all: improve unused variable warning (fix `x = 1`, `x += 1` etc)

thirdparty/sokol/sokol_app2.h

@@ -1,14 +1,14 @@
 
 @implementation MyView2
 
-int xx = 0;
+int __v_sokol_inited = 0;
 
 // Alternative drawRect which calls a frame function with native Cocoa calls
 - (void)drawRect:(NSRect)rect {
-	puts("drawRect()");
-	if (xx == 0) {
+	//puts("drawRect()");
+	if (__v_sokol_inited == 0) {
         _sapp_call_init();
-       xx = 1;
+       __v