cgen: fix shared array slice (fix #23426) (#23427)

vlib/v/checker/assign.v

@@ -378,7 +378,10 @@ fn (mut c Checker) assign_stmt(mut node ast.AssignStmt) {
 							left_type = left_type.set_nr_muls(1)
 						}
 					} else if left_type.has_flag(.shared_f) {
-						left_type = left_type.clear_flag(.shared_f).deref()
+						left_type = left_type.clear_flag(.shared_f)
+						if left_type.is_ptr() {
+							left_type = left_type.deref()
+						}
 					}
 					if ident_var_info.share == .atomic_t {
 						left_type = left_type.set_flag(.atomic_f)

vlib/v/checker/checker.v

@@ -5463,6 +5463,9 @@ fn (mut c Checker) fail_if_unreadable(expr ast.Expr, typ ast.Type, what string)
 			if c.fail_if_unreadable(expr.left, expr.left_type, what) {
 				return true
 			}
+			if typ.has_flag(.shared_f) && expr.left is ast.SelectorExpr {
+				return false
+			}
 		}
 		ast.InfixExpr {
 			pos = expr.left.pos().extend(expr.pos)

vlib/v/gen/c/cgen.v

@@ -2928,7 +2928,9 @@ fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type_raw ast.Type, expected_typ
 			g.write('&')
 		}
 		g.expr(expr)
-		g.write('->val')
+		if expr !is ast.IndexExpr {
+			g.write('->val')
+		}
 		return
 	}
 	if got_is_ptr && !expected_is_ptr && neither_void && exp_sym.kind != .placeholder

vlib/v/gen/c/index.v

@@ -64,10 +64,12 @@ fn (mut g Gen) index_expr(node ast.IndexExpr) {
 }
 
 fn (mut g Gen) index_range_expr(node ast.IndexExpr, range ast.RangeExpr) {
-	sym := g.table.final_sym(g.unwrap_generic(node.left_type))
+	unwrapped_left_type := g.unwrap_generic(node.left_type)
+	sym := g.table.final_sym(unwrapped_left_type)
 	mut tmp_opt := ''
 	mut cur_line := ''
 	mut gen_or := node.or_expr.kind != .absent || node.is_option
+	left_is_shared := unwrapped_left_type.has_flag(.shared_f)
 	if sym.kind == .string {
 		if node.is_gated {
 			g.write('string_substr_ni(')
@@ -92,10 +94,16 @@ fn (mut g Gen) index_range_expr(node ast.IndexExpr, range ast.RangeExpr) {
 		} else {
 			g.write('array_slice(')
 		}
+		if left_is_shared {
+			g.write('(')
+		}
 		if node.left_type.is_ptr() {
 			g.write('*')
 		}
 		g.expr(node.left)
+		if left_is_shared {
+			g.write(').val')
+		}
 	} else if sym.info is ast.ArrayFixed {
 		// Convert a fixed array to V array when doing `fixed_arr[start..end]`
 		noscan := g.check_noscan(sym.info.elem_type)
@@ -107,6 +115,9 @@ fn (mut g Gen) index_range_expr(node ast.IndexExpr, range ast.RangeExpr) {
 		g.write('new_array_from_c_array${noscan}(')
 		ctype := g.styp(sym.info.elem_type)
 		g.write('${sym.info.size}, ${sym.info.size}, sizeof(${ctype}), ')
+		if left_is_shared {
+			g.write('(')
+		}
 		if node.left_type.is_ptr() {
 			g.write('*')
 		}
@@ -118,11 +129,14 @@ fn (mut g Gen) index_range_expr(node ast.IndexExpr, range ast.RangeExpr) {
 			g.write('${styp} ${var} = ')
 			g.expr(node.left)
 			g.writeln(';')
-			g.write2(line, ' ${var})')
+			g.write2(line, ' ${var}')
 		} else {
 			g.expr(node.left)
-			g.write(')')
 		}
+		if left_is_shared {
+			g.write(').val')
+		}
+		g.write(')')
 	} else {
 		g.expr(node.left)
 	}
@@ -192,7 +206,7 @@ fn (mut g Gen) index_of_array(node ast.IndexExpr, sym ast.TypeSymbol) {
 		}
 
 		if left_is_shared {
-			if left_is_ptr {
+			if node.index !is ast.RangeExpr && left_is_ptr {
 				g.write('->val')
 			} else {
 				g.write('.val')

vlib/v/tests/concurrency/shared_array_slice_test.v

@@ -0,0 +1,27 @@
+struct Foo {
+pub mut:
+	buf  shared []u8 = []u8{len: 20, init: 6}
+	buf2 shared [20]u8
+}
+
+fn test_main() {
+	mut foo := Foo{
+		buf2: [20]u8{init: 5}
+	}
+	rlock foo.buf {
+		if foo.buf.len > 0 {
+			x := 10
+			println('first ${x} bytes: ' + foo.buf[..x].str())
+			sliced := foo.buf[..x]
+			assert sliced == [u8(6), 6, 6, 6, 6, 6, 6, 6, 6, 6]
+		} else {
+			println('no data')
+			assert false
+		}
+	}
+	rlock foo.buf2 {
+		x := 4
+		println('first ${x} bytes: ' + foo.buf2[..x].str())
+		assert foo.buf2[..x] == [u8(5), 5, 5, 5]
+	}
+}