned when defining.
This changes how a redefinition is handled (replaced, rather than
merged). I don't know whether that's ideal, but I think it results in
easy-to-understand consequences, and it's more consistent with how `fn`
works.
There's enough work here that this felt like a decent cut point,
particularly as the amount of work to actually add `extern` tracking
will be significant.
Adds ImportIRId::ApiForImpl to reserve a specific slot for the `api`
import, so that the code can trivially determine whether an import is
from the same library. This is then used for merging function
declarations, because the rules for redeclarations in the same library
slightly differ as compared to other imports (note they're also not
identical to same-file rules).
The main thing this leaves from the recent #3762 is verifying that
entities forward declared in the `impl` file are also defined, but
that's not in-scope for merging; it's moreso post-checking validation.
Note, a lot of our `invalid <entity> ID` comments in ids.h were
incorrectly copy-pasted, so I've cut `<entity>`.
LookupNameInDecl is only called from DeclNameStack, but I'm adding
mark_imports_used there because it feels more consistent. Not sure if we
want a better API boundary. I admit I'm also suspicious of its call to
LookupInCurrentScope but maybe it's okay due to how imports work.
I was choosing to print multiple diagnostics when a declaration is
previously used _and_ doesn't match because I think the "previously
used" is more important, but the "doesn't match" may give an additional
hint about why it didn't work.
The merge.h utility function is because I think we can follow a similar
model for identifying errors with other declarations: classes,
interfaces, etc.
This doesn't significantly change logic, although I'm trying to add the
location to used state.
The issue I'm trying to address is how to identify a declaration as
"allowed to be redeclared". Consider:
```
library "a" api;
extern fn F();
```
```
library "b" api;
extern fn F();
```
```
library "c" api;
import library "a";
import library "b";
var x: auto = F();
fn F();
```
What currently happens is:
1. On import of "a", `F` becomes ImportRefUnused
2. On import of "b", `F` becomes ImportRefUsed in order to merge.
3. In "c", the call `F()` doesn't change the state.
4. In "c", the declaration `fn F();` needs some breadcrumb to understand
whether "F" has been referenced, as in step (3) here.
What I want to happen is:
1. On import of "a", `F` becomes ImportRefUnloaded
2. On import of "b", `F` becomes ImportRefLoaded in order to merge.
3. In "c", the call `F()` causes `F` to become ImportRefUsed
4. In "c", the declaration `fn F();` detects that `F` is already
ImportRefUsed, and can use the associated `used_id` for a diagnostic
about why redeclaring is invalid.
Note this PR isn't implementing (4). I'm focused on the refactoring to
add a new ImportRef state here.
Note we only identify conflicts between libraries in the current package
during import.
This restructures the BUILD because of dependency cycles between cpp
files... We're going to need context's name lookup to handle things such
as merging, merging requires function logic, function logic requires
context access. Per discussion, going with a single large cc_library for
now rather than trying to split out small libraries.
I'm envisioning the new merge.* as a hub for cross-declaration merge
logic. Note function.cpp is already pretty sizable, and I think it may
lean a little function-specific even if there are some utilities that
could be split out.
Jon Ross-Perkins
