[Parser] Parse 'each' as a contextual keyword applied to pack references.

Author: hborla

lib/Parse/ParsePattern.cpp

@@ -162,7 +162,8 @@ bool Parser::startsParameterName(bool isClosure) {
     // If the first name wasn't "isolated", we're done.
     if (!Tok.isContextualKeyword("isolated") &&
         !Tok.isContextualKeyword("some") &&
-        !Tok.isContextualKeyword("any"))
+        !Tok.isContextualKeyword("any") &&
+        !Tok.isContextualKeyword("each"))
       return true;
 
     // "isolated" can be an argument label, but it's also a contextual keyword,

lib/Parse/ParseType.cpp

@@ -780,8 +780,8 @@ Parser::parseTypeIdentifier(bool isParsingQualifiedDeclBaseType) {
 ///     type-composition '&' type-simple
 ParserResult<TypeRepr>
 Parser::parseTypeSimpleOrComposition(Diag<> MessageID, ParseTypeReason reason) {
-  // Check for the opaque modifier.
-  // This is only semantically allowed in certain contexts, but we parse it
+  // Check for the contextual keyword modifiers on types.
+  // These are only semantically allowed in certain contexts, but we parse it
   // generally for diagnostics and recovery.
   SourceLoc opaqueLoc;
   SourceLoc anyLoc;
@@ -793,6 +793,16 @@ Parser::parseTypeSimpleOrComposition(Diag<> MessageID, ParseTypeReason reason) {
     // Treat any as a keyword.
     TokReceiver->registerTokenKindChange(Tok.getLoc(), tok::contextual_keyword);
     anyLoc = consumeToken();
+  } else if (Tok.isContextualKeyword("each")) {
+    // Treat 'each' as a keyword.
+    TokReceiver->registerTokenKindChange(Tok.getLoc(), tok::contextual_keyword);
+    SourceLoc eachLoc = consumeToken();
+    ParserResult<TypeRepr> packRef = parseTypeSimple(MessageID, reason);
+    if (packRef.isNull())
+      return packRef;
+
+    auto *typeRepr = new (Context) PackReferenceTypeRepr(eachLoc, packRef.get());
+    return makeParserResult(ParserStatus(packRef), typeRepr);
   }
 
   auto applyOpaque = [&](TypeRepr *type) -> TypeRepr * {
@@ -1393,6 +1403,8 @@ bool Parser::canParseType() {
     consumeToken();
   } else if (Tok.isContextualKeyword("any")) {
     consumeToken();
+  } else if (Tok.isContextualKeyword("each")) {
+    consumeToken();
   }
 
   switch (Tok.getKind()) {

lib/Sema/TypeCheckDecl.cpp

@@ -2261,6 +2261,7 @@ static Type validateParameterType(ParamDecl *decl) {
     // @escaping in this case.
     options.setContext(TypeResolverContext::VariadicFunctionInput);
     options |= TypeResolutionFlags::Direct;
+    options |= TypeResolutionFlags::AllowPackReferences;
 
     // FIXME: This duplicates code found elsewhere
     auto *patternRepr = packExpansionRepr->getPatternType();

lib/Sema/TypeCheckType.cpp

@@ -4268,7 +4268,7 @@ NeverNullType TypeResolver::resolvePackReference(PackReferenceTypeRepr *repr,
     ctx.Diags.diagnose(repr->getLoc(),
                        diag::pack_reference_outside_expansion,
                        packReference);
-    return packReference;
+    return ErrorType::get(ctx);
   }
 
   return packReference;

test/type/pack_expansion.swift

@@ -63,4 +63,14 @@ struct Outer<T...> {
   struct AlsoGood<U...> {
     typealias Value = ((T, E<U... >)...)
   }
-}
+}
+
+func packRef<T...>(_: (each T)...) where each T: P {}
+
+func packMemberRef<T...>(_: (each T.T)...) where each T: P {}
+
+// expected-error@+1 {{'each' cannot be applied to non-pack type 'Int'}}
+func invalidPackRef(_: each Int) {}
+
+// expected-error@+1 {{pack reference 'T' can only appear in pack expansion or generic requirement}}
+func packRefOutsideExpansion<T...>(_: each T) {}