v: allow alias as fixed array on return (#18817)

vlib/v/ast/types.v

@@ -887,6 +887,30 @@ pub fn (t &TypeSymbol) is_heap() bool {
 	}
 }
 
+pub fn (t &ArrayFixed) is_compatible(t2 ArrayFixed) bool {
+	return t.size == t2.size && t.elem_type == t2.elem_type
+}
+
+pub fn (t &TypeSymbol) is_array_fixed() bool {
+	if t.info is ArrayFixed {
+		return true
+	} else if t.info is Alias {
+		return global_table.final_sym(t.info.parent_type).is_array_fixed()
+	} else {
+		return false
+	}
+}
+
+pub fn (t &TypeSymbol) is_array_fixed_ret() bool {
+	if t.info is ArrayFixed {
+		return t.info.is_fn_ret
+	} else if t.info is Alias {
+		return global_table.final_sym(t.info.parent_type).is_array_fixed_ret()
+	} else {
+		return false
+	}
+}
+
 pub fn (mut t Table) register_builtin_type_symbols() {
 	// reserve index 0 so nothing can go there
 	// save index check, 0 will mean not found

vlib/v/checker/fn.v

@@ -129,8 +129,6 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 						node.return_type_pos)
 				}
 			}
-		} else if c.table.sym(node.return_type).kind == .alias && return_sym.kind == .array_fixed {
-			c.error('fixed array cannot be returned by function using alias', node.return_type_pos)
 		}
 		// Ensure each generic type of the parameter was declared in the function's definition
 		if node.return_type.has_flag(.generic) {
@@ -1521,6 +1519,16 @@ fn (mut c Checker) cast_fixed_array_ret(typ ast.Type, sym ast.TypeSymbol) ast.Ty
 	return typ
 }
 
+// cast_to_fixed_array_ret casts a ArrayFixed type created to do not return to a returning one
+fn (mut c Checker) cast_to_fixed_array_ret(typ ast.Type, sym ast.TypeSymbol) ast.Type {
+	if sym.kind == .array_fixed && !(sym.info as ast.ArrayFixed).is_fn_ret {
+		info := sym.info as ast.ArrayFixed
+		return c.table.find_or_register_array_fixed(info.elem_type, info.size, info.size_expr,
+			true)
+	}
+	return typ
+}
+
 fn (mut c Checker) method_call(mut node ast.CallExpr) ast.Type {
 	left_type := c.expr(mut node.left)
 	if left_type == ast.void_type {

vlib/v/checker/return.v

@@ -208,8 +208,11 @@ fn (mut c Checker) return_stmt(mut node ast.Return) {
 					}
 					continue
 				}
-				if exp_type_sym.kind == .array_fixed && got_type_sym.kind == .array_fixed {
-					if (exp_type_sym.info as ast.ArrayFixed).size == (got_type_sym.info as ast.ArrayFixed).size && (exp_type_sym.info as ast.ArrayFixed).elem_type == (got_type_sym.info as ast.ArrayFixed).elem_type {
+				exp_final_sym := c.table.final_sym(exp_type)
+				got_final_sym := c.table.final_sym(got_type)
+				if exp_final_sym.kind == .array_fixed && got_final_sym.kind == .array_fixed {
+					got_arr_sym := c.table.sym(c.cast_to_fixed_array_ret(got_type, got_final_sym))
+					if (exp_final_sym.info as ast.ArrayFixed).is_compatible(got_arr_sym.info as ast.ArrayFixed) {
 						continue
 					}
 				}

vlib/v/checker/tests/return_fixed_array.out

@@ -1,7 +0,0 @@
-vlib/v/checker/tests/return_fixed_array.vv:11:25: error: fixed array cannot be returned by function using alias
-    9 | }
-   10 | 
-   11 | fn return_fixed_array() Abc {
-      |                         ~~~
-   12 |     return [1, 2, 3]!
-   13 | }

vlib/v/checker/tests/return_fixed_array.vv

@@ -1,13 +0,0 @@
-type Abc = [3]int
-
-fn return_fixed_array() [3]int {
-	return [1, 2, 3]!
-}
-
-fn return_fixed_array_in_multi_return() ([3]int, [3]int) {
-	return [1, 2, 3]!, [4, 5, 6]!
-}
-
-fn return_fixed_array() Abc {
-	return [1, 2, 3]!
-}

