checker, cgen: fix generic container init (fix #23910) (#23912)

vlib/v/checker/containers.v

@@ -110,6 +110,16 @@ fn (mut c Checker) array_init(mut node ast.ArrayInit) ast.Type {
 		if node.has_len {
 			c.check_elements_ref_fields_initialized(unwrap_elem_type, node.pos)
 		}
+		// T{0} initialization when T is an array
+		if !node.is_fixed && node.expr_types.len == 0 {
+			for mut expr in node.exprs {
+				typ := c.expr(mut expr)
+				c.check_expected(typ, node.elem_type) or {
+					c.error('invalid array element: ${err.msg()}', expr.pos())
+				}
+				node.expr_types << typ
+			}
+		}
 		return node.typ
 	}
 

vlib/v/checker/tests/generic_array_init_err.out

@@ -0,0 +1,6 @@
+vlib/v/checker/tests/generic_array_init_err.vv:2:9: error: invalid array element: expected `u8`, not `string`
+    1 | fn decode[T]() {
+    2 |     _ := T{''}
+      |            ~~
+    3 |     _ := T{0}
+    4 |     _ := T{u8(1)}

vlib/v/checker/tests/generic_array_init_err.vv

@@ -0,0 +1,9 @@
+fn decode[T]() {
+	_ := T{''}
+	_ := T{0}
+	_ := T{u8(1)}
+}
+
+fn main() {
+	decode[[]u8]()
+}

vlib/v/gen/c/array.v

@@ -47,10 +47,11 @@ fn (mut g Gen) array_init(node ast.ArrayInit, var_name string) {
 		}
 		is_sumtype := elem_sym.kind == .sum_type
 		for i, expr in node.exprs {
-			if node.expr_types[i] == ast.string_type
+			expr_type := if node.expr_types.len > i { node.expr_types[i] } else { node.elem_type }
+			if expr_type == ast.string_type
 				&& expr !in [ast.IndexExpr, ast.CallExpr, ast.StringLiteral, ast.StringInterLiteral, ast.InfixExpr] {
 				if is_sumtype {
-					g.expr_with_cast(expr, node.expr_types[i], node.elem_type)
+					g.expr_with_cast(expr, expr_type, node.elem_type)
 				} else {
 					g.write('string_clone(')
 					g.expr(expr)
@@ -58,14 +59,14 @@ fn (mut g Gen) array_init(node ast.ArrayInit, var_name string) {
 				}
 			} else {
 				if node.elem_type.has_flag(.option) {
-					g.expr_with_opt(expr, node.expr_types[i], node.elem_type)
+					g.expr_with_opt(expr, expr_type, node.elem_type)
 				} else if elem_type.unaliased_sym.kind == .array_fixed
 					&& expr in [ast.Ident, ast.SelectorExpr] {
 					info := elem_type.unaliased_sym.info as ast.ArrayFixed
 					g.fixed_array_var_init(g.expr_string(expr), expr.is_auto_deref_var(),
 						info.elem_type, info.size)
 				} else {
-					g.expr_with_cast(expr, node.expr_types[i], node.elem_type)
+					g.expr_with_cast(expr, expr_type, node.elem_type)
 				}
 			}
 			if i != len - 1 {

vlib/v/tests/generics/generic_array_init_test.v

@@ -0,0 +1,9 @@
+fn decode[T]() {
+	a := T{123}
+	b := T{u8(123)}
+	assert a == b
+}
+
+fn test_main() {
+	decode[[]u8]()
+}