Exempt Swift Interface Files From Whole-Module ObjC Errors

We don't expect swiftinterface files to have anything meaningful to
report from these checks anyhow - they will have been run at module
generation time anyways.

In fact, the linked radar demonstrates how this kind of checking can be
detrimental to the usability of the compiler. The test committed here
declares the CoreFeatures framework, an Objective-c (root) class and a
set of Objective-C protocols. Now for the fun part: The Objective-C
class is made to conform to the Objective-C protocols in a Swift
extension. This extension is then printed into the generated
CoreFeatures-Swift header and made available to clients of the module.

Now, because we have an Objective-C protocol and a base class that is
imported from Objective-C, we mirror-in the members of RootProtocol.
The sum total of the monster we have built is that we now have a Swift
class that implements some requirements, and an Objective-C protocol
that has requirements mirrored into that same class. The result is
a raft of spurious selector conflict diagnostics that the user cannot
work around unless they own both the class and the protocol.

Exempt swiftinterface files from this checking.

rdar://69550935

Author: CodaFi

lib/Sema/TypeCheckDeclObjC.cpp

@@ -2387,6 +2387,7 @@ bool swift::diagnoseObjCUnsatisfiedOptReqConflicts(SourceFile &sf) {
         break;
       }
     }
+    assert(req != bestConflict && "requirement conflicts with itself?");
 
     // Diagnose the conflict.
     auto reqDiagInfo = getObjCMethodDiagInfo(unsatisfied.second);

lib/Sema/TypeChecker.cpp

@@ -344,9 +344,19 @@ void swift::performWholeModuleTypeChecking(SourceFile &SF) {
   auto &Ctx = SF.getASTContext();
   FrontendStatsTracer tracer(Ctx.Stats,
                              "perform-whole-module-type-checking");
-  diagnoseObjCMethodConflicts(SF);
-  diagnoseObjCUnsatisfiedOptReqConflicts(SF);
-  diagnoseUnintendedObjCMethodOverrides(SF);
+  switch (SF.Kind) {
+  case SourceFileKind::Library:
+  case SourceFileKind::Main:
+    diagnoseObjCMethodConflicts(SF);
+    diagnoseObjCUnsatisfiedOptReqConflicts(SF);
+    diagnoseUnintendedObjCMethodOverrides(SF);
+    return;
+  case SourceFileKind::SIL:
+  case SourceFileKind::Interface:
+    // SIL modules and .swiftinterface files don't benefit from whole-module
+    // ObjC checking - skip it.
+    return;
+  }
 }
 
 bool swift::isAdditiveArithmeticConformanceDerivationEnabled(SourceFile &SF) {

test/ClangImporter/Inputs/requirement-conflict/CoreFeatures.framework/CoreFeatures

@@ -0,0 +1 @@
+Versions/Current/CoreFeatures

test/ClangImporter/Inputs/requirement-conflict/CoreFeatures.framework/Headers

@@ -0,0 +1 @@
+Versions/Current/Headers

test/ClangImporter/Inputs/requirement-conflict/CoreFeatures.framework/Modules

@@ -0,0 +1 @@
+Versions/Current/Modules