[SE-0296] Enable async/await by default.

CHANGELOG.md

@@ -25,6 +25,30 @@ CHANGELOG
 
 </details>
 
+Swift Next
+----------
+* [SE-0296][]:
+
+	Asynchronous programming is now natively supported using async/await. Asynchronous functions can be defined using `async`:
+
+	```swift
+	func loadWebResource(_ path: String) async throws -> Resource { ... }
+  func decodeImage(_ r1: Resource, _ r2: Resource) async throws -> Image
+  func dewarpAndCleanupImage(_ i : Image) async -> Image
+	```
+
+	Calls to `async` functions may suspend, meaning that they give up the thread on which they are executing and will be scheduled to run again later. The potential for suspension on asynchronous calls requires the `await` keyword, similarly to the way in which `try` acknowledges a call to a `throws` function:
+
+	```swift
+  func processImageData() async throws -> Image {
+    let dataResource  = try await loadWebResource("dataprofile.txt")
+    let imageResource = try await loadWebResource("imagedata.dat")
+    let imageTmp      = try await decodeImage(dataResource, imageResource)
+    let imageResult   = await dewarpAndCleanupImage(imageTmp)
+    return imageResult
+  }
+  ```
+
 Swift 5.4
 ---------
 
@@ -8178,6 +8202,7 @@ Swift 1.0
 [SE-0284]: <https://github.com/apple/swift-evolution/blob/main/proposals/0284-multiple-variadic-parameters.md>
 [SE-0286]: <https://github.com/apple/swift-evolution/blob/main/proposals/0286-forward-scan-trailing-closures.md>
 [SE-0287]: <https://github.com/apple/swift-evolution/blob/main/proposals/0287-implicit-member-chains.md>
+[SE-0296]: <https://github.com/apple/swift-evolution/blob/main/proposals/0296-async-await.md>
 
 [SR-75]: <https://bugs.swift.org/browse/SR-75>
 [SR-106]: <https://bugs.swift.org/browse/SR-106>

include/swift/AST/DiagnosticsParse.def

@@ -1229,9 +1229,6 @@ NOTE(super_in_closure_with_capture_here,none,
      "'self' explicitly captured here", ())
 
 WARNING(await_before_try,none, "'try' must precede 'await'", ())
-WARNING(warn_await_keyword,none, 
-      "future versions of Swift reserve the word 'await'; "
-      "if this name is unavoidable, use backticks to escape it", ())
 
 // Tuples and parenthesized expressions
 ERROR(expected_expr_in_expr_list,none,

lib/IDE/CodeCompletion.cpp

@@ -5818,15 +5818,12 @@ static void addObserverKeywords(CodeCompletionResultSink &Sink) {
   addKeyword(Sink, "didSet", CodeCompletionKeywordKind::None);
 }
 
-static void addExprKeywords(CodeCompletionResultSink &Sink,
-                            bool IsConcurrencyEnabled) {
+static void addExprKeywords(CodeCompletionResultSink &Sink) {
   // Expr keywords.
   addKeyword(Sink, "try", CodeCompletionKeywordKind::kw_try);
   addKeyword(Sink, "try!", CodeCompletionKeywordKind::kw_try);
   addKeyword(Sink, "try?", CodeCompletionKeywordKind::kw_try);
-  if (IsConcurrencyEnabled) {
-    addKeyword(Sink, "await", CodeCompletionKeywordKind::None);
-  }
+  addKeyword(Sink, "await", CodeCompletionKeywordKind::None);
 }
 
 static void addOpaqueTypeKeyword(CodeCompletionResultSink &Sink) {
@@ -5865,8 +5862,7 @@ void CodeCompletionCallbacksImpl::addKeywords(CodeCompletionResultSink &Sink,
     break;
 
