[borrow-expr] Add simple support for borrow-expr but don't wire it up to anything.

Author: gottesmm

include/swift/AST/DiagnosticsParse.def

@@ -1348,6 +1348,10 @@ ERROR(expected_expr_after_try, none,
       "expected expression after 'try'", ())
 ERROR(expected_expr_after_await, none,
       "expected expression after 'await'", ())
+ERROR(expected_expr_after_move, none,
+      "expected expression after '_move'", ())
+ERROR(expected_expr_after_borrow, none,
+      "expected expression after '_borrow'", ())
 
 // Cast expressions
 ERROR(expected_type_after_is,none,

include/swift/AST/Expr.h

@@ -2076,6 +2076,37 @@ class MoveExpr final : public IdentityExpr {
   static bool classof(const Expr *e) { return e->getKind() == ExprKind::Move; }
 };
 
+/// BorrowExpr - A 'borrow' surrounding an lvalue/accessor expression at an
+/// apply site marking the lvalue/accessor as being borrowed when passed to the
+/// callee.
+///
+/// getSemanticsProvidingExpr() looks through this because it doesn't
+/// provide the value and only very specific clients care where the
+/// 'borrow' was written.
+class BorrowExpr final : public IdentityExpr {
+  SourceLoc BorrowLoc;
+
+public:
+  BorrowExpr(SourceLoc borrowLoc, Expr *sub, Type type = Type(),
+             bool implicit = false)
+      : IdentityExpr(ExprKind::Borrow, sub, type, implicit),
+        BorrowLoc(borrowLoc) {}
+
+  static BorrowExpr *createImplicit(ASTContext &ctx, SourceLoc borrowLoc,
+                                    Expr *sub, Type type = Type()) {
+    return new (ctx) BorrowExpr(borrowLoc, sub, type, /*implicit=*/true);
+  }
+
+  SourceLoc getLoc() const { return BorrowLoc; }
+
+  SourceLoc getStartLoc() const { return BorrowLoc; }
+  SourceLoc getEndLoc() const { return getSubExpr()->getEndLoc(); }
+
+  static bool classof(const Expr *e) {
+    return e->getKind() == ExprKind::Borrow;
+  }
+};
+
 /// TupleExpr - Parenthesized expressions like '(a: x+x)' and '(x, y, 4)'. Note
 /// that expressions like '(4)' are represented with a ParenExpr.
 class TupleExpr final : public Expr,

include/swift/AST/ExprNodes.def

@@ -108,6 +108,7 @@ ABSTRACT_EXPR(Identity, Expr)
   EXPR(DotSelf, IdentityExpr)
   EXPR(Await, IdentityExpr)
   EXPR(Move, IdentityExpr)
+  EXPR(Borrow, IdentityExpr)
   EXPR(UnresolvedMemberChainResult, IdentityExpr)
   EXPR_RANGE(Identity, Paren, UnresolvedMemberChainResult)
 ABSTRACT_EXPR(AnyTry, Expr)

lib/AST/ASTDumper.cpp

@@ -2191,6 +2191,12 @@ class PrintExpr : public ExprVisitor<PrintExpr> {
     printRec(E->getSubExpr());
     PrintWithColorRAII(OS, ParenthesisColor) << ')';
   }
+  void visitBorrowExpr(BorrowExpr *E) {
+    printCommon(E, "borrow_expr");
+    OS << '\n';
+    printRec(E->getSubExpr());
+    PrintWithColorRAII(OS, ParenthesisColor) << ')';
+  }
   void visitUnresolvedMemberChainResultExpr(UnresolvedMemberChainResultExpr *E){
     printCommon(E, "unresolved_member_chain_expr");
     OS << '\n';

lib/AST/ASTPrinter.cpp

@@ -4689,6 +4689,11 @@ void PrintAST::visitMoveExpr(MoveExpr *expr) {
   visit(expr->getSubExpr());
 }
 
