checker: check variable mutability for postfix exprs

vlib/bitfield/bitfield.v

@@ -136,7 +136,6 @@ pub fn bfand(input1 BitField, input2 BitField) BitField {
 	mut output := new(size)
 	for i in 0..bitnslots {
 		output.field[i] = input1.field[i] & input2.field[i]
-		i++
 	}
 	output.cleartail()
 	return output
@@ -149,7 +148,6 @@ pub fn bfnot(input BitField) BitField {
 	mut output := new(size)
 	for i in 0..bitnslots {
 		output.field[i] = ~input.field[i]
-		i++
 	}
 	output.cleartail()
 	return output
@@ -164,7 +162,6 @@ pub fn bfor(input1 BitField, input2 BitField) BitField {
 	mut output := new(size)
 	for i in 0..bitnslots {
 		output.field[i] = input1.field[i] | input2.field[i]
-		i++
 	}
 	output.cleartail()
 	return output
@@ -179,7 +176,6 @@ pub fn bfxor(input1 BitField, input2 BitField) BitField {
 	mut output := new(size)
 	for i in 0..bitnslots {
 		output.field[i] = input1.field[i] ^ input2.field[i]
-		i++
 	}
 	output.cleartail()
 	return output
@@ -241,7 +237,6 @@ pub fn (instance BitField) clone() BitField {
 	mut output := new(instance.size)
 	for i in 0..bitnslots {
 		output.field[i] = instance.field[i]
-		i++
 	}
 	return output
 }

vlib/strings/builder_test.v

@@ -5,14 +5,14 @@ fn test_sb() {
 	sb.write('hi')
 	sb.write('!')
 	sb.write('hello')
-	assert sb.str() == 'hi!hello'
 	assert sb.len == 8
+	assert sb.str() == 'hi!hello'
+	assert sb.len == 0
 	sb = strings.new_builder(10)
 	sb.write('a')
 	sb.write('b')
-	println(sb.str())
-	assert sb.str() == 'ab'
 	assert sb.len == 2
+	assert sb.str() == 'ab'
 }
 
 const (

vlib/v/checker/checker.v

@@ -484,11 +484,11 @@ fn (mut c Checker) fail_if_immutable(expr ast.Expr) {
 					// TODO Remove `crypto.rand` when possible (see vlib/crypto/rand/rand.v,
 					// if `c_array_to_bytes_tmp` doesn't exist, then it's safe to remove it)
 					if c.file.mod.name !in ['builtin', 'crypto.rand'] {
-						c.error('`$typ_sym.kind` can not be modified', expr.position())
+						c.error('`$typ_sym.kind` can not be modified', it.pos)
 					}
 				}
 				else {
-					c.error('unexpected symbol `${typ_sym.kind}`', expr.position())
+					c.error('unexpected symbol `${typ_sym.kind}`', it.pos)
 				}
 			}
 		}
@@ -1802,20 +1802,14 @@ pub fn (mut c Checker) if_expr(node mut ast.IfExpr) table.Type {
 }
 
 pub fn (mut c Checker) postfix_expr(node ast.PostfixExpr) table.Type {
-	/*
-	match node.expr {
-		ast.IdentVar {
-			println('postfix identvar')
-		}
-		else {}
-	}
-	*/
 	typ := c.expr(node.expr)
 	typ_sym := c.table.get_type_symbol(typ)
 	// if !typ.is_number() {
 	if !typ_sym.is_number() {
 		println(typ_sym.kind.str())
 		c.error('invalid operation: $node.op.str() (non-numeric type `$typ_sym.name`)', node.pos)
+	} else {
+		c.fail_if_immutable(node.expr)
 	}
 	return typ
 }

