Attach Lazy ClangImporter Diagnostics as Notes to Sema Diagnostics

[NuriAmari]

Behaviour Change

Clang importer diagnostics that are produced as a result of a reference in Swift code are attached as notes to the Sema produced diagnostic that indicates the declaration is unavailable.

This has the added benefit that ClangDiagnostics are produced as many times as referenced from Swift, whereas previosly it was just the first time.

Old Behaviour

badCFunc()
// CHECK: warning: 'badCFunc' could not be imported
// ...
// CHECK: error: cannot find 'badCFunc' in scope
badCFunc()
// CHECK: error: cannot find 'badCFunc' in scope

New Behaviour

badCFunc()
// CHECK: error: cannot find 'badCFunc' in scope
// CHECK: enote: 'badCFunc' could not be imported
// ...
badCFunc()
// CHECK: error: cannot find 'badCFunc' in scope
// CHECK: enote: 'badCFunc' could not be imported
// ...

As a result of this change, the eager diagnostic mode only produces notes. This is somewhat unorthodox, notes are typically attached to some other error or warning. This can be addressed if it is a concern.

Implementation Change

Previously, diagnostics were produced via calls to one of diagnoseValue, diagnoseMissingMember or diagnoseDeclDirectly from outside the ClangImporter. As I mention, these calls were made outside the ClangImporter, but still relatively close. This had the above "only report diagnostics for the first usage" effect. The aforementioned methods have been consolidated into diagnoseTopLevelValue and diagnoseMemberValue. These calls are made in Sema, directly after the diagnostic reporting the declaration could not be found is produced.

diagnoseTopLevelValue

This method is to be used to look up top level declarations whose containing context
is not known (ex: A C function, a macro etc).

/// Emits diagnostics for any declarations named name
/// whose direct declaration context is a TU.
virtual void diagnoseTopLevelValue(const DeclName &name) = 0;

diagnoseMemberValue

This method is to be used to look up declarations where the context
is required to disambiguate between declarations. Typically, this means
members (the context being the containing decl). You could use this
to diagnose a top level declaration from a specific translation unit,
but there no point in doing so.

/// Emit diagnostics for declarations named name that are members
/// of the provided baseType.
virtual void diagnoseMemberValue(const DeclName &name,
                                 const Type &baseType) = 0;

[zoecarver]

I love to see this getting better and better.

As always, thank you for the high quality work, Nuri!

[zoecarver]

@swift-ci please smoke test.

[zoecarver]

@swift-ci please smoke test macOS.

[NuriAmari]

Couple changes here. Since this call is made from Sema, the baseType could be anything (not just an imported ClangType). I discovered a few more checks are needed here.

First, extractDirectlyReferencedNominalTypes only knows how to handle small set of types of types. If you pass something it isn't expecting, we hit an llvm_unreachable. The getAnyNominal check takes care of this (I figure all imported types referencable from swift are nominal).

Lastly, I added checks that getClangDecl() returns a non-null value, and that this value is a clang::DeclContext. Otherwise, if either of these checks fail, but the value is passed to cast<clang::DeclContext>() anyways, it'll throw.

[zoecarver]

@swift-ci please smoke test.

[zoecarver]

@swift-ci please smoke test macOS.