checker: implement implicit conversions/promotions to `rune` (#6249)

vlib/v/checker/check_types.v

@@ -217,8 +217,8 @@ fn (c &Checker) promote_num(left_type, right_type table.Type) table.Type {
 		}
 	} else if idx_lo >= table.byte_type_idx { // both operands are unsigned
 		return type_hi
-	} else if idx_lo >= table.i8_type_idx && idx_hi <= table.i64_type_idx { // both signed
+	} else if idx_lo >= table.i8_type_idx && (idx_hi <= table.i64_type_idx || idx_hi == table.rune_type_idx) { // both signed
-		return type_hi
+		return if idx_lo == table.i64_type_idx { type_lo } else { type_hi }
 	} else if idx_hi - idx_lo < (table.byte_type_idx - table.i8_type_idx) {
 		return type_lo // conversion unsigned -> signed if signed type is larger
 	} else {

vlib/v/table/atypes.v

@@ -255,12 +255,11 @@ pub const (
 	array_type_idx   = 20
 	map_type_idx     = 21
 	chan_type_idx    = 22
-	any_type_idx     = 23
+	sizet_type_idx   = 23
-	// t_type_idx       = 23
+	rune_type_idx    = 24
-	any_flt_type_idx = 24
+	any_type_idx     = 25
-	any_int_type_idx = 25
+	any_flt_type_idx = 26
-	sizet_type_idx   = 26
+	any_int_type_idx = 27
-	rune_type_idx    = 27
 )
 
 pub const (
@@ -300,11 +299,10 @@ pub const (
 	array_type   = new_type(array_type_idx)
 	map_type     = new_type(map_type_idx)
 	chan_type    = new_type(chan_type_idx)
+	rune_type    = new_type(rune_type_idx)
 	any_type     = new_type(any_type_idx)
-	// t_type       = new_type(t_type_idx)
 	any_flt_type = new_type(any_flt_type_idx)
 	any_int_type = new_type(any_int_type_idx)
-	rune_type    = new_type(rune_type_idx)
 )
 
 pub const (
@@ -569,18 +567,24 @@ pub fn (mut t Table) register_builtin_type_symbols() {
 		source_name: 'chan'
 		mod: 'builtin'
 	})
+	t.register_type_symbol({
+		kind: .size_t
+		name: 'size_t'
+		source_name: 'size_t'
+		mod: 'builtin'
+	})
+	t.register_type_symbol({
+		kind: .rune
+		name: 'rune'
+		source_name: 'rune'
+		mod: 'builtin'
+	})
 	t.register_type_symbol({
 		kind: .any
 		name: 'any'
 		source_name: 'any'
 		mod: 'builtin'
 	})
-	// t.register_type_symbol({
-	// kind: .any
-	// name: 'T'
-	// mod: 'builtin'
-	// is_public: true
-	// })
 	t.register_type_symbol({
 		kind: .any_float
 		name: 'any_float'
@@ -593,18 +597,6 @@ pub fn (mut t Table) register_builtin_type_symbols() {
 		source_name: 'any_int'
 		mod: 'builtin'
 	})
-	t.register_type_symbol({
-		kind: .size_t
-		name: 'size_t'
-		source_name: 'size_t'
-		mod: 'builtin'
-	})
-	t.register_type_symbol({
-		kind: .size_t
-		name: 'rune'
-		source_name: 'rune'
-		mod: 'builtin'
-	})
 	// TODO: remove. for v1 map compatibility
 	map_string_string_idx := t.find_or_register_map(string_type, string_type)
 	map_string_int_idx := t.find_or_register_map(string_type, int_type)

vlib/v/tests/type_promotion_test.v

@@ -80,3 +80,21 @@ fn test_f32_int() {
 	d := u64(300)
 	assert d + c == 316.75
 }
+
+fn test_rune() {
+	a := 3
+	mut b := rune(67)
+	b = a
+	assert b == rune(3)
+	b = rune(67)
+	mut x := 5
+	x = int(b)
+	assert x == 67
+	c := b + a
+	assert c == rune(70)
+	assert typeof(c) == 'rune'
+	d := i64(12)
+	e := b + d
+	assert e == i64(79)
+	assert typeof(e) == 'i64'
+}