vlib/v/checker/tests/division_by_zero_err.v

@@ -0,0 +1,3 @@
+fn main() {
+	println(1/0)
+}

vlib/v/checker/tests/immutable_field_postfix.out

@@ -0,0 +1,13 @@
+vlib/v/checker/tests/immutable_field_postfix.v:7:4: error: field `i` of struct `A` is immutable
+    5| fn main() {
+    6|     mut a := A{}
+    7|     a.i++
+             ^
+    8|     a.i--
+    9| }
+vlib/v/checker/tests/immutable_field_postfix.v:8:4: error: field `i` of struct `A` is immutable
+    6|     mut a := A{}
+    7|     a.i++
+    8|     a.i--
+             ^
+    9| }

vlib/v/checker/tests/immutable_field_postfix.v

@@ -0,0 +1,9 @@
+struct A {
+	i int
+}
+
+fn main() {
+	mut a := A{}
+	a.i++
+	a.i--
+}

vlib/v/checker/tests/immutable_field_postfix.vv

@@ -0,0 +1,9 @@
+struct A {
+	i int
+}
+
+fn main() {
+	mut a := A{}
+	a.i++
+	a.i--
+}

vlib/v/checker/tests/immutable_map_postfix.out

@@ -0,0 +1,13 @@
+vlib/v/checker/tests/immutable_map_postfix.v:3:2: error: `m` is immutable, declare it with `mut` to make it mutable
+    1| fn main() {
+    2|     m := map[string]int
+    3|     m['test']++
+           ^
+    4|     m['test']--
+    5| }
+vlib/v/checker/tests/immutable_map_postfix.v:4:2: error: `m` is immutable, declare it with `mut` to make it mutable
+    2|     m := map[string]int
+    3|     m['test']++
+    4|     m['test']--
+           ^
+    5| }

vlib/v/checker/tests/immutable_map_postfix.v

@@ -0,0 +1,5 @@
+fn main() {
+	m := map[string]int
+	m['test']++
+	m['test']--
+}

vlib/v/checker/tests/immutable_map_postfix.vv

@@ -0,0 +1,5 @@
+fn main() {
+	m := map[string]int
+	m['test']++
+	m['test']--
+}

vlib/v/checker/tests/immutable_struct_postfix.out

@@ -0,0 +1,13 @@
+vlib/v/checker/tests/immutable_struct_postfix.v:8:2: error: `a` is immutable, declare it with `mut` to make it mutable
+    6| fn main() {
+    7|     a := A{}
+    8|     a.i++
+           ^
+    9|     a.i--
+   10| }
+vlib/v/checker/tests/immutable_struct_postfix.v:9:2: error: `a` is immutable, declare it with `mut` to make it mutable
+    7|     a := A{}
+    8|     a.i++
+    9|     a.i--
+           ^
+   10| }

vlib/v/checker/tests/immutable_struct_postfix.v

@@ -0,0 +1,10 @@
+struct A {
+mut:
+	i int
+}
+
+fn main() {
+	a := A{}
+	a.i++
+	a.i--
+}

vlib/v/checker/tests/immutable_struct_postfix.vv

@@ -0,0 +1,10 @@
+struct A {
+mut:
+	i int
+}
+
+fn main() {
+	a := A{}
+	a.i++
+	a.i--
+}

vlib/v/checker/tests/immutable_var_postfix.out

@@ -0,0 +1,13 @@
+vlib/v/checker/tests/immutable_var_postfix.v:3:2: error: `a` is immutable, declare it with `mut` to make it mutable
+    1| fn main() {
+    2|     a := 1
+    3|     a++
+           ^
+    4|     a--
+    5| }
+vlib/v/checker/tests/immutable_var_postfix.v:4:2: error: `a` is immutable, declare it with `mut` to make it mutable
+    2|     a := 1
+    3|     a++
+    4|     a--
+           ^
+    5| }

vlib/v/checker/tests/immutable_var_postfix.v

@@ -0,0 +1,5 @@
+fn main() {
+	a := 1
+	a++
+	a--
+}

vlib/v/checker/tests/immutable_var_postfix.vv

@@ -0,0 +1,5 @@
+fn main() {
+	a := 1
+	a++
+	a--
+}