[Concurrency] Implement parsing and semantic analysis of await operator

include/swift/AST/DiagnosticsParse.def

@@ -1256,6 +1256,10 @@ ERROR(expected_colon_after_if_question,none,
       "expected ':' after '? ...' in ternary expression", ())
 ERROR(expected_expr_after_if_colon,none,
       "expected expression after '? ... :' in ternary expression", ())
+ERROR(expected_expr_after_try, none,
+      "expected expression after 'try'", ())
+ERROR(expected_expr_after_await, none,
+      "expected expression after 'await'", ())
 
 // Cast expressions
 ERROR(expected_type_after_is,none,

include/swift/AST/DiagnosticsSema.def

@@ -3320,7 +3320,7 @@ ERROR(missing_builtin_precedence_group,none,
       (Identifier))
 
 // If you change this, also change enum TryKindForDiagnostics.
-#define TRY_KIND_SELECT(SUB) "%select{try|try!|try?}" #SUB
+#define TRY_KIND_SELECT(SUB) "%select{try|try!|try?|await}" #SUB
 
 ERROR(try_rhs,none,
       "'" TRY_KIND_SELECT(0) "' cannot appear to the right of a "
@@ -4019,6 +4019,10 @@ NOTE(note_error_to_optional,none,
       "did you mean to handle error as optional value?", ())
 NOTE(note_disable_error_propagation,none,
       "did you mean to disable error propagation?", ())
+ERROR(async_call_without_await,none,
+      "call is 'async' but is not marked with 'await'", ())
+WARNING(no_async_in_await,none,
+        "no calls to 'async' functions occur within 'await' expression", ())
 
 WARNING(no_throw_in_try,none,
         "no calls to throwing functions occur within 'try' expression", ())

include/swift/AST/Expr.h

@@ -1964,7 +1964,7 @@ class TryExpr : public AnyTryExpr {
 /// ForceTryExpr - A 'try!' surrounding an expression, marking that
 /// the expression contains code which might throw, but that the code
 /// should dynamically assert if it does.
-class ForceTryExpr : public AnyTryExpr {
+class ForceTryExpr final : public AnyTryExpr {
   SourceLoc ExclaimLoc;
 
 public:
@@ -1983,7 +1983,7 @@ class ForceTryExpr : public AnyTryExpr {
 /// A 'try?' surrounding an expression, marking that the expression contains
 /// code which might throw, and that the result should be injected into an
 /// Optional. If the code does throw, \c nil is produced.
-class OptionalTryExpr : public AnyTryExpr {
+class OptionalTryExpr final : public AnyTryExpr {
   SourceLoc QuestionLoc;
 
 public:
@@ -2002,7 +2002,6 @@ class OptionalTryExpr : public AnyTryExpr {
 /// An expression node that does not affect the evaluation of its subexpression.
 class IdentityExpr : public Expr {
   Expr *SubExpr;
-
 public:
   IdentityExpr(ExprKind kind,
                Expr *subExpr, Type ty = Type(),
@@ -2093,6 +2092,32 @@ class ParenExpr : public IdentityExpr {
   static bool classof(const Expr *E) { return E->getKind() == ExprKind::Paren; }
 };
 
+/// AwaitExpr - An 'await' surrounding an expression, marking that the
+/// expression contains code which is a coroutine that may block.
+///
+/// getSemanticsProvidingExpr() looks through this because it doesn't
+/// provide the value and only very specific clients care where the
+/// 'await' was written.
+class AwaitExpr final : public IdentityExpr {
+  SourceLoc AwaitLoc;
+public:
+  AwaitExpr(SourceLoc awaitLoc, Expr *sub, Type type = Type(),
+            bool implicit = false)
+    : IdentityExpr(ExprKind::Await, sub, type, implicit), AwaitLoc(awaitLoc) {
+  }
+
+  SourceLoc getLoc() const { return AwaitLoc; }
+
+  SourceLoc getAwaitLoc() const { return AwaitLoc; }
+  SourceLoc getStartLoc() const { return AwaitLoc; }
+  SourceLoc getEndLoc() const { return getSubExpr()->getEndLoc(); }
+
+  static bool classof(const Expr *e) {
+    return e->getKind() == ExprKind::Await;
+  }
+};
+
+
 /// TupleExpr - Parenthesized expressions like '(a: x+x)' and '(x, y, 4)'.  Also
 /// used to represent the operands to a binary operator.  Note that
 /// expressions like '(4)' are represented with a ParenExpr.
@@ -3691,6 +3716,9 @@ class AbstractClosureExpr : public DeclContext, public Expr {
   /// Return whether this closure is throwing when fully applied.
   bool isBodyThrowing() const;
 
