SIL: make a linkage mismatch during de-serialization a human readable diagnostic

Although this error can only happen when tinkering with the stdlib's runtime functions, it's nice to get a readable error message.
So far, the compiler just crashed later without a hint to the original problem.

Author: eeckstein

include/swift/AST/DiagnosticsSIL.def

@@ -142,6 +142,10 @@ ERROR(deserialize_function_type_mismatch,Fatal,
       "type mismatch of function '%0', declared as %1 but used in a swift module as %2",
       (StringRef, Type, Type))
 
+ERROR(deserialize_function_linkage_mismatch,Fatal,
+      "linkage mismatch of function '%0', declared as %1but expected as %2",
+      (StringRef, StringRef, StringRef))
+
 ERROR(without_actually_escaping_on_isolated_any,none,
       "withoutActuallyEscaping is currently unimplemented for '@isolated(any)' "
       "function values", ())

include/swift/SIL/SILLinkage.h

@@ -421,6 +421,9 @@ inline bool fixmeWitnessHasLinkageThatNeedsToBePublic(SILDeclRef witness,
          (!hasSharedVisibility(witnessLinkage) || !witness.isSerialized());
 }
 
+// Defined in SILPrinter
+StringRef getLinkageString(SILLinkage linkage);
+
 } // end swift namespace
 
 #endif

lib/SIL/IR/SILPrinter.cpp

@@ -3505,7 +3505,7 @@ void SILFunction::dump(const char *FileName) const {
   print(os);
 }
 
-static StringRef getLinkageString(SILLinkage linkage) {
+StringRef swift::getLinkageString(SILLinkage linkage) {
   switch (linkage) {
   case SILLinkage::Public: return "public ";
   case SILLinkage::PublicNonABI: return "non_abi ";

lib/Serialization/SerializedSILLoader.cpp

@@ -16,6 +16,8 @@
 #include "ModuleFile.h"
 
 #include "swift/AST/ASTMangler.h"
+#include "swift/AST/DiagnosticsSIL.h"
+#include "swift/Demangling/Demangle.h"
 #include "swift/SIL/SILModule.h"
 #include "swift/SIL/SILMoveOnlyDeinit.h"
 #include "swift/Serialization/SerializedModuleLoader.h"
@@ -72,13 +74,16 @@ SerializedSILLoader::lookupSILFunction(StringRef Name,
       if (Linkage) {
         // This is not the linkage we are looking for.
         if (Func->getLinkage() != *Linkage) {
-          LLVM_DEBUG(llvm::dbgs()
-                     << "Wrong linkage for Function: "
-                     << Func->getName() << " : "
-                     << (int)Func->getLinkage() << "\n");
-          Des->invalidateFunction(Func);
-          Func->getModule().eraseFunction(Func);
-          continue;
+
+          auto fnName = Demangle::demangleSymbolAsString(Func->getName(),
+                          Demangle::DemangleOptions::SimplifiedUIDemangleOptions());
+          auto &diags = Func->getModule().getASTContext().Diags;
+          diags.diagnose(Func->getLocation().getSourceLoc(),
+                         diag::deserialize_function_linkage_mismatch,
+                         fnName, getLinkageString(Func->getLinkage()),
+                         getLinkageString(*Linkage));
+          diags.flushConsumers();
+          exit(1);
         }
       }
       return Func;