AST: Fix crashes when name lookup finds declarations outside of a protocol or extension that's nested in another type

When performing a name lookup from inside of a protocol
or extension, skip directly to the source file context
when we are done visiting the protocol or extension.

Otherwise, if we have invalid code where the protocol
or extension is nested inside another type, we might
find a member whose type contains generic parameters
of the outer type; these parameters will not resolve,
since we do not model protocols or extensions nested
inside generic contexts (yet?).

This supercedes an earlier workaround for a similar
issue; the new workaround fixes more crashes.

This is needed to avoid crasher regressions with an
upcoming patch.

Author: slavapestov

include/swift/AST/DeclContext.h

@@ -363,6 +363,9 @@ class alignas(1 << DeclContextAlignInBits) DeclContext {
     return ParentAndKind.getPointer();
   }
 
+  /// Returns the semantic parent for purposes of name lookup.
+  DeclContext *getParentForLookup() const;
+
   /// Return true if this is a child of the specified other decl context.
   bool isChildContextOf(const DeclContext *Other) const {
     if (this == Other) return false;

lib/AST/DeclContext.cpp

@@ -406,6 +406,16 @@ Decl *DeclContext::getInnermostDeclarationDeclContext() {
   return nullptr;
 }
 
+DeclContext *DeclContext::getParentForLookup() const {
+  if (isa<ProtocolDecl>(this) || isa<ExtensionDecl>(this)) {
+    // If we are inside a protocol or an extension, skip directly
+    // to the module scope context, without looking at any (invalid)
+    // outer types.
+    return getModuleScopeContext();
+  }
+  return getParent();
+}
+
 ModuleDecl *DeclContext::getParentModule() const {
   const DeclContext *DC = this;
   while (!DC->isModuleContext())

lib/AST/NameLookup.cpp

@@ -857,7 +857,7 @@ UnqualifiedLookup::UnqualifiedLookup(DeclName Name, DeclContext *DC,
           }
         }
 
-        DC = DC->getParent();
+        DC = DC->getParentForLookup();
       }
 
       if (!isCascadingUse.hasValue())

lib/Sema/TypeCheckType.cpp

@@ -330,11 +330,6 @@ findDeclContextForType(TypeChecker &TC,
     }
 
     // We're going to check the next parent context.
-
-    // FIXME: Horrible hack. Don't allow us to reference a generic parameter
-    // from a context outside a ProtocolDecl.
-    if (isa<ProtocolDecl>(parentDC) && isa<GenericTypeParamDecl>(typeDecl))
-      return std::make_tuple(Type(), false);
   }
 
   // If we didn't find the member in an immediate parent context and
@@ -447,11 +442,6 @@ findDeclContextForType(TypeChecker &TC,
       // If not, walk into the refined protocols, if any.
       pushRefined(protoDecl);
     }
-
-    // FIXME: Horrible hack. Don't allow us to reference a generic parameter
-    // or associated type from a context outside a ProtocolDecl.
-    if (isa<ProtocolDecl>(parentDC) && isa<AbstractTypeParamDecl>(typeDecl))
-      return std::make_tuple(Type(), false);
   }
 
   assert(false && "Should have found context by now");
@@ -943,7 +933,7 @@ static Type diagnoseUnknownType(TypeChecker &tc, DeclContext *dc,
     // Try ignoring access control.
     DeclContext *lookupDC = dc;
     if (options.contains(TR_GenericSignature))
-      lookupDC = dc->getParent();
+      lookupDC = dc->getParentForLookup();
 
     NameLookupOptions relookupOptions = lookupOptions;
     relookupOptions |= NameLookupFlags::KnownPrivate;
@@ -1232,8 +1222,7 @@ resolveTopLevelIdentTypeComponent(TypeChecker &TC, DeclContext *DC,
     if (!DC->isCascadingContextForLookup(/*excludeFunctions*/false))
       options |= TR_KnownNonCascadingDependency;
 
-    // The remaining lookups will be in the parent context.
-    lookupDC = DC->getParent();
+    lookupDC = DC->getParentForLookup();
   }
 
   // We need to be able to perform unqualified lookup into the given

test/decl/nested/protocol.swift

@@ -7,15 +7,15 @@ struct OuterGeneric<D> {
   protocol InnerProtocol { // expected-error{{protocol 'InnerProtocol' cannot be nested inside another declaration}}
     associatedtype Rooster
     func flip(_ r: Rooster)
-    func flop(_ t: D)
+    func flop(_ t: D) // expected-error{{use of undeclared type 'D'}}
   }
 }
 
 class OuterGenericClass<T> {
   protocol InnerProtocol { // expected-error{{protocol 'InnerProtocol' cannot be nested inside another declaration}}
     associatedtype Rooster
     func flip(_ r: Rooster)
-    func flop(_ t: T)
+    func flop(_ t: T) // expected-error{{use of undeclared type 'T'}}
   }
 }
 
