favor return over return _ (void return); newline/closing terminates

compiler/parser/parser.odin

@@ -1282,14 +1282,11 @@ finish_statement :: proc(parser: ^Parser, allow_closing_brace := false) -> sourc
 
 parse_return :: proc(parser: ^Parser) -> ast.Stmt_Id {
 	start := advance(parser)
-	skip_newlines(parser)
-	if current(parser).kind == .Underscore {
-		end := advance(parser)
+	if current(parser).kind == .Newline || current(parser).kind == .Right_Brace || current(parser).kind == .Eof {
 		id := ast.stmt_id(len(parser.module.statements))
 		append(&parser.module.statements, ast.Stmt{
 			kind=.Return,
-			span=span_from(start.span, end.span),
-			name=end.symbol,
+			span=start.span,
 			expr=ast.INVALID_EXPR,
 			diagnostic=source.INVALID_DIAGNOSTIC,
 		})
@@ -1321,12 +1318,10 @@ parse_return :: proc(parser: ^Parser) -> ast.Stmt_Id {
 	return id
 }
 
-// `yield <expr>` supplies the value of the enclosing value block. The checker
-// only accepts it as the final statement of a value block (a `{ ... }` on the
-// right of a declaration/assignment); it is the block analogue of `return`.
+// `yield <expr>` supplies a non-void value to an enclosing value construct.
+// The expression must start on the same line; `break` handles valueless exits.
 parse_yield :: proc(parser: ^Parser) -> ast.Stmt_Id {
 	start := advance(parser) // consume 'yield'
-	skip_newlines(parser)
 	// `yield :blk x` targets the loop labeled `blk`; a bare `yield x` targets
 	// the directly-enclosing value block / if branch. No expression starts with
 	// ':', so a leading colon is unambiguously a label.
@@ -1335,9 +1330,21 @@ parse_yield :: proc(parser: ^Parser) -> ast.Stmt_Id {
 		if name, name_ok := allow(parser, .Identifier); name_ok {
 			label = name.symbol
 		} else {
-			source.add(parser.diagnostics, current(parser).span, "expected a loop label after ':'")
+			source.add(parser.diagnostics, current(parser).span, "expected a yield target label after ':'")
 		}
 	}
+	if current(parser).kind == .Newline || current(parser).kind == .Right_Brace || current(parser).kind == .Eof {
+		expr := invalid_expr(parser, start.span, "'yield' must produce a value")
+		id := ast.stmt_id(len(parser.module.statements))
+		append(&parser.module.statements, ast.Stmt{
+			kind=.Yield,
+			span=start.span,
+			label=label,
+			expr=expr,
+			diagnostic=source.INVALID_DIAGNOSTIC,
+		})
+		return id
+	}
 	if cf, is_cf := parse_value_control_flow(parser); is_cf {
 		cf_span := parser.module.statements[cf].span
 		body := make([]ast.Stmt_Id, 1, parser.module.allocator)