checker: turn the option/result split warning into an error; readme: better wording

README.md

@@ -41,20 +41,22 @@
 - C and JavaScript backends
 - Great for writing low-level software ([Vinix OS](https://github.com/vlang/vinix))
 
-## Stability guarantee and future changes
+## Stability, future changes, post 1.0 freeze
 
-Despite being at an early development stage, the V language is relatively stable and has
-backwards compatibility guarantee, meaning that the code you write today is guaranteed
-to work a month, a year, or five years from now.
+Despite being at an early development stage, the V language is relatively stable, and doesn't
+change often. But there will bechanges before 1.0.
+Most changes in the syntax are handled via vfmt automatically.
 
-There still may be minor syntax changes before the 1.0 release, but they will be handled
-automatically via `vfmt`, as has been done in the past.
-
-The V core APIs (primarily the `os` module) will still have minor changes until
+The V core APIs (primarily the `os` module) will also have minor changes until
 they are stabilized in V 1.0. Of course the APIs will grow after that, but without breaking
 existing code.
 
-Unlike many other languages, V is not going to be always changing, with new features
+After the 1.0 release V is going to be in the "feature freeze" mode. That means no breaking changes
+in the language, only bug fixes and performance improvements. Similar to Go.
+
+Will there be V 2.0? Not within a decade after 1.0, perhaps not ever.
+
+To sum it up, unlike many other languages, V is not going to be always changing, with new features
 being introduced and old features modified. It is always going to be a small and simple
 language, very similar to the way it is right now.
 

vlib/v/checker/return.v

@@ -121,10 +121,10 @@ fn (mut c Checker) return_stmt(mut node ast.Return) {
 	result_type_idx := c.table.type_idxs['_result']
 	got_types_0_idx := got_types[0].idx()
 	if exp_is_option && got_types_0_idx == ast.error_type_idx {
-		c.warn('Option and Result types have been split, use `!Foo` to return errors',
+		c.error('Option and Result types have been split, use `!Foo` to return errors',
 			node.pos)
 	} else if exp_is_result && got_types_0_idx == ast.none_type_idx {
-		c.warn('Option and Result types have been split, use `?` to return none', node.pos)
+		c.error('Option and Result types have been split, use `?` to return none', node.pos)
 	}
 	if (exp_is_option
 		&& got_types_0_idx in [ast.none_type_idx, ast.error_type_idx, option_type_idx])

vlib/v/checker/tests/option_fn_return_error.out

@@ -1,4 +1,4 @@
-vlib/v/checker/tests/option_fn_return_error.vv:2:2: warning: Option and Result types have been split, use `!Foo` to return errors
+vlib/v/checker/tests/option_fn_return_error.vv:2:2: error: Option and Result types have been split, use `!Foo` to return errors
     1 | fn func() ?int {
     2 |     return error('Some error')
       |     ~~~~~~~~~~~~~~~~~~~~~~~~~~

vlib/v/checker/tests/void_fn_multiple_ret_err.out

@@ -1,21 +1,14 @@
-vlib/v/checker/tests/void_fn_multiple_ret_err.vv:6:2: warning: Option and Result types have been split, use `?` to return none
-    4 | 
-    5 | fn foo_result_2() ! {
-    6 |     return none
-      |     ~~~~~~~~~~~
-    7 | }
-    8 |
 vlib/v/checker/tests/void_fn_multiple_ret_err.vv:2:9: error: functions with Result-only return types can only return an error
     1 | fn foo_result_1() ! {
     2 |     return none, 100
       |            ~~~~
     3 | }
     4 |
-vlib/v/checker/tests/void_fn_multiple_ret_err.vv:6:9: error: cannot use `none` as Result type in return argument
+vlib/v/checker/tests/void_fn_multiple_ret_err.vv:6:2: error: Option and Result types have been split, use `?` to return none
     4 | 
     5 | fn foo_result_2() ! {
     6 |     return none
-      |            ~~~~
+      |     ~~~~~~~~~~~
     7 | }
     8 |
 vlib/v/checker/tests/void_fn_multiple_ret_err.vv:14:9: error: cannot use `int literal` as Result type in return argument

vlib/v/gen/c/testdata/for_in.vv

@@ -1,15 +1,17 @@
 struct CustomIter {
 mut:
-  idx int
+	idx int
 }
 
 fn new_custom_iter() CustomIter {
-	return CustomIter{ idx: 0 }
+	return CustomIter{
+		idx: 0
+	}
 }
 