   case CompletionKind::EffectsSpecifier: {
-    if (!llvm::is_contained(ParsedKeywords, "async") &&
-        Context.LangOpts.EnableExperimentalConcurrency)
+    if (!llvm::is_contained(ParsedKeywords, "async"))
       addKeyword(Sink, "async", CodeCompletionKeywordKind::None);
     if (!llvm::is_contained(ParsedKeywords, "throws"))
       addKeyword(Sink, "throws", CodeCompletionKeywordKind::kw_throws);
@@ -5902,7 +5898,7 @@ void CodeCompletionCallbacksImpl::addKeywords(CodeCompletionResultSink &Sink,
   case CompletionKind::ForEachSequence:
     addSuperKeyword(Sink);
     addLetVarKeywords(Sink);
-    addExprKeywords(Sink, Context.LangOpts.EnableExperimentalConcurrency);
+    addExprKeywords(Sink);
     addAnyTypeKeyword(Sink, CurDeclContext->getASTContext().TheAnyType);
     break;
 
@@ -6729,7 +6725,7 @@ void CodeCompletionCallbacksImpl::doneParsing() {
           addStmtKeywords(Sink, MaybeFuncBody);
           addSuperKeyword(Sink);
           addLetVarKeywords(Sink);
-          addExprKeywords(Sink, Context.LangOpts.EnableExperimentalConcurrency);
+          addExprKeywords(Sink);
           addAnyTypeKeyword(Sink, Context.TheAnyType);
           DoPostfixExprBeginning();
         }

lib/IDE/Refactoring.cpp

@@ -5219,9 +5219,6 @@ bool RefactoringActionConvertCallToAsyncAlternative::isApplicable(
     const ResolvedCursorInfo &CursorInfo, DiagnosticEngine &Diag) {
   using namespace asyncrefactorings;
 
-  if (!CursorInfo.SF->getASTContext().LangOpts.EnableExperimentalConcurrency)
-    return false;
-
   // Currently doesn't check that the call is in an async context. This seems
   // possibly useful in some situations, so we'll see what the feedback is.
   // May need to change in the future
@@ -5263,9 +5260,6 @@ bool RefactoringActionConvertToAsync::isApplicable(
     const ResolvedCursorInfo &CursorInfo, DiagnosticEngine &Diag) {
   using namespace asyncrefactorings;
 
-  if (!CursorInfo.SF->getASTContext().LangOpts.EnableExperimentalConcurrency)
-    return false;
-
   // As with the call refactoring, should possibly only apply if there's
   // actually calls to async alternatives. At the moment this will just add
   // `async` if there are no calls, which is probably fine.
@@ -5295,9 +5289,6 @@ bool RefactoringActionAddAsyncAlternative::isApplicable(
     const ResolvedCursorInfo &CursorInfo, DiagnosticEngine &Diag) {
   using namespace asyncrefactorings;
 
-  if (!CursorInfo.SF->getASTContext().LangOpts.EnableExperimentalConcurrency)
-    return false;
-
   auto *FD = findFunction(CursorInfo);
   if (!FD)
     return false;

lib/Parse/ParseExpr.cpp

@@ -337,8 +337,7 @@ ParserResult<Expr> Parser::parseExprSequence(Diag<> Message,
     case tok::identifier: {
       // 'async' followed by 'throws' or '->' implies that we have an arrow
       // expression.
-      if (!(shouldParseExperimentalConcurrency() &&
-            Tok.isContextualKeyword("async") &&
+      if (!(Tok.isContextualKeyword("async") &&
             peekToken().isAny(tok::arrow, tok::kw_throws)))
         goto done;
 
@@ -399,38 +398,33 @@ ParserResult<Expr> Parser::parseExprSequenceElement(Diag<> message,
   SyntaxParsingContext ElementContext(SyntaxContext,
                                       SyntaxContextKind::Expr);
 
