Add some more PrettyStackTrace entries to AST (swiftlang#17208)

No functionality change.

Author: jrose-apple

include/swift/AST/PrettyStackTrace.h

@@ -20,6 +20,7 @@
 
 #include "llvm/Support/PrettyStackTrace.h"
 #include "swift/Basic/SourceLoc.h"
+#include "swift/AST/Identifier.h"
 #include "swift/AST/Type.h"
 
 namespace swift {
@@ -148,6 +149,15 @@ class PrettyStackTraceGenericSignature : public llvm::PrettyStackTraceEntry {
   void print(llvm::raw_ostream &out) const override;
 };
 
+class PrettyStackTraceSelector : public llvm::PrettyStackTraceEntry {
+  ObjCSelector Selector;
+  const char *Action;
+public:
+  PrettyStackTraceSelector(const char *action, ObjCSelector S)
+    : Selector(S), Action(action) {}
+  void print(llvm::raw_ostream &OS) const override;
+};
+
 } // end namespace swift
 
 #endif

lib/AST/ASTContext.cpp

@@ -30,6 +30,7 @@
 #include "swift/AST/ModuleLoader.h"
 #include "swift/AST/NameLookup.h"
 #include "swift/AST/ParameterList.h"
+#include "swift/AST/PrettyStackTrace.h"
 #include "swift/AST/ProtocolConformance.h"
 #include "swift/AST/RawComment.h"
 #include "swift/AST/SubstitutionMap.h"
@@ -1401,6 +1402,7 @@ void ASTContext::addModuleLoader(std::unique_ptr<ModuleLoader> loader,
 
 void ASTContext::loadExtensions(NominalTypeDecl *nominal,
                                 unsigned previousGeneration) {
+  PrettyStackTraceDecl stackTrace("loading extensions for", nominal);
   for (auto &loader : getImpl().ModuleLoaders) {
     loader->loadExtensions(nominal, previousGeneration);
   }
@@ -1412,6 +1414,8 @@ void ASTContext::loadObjCMethods(
        bool isInstanceMethod,
        unsigned previousGeneration,
        llvm::TinyPtrVector<AbstractFunctionDecl *> &methods) {
+  PrettyStackTraceSelector stackTraceSelector("looking for", selector);
+  PrettyStackTraceDecl stackTraceDecl("...in", classDecl);
   for (auto &loader : getImpl().ModuleLoaders) {
     loader->loadObjCMethods(classDecl, selector, isInstanceMethod,
                             previousGeneration, methods);

lib/AST/PrettyStackTrace.cpp

@@ -221,3 +221,7 @@ void PrettyStackTraceGenericSignature::print(llvm::raw_ostream &out) const {
   }
   out << '\n';
 }
+
+void PrettyStackTraceSelector::print(llvm::raw_ostream &out) const {
+  out << "While " << Action << " '" << Selector << "'";
+}