checker: disallow references to constants (fix #23935) (#23942)

vlib/v/checker/assign.v

@@ -899,6 +899,7 @@ or use an explicit `unsafe{ a[..] }`, if you do not want a copy of the slice.',
 	// Check `x := &y` and `mut x := <-ch`
 	if mut right_first is ast.PrefixExpr {
 		mut right_node := right_first
+		is_amp := right_first.op == .amp
 		left_first := node.left[0]
 		if left_first is ast.Ident {
 			assigned_var := left_first
@@ -920,6 +921,10 @@ or use an explicit `unsafe{ a[..] }`, if you do not want a copy of the slice.',
 						v := expr.obj
 						right_first_type = v.typ
 					}
+					if is_amp && !node.left[0].is_blank_ident() && expr.obj is ast.ConstField {
+						c.error('cannot have mutable reference to const `${expr.name}`',
+							right_node.pos)
+					}
 					if !c.inside_unsafe && assigned_var.is_mut() && !expr.is_mut() {
 						c.error('`${expr.name}` is immutable, cannot have a mutable reference to it',
 							right_node.pos)

vlib/v/checker/tests/assign_const_ptr_int_literal_err.out

@@ -7,3 +7,10 @@ vlib/v/checker/tests/assign_const_ptr_int_literal_err.vv:4:8: error: cannot assi
     6 | }
 Details: Specify the type for the constant value. Example:
          `const a = int(3)`
+vlib/v/checker/tests/assign_const_ptr_int_literal_err.vv:4:7: error: cannot have mutable reference to const `a`
+    2 | 
+    3 | fn main() {
+    4 |     b := &a
+      |          ^
+    5 |     dump(b)
+    6 | }

vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.out

@@ -12,6 +12,13 @@ vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:12:1
       |               ~~~~~~~~~~~~~~
    13 |     println(a)
    14 |     println(b)
+vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:10:11: error: cannot have mutable reference to const `a_char`
+    8 | 
+    9 | fn foo() {
+   10 |     mut a := &(a_char)
+      |              ^
+   11 |     mut b := &((a_char))
+   12 |     mut c := &((((a_char))))
 vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:10:11: error: `a_char` is immutable, cannot have a mutable reference to it
     8 | 
     9 | fn foo() {
@@ -19,6 +26,13 @@ vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:10:1
       |              ^
    11 |     mut b := &((a_char))
    12 |     mut c := &((((a_char))))
+vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:11:11: error: cannot have mutable reference to const `a_char`
+    9 | fn foo() {
+   10 |     mut a := &(a_char)
+   11 |     mut b := &((a_char))
+      |              ^
+   12 |     mut c := &((((a_char))))
+   13 |     println(a)
 vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:11:11: error: `a_char` is immutable, cannot have a mutable reference to it
     9 | fn foo() {
    10 |     mut a := &(a_char)
@@ -26,6 +40,13 @@ vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:11:1
       |              ^
    12 |     mut c := &((((a_char))))
    13 |     println(a)
+vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:12:11: error: cannot have mutable reference to const `a_char`
+   10 |     mut a := &(a_char)
+   11 |     mut b := &((a_char))
+   12 |     mut c := &((((a_char))))
+      |              ^
+   13 |     println(a)
+   14 |     println(b)
 vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:12:11: error: `a_char` is immutable, cannot have a mutable reference to it
    10 |     mut a := &(a_char)
    11 |     mut b := &((a_char))

vlib/v/checker/tests/const_reference_write_err.out

@@ -0,0 +1,14 @@
+vlib/v/checker/tests/const_reference_write_err.vv:14:10: error: cannot have mutable reference to const `a_string`
+   12 |     }
+   13 |     unsafe {
+   14 |         ptr := &a_string
+      |                ^
+   15 |         *ptr = f
+   16 |
+vlib/v/checker/tests/const_reference_write_err.vv:17:11: error: cannot have mutable reference to const `a_struct`
+   15 |         *ptr = f
+   16 | 
+   17 |         ptr2 := &a_struct
+      |                 ^
+   18 |         *ptr2 = a
+   19 |     }

vlib/v/checker/tests/const_reference_write_err.vv

@@ -0,0 +1,23 @@
+const a_string = ''
+const a_struct = A1{}
+
+struct A1 {
+	a_string string
+}
+
+fn main() {
+	f := '123'
+	a := A1{
+		a_string: f
+	}
+	unsafe {
+		ptr := &a_string
+		*ptr = f
+
+		ptr2 := &a_struct
+		*ptr2 = a
+	}
+	println('f: ${f} vs. a_string: ${a_string} vs. a_struct.a_string: ${a_struct.a_string}')
+	println('f == a_string : ${a_string == f}')
+	println('f == a_struct.a_string : ${a_struct.a_string == f}')
+}

vlib/v/checker/tests/immutable_deref.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/immutable_deref.vv:6:7: error: cannot have mutable reference to const `ctx_ptr`
+    4 | 
+    5 | fn main() {
+    6 |     x := &ctx_ptr
+      |          ^
+    7 |     unsafe {
+    8 |         *x = &Context{}

vlib/v/checker/tests/immutable_deref.vv

@@ -3,7 +3,6 @@ struct Context {}
 const ctx_ptr = &Context(unsafe { nil })
 
 fn main() {
-	// TODO: unsafe bug, having this declaration inside `unsafe` results in an error
 	x := &ctx_ptr
 	unsafe {
 		*x = &Context{}

vlib/v/checker/tests/mut_assign_ref.out

@@ -12,6 +12,13 @@ vlib/v/checker/tests/mut_assign_ref.vv:11:7: error: `f` is immutable, cannot hav
       |          ^
    12 |     p := &f
    13 |     _ = p
+vlib/v/checker/tests/mut_assign_ref.vv:15:11: error: cannot have mutable reference to const `constant`
+   13 |     _ = p
+   14 | 
+   15 |     mut c := &constant
+      |              ^
+   16 |     c.value = 200
+   17 |     c = &constant
 vlib/v/checker/tests/mut_assign_ref.vv:15:11: error: `constant` is immutable, cannot have a mutable reference to it
    13 |     _ = p
    14 | 
@@ -19,10 +26,24 @@ vlib/v/checker/tests/mut_assign_ref.vv:15:11: error: `constant` is immutable, ca
       |              ^
    16 |     c.value = 200
    17 |     c = &constant
+vlib/v/checker/tests/mut_assign_ref.vv:17:6: error: cannot have mutable reference to const `constant`
+   15 |     mut c := &constant
+   16 |     c.value = 200
+   17 |     c = &constant
+      |         ^
+   18 |     ic := &constant
+   19 |     _ = ic
 vlib/v/checker/tests/mut_assign_ref.vv:17:6: error: `constant` is immutable, cannot have a mutable reference to it
    15 |     mut c := &constant
    16 |     c.value = 200
    17 |     c = &constant
       |         ^
-   18 |     ic := &constant // ok
+   18 |     ic := &constant
    19 |     _ = ic
+vlib/v/checker/tests/mut_assign_ref.vv:18:8: error: cannot have mutable reference to const `constant`
+   16 |     c.value = 200
+   17 |     c = &constant
+   18 |     ic := &constant
+      |           ^
+   19 |     _ = ic
+   20 |

vlib/v/checker/tests/mut_assign_ref.vv

@@ -15,7 +15,7 @@ fn main() {
 	mut c := &constant
 	c.value = 200
 	c = &constant
-	ic := &constant // ok
+	ic := &constant
 	_ = ic
 
 	mut mf := f