-  if (shouldParseExperimentalConcurrency()) {
-    // A function called "async" is possible, so we don't want to replace it
-    // with await.
-    bool isReplaceableAsync = Tok.isContextualKeyword("async") &&
-                              !peekToken().is(tok::l_paren);
-    if (Tok.isContextualKeyword("await") || isReplaceableAsync) {
-      // Error on a replaceable async
-      if (isReplaceableAsync) {
-        diagnose(Tok.getLoc(), diag::expected_await_not_async)
-          .fixItReplace(Tok.getLoc(), "await");
-      }
-      SourceLoc awaitLoc = consumeToken();
-      ParserResult<Expr> sub =
-        parseExprSequenceElement(diag::expected_expr_after_await, isExprBasic);
-      if (!sub.hasCodeCompletion() && !sub.isNull()) {
-        if (auto anyTry = dyn_cast<AnyTryExpr>(sub.get())) {
-          // "try" must precede "await".
-          diagnose(awaitLoc, diag::await_before_try)
-            .fixItRemove(awaitLoc)
-            .fixItInsert(anyTry->getSubExpr()->getStartLoc(), "await ");
-        }
-
-        ElementContext.setCreateSyntax(SyntaxKind::AwaitExpr);
-        sub = makeParserResult(new (Context) AwaitExpr(awaitLoc, sub.get()));
+  // Check whether the user mistyped "async" for "await", but only in cases
+  // where we are sure that "async" would be ill-formed as an identifier.
+  bool isReplaceableAsync = Tok.isContextualKeyword("async") &&
+    !peekToken().isAtStartOfLine() &&
+    (peekToken().is(tok::identifier) || peekToken().is(tok::kw_try));
+  if (Tok.isContextualKeyword("await") || isReplaceableAsync) {
+    // Error on a replaceable async
+    if (isReplaceableAsync) {
+      diagnose(Tok.getLoc(), diag::expected_await_not_async)
+        .fixItReplace(Tok.getLoc(), "await");
+    }
+    SourceLoc awaitLoc = consumeToken();
+    ParserResult<Expr> sub =
+      parseExprSequenceElement(diag::expected_expr_after_await, isExprBasic);
+    if (!sub.hasCodeCompletion() && !sub.isNull()) {
+      if (auto anyTry = dyn_cast<AnyTryExpr>(sub.get())) {
+        // "try" must precede "await".
+        diagnose(awaitLoc, diag::await_before_try)
+          .fixItRemove(awaitLoc)
+          .fixItInsert(anyTry->getSubExpr()->getStartLoc(), "await ");
       }
 
-     return sub;
+      ElementContext.setCreateSyntax(SyntaxKind::AwaitExpr);
+      sub = makeParserResult(new (Context) AwaitExpr(awaitLoc, sub.get()));
     }
-  } else if (Tok.isContextualKeyword("await")) {
-    // warn that future versions of Swift will parse this token differently.
-    diagnose(Tok.getLoc(), diag::warn_await_keyword)
-      .fixItReplace(Tok.getLoc(), "`await`");
+
+   return sub;
   }
 
   SourceLoc tryLoc;

lib/Parse/ParsePattern.cpp

@@ -825,8 +825,7 @@ bool Parser::isEffectsSpecifier(const Token &T) {
   // NOTE: If this returns 'true', that token must be handled in
   //       'parseEffectsSpecifiers()'.
 
-  if (shouldParseExperimentalConcurrency() &&
-      T.isContextualKeyword("async"))
+  if (T.isContextualKeyword("async"))
     return true;
 
   if (T.isAny(tok::kw_throws, tok::kw_rethrows) ||
@@ -844,8 +843,7 @@ ParserStatus Parser::parseEffectsSpecifiers(SourceLoc existingArrowLoc,
 
   while (true) {
     // 'async'
-    if (shouldParseExperimentalConcurrency() &&
-        Tok.isContextualKeyword("async")) {
+    if (Tok.isContextualKeyword("async")) {
 
       if (asyncLoc.isValid()) {
         diagnose(Tok, diag::duplicate_effects_specifier, Tok.getText())

lib/Parse/ParseStmt.cpp

@@ -2128,10 +2128,10 @@ ParserResult<Stmt> Parser::parseStmtForEach(LabeledStmtInfo LabelInfo) {
   SourceLoc TryLoc;
 
