[Parse] Properly reject labeled yield

Instead of asserting, emit a diagnostic with a
fix-it to remove the label.

SR-15066
rdar://82132821

Author: hamishknight

include/swift/AST/DiagnosticsParse.def

@@ -1030,6 +1030,8 @@ ERROR(expected_await_not_async,none,
 // Yield Statment
 ERROR(expected_expr_yield,PointsToFirstBadToken,
       "expected expression in 'yield' statement", ())
+ERROR(unexpected_label_yield,none,
+      "unexpected label in 'yield' statement", ())
 
 // Defer Statement
 ERROR(expected_lbrace_after_defer,PointsToFirstBadToken,

lib/Parse/ParseStmt.cpp

@@ -844,8 +844,11 @@ ParserResult<Stmt> Parser::parseStmtYield(SourceLoc tryLoc) {
     status = parseExprList(tok::l_paren, tok::r_paren, /*isArgumentList*/ false,
                            lpLoc, yieldElts, rpLoc, SyntaxKind::ExprList);
     for (auto &elt : yieldElts) {
-      assert(elt.Label.empty());
-      assert(elt.LabelLoc.isInvalid());
+      // We don't accept labels in a list of yields.
+      if (elt.LabelLoc.isValid()) {
+        diagnose(elt.LabelLoc, diag::unexpected_label_yield)
+          .fixItRemoveChars(elt.LabelLoc, elt.E->getStartLoc());
+      }
       yields.push_back(elt.E);
     }
   } else {

test/stmt/yield.swift

@@ -92,3 +92,16 @@ struct YieldInDefer {
     }
   }
 }
+
+// SR-15066
+struct InvalidYieldParsing {
+  var property: String {
+    _read {
+      yield(x: "test") // expected-error {{unexpected label in 'yield' statement}} {{13-16=}}
+      yield(x: "test", y:   {0}) // expected-error {{expected 1 yield value(s)}}
+      // expected-error@-1 {{unexpected label in 'yield' statement}} {{13-16=}}
+      // expected-error@-2 {{unexpected label in 'yield' statement}} {{24-29=}}
+      yield(_: "test") // expected-error {{unexpected label in 'yield' statement}} {{13-16=}}
+    }
+  }
+}