fix: semantic restrictions for global variables, constant folding

src/error_tests.zig

@@ -68,6 +68,29 @@ test "compiler: invalid divert target" {
     );
 }
 
+test "compiler: global variable restrictions" {
+    try testEqual(
+        \\VAR a = b
+        \\VAR b = a
+    ,
+        \\<STDIN>:1:9: error: global variable assignments cannot refer to other variables
+        \\1    | VAR a = b
+        \\     |         ^
+        \\
+    );
+}
+
+test "compiler: constant cycle detection" {
+    try testEqual(
+        \\CONST a = a
+    ,
+        \\<STDIN>:1:11: error: cycle detected in constant initializer
+        \\1    | CONST a = a
+        \\     |           ^
+        \\
+    );
+}
+
 fn testEqual(source_bytes: [:0]const u8, expected_error: []const u8) !void {
     const gpa = std.testing.allocator;
     var arena_allocator = std.heap.ArenaAllocator.init(gpa);