all: fix map = map2 assignment (#8581)

vlib/v/checker/checker.v

@@ -2713,7 +2713,14 @@ pub fn (mut c Checker) assign_stmt(mut assign_stmt ast.AssignStmt) {
 			&& right_sym.kind == .array && (left is ast.Ident && !left.is_blank_ident())
 			&& right is ast.Ident {
 			// Do not allow `a = b`, only `a = b.clone()`
-			c.error('use `array2 = array1.clone()` instead of `array2 = array1` (or use `unsafe`)',
+			c.error('use `array2 $assign_stmt.op.str() array1.clone()` instead of `array2 $assign_stmt.op.str() array1` (or use `unsafe`)',
+				assign_stmt.pos)
+		}
+		if left_sym.kind == .map && !c.inside_unsafe && assign_stmt.op in [.assign, .decl_assign]
+			&& right_sym.kind == .map && (left is ast.Ident && !left.is_blank_ident())
+			&& right is ast.Ident {
+			// Do not allow `a = b`, only `a = b.clone()`
+			c.error('use `map2 $assign_stmt.op.str() map1.clone()` instead of `map2 $assign_stmt.op.str() map1` (or use `unsafe`)',
 				assign_stmt.pos)
 		}
 		left_is_ptr := left_type.is_ptr() || left_sym.is_pointer()

vlib/v/checker/tests/array_or_map_assign_err.out

@@ -0,0 +1,27 @@
+vlib/v/checker/tests/array_or_map_assign_err.vv:3:5: error: use `array2 := array1.clone()` instead of `array2 := array1` (or use `unsafe`)
+    1 | fn main() {
+    2 |     a1 := [1, 2, 3]
+    3 |     a2 := a1
+      |        ~~
+    4 |     mut a3 := []int{}
+    5 |     a3 = a1
+vlib/v/checker/tests/array_or_map_assign_err.vv:5:5: error: use `array2 = array1.clone()` instead of `array2 = array1` (or use `unsafe`)
+    3 |     a2 := a1
+    4 |     mut a3 := []int{}
+    5 |     a3 = a1
+      |        ^
+    6 |
+    7 |     m1 := {'one': 1}
+vlib/v/checker/tests/array_or_map_assign_err.vv:8:5: error: use `map2 := map1.clone()` instead of `map2 := map1` (or use `unsafe`)
+    6 |
+    7 |     m1 := {'one': 1}
+    8 |     m2 := m1
+      |        ~~
+    9 |     mut m3 := map[string]int{}
+   10 |     m3 = m1
+vlib/v/checker/tests/array_or_map_assign_err.vv:10:5: error: use `map2 = map1.clone()` instead of `map2 = map1` (or use `unsafe`)
+    8 |     m2 := m1
+    9 |     mut m3 := map[string]int{}
+   10 |     m3 = m1
+      |        ^
+   11 | }

vlib/v/checker/tests/array_or_map_assign_err.vv

@@ -0,0 +1,11 @@
+fn main() {
+    a1 := [1, 2, 3]
+	a2 := a1
+	mut a3 := []int{}
+	a3 = a1
+
+	m1 := {'one': 1}
+	m2 := m1
+	mut m3 := map[string]int{}
+	m3 = m1
+}