+  /// \brief Return whether this closure is async when fully applied.
+  bool isBodyAsync() const;
+
   /// Whether this closure consists of a single expression.
   bool hasSingleExpressionBody() const;
 

include/swift/AST/ExprNodes.def

@@ -103,7 +103,8 @@ UNCHECKED_EXPR(Sequence, Expr)
 ABSTRACT_EXPR(Identity, Expr)
   EXPR(Paren, IdentityExpr)
   EXPR(DotSelf, IdentityExpr)
-  EXPR_RANGE(Identity, Paren, DotSelf)
+  EXPR(Await, IdentityExpr)
+  EXPR_RANGE(Identity, Paren, Await)
 ABSTRACT_EXPR(AnyTry, Expr)
   EXPR(Try, AnyTryExpr)
   EXPR(ForceTry, AnyTryExpr)

lib/AST/ASTDumper.cpp

@@ -2130,6 +2130,13 @@ class PrintExpr : public ExprVisitor<PrintExpr> {
     printRec(E->getSubExpr());
     PrintWithColorRAII(OS, ParenthesisColor) << ')';
   }
+  void visitAwaitExpr(AwaitExpr *E) {
+    printCommon(E, "await_expr");
+    OS << '\n';
+    printRec(E->getSubExpr());
+    PrintWithColorRAII(OS, ParenthesisColor) << ')';
+  }
+
   void visitTupleExpr(TupleExpr *E) {
     printCommon(E, "tuple_expr");
     if (E->hasTrailingClosure())

lib/AST/Expr.cpp

@@ -289,6 +289,7 @@ ConcreteDeclRef Expr::getReferencedDecl(bool stopAtParenExpr) const {
                ->getSubExpr()->getReferencedDecl(stopAtParenExpr);
 
   PASS_THROUGH_REFERENCE(DotSelf, getSubExpr);
+  PASS_THROUGH_REFERENCE(Await, getSubExpr);
   PASS_THROUGH_REFERENCE(Try, getSubExpr);
   PASS_THROUGH_REFERENCE(ForceTry, getSubExpr);
   PASS_THROUGH_REFERENCE(OptionalTry, getSubExpr);
@@ -623,6 +624,7 @@ bool Expr::canAppendPostfixExpression(bool appendingPostfixOperator) const {
   case ExprKind::DynamicType:
     return true;
 
+  case ExprKind::Await:
   case ExprKind::Try:
   case ExprKind::ForceTry:
   case ExprKind::OptionalTry:
@@ -1929,10 +1931,17 @@ Type AbstractClosureExpr::getResultType(
 bool AbstractClosureExpr::isBodyThrowing() const {
   if (getType()->hasError())
     return false;
-
+  
   return getType()->castTo<FunctionType>()->getExtInfo().throws();
 }
 
+bool AbstractClosureExpr::isBodyAsync() const {
+  if (getType()->hasError())
+    return false;
+
+  return getType()->castTo<FunctionType>()->getExtInfo().async();
+}
+
 bool AbstractClosureExpr::hasSingleExpressionBody() const {
   if (auto closure = dyn_cast<ClosureExpr>(this))
     return closure->hasSingleExpressionBody();
@@ -2485,3 +2494,4 @@ const UnifiedStatsReporter::TraceFormatter*
 FrontendStatsTracer::getTraceFormatter<const Expr *>() {
   return &TF;
 }
+

lib/Parse/ParseExpr.cpp

@@ -379,9 +379,10 @@ ParserResult<Expr> Parser::parseExprSequence(Diag<> Message,
 /// parseExprSequenceElement
 ///
 ///   expr-sequence-element(Mode):
-///     'try' expr-unary(Mode)
-///     'try' '?' expr-unary(Mode)
-///     'try' '!' expr-unary(Mode)
+///     '__await' expr-sequence-element(Mode)
+///     'try' expr-sequence-element(Mode)
+///     'try' '?' expr-sequence-element(Mode)
+///     'try' '!' expr-sequence-element(Mode)
 ///     expr-unary(Mode)
 ///
 /// 'try' is not actually allowed at an arbitrary position of a
@@ -390,6 +391,19 @@ ParserResult<Expr> Parser::parseExprSequenceElement(Diag<> message,
                                                     bool isExprBasic) {
   SyntaxParsingContext ElementContext(SyntaxContext,
                                       SyntaxContextKind::Expr);
+
+  if (Context.LangOpts.EnableExperimentalConcurrency &&
+      Tok.is(tok::kw___await)) {
+    SourceLoc awaitLoc = consumeToken(tok::kw___await);
+    ParserResult<Expr> sub = parseExprUnary(message, isExprBasic);
+    if (!sub.hasCodeCompletion() && !sub.isNull()) {
+      ElementContext.setCreateSyntax(SyntaxKind::TryExpr);
+      sub = makeParserResult(new (Context) AwaitExpr(awaitLoc, sub.get()));
+    }
+
+    return sub;
+  }
+
   SourceLoc tryLoc;
   bool hadTry = consumeIf(tok::kw_try, tryLoc);
   Optional<Token> trySuffix;

lib/Parse/ParseStmt.cpp

@@ -71,7 +71,7 @@ bool Parser::isStartOfStmt() {
 
   case tok::kw_try: {
     // "try" cannot actually start any statements, but we parse it there for
-    // better recovery.
+    // better recovery in cases like 'try return'.
     Parser::BacktrackingScope backtrack(*this);
     consumeToken(tok::kw_try);
     return isStartOfStmt();