From e8d98e10adf3749e80ed48f8a6b88854d9b5bc0f Mon Sep 17 00:00:00 2001
From: Krchi <997054144@qq.com>
Date: Thu, 25 Dec 2025 18:22:05 +0800
Subject: [PATCH] cgen: clean code in return stmt (fix #25968) (#26118)

---
 vlib/v/gen/c/cgen.v                           | 87 ++++++++-----------
 .../gen/c/testdata/autofree_toml.c.must_have  |  2 +-
 ...ed_array_return_fn_propagate_result_test.v | 33 +++++++
 3 files changed, 70 insertions(+), 52 deletions(-)
 create mode 100644 vlib/v/tests/fns/fn_return_result_fixed_array_return_fn_propagate_result_test.v

diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 71d2adafb..65ee1276d 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -2359,10 +2359,16 @@ fn (mut g Gen) expr_with_tmp_var(expr ast.Expr, expr_typ ast.Type, ret_typ ast.T
 		panic('cgen: parameter `ret_typ` of function `expr_with_tmp_var()` must be an Option or Result')
 	}
 
+	assign_op := g.assign_op
+	defer {
+		g.assign_op = assign_op
+	}
+	g.assign_op = .unknown
 	stmt_str := g.go_before_last_stmt().trim_space()
 	mut styp := g.base_type(ret_typ)
 	g.empty_line = true
 	final_expr_sym := g.table.final_sym(expr_typ)
+	mut expected_type := ret_typ
 
 	if final_expr_sym.kind == .none {
 		g.write('${g.styp(ret_typ)} ${tmp_var} = ')
@@ -2435,11 +2441,6 @@ fn (mut g Gen) expr_with_tmp_var(expr ast.Expr, expr_typ ast.Type, ret_typ ast.T
 					&& (expr.right as ast.StructInit).init_fields.len == 0 {
 					g.write('builtin___option_none(&(${styp}[]) { ')
 				} else if final_expr_sym.kind == .array_fixed {
-					assign_op := g.assign_op
-					defer(fn) {
-						g.assign_op = assign_op
-					}
-					g.assign_op = .unknown
 					expr_is_fixed_array_var = true
 					info := final_expr_sym.array_fixed_info()
 					mut no_cast := false
@@ -2486,10 +2487,29 @@ fn (mut g Gen) expr_with_tmp_var(expr ast.Expr, expr_typ ast.Type, ret_typ ast.T
 				}
 			}
 		} else {
-			g.write('builtin___result_ok(&(${styp}[]) { ')
+			if final_expr_sym.kind == .array_fixed {
+				expr_is_fixed_array_var = true
+				info := final_expr_sym.array_fixed_info()
+				mut no_cast := false
+				if expr in [ast.CastExpr, ast.CallExpr, ast.Ident, ast.SelectorExpr] {
+					no_cast = true
+				}
+				elem_sym := g.table.sym(info.elem_type)
+				if elem_sym.kind == .struct {
+					expr_is_fixed_array_var = false
+					g.write('builtin___result_ok(&(${styp}[]) { ')
+				} else if no_cast {
+					g.write('builtin___result_ok(')
+				} else {
+					g.write('builtin___result_ok((${g.styp(final_expr_sym.idx)})')
+				}
+			} else {
+				g.write('builtin___result_ok(&(${styp}[]) { ')
+				expected_type = ret_typ.clear_flag(.result)
+			}
 		}
 		if !already_generated {
-			g.expr_with_cast(expr, expr_typ, ret_typ)
+			g.expr_with_cast(expr, expr_typ, expected_type)
 		}
 
