fix missing compile error on while/for missing block

lib/std/zig/ast.zig

@@ -13,7 +13,6 @@ pub const Tree = struct {
     token_ids: []const Token.Id,
     token_locs: []const Token.Loc,
     errors: []const Error,
-    /// undefined on parse error (when errors field is not empty)
     root_node: *Node.Root,
 
     arena: std.heap.ArenaAllocator.State,

lib/std/zig/parse.zig

@@ -878,8 +878,9 @@ const Parser = struct {
             return node;
         }
 
-        if (try p.parseAssignExpr()) |assign_expr| {
-            for_prefix.body = assign_expr;
+        for_prefix.body = try p.expectNode(parseAssignExpr, .{
+            .ExpectedBlockOrAssignment = .{ .token = p.tok_i },
+        });
 
         if (p.eatToken(.Semicolon) != null) return node;
 
@@ -905,9 +906,6 @@ const Parser = struct {
         return node;
     }
 
-        return null;
-    }
-
     /// WhileStatement
     ///     <- WhilePrefix BlockExpr ( KEYWORD_else Payload? Statement )?
     ///      / WhilePrefix AssignExpr ( SEMICOLON / KEYWORD_else Payload? Statement )
@@ -939,8 +937,10 @@ const Parser = struct {
             return node;
         }
 
-        if (try p.parseAssignExpr()) |assign_expr_node| {
-            while_prefix.body = assign_expr_node;
+
+        while_prefix.body = try p.expectNode(parseAssignExpr, .{
+            .ExpectedBlockOrAssignment = .{ .token = p.tok_i },
+        });
 
         if (p.eatToken(.Semicolon) != null) return node;
 
@@ -968,9 +968,6 @@ const Parser = struct {
         return node;
     }
 
-        return null;
-    }
-
     /// BlockExprStatement
     ///     <- BlockExpr
     ///      / AssignExpr SEMICOLON

lib/std/zig/parser_test.zig

@@ -210,6 +210,19 @@ test "recovery: invalid comptime" {
     });
 }
 
+test "recovery: missing block after for/while loops" {
+    try testError(
+        \\test "" { while (foo) }
+    , &[_]Error{
+        .ExpectedBlockOrAssignment,
+    });
+    try testError(
+        \\test "" { for (foo) |bar| }
+    , &[_]Error{
+        .ExpectedBlockOrAssignment,
+    });
+}
+
 test "zig fmt: if statment" {
     try testCanonical(
         \\test "" {