[Strict memory safety] Only diagnose unsafe types in the canonical type

Typealiases involving unsafe types that resolve to safe types
should not be diagnosed.

(cherry picked from commit 0405f61)

Author: DougGregor

lib/AST/Decl.cpp

@@ -1212,12 +1212,14 @@ ExplicitSafety Decl::getExplicitSafety() const {
                              ExplicitSafety::Unspecified);
   }
 
-  // Inference: Check the enclosing context.
-  if (auto enclosingDC = getDeclContext()) {
-    // Is this an extension with @safe or @unsafe on it?
-    if (auto ext = dyn_cast<ExtensionDecl>(enclosingDC)) {
-      if (auto extSafety = getExplicitSafetyFromAttrs(ext))
-        return *extSafety;
+  // Inference: Check the enclosing context, unless this is a type.
+  if (!isa<TypeDecl>(this)) {
+    if (auto enclosingDC = getDeclContext()) {
+      // Is this an extension with @safe or @unsafe on it?
+      if (auto ext = dyn_cast<ExtensionDecl>(enclosingDC)) {
+        if (auto extSafety = getExplicitSafetyFromAttrs(ext))
+          return *extSafety;
+      }
     }
   }
 

lib/Sema/TypeCheckUnsafe.cpp

@@ -375,21 +375,28 @@ void swift::diagnoseUnsafeType(ASTContext &ctx, SourceLoc loc, Type type,
   if (!ctx.LangOpts.hasFeature(Feature::StrictMemorySafety))
     return;
 
-  if (!type->isUnsafe() && !type->getCanonicalType()->isUnsafe())
+  if (!type->getCanonicalType()->isUnsafe())
     return;
 
-  // Look for a specific @unsafe nominal type.
-  Type specificType;
-  type.findIf([&specificType](Type type) {
-    if (auto typeDecl = type->getAnyNominal()) {
-      if (typeDecl->getExplicitSafety() == ExplicitSafety::Unsafe) {
-        specificType = type;
-        return false;
+  // Look for a specific @unsafe nominal type along the way.
+  auto findSpecificUnsafeType = [](Type type) {
+    Type specificType;
+    (void)type.findIf([&specificType](Type type) {
+      if (auto typeDecl = type->getAnyNominal()) {
+        if (typeDecl->getExplicitSafety() == ExplicitSafety::Unsafe) {
+          specificType = type;
+          return false;
+        }
       }
-    }
 
-    return false;
-  });
+      return false;
+    });
+    return specificType;
+  };
+
+  Type specificType = findSpecificUnsafeType(type);
+  if (!specificType)
+    specificType = findSpecificUnsafeType(type->getCanonicalType());
 
   diagnose(specificType ? specificType : type);
 }

test/Unsafe/safe.swift

@@ -271,3 +271,16 @@ struct UnsafeWrapTest {
 
 @safe @unsafe
 struct ConfusedStruct { } // expected-error{{struct 'ConfusedStruct' cannot be both @safe and @unsafe}}
+
+@unsafe
+struct UnsafeContainingUnspecified {
+  typealias A = Int
+
+  func getA() -> A { 0 }
+}
+
+
+@unsafe func f(x: UnsafeContainingUnspecified) {
+  let a = unsafe x.getA()
+  _ = a
+}