 		if fn_option_clone {
@@ -2504,7 +2524,11 @@ fn (mut g Gen) expr_with_tmp_var(expr ast.Expr, expr_typ ast.Type, ret_typ ast.T
 				g.writeln(' }, (${option_name}*)(&${tmp_var}), sizeof(${styp}));')
 			}
 		} else {
-			g.writeln(' }, (${result_name}*)(&${tmp_var}), sizeof(${styp}));')
+			if expr_is_fixed_array_var {
+				g.writeln(', (${result_name}*)(&${tmp_var}), sizeof(${styp}));')
+			} else {
+				g.writeln(' }, (${result_name}*)(&${tmp_var}), sizeof(${styp}));')
+			}
 		}
 		g.set_current_pos_as_last_stmt_pos()
 	}
@@ -6444,17 +6468,6 @@ fn (mut g Gen) return_stmt(node ast.Return) {
 				type0.has_flag(.option)
 			}
 		}
-		if fn_return_is_option && !expr_type_is_opt && return_sym.name != option_name {
-			g.expr_with_tmp_var(expr0, type0, fn_ret_type, tmpvar, false)
-			g.writeln('')
-			g.write_defer_stmts_when_needed(node.scope, true, node.pos)
-			if g.is_autofree {
-				g.detect_used_var_on_return(expr0)
-			}
-			g.autofree_scope_vars(node.pos.pos - 1, node.pos.line_nr, true)
-			g.writeln('return ${tmpvar};')
-			return
-		}
 		expr_type_is_result := match expr0 {
 			ast.CallExpr {
 				expr0.return_type.has_flag(.result) && expr0.or_block.kind == .absent
@@ -6463,38 +6476,10 @@ fn (mut g Gen) return_stmt(node ast.Return) {
 				type0.has_flag(.result)
 			}
 		}
-		if fn_return_is_result && !expr_type_is_result && return_sym.name != result_name {
-			g.writeln('${ret_typ} ${tmpvar} = {0};')
-			if fn_return_is_fixed_array && expr0 !is ast.ArrayInit
-				&& g.table.final_sym(type0).kind == .array_fixed {
-				styp := g.styp(fn_ret_type.clear_option_and_result())
-				g.write('memcpy(${tmpvar}.data, ')
-				if expr0 in [ast.CallExpr, ast.StructInit] {
-					g.expr_with_opt(expr0, type0, fn_ret_type)
-					g.write('.data')
-				} else {
-					g.expr(expr0)
-				}
-				g.writeln(', sizeof(${styp}));')
-			} else {
-				styp := g.base_type(fn_ret_type)
-				g.write('builtin___result_ok(&(${styp}[]) { ')
-				if !fn_ret_type.is_ptr() && type0.is_ptr() {
-					if !((expr0 is ast.Ident && !g.is_amp) || sym.kind == .interface) {
-						g.write('*')
-					}
-				}
-				if fn_ret_type.has_flag(.option) {
-					g.expr_with_opt(expr0, type0, fn_ret_type.clear_flag(.result))
-				} else if return_sym.kind == .array_fixed && expr0 !is ast.ArrayInit {
-					info := return_sym.info as ast.ArrayFixed
-					g.fixed_array_var_init(g.expr_string(expr0), expr0.is_auto_deref_var(),
-						info.elem_type, info.size)
-				} else {
-					g.expr_with_cast(expr0, type0, fn_ret_type.clear_flag(.result))
-				}
-				g.writeln(' }, (${result_name}*)(&${tmpvar}), sizeof(${styp}));')
-			}
+		if (fn_return_is_option && !expr_type_is_opt && return_sym.name != option_name)
+			|| (fn_return_is_result && !expr_type_is_result && return_sym.name != result_name) {
+			g.expr_with_tmp_var(expr0, type0, fn_ret_type, tmpvar, false)
+			g.writeln('')
 			g.write_defer_stmts_when_needed(node.scope, true, node.pos)
 			if g.is_autofree {
 				g.detect_used_var_on_return(expr0)
diff --git a/vlib/v/gen/c/testdata/autofree_toml.c.must_have b/vlib/v/gen/c/testdata/autofree_toml.c.must_have
index 15ce0a8b8..4894be520 100644
--- a/vlib/v/gen/c/testdata/autofree_toml.c.must_have
+++ b/vlib/v/gen/c/testdata/autofree_toml.c.must_have
@@ -1,5 +1,5 @@
 _result_toml__scanner__Scanner_ptr toml__scanner__new_scanner(toml__scanner__Config config) {
-	_result_toml__scanner__Scanner_ptr _t3 = {0};
+	_result_toml__scanner__Scanner_ptr _t3;
 	builtin___result_ok(&(toml__scanner__Scanner*[]) { s }, (_result*)(&_t3), sizeof(toml__scanner__Scanner*));
 	return _t3;
 }
diff --git a/vlib/v/tests/fns/fn_return_result_fixed_array_return_fn_propagate_result_test.v b/vlib/v/tests/fns/fn_return_result_fixed_array_return_fn_propagate_result_test.v
new file mode 100644
index 000000000..5211bcf90
--- /dev/null
+++ b/vlib/v/tests/fns/fn_return_result_fixed_array_return_fn_propagate_result_test.v
@@ -0,0 +1,33 @@
+import strconv
+
+pub fn valid_triangle(a u8, b u8, c u8) ![3]u8 {
+	if int(a) + int(b) <= int(c) {
+		return error('Invalid: a + b <= c')
+	}
+	if int(b) + int(c) <= int(a) {
+		return error('Invalid: b + c <= a')
+	}
+	if int(c) + int(a) <= int(b) {
+		return error('Invalid: c + a <= b')
+	}
+	return [a, b, c]!
+}
+
+pub fn triangle_from_string(sides string) ![3]u8 {
+	s := sides.split(',')
+	if s.len != 3 {
+		return error('Invalid: number of sides')
+	}
+	a := strconv.atou8(s[0])!
+	b := strconv.atou8(s[1])!
+	c := strconv.atou8(s[2])!
+	// warning: don't append `!` to next call
+	// will confuse with fixed and return `garbage`.
+	return valid_triangle(a, b, c)!
+}
+
+fn test_main() {
+	assert triangle_from_string('3,4,5')![0] == 3
+	assert triangle_from_string('3,4,5')![1] == 4
+	assert triangle_from_string('3,4,5')![2] == 5
+}
-- 
2.39.5