checker: fix assigning an array slice (fix #19120) (#19137)

vlib/builtin/string.v

@@ -2190,12 +2190,12 @@ pub fn (s string) trim_indent() string {
 
 	// trim first line if it's blank
 	if lines.len > 0 && lines.first().is_blank() {
-		lines = lines[1..]
+		lines = unsafe { lines[1..] }
 	}
 
 	// trim last line if it's blank
 	if lines.len > 0 && lines.last().is_blank() {
-		lines = lines[..lines.len - 1]
+		lines = unsafe { lines[..lines.len - 1] }
 	}
 
 	mut trimmed_lines := []string{cap: lines.len}

vlib/encoding/base32/base32.v

@@ -212,8 +212,8 @@ fn (enc &Encoding) encode_(src_ []u8, mut dst []u8) {
 
 			break
 		}
-		src = src[5..]
-		dst = dst[8..]
+		src = unsafe { src[5..] }
+		dst = unsafe { dst[8..] }
 	}
 }
 

vlib/flag/flag.v

@@ -138,7 +138,7 @@ pub fn new_flag_parser(args []string) &FlagParser {
 	if idx_dashdash >= 0 {
 		all_before_dashdash.trim(idx_dashdash)
 		if idx_dashdash < original_args.len {
-			all_after_dashdash = original_args[idx_dashdash + 1..]
+			all_after_dashdash = unsafe { original_args[idx_dashdash + 1..] }
 		}
 	}
 	return &FlagParser{

vlib/net/urllib/urllib.v

@@ -889,7 +889,7 @@ fn resolve_path(base string, ref string) string {
 			}
 			'..' {
 				if dst.len > 0 {
-					dst = dst[..dst.len - 1]
+					dst = unsafe { dst[..dst.len - 1] }
 				}
 			}
 			else {

vlib/regex/regex_util.v

@@ -526,9 +526,9 @@ pub fn (mut re RE) replace_n(in_txt string, repl_str string, count int) string {
 	mut lst := re.find_all(in_txt)
 
 	if count < 0 { // start from the right of the string
-		lst = lst#[count * 2..] // limitate the number of substitions
+		lst = unsafe { lst#[count * 2..] } // limitate the number of substitions
 	} else if count > 0 { // start from the left of the string
-		lst = lst#[..count * 2] // limitate the number of substitions
+		lst = unsafe { lst#[..count * 2] } // limitate the number of substitions
 	} else if count == 0 { // no replace
 		return in_txt
 	}

vlib/v/checker/assign.v

@@ -483,6 +483,28 @@ fn (mut c Checker) assign_stmt(mut node ast.AssignStmt) {
 							}
 						}
 					}
+				} else if mut left is ast.Ident && right is ast.IndexExpr {
+					if (right as ast.IndexExpr).left is ast.Ident
+						&& (right as ast.IndexExpr).index is ast.RangeExpr
+						&& ((right as ast.IndexExpr).left.is_mut() || left.is_mut())
+						&& !c.inside_unsafe {
+						// `mut a := arr[..]` auto add clone() -> `mut a := arr[..].clone()`
+						c.add_error_detail_with_pos('To silence this notice, use either an explicit `a[..].clone()`,
+or use an explicit `unsafe{ a[..] }`, if you do not want a copy of the slice.',
+							right.pos())
+						c.note('an implicit clone of the slice was done here', right.pos())
+						right = ast.CallExpr{
+							name: 'clone'
+							left: right
+							left_type: left_type
+							is_method: true
+							receiver_type: left_type
+							return_type: left_type
+							scope: c.fn_scope
+						}
+						right_type = c.expr(mut right)
+						node.right[i] = right
+					}
 				}
 			}
 			if node.op == .assign {

vlib/v/checker/tests/slice_clone_notice.out

@@ -0,0 +1,15 @@
+vlib/v/checker/tests/slice_clone_notice.vv:4:13: notice: an implicit clone of the slice was done here
+    2 |     xs := [1, 2, 3, 4, 5, 6, 7, 8]
+    3 |
+    4 |     mut s := xs[1..]
+      |                ~~~~~
+    5 |
+    6 |     s.sort(a > b)
+Details: vlib/v/checker/tests/slice_clone_notice.vv:4:13: details: To silence this notice, use either an explicit `a[..].clone()`,
+or use an explicit `unsafe{ a[..] }`, if you do not want a copy of the slice.
+    2 |     xs := [1, 2, 3, 4, 5, 6, 7, 8]
+    3 |
+    4 |     mut s := xs[1..]
+      |                ~~~~~
+    5 |
+    6 |     s.sort(a > b)

vlib/v/checker/tests/slice_clone_notice.vv

@@ -0,0 +1,12 @@
+fn main() {
+	xs := [1, 2, 3, 4, 5, 6, 7, 8]
+
+	mut s := xs[1..]
+
+	s.sort(a > b)
+
+	println(s)
+	assert s == [8, 7, 6, 5, 4, 3, 2]
+	println(xs)
+	assert xs == [1, 2, 3, 4, 5, 6, 7, 8]
+}

vlib/v/gen/js/tests/array.v

@@ -24,9 +24,9 @@ fn main() {
 	mut arr2 := [1, 2, 3, 4, 5]
 
 	// Array slices
-	slice1 := arr1[1..3]
-	slice2 := arr2[..3]
-	slice3 := arr2[3..]
+	slice1 := unsafe { arr1[1..3] }
+	slice2 := unsafe { arr2[..3] }
+	slice3 := unsafe { arr2[3..] }
 
 	// Array indexes
 	idx1 := slice1[1]
@@ -45,7 +45,7 @@ fn main() {
 	println('\n\n')
 
 	// String slices
-	mut slice4 := idx1[..4]
+	mut slice4 := unsafe { idx1[..4] }
 	print('Back\t=> ')
 	println(slice4) // 'Back'
 

vlib/v/tests/array_slice_assign_test.v

@@ -0,0 +1,12 @@
+fn test_array_slice_assign() {
+	xs := [1, 2, 3, 4, 5, 6, 7, 8]
+
+	mut s := xs[1..].clone()
+
+	s.sort(a > b)
+
+	println(s)
+	assert s == [8, 7, 6, 5, 4, 3, 2]
+	println(xs)
+	assert xs == [1, 2, 3, 4, 5, 6, 7, 8]
+}

vlib/v/tests/array_slice_test.v

@@ -82,8 +82,8 @@ fn test_self_slice_push() {
 
 fn test_slice_push_child() {
 	mut a := [1.0, 2.0625, 3.5, -7.75, 7.125, 8.4375, 0.5]
-	mut b := a[2..6] // `b` is initially created as reference
-	mut c := b[1..3] // `c` is initiall reference to `a` and `b`
+	mut b := unsafe { a[2..6] } // `b` is initially created as reference
+	mut c := unsafe { b[1..3] } // `c` is initiall reference to `a` and `b`
 	b << -2.25 // `b` should be reallocated, so `a` doesn't change
 	c[1] = -13.5 // this should change `c` and `a` but not `b`
 	assert c == [-7.75, -13.5]
@@ -93,7 +93,7 @@ fn test_slice_push_child() {
 
 fn test_predictable_reallocation_parent() {
 	mut a := []i64{len: 4, cap: 6, init: -25}
-	mut b := a[1..3]
+	mut b := unsafe { a[1..3] }
 	b[1] = -5238543910438573201
 	assert a == [i64(-25), -25, -5238543910438573201, -25]
 	a << 5