   if (shouldParseExperimentalConcurrency() && 
-    Tok.isContextualKeyword("await")) {
+      Tok.isContextualKeyword("await")) {
     AwaitLoc = consumeToken();
-  } if (shouldParseExperimentalConcurrency() && 
-    Tok.is(tok::kw_try)) {
+  } else if (shouldParseExperimentalConcurrency() &&
+      Tok.is(tok::kw_try)) {
     TryLoc = consumeToken();
     if (Tok.isContextualKeyword("await")) {
       AwaitLoc = consumeToken();

lib/Parse/ParseType.cpp

@@ -1108,8 +1108,7 @@ ParserResult<TypeRepr> Parser::parseTypeTupleBody() {
 
   bool isFunctionType =
       Tok.isAny(tok::arrow, tok::kw_throws, tok::kw_rethrows) ||
-      (shouldParseExperimentalConcurrency() &&
-       Tok.isContextualKeyword("async"));
+      Tok.isContextualKeyword("async");
 
   // If there were any labels, figure out which labels should go into the type
   // representation.

test/Concurrency/await_typo_correction.swift

@@ -29,3 +29,8 @@ func async() throws { }
     try async()
   }
 }
+
+func varNamedAsync(async: Bool) async {
+  if async { }
+  let _ = async
+}

test/SourceKit/Refactoring/basic.swift

@@ -166,10 +166,8 @@ func hasCallToAsyncAlternative() {
 // RUN: %sourcekitd-test -req=cursor -pos=117:16  -cursor-action %s -- %s | %FileCheck %s -check-prefix=CHECK-GLOBAL
 // RUN: %sourcekitd-test -req=cursor -pos=117:17  -cursor-action %s -- %s | %FileCheck %s -check-prefix=CHECK-GLOBAL
 
-// RUN: %sourcekitd-test -req=cursor -pos=119:6  -cursor-action %s -- -Xfrontend -enable-experimental-concurrency %s | %FileCheck %s -check-prefix=CHECK-ASYNC
-// RUN: %sourcekitd-test -req=cursor -pos=121:3  -cursor-action %s -- -Xfrontend -enable-experimental-concurrency %s | %FileCheck %s -check-prefix=CHECK-CALLASYNC
-// RUN: %sourcekitd-test -req=cursor -pos=119:6  -cursor-action %s -- %s | %FileCheck %s -check-prefix=CHECK-NOASYNC
-// RUN: %sourcekitd-test -req=cursor -pos=121:3  -cursor-action %s -- %s | %FileCheck %s -check-prefix=CHECK-NOASYNC
+// RUN: %sourcekitd-test -req=cursor -pos=119:6  -cursor-action %s -- %s | %FileCheck %s -check-prefix=CHECK-ASYNC
+// RUN: %sourcekitd-test -req=cursor -pos=121:3  -cursor-action %s -- %s | %FileCheck %s -check-prefix=CHECK-CALLASYNC
 
 // RUN: %sourcekitd-test -req=cursor -pos=35:10 -end-pos=35:16 -cursor-action %s -- %s | %FileCheck %s -check-prefix=CHECK-RENAME-EXTRACT
 // RUN: %sourcekitd-test -req=cursor -pos=35:10 -end-pos=35:16 -cursor-action %s -- %s | %FileCheck %s -check-prefix=CHECK-RENAME-EXTRACT
@@ -258,10 +256,4 @@ func hasCallToAsyncAlternative() {
 // CHECK-ASYNC-NOT: source.refactoring.kind.convert.func-to-async
 // CHECK-CALLASYNC: ACTIONS END
 
-// CHECK-NOASYNC: ACTIONS BEGIN
-// CHECK-NOASYNC-NOT: source.refactoring.kind.add.async-alternative
-// CHECK-NOASYNC-NOT: source.refactoring.kind.convert.func-to-async
-// CHECK-NOASYNC-NOT: source.refactoring.kind.convert.call-to-async
-// CHECK-NOASYNC: ACTIONS END
-
 // REQUIRES: OS=macosx || OS=linux-gnu