SILGen: Increase test coverage for lazy typechecking.

None of these additional test cases actually uncovered any problems but it
seems valuable to have them.

Also, add pretty stack traces for a couple paths through SILGen.

Author: tshortli

lib/SILGen/SILGenType.cpp

@@ -260,6 +260,8 @@ class SILGenVTable : public SILVTableVisitor<SILGenVTable> {
   }
 
   void emitVTable() {
+    PrettyStackTraceDecl("silgen emitVTable", theClass);
+
     // Imported types don't have vtables right now.
     if (theClass->hasClangNode())
       return;
@@ -1118,6 +1120,8 @@ class SILGenType : public TypeMemberVisitor<SILGenType> {
 
   /// Emit SIL functions for all the members of the type.
   void emitType() {
+    PrettyStackTraceDecl("silgen emitType", theType);
+
     SGM.emitLazyConformancesForType(theType);
 
     for (Decl *member : theType->getABIMembers()) {
@@ -1292,6 +1296,8 @@ class SILGenExtension : public TypeMemberVisitor<SILGenExtension> {
 
   /// Emit SIL functions for all the members of the extension.
   void emitExtension(ExtensionDecl *e) {
+    PrettyStackTraceDecl("silgen emitExtension", e);
+
     // Arguably, we should divert to SILGenType::emitType() here if it's an
     // @_objcImplementation extension, but we don't actually need to do any of
     // the stuff that it currently does.

test/SILGen/lazy_typecheck_errors.swift

@@ -1,4 +1,7 @@
-// RUN: %target-swift-frontend -emit-silgen %s -parse-as-library -module-name Test -enable-library-evolution -experimental-lazy-typecheck -verify
+// RUN: %target-swift-frontend -emit-silgen %s -parse-as-library -enable-library-evolution -module-name Test -experimental-lazy-typecheck -verify
+// RUN: %target-swift-frontend -emit-silgen %s -parse-as-library -enable-library-evolution -module-name Test -experimental-lazy-typecheck -experimental-skip-non-inlinable-function-bodies -verify
+// RUN: %target-swift-frontend -emit-silgen %s -parse-as-library -enable-library-evolution -module-name Test -experimental-lazy-typecheck -experimental-skip-non-inlinable-function-bodies -experimental-skip-non-exportable-decls -verify
+
 
 public protocol Proto {
   func req()
@@ -21,3 +24,32 @@ public protocol ProtoWithAssociatedType {
 public struct ConformsToProtoProtoWithAssociatedType: ProtoWithAssociatedType {
   // expected-error@-1 {{type 'ConformsToProtoProtoWithAssociatedType' does not conform to protocol 'ProtoWithAssociatedType'}}
 }
+
+public struct GenericStruct<T> {
+  public var t: T
+}
+
+public struct GenericStructWithInvalidParameterConstraint<T: NonExistent> {
+  // expected-error@-1 {{cannot find type 'NonExistent' in scope}}
+}
+
+extension GenericStruct where T == NonExistent {
+  // expected-error@-1 {{cannot find type 'NonExistent' in scope}}
+  public func methodInExtensionWithInvalidWhereClause() {}
+}
+
+public class ValidClass {
+  public func methodReturningNonExistentType() -> NonExistent {}
+  // expected-error@-1 {{cannot find type 'NonExistent' in scope}}
+}
+
+public class DerivedFromValidClass: ValidClass {
+  override public func methodReturningNonExistentType() -> NonExistent {}
+  // expected-error@-1 {{cannot find type 'NonExistent' in scope}}
+}
+
+public class DerivedFromNonExistent: NonExistent {
+  // expected-error@-1 {{cannot find type 'NonExistent' in scope}}
+
+  public func method() {}
+}