@@ -25,7 +25,7 @@ protocol OuterProtocol {
   // expected-note@-1 {{did you mean 'InnerProtocol'?}}
     associatedtype Rooster
     func flip(_ r: Rooster)
-    func flop(_ h: Hen)
+    func flop(_ h: Hen) // expected-error{{use of undeclared type 'Hen'}}
   }
 }
 

validation-test/IDE/crashers_2/0010-reference-to-self-in-extension-init.swift

@@ -0,0 +1,6 @@
+// RUN: %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
+
+extension Integer { 
+#^A^#
+  extension {
+        var : Self   

validation-test/IDE/crashers_2_fixed/0010-reference-to-self-in-extension-init.swift

@@ -6,5 +6,5 @@
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
 // REQUIRES: asserts
-// RUN: not --crash %target-swift-frontend %s -emit-ir
+// RUN: not %target-swift-frontend %s -emit-ir
 protocol P{class a}class C:P{protocol A:a

validation-test/compiler_crashers/28701-false-should-have-found-context-by-now.swift renamed to validation-test/compiler_crashers_fixed/28701-false-should-have-found-context-by-now.swift

@@ -6,5 +6,5 @@
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
 // REQUIRES: asserts
-// RUN: not --crash %target-swift-frontend %s -emit-ir
+// RUN: not %target-swift-frontend %s -emit-ir
 struct B{let f=a}protocol P{}extension P{extension{func&(U=

validation-test/compiler_crashers/28725-gpdecl-getdepth-generictypeparamdecl-invaliddepth-parameter-hasnt-been-validated.swift renamed to validation-test/compiler_crashers_fixed/28725-gpdecl-getdepth-generictypeparamdecl-invaliddepth-parameter-hasnt-been-validated.swift

@@ -6,5 +6,5 @@
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
 // REQUIRES: asserts
-// RUN: not --crash %target-swift-frontend %s -emit-ir
+// RUN: not %target-swift-frontend %s -emit-ir
 protocol P}extension P{lazy var f={extension{var f=((self

validation-test/compiler_crashers/28727-objectty-haserror-cannot-have-errortype-wrapped-inside-lvaluetype.swift renamed to validation-test/compiler_crashers_fixed/28727-objectty-haserror-cannot-have-errortype-wrapped-inside-lvaluetype.swift

@@ -6,7 +6,7 @@
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
 // REQUIRES: asserts
-// RUN: not --crash %target-swift-frontend %s -emit-ir
+// RUN: not %target-swift-frontend %s -emit-ir
 protocol P{
 protocol
 P{typealias a{}struct B{extension{protocol P{

validation-test/compiler_crashers/28729-archetype-bad-generic-context-nesting.swift renamed to validation-test/compiler_crashers_fixed/28729-archetype-bad-generic-context-nesting.swift

@@ -6,7 +6,7 @@
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
 // REQUIRES: asserts
-// RUN: not --crash %target-swift-frontend %s -emit-ir
+// RUN: not %target-swift-frontend %s -emit-ir
 protocol P{typealias a
 struct A{{}func a:a
 {

validation-test/compiler_crashers/28734-conformingreplacementtype-is-substitutabletype-conformingreplacementtype-is-depe.swift renamed to validation-test/compiler_crashers_fixed/28734-conformingreplacementtype-is-substitutabletype-conformingreplacementtype-is-depe.swift

@@ -6,5 +6,5 @@
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
 // REQUIRES: asserts
-// RUN: not --crash %target-swift-frontend %s -emit-ir
+// RUN: not %target-swift-frontend %s -emit-ir
 protocol A{protocol A:A{class a{let c=a}typealias a

validation-test/compiler_crashers/28735-reftype-hastypeparameter-cannot-have-a-dependent-type-here.swift renamed to validation-test/compiler_crashers_fixed/28735-reftype-hastypeparameter-cannot-have-a-dependent-type-here.swift

@@ -5,6 +5,6 @@
 // See https://swift.org/LICENSE.txt for license information
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
-// RUN: not --crash %target-swift-frontend %s -emit-ir
+// RUN: not %target-swift-frontend %s -emit-ir
 protocol A{{}struct A{typealias a:Self
 protocol P{extension{lazy var f=A.a