 fn (mut a CustomIter) next() ?int {
 	if a.idx == 4 {
-		return error('')
+		return none
 	} else {
 		a.idx++
 		return a.idx * 2
@@ -18,10 +20,10 @@ fn (mut a CustomIter) next() ?int {
 
 fn main() {
 	for x in new_custom_iter() {
-		println('a.$x')
+		println('a.${x}')
 	}
 	for ix, val in new_custom_iter() {
-		println('b.$ix=$val')
+		println('b.${ix}=${val}')
 	}
 	println('end')
 }

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

@@ -139,7 +139,7 @@ fn (it Companies) method() int {
 	return 0
 }
 
-fn error_if_even(num int) ?int {
+fn error_if_even(num int) !int {
 	if num % 2 == 0 {
 		return error('number is even')
 	}

vlib/v/slow_tests/inout/option_fn_arg.vv

@@ -1,10 +1,10 @@
 module main
 
-fn test(f fn () ?) ? {
+fn test(f fn () !) ! {
 	return error('test')
 }
 
-fn test1() ? {
+fn test1() ! {
 	return error('test1')
 }
 

vlib/v/slow_tests/valgrind/1.strings_and_arrays.v

@@ -175,7 +175,7 @@ fn option_str() {
 	}
 }
 
-fn return_error_with_freed_expr() ?string {
+fn return_error_with_freed_expr() !string {
 	if true {
 		msg := 'oops'
 		return error('hm ${msg}')
@@ -357,7 +357,7 @@ fn return_sb_str() string {
 	return sb.str() // sb should be freed, but only after .str() is called
 }
 
-fn parse_header0(s string) ?string {
+fn parse_header0(s string) !string {
 	if !s.contains(':') {
 		return error('missing colon in header')
 	}
@@ -366,7 +366,7 @@ fn parse_header0(s string) ?string {
 	return x
 }
 
-fn parse_header1(s string) ?string {
+fn parse_header1(s string) !string {
 	if !s.contains(':') {
 		return error('missing colon in header')
 	}

vlib/v/tests/option_test.v

@@ -1,5 +1,5 @@
 // TODO: remove this after the deprecation period for `?Type` representing both Result and Option passes.
-fn opt_err_with_code(code int) ?string {
+fn opt_err_with_code(code int) !string {
 	return error_with_code('hi', code)
 }
 
@@ -20,7 +20,7 @@ fn test_err_with_code() {
 	_ := v
 }
 
-fn opt_err() ?string {
+fn opt_err() !string {
 	return error('hi')
 }
 
@@ -33,7 +33,7 @@ fn test_err() {
 	println(v) // suppress not used error
 }
 
-fn err_call(ok bool) ?int {
+fn err_call(ok bool) !int {
 	if !ok {
 		return error('Not ok!')
 	}
@@ -79,7 +79,7 @@ fn test_if_else_opt() {
 	}
 }
 
-fn for_opt_default() ?string {
+fn for_opt_default() !string {
 	return error('awww')
 }
 
@@ -137,7 +137,7 @@ fn or_return_val() int {
 	return a
 }
 
-fn or_return_error() ?int {
+fn or_return_error() !int {
 	a := ret_none() or { return error('Nope') }
 	return a
 }
@@ -282,7 +282,7 @@ fn test_option_val_with_empty_or() {
 }
 
 fn test_option_void_return_types_of_anon_fn() {
-	f := fn (i int) ? {
+	f := fn (i int) ! {
 		if i == 0 {
 			return error('0')
 		}
@@ -297,12 +297,12 @@ fn test_option_void_return_types_of_anon_fn() {
 }
 
 struct Foo {
-	f fn (int) ?
+	f fn (int) !
 }
 
 fn test_option_void_return_types_of_anon_fn_in_struct() {
 	foo := Foo{
-		f: fn (i int) ? {
+		f: fn (i int) ! {
 			if i == 0 {
 				return error('0')
 			}
@@ -327,7 +327,7 @@ struct CC {
 	str string
 }
 
-fn option_sum_type(a int) ?AA {
+fn option_sum_type(a int) !AA {
 	match a {
 		1 {
 			return BB{'Test'}