[NameLookup] Ensure extensions are updated after module load

[hamishknight]

Call prepareExtensions in prepareLookupTable to make sure we load in any new extensions brought in by modules loaded after-the-fact. This isn't an issue for normal compilations as we load all the modules up-front in import resolution, but clients such as the LLDB REPL may load in modules later.

As the LLDB REPL appears to be the only client affected by this, the test case is in swiftlang/llvm-project#1338.

Resolves rdar://64040436.

[hamishknight]

swiftlang/llvm-project#1338

@swift-ci please test

[hamishknight]

@swift-ci please test source compatibility

[CodaFi]

Isn't this exploiting this problem?

    // FIXME: If disableAdditionalExtensionLoading is true, we should
    // not mark the entry as complete.
    Table.markLazilyComplete(baseName);

Can we fix this bug by moving the marking under the condition above?

[hamishknight]

@CodaFi Unfortunately that doesn't fix it (though I can include it in this patch if you want) – in this case we initially do a member lookup, which loads in and looks through extensions, and marks the table lazily complete for that name. We then load a module, but because the table is already marked lazily complete, any further lookups bail with the previous set of results.

That being said, I totally forgot we had the IgnoreNewExtensions flag, we could optimize this fix slightly by doing:

if (!disableAdditionalExtensionLoading)
  decl->prepareExtensions();

How does that sound?

[CodaFi]

Should we just invalidate the lookup caches when performing a module load, then? (I would have expected binding new extensions to already handle this...)

[hamishknight]

@CodaFi You mean the lookup caches for all the nominal types? Or eagerly deserializing all the module's extension decls (thereby invalidating the lookup caches for the nominals being extended)? In either case IMO that seems unnecessarily expensive if we never need to do any lookups.

(I would have expected binding new extensions to already handle this...)

Right, it does, but that only happens when we load in the extensions. This patch ensures that we load in all the relevant extensions prior to consulting the lazily complete cache (thereby ensuring it's up-to-date).

[CodaFi]

Right. Let's take the

if (!disableAdditionalExtensionLoading)
  decl->prepareExtensions();

version then.

[hamishknight]

swiftlang/llvm-project#1338

@swift-ci please test