+void PrintAST::visitBorrowExpr(BorrowExpr *expr) {
+  Printer << "borrow ";
+  visit(expr->getSubExpr());
+}
+
 void PrintAST::visitInOutExpr(InOutExpr *expr) {
   visit(expr->getSubExpr());
 }

lib/AST/Expr.cpp

@@ -370,6 +370,7 @@ ConcreteDeclRef Expr::getReferencedDecl(bool stopAtParenExpr) const {
   PASS_THROUGH_REFERENCE(DotSelf, getSubExpr);
   PASS_THROUGH_REFERENCE(Await, getSubExpr);
   PASS_THROUGH_REFERENCE(Move, getSubExpr);
+  PASS_THROUGH_REFERENCE(Borrow, getSubExpr);
   PASS_THROUGH_REFERENCE(Try, getSubExpr);
   PASS_THROUGH_REFERENCE(ForceTry, getSubExpr);
   PASS_THROUGH_REFERENCE(OptionalTry, getSubExpr);
@@ -729,6 +730,7 @@ bool Expr::canAppendPostfixExpression(bool appendingPostfixOperator) const {
 
   case ExprKind::Await:
   case ExprKind::Move:
+  case ExprKind::Borrow:
   case ExprKind::Try:
   case ExprKind::ForceTry:
   case ExprKind::OptionalTry:
@@ -914,6 +916,7 @@ bool Expr::isValidParentOfTypeExpr(Expr *typeExpr) const {
   case ExprKind::Paren:
   case ExprKind::Await:
   case ExprKind::Move:
+  case ExprKind::Borrow:
   case ExprKind::UnresolvedMemberChainResult:
   case ExprKind::Try:
   case ExprKind::ForceTry:

lib/Parse/ParseExpr.cpp

@@ -370,6 +370,7 @@ ParserResult<Expr> Parser::parseExprSequence(Diag<> Message,
 ///     'try' '?' expr-sequence-element(Mode)
 ///     'try' '!' expr-sequence-element(Mode)
 ///     '_move' expr-sequence-element(Mode)
+///     'borrow' expr-sequence-element(Mode)
 ///     expr-unary(Mode)
 ///
 /// 'try' is not actually allowed at an arbitrary position of a
@@ -405,17 +406,28 @@ ParserResult<Expr> Parser::parseExprSequenceElement(Diag<> message,
    return sub;
   }
 
-  if (Context.LangOpts.hasFeature(Feature::MoveOnly)
-      && Tok.isContextualKeyword("_move")) {
-    Tok.setKind(tok::contextual_keyword);
-    SourceLoc awaitLoc = consumeToken();
-    ParserResult<Expr> sub =
-        parseExprSequenceElement(diag::expected_expr_after_await, isExprBasic);
-    if (!sub.hasCodeCompletion() && !sub.isNull()) {
-      sub = makeParserResult(new (Context) MoveExpr(awaitLoc, sub.get()));
+  if (Context.LangOpts.hasFeature(Feature::MoveOnly)) {
+    if (Tok.isContextualKeyword("_move")) {
+      Tok.setKind(tok::contextual_keyword);
+      SourceLoc awaitLoc = consumeToken();
+      ParserResult<Expr> sub =
+          parseExprSequenceElement(diag::expected_expr_after_move, isExprBasic);
+      if (!sub.hasCodeCompletion() && !sub.isNull()) {
+        sub = makeParserResult(new (Context) MoveExpr(awaitLoc, sub.get()));
+      }
+      return sub;
     }
 
-    return sub;
+    if (Tok.isContextualKeyword("_borrow")) {
+      Tok.setKind(tok::contextual_keyword);
+      SourceLoc awaitLoc = consumeToken();
+      ParserResult<Expr> sub = parseExprSequenceElement(
+          diag::expected_expr_after_borrow, isExprBasic);
+      if (!sub.hasCodeCompletion() && !sub.isNull()) {
+        sub = makeParserResult(new (Context) BorrowExpr(awaitLoc, sub.get()));
+      }
+      return sub;
+    }
   }
 
   SourceLoc tryLoc;

test/Parse/borrow_expr.swift

@@ -0,0 +1,19 @@
+// RUN: %target-typecheck-verify-swift  -disable-availability-checking -enable-experimental-move-only
+
+var global: Int = 5
+func testGlobal() {
+    let _ = _borrow global
+}
+
+func testLet() {
+    let t = String()
+    let _ = _borrow t
+}
+
+func testVar() {
+    var t = String()
+    t = String()
+    let _ = _borrow t
+}
+
+

test/Sema/borrow_expr.swift

@@ -0,0 +1,23 @@
+// RUN: %target-typecheck-verify-swift  -disable-availability-checking -enable-experimental-move-only
+
+class Klass {
+    var k: Klass? = nil
+}
+
+func useString(_ x: String) {}
+
+var global: String = "5"
+func testGlobal() {
+    useString(_borrow global)
+}
+
+func testLet() {
+    let t = String()
+    useString(_borrow t)
+}
+
+func testVar() {
+    var t = String()
+    t = String()
+    useString(_borrow t)
+}