Disallow `for in` in favour of `for _ in`

core/c/frontend/tokenizer/tokenizer.odin

@@ -127,7 +127,7 @@ advance_rune :: proc(t: ^Tokenizer) {
 }
 
 advance_rune_n :: proc(t: ^Tokenizer, n: int) {
-	for in 0..<n {
+	for _ in 0..<n {
 		advance_rune(t)
 	}
 }

core/fmt/fmt.odin

@@ -1565,7 +1565,7 @@ fmt_bit_set :: proc(fi: ^Info, v: any, name: string = "") {
 // - fi: A pointer to the Info structure where the indents will be written.
 //
 fmt_write_indent :: proc(fi: ^Info) {
-	for in 0..<fi.indent {
+	for _ in 0..<fi.indent {
 		io.write_byte(fi.writer, '\t', &fi.n)
 	}
 }
@@ -1720,7 +1720,7 @@ fmt_struct :: proc(fi: ^Info, v: any, the_verb: rune, info: runtime.Type_Info_St
 	}
 	defer {
 		if hash {
-			for in 0..<indent { io.write_byte(fi.writer, '\t', &fi.n) }
+			for _ in 0..<indent { io.write_byte(fi.writer, '\t', &fi.n) }
 		}
 		io.write_byte(fi.writer, ']' if is_soa else '}', &fi.n)
 	}
@@ -1956,7 +1956,7 @@ fmt_named :: proc(fi: ^Info, v: any, verb: rune, info: runtime.Type_Info_Named)
 		for x := i; x >= 10; x /= 10 {
 			n -= 1
 		}
-		for in 0..<n {
+		for _ in 0..<n {
 			io.write_byte(fi.writer, '0', &fi.n)
 		}
 		io.write_i64(fi.writer, i, 10, &fi.n)
@@ -1989,7 +1989,7 @@ fmt_named :: proc(fi: ^Info, v: any, verb: rune, info: runtime.Type_Info_Named)
 			v := v
 			w := len(buf)
 			print := false
-			for in 0..<prec {
+			for _ in 0..<prec {
 				digit := v % 10
 				print = print || digit != 0
 				if print {

core/image/qoi/qoi.odin

@@ -299,7 +299,7 @@ load_from_context :: proc(ctx: ^$C, options := Options{}, allocator := context.a
 					if length := int(data & 63) + 1; (length * img.channels) > len(pixels) {
 						return img, .Corrupt
 					} else {
-						#no_bounds_check for in 0..<length {
+						#no_bounds_check for _ in 0..<length {
 							copy(pixels, pix[:img.channels])
 							pixels = pixels[img.channels:]
 						}

core/path/filepath/path.odin

@@ -416,7 +416,7 @@ rel :: proc(base_path, target_path: string, allocator := context.allocator) -> (
 		}
 		buf := make([]byte, size)
 		n := copy(buf, "..")
-		for in 0..<seps {
+		for _ in 0..<seps {
 			buf[n] = SEPARATOR
 			copy(buf[n+1:], "..")
 			n += 3

core/text/scanner/scanner.odin

@@ -200,7 +200,7 @@ peek :: proc(s: ^Scanner, n := 0) -> (ch: rune) {
 	ch = s.ch
 	if n > 0 {
 		prev_s := s^
-		for in 0..<n {
+		for _ in 0..<n {
 			next(s)
 		}
 		ch = s.ch
@@ -214,7 +214,7 @@ peek :: proc(s: ^Scanner, n := 0) -> (ch: rune) {
 peek_token :: proc(s: ^Scanner, n := 0) -> (tok: rune) {
 	assert(n >= 0)
 	prev_s := s^
-	for in 0..<n {
+	for _ in 0..<n {
 		tok = scan(s)
 	}
 	tok = scan(s)

examples/demo/demo.odin

@@ -1155,7 +1155,7 @@ threading_example :: proc() {
 		threads := make([dynamic]^thread.Thread, 0, len(prefix_table))
 		defer delete(threads)
 
-		for in prefix_table {
+		for _ in prefix_table {
 			if t := thread.create(worker_proc); t != nil {
 				t.init_context = context
 				t.user_index = len(threads)

src/parser.cpp

@@ -4271,6 +4271,8 @@ gb_internal Ast *parse_for_stmt(AstFile *f) {
 
 		if (f->curr_token.kind == Token_in) {
 			Token in_token = expect_token(f, Token_in);
+			syntax_error(in_token, "Prefer 'for _ in' over 'for in'");
+
 			Ast *rhs = nullptr;
 			bool prev_allow_range = f->allow_range;
 			f->allow_range = true;
@@ -4282,6 +4284,7 @@ gb_internal Ast *parse_for_stmt(AstFile *f) {
 			} else {
 				body = parse_block_stmt(f, false);
 			}
+
 			return ast_range_stmt(f, token, {}, in_token, rhs, body);
 		}