ModuleInterface: Avoid crashing on invalid extensions in lazy typechecking mode.

With `-experimental-lazy-typecheck` specified during module interface emission,
`collectProtocols()` may be the first piece of code to request the extended
type for a given extension and it therefore needs to ignore invalid extensions
and ensure that diagnostics are emitted.

Also, add some `PrettyStackTrace` coverage to `ModuleInterfaceSupport.cpp` to make
investigating future issues easier.

Resolves rdar://126232836.

include/swift/Frontend/ModuleInterfaceSupport.h

@@ -13,6 +13,7 @@
 #ifndef SWIFT_FRONTEND_MODULEINTERFACESUPPORT_H
 #define SWIFT_FRONTEND_MODULEINTERFACESUPPORT_H
 
+#include "swift/AST/PrintOptions.h"
 #include "swift/Basic/LLVM.h"
 #include "swift/Basic/Version.h"
 #include "llvm/Support/Regex.h"

lib/Frontend/ModuleInterfaceSupport.cpp

@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "swift/Frontend/ModuleInterfaceSupport.h"
 #include "swift/AST/ASTContext.h"
 #include "swift/AST/ASTPrinter.h"
 #include "swift/AST/Decl.h"
@@ -20,13 +21,13 @@
 #include "swift/AST/Module.h"
 #include "swift/AST/ModuleNameLookup.h"
 #include "swift/AST/NameLookupRequests.h"
+#include "swift/AST/PrettyStackTrace.h"
 #include "swift/AST/ProtocolConformance.h"
 #include "swift/AST/TypeCheckRequests.h"
 #include "swift/AST/TypeRepr.h"
 #include "swift/Basic/Assertions.h"
 #include "swift/Basic/STLExtras.h"
 #include "swift/Frontend/Frontend.h"
-#include "swift/Frontend/ModuleInterfaceSupport.h"
 #include "swift/Frontend/PrintingDiagnosticConsumer.h"
 #include "swift/SILOptimizer/PassManager/Passes.h"
 #include "swift/Serialization/SerializationOptions.h"
@@ -530,6 +531,7 @@ class InheritedProtocolCollector {
   /// protocols.
   void recordProtocols(InheritedTypes directlyInherited, const Decl *D,
                        bool skipExtra = false) {
+    PrettyStackTraceDecl stackTrace("recording protocols for", D);
     std::optional<AvailableAttrList> availableAttrs;
 
     for (int i : directlyInherited.getIndices()) {
@@ -602,11 +604,19 @@ public:
   ///
   /// \sa recordProtocols
   static void collectProtocols(PerTypeMap &map, const Decl *D) {
+    PrettyStackTraceDecl stackTrace("collecting protocols for", D);
     InheritedTypes directlyInherited = InheritedTypes(D);
     const NominalTypeDecl *nominal;
     const IterableDeclContext *memberContext;
 
     auto shouldInclude = [](const ExtensionDecl *extension) {
+      // In lazy typechecking mode we may be resolving the extended type for the
+      // first time here, so we need to call getExtendedType() to cause
+      // diagnostics to be emitted if necessary.
+      (void)extension->getExtendedType();
+      if (extension->isInvalid())
+        return false;
+
       if (extension->isConstrainedExtension()) {
         // Conditional conformances never apply to inherited protocols, nor
         // can they provide unconditional conformances that might be used in
@@ -615,9 +625,9 @@ public:
       }
       return true;
     };
+
     if ((nominal = dyn_cast<NominalTypeDecl>(D))) {
       memberContext = nominal;
-
     } else if (auto *extension = dyn_cast<ExtensionDecl>(D)) {
       if (!shouldInclude(extension)) {
         return;
@@ -697,6 +707,9 @@ public:
                                     const PrintOptions &printOptions,
                                     ModuleDecl *M,
                                     const NominalTypeDecl *nominal) const {
+    PrettyStackTraceDecl stackTrace("printing synthesized extensions for",
+                                    nominal);
+
     if (ExtraProtocols.empty())
       return;
 
@@ -881,6 +894,8 @@ const StringLiteral InheritedProtocolCollector::DummyProtocolName =
 bool swift::emitSwiftInterface(raw_ostream &out,
                                ModuleInterfaceOptions const &Opts,
                                ModuleDecl *M) {
+  PrettyStackTraceDecl stackTrace("emitting swiftinterface for", M);
+
   assert(M);
 
   llvm::SmallSet<StringRef, 4> aliasModuleNamesTargets;

test/ModuleInterface/lazy-typecheck-errors.swift

@@ -0,0 +1,7 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-emit-module-interface(%t/Test.swiftinterface) -module-name Test %s -experimental-lazy-typecheck -verify
+
+extension DoesNotExist { // expected-error {{cannot find type 'DoesNotExist' in scope}}
+  public func method() {}
+}

test/Serialization/lazy-typecheck-errors.swift

@@ -32,3 +32,7 @@ public var varWithImplicitInvalidType = (1 as InvalidType)
 // expected-serialization-remark@-3 {{serialization skipped for invalid type}}
 
 public var _: InvalidType
+
+extension InvalidType {
+  public func method() {}
+}