vlib/v/gen/c/assign.v

@@ -578,9 +578,22 @@ fn (mut g Gen) assign_stmt(node_ ast.AssignStmt) {
 							}
 						}
 						if !is_used_var_styp {
-							if !val_type.has_flag(.option) && left_sym.info is ast.ArrayFixed
-								&& left_sym.info.is_fn_ret {
-								g.write('${styp[3..]} ')
+							if !val_type.has_flag(.option) && left_sym.is_array_fixed() {
+								if left_sym.kind == .alias {
+									parent_sym := g.table.final_sym((left_sym.info as ast.Alias).parent_type)
+									styp = g.typ((left_sym.info as ast.Alias).parent_type)
+									if !parent_sym.is_array_fixed_ret() {
+										g.write('${styp} ')
+									} else {
+										g.write('${styp[3..]} ')
+									}
+								} else {
+									if !left_sym.is_array_fixed_ret() {
+										g.write('${styp} ')
+									} else {
+										g.write('${styp[3..]} ')
+									}
+								}
 							} else {
 								g.write('${styp} ')
 							}

vlib/v/gen/c/cgen.v

@@ -4760,7 +4760,7 @@ fn (mut g Gen) return_stmt(node ast.Return) {
 	fn_return_is_multi := sym.kind == .multi_return
 	fn_return_is_option := fn_ret_type.has_flag(.option)
 	fn_return_is_result := fn_ret_type.has_flag(.result)
-	fn_return_is_fixed_array := sym.kind == .array_fixed && !fn_ret_type.has_flag(.option)
+	fn_return_is_fixed_array := sym.is_array_fixed() && !fn_ret_type.has_flag(.option)
 
 	mut has_semicolon := false
 	if node.exprs.len == 0 {
@@ -4782,6 +4782,8 @@ fn (mut g Gen) return_stmt(node ast.Return) {
 	mut ret_typ := g.typ(g.unwrap_generic(fn_ret_type))
 	if fn_ret_type.has_flag(.generic) && fn_return_is_fixed_array {
 		ret_typ = '_v_${ret_typ}'
+	} else if sym.kind == .alias && fn_return_is_fixed_array {
+		ret_typ = '_v_' + g.typ((sym.info as ast.Alias).parent_type)
 	}
 	mut use_tmp_var := g.defer_stmts.len > 0 || g.defer_profile_code.len > 0
 		|| g.cur_lock.lockeds.len > 0

vlib/v/gen/c/dumpexpr.v

@@ -100,6 +100,7 @@ fn (mut g Gen) dump_expr_definitions() {
 			}
 			str_dumparg_type += g.cc_type(dump_type, true) + ptr_asterisk
 		}
+		mut is_fixed_arr_ret := false
 		if dump_sym.kind == .function {
 			fninfo := dump_sym.info as ast.FnType
 			str_dumparg_type = 'DumpFNType_${name}'
@@ -109,14 +110,30 @@ fn (mut g Gen) dump_expr_definitions() {
 			g.go_back(str_tdef.len)
 			dump_typedefs['typedef ${str_tdef};'] = true
 			str_dumparg_ret_type = str_dumparg_type
-		} else if !typ.has_flag(.option) && dump_sym.kind == .array_fixed {
-			if (dump_sym.info as ast.ArrayFixed).is_fn_ret {
-				str_dumparg_ret_type = str_dumparg_type
-				str_dumparg_type = str_dumparg_type.trim_string_left('_v_')
-			} else {
-				// fixed array returned from function
-				str_dumparg_ret_type = '_v_' + str_dumparg_type
+		} else if !typ.has_flag(.option) && dump_sym.is_array_fixed() {
+			match dump_sym.kind {
+				.array_fixed {
+					if (dump_sym.info as ast.ArrayFixed).is_fn_ret {
+						str_dumparg_ret_type = str_dumparg_type
+						str_dumparg_type = str_dumparg_type.trim_string_left('_v_')
+					} else {
+						// fixed array returned from function
+						str_dumparg_ret_type = '_v_' + str_dumparg_type
+					}
+				}
+				.alias {
+					parent_sym := g.table.sym((dump_sym.info as ast.Alias).parent_type)
+					if parent_sym.kind == .array_fixed {
+						str_dumparg_ret_type =
+							if (parent_sym.info as ast.ArrayFixed).is_fn_ret { '' } else { '_v_' } +
+							g.cc_type((dump_sym.info as ast.Alias).parent_type, true)
+						str_dumparg_type = str_dumparg_ret_type.trim_string_left('_v_')
+						is_fixed_arr_ret = true
+					}
+				}
+				else {}
 			}
+			is_fixed_arr_ret = true
 		} else {
 			str_dumparg_ret_type = str_dumparg_type
 		}
@@ -173,7 +190,7 @@ fn (mut g Gen) dump_expr_definitions() {
 		dump_fns.writeln('\tstrings__Builder_write_string(&sb, value);')
 		dump_fns.writeln("\tstrings__Builder_write_rune(&sb, '\\n');")
 		surrounder.builder_write_afters(mut dump_fns)
-		if !typ.has_flag(.option) && dump_sym.kind == .array_fixed {
+		if is_fixed_arr_ret {
 			tmp_var := g.new_tmp_var()
 			dump_fns.writeln('\t${str_dumparg_ret_type} ${tmp_var} = {0};')
 			dump_fns.writeln('\tmemcpy(${tmp_var}.ret_arr, dump_arg, sizeof(${str_dumparg_type}));')

vlib/v/gen/c/fn.v

@@ -225,8 +225,16 @@ fn (mut g Gen) gen_fn_decl(node &ast.FnDecl, skip bool) {
 	mut name := g.c_fn_name(node)
 	mut type_name := g.typ(g.unwrap_generic(node.return_type))
 
-	if node.return_type.has_flag(.generic) && g.table.sym(node.return_type).kind == .array_fixed {
+	ret_sym := g.table.sym(node.return_type)
+	if node.return_type.has_flag(.generic) && ret_sym.kind == .array_fixed {
 		type_name = '_v_${type_name}'
+	} else if ret_sym.kind == .alias && !node.return_type.has_flag(.option) {
+		unalias_typ := g.table.unaliased_type(node.return_type)
+		unalias_sym := g.table.sym(unalias_typ)
+		if unalias_sym.kind == .array_fixed {
+			type_name = if !(unalias_sym.info as ast.ArrayFixed).is_fn_ret { '_v_' } else { '' } +
+				g.typ(unalias_typ)
+		}
 	}
 
 	if g.pref.obfuscate && g.cur_mod.name == 'main' && name.starts_with('main__') && !node.is_main

vlib/v/parser/parse_type.v

@@ -64,6 +64,10 @@ fn (mut p Parser) parse_array_type(expecting token.Kind, is_option bool) ast.Typ
 			}
 		}
 		p.check(.rsbr)
+		p.fixed_array_dim++
+		defer {
+			p.fixed_array_dim--
+		}
 		elem_type := p.parse_type()
 		if elem_type.idx() == 0 {
 			// error is handled by parse_type
@@ -73,7 +77,7 @@ fn (mut p Parser) parse_array_type(expecting token.Kind, is_option bool) ast.Typ
 			p.error_with_pos('fixed size cannot be zero or negative', size_expr.pos())
 		}
 		idx := p.table.find_or_register_array_fixed(elem_type, fixed_size, size_expr,
-			!is_option && p.inside_fn_return)
+			p.fixed_array_dim == 1 && !is_option && p.inside_fn_return)
 		if elem_type.has_flag(.generic) {
 			return ast.new_type(idx).set_flag(.generic)
 		}
@@ -705,6 +709,16 @@ fn (mut p Parser) find_type_or_add_placeholder(name string, language ast.Languag
 					typ = ast.new_type(idx)
 				}
 			}
+			ast.Alias {
+				if p.inside_fn_return {
+					parent_sym := p.table.sym(sym.info.parent_type)
+					if parent_sym.kind == .array_fixed {
+						info := parent_sym.array_fixed_info()
+						typ = p.table.find_or_register_array_fixed(info.elem_type, info.size,
+							info.size_expr, p.inside_fn_return)
+					}
+				}
+			}
 			else {}
 		}
 		return typ

vlib/v/parser/parser.v

@@ -65,6 +65,7 @@ mut:
 	inside_map_init           bool
 	inside_orm                bool
 	inside_chan_decl          bool
+	fixed_array_dim           int        // fixed array dim parsing level
 	or_is_handled             bool       // ignore `or` in this expression
 	builtin_mod               bool       // are we in the `builtin` module?
 	mod                       string     // current module name

vlib/v/tests/return_aliases_of_fixed_array_test.v

@@ -1,10 +1,13 @@
 type Mat = [2][2]int
 
-fn main() {
+fn test_main() {
 	a := Mat([[1, 2]!, [3, 4]!]!)
 	println(a.foo())
+	z := a.foo()
+	assert z == [[1, 2]!, [3, 4]!]!
 }
 
+// vfmt off
 fn (v Mat) foo() Mat {
 	return v
 }
@@ -12,3 +15,4 @@ fn (v Mat) foo() Mat {
 fn bar() Mat {
 	return Mat([[1, 2]!, [3, 4]!]!)
 }
+// vfmt on

vlib/v/tests/return_fixed_array_test.v

@@ -0,0 +1,25 @@
+type Abc = [3]int
+
+fn return_fixed_array() [3]int {
+	return [1, 2, 3]!
+}
+
+fn return_fixed_array_in_multi_return() ([3]int, [3]int) {
+	return [1, 2, 3]!, [4, 5, 6]!
+}
+
+// vfmt off
+fn return_fixed_array_with_alias() Abc {
+	return [1, 2, 3]!
+}
+// vfmt on
+
+fn test_with_alias() {
+	a := return_fixed_array_with_alias()
+	assert a == [1, 2, 3]!
+}
+
+fn test_without_alias() {
+	a := return_fixed_array()
+	assert a == [1, 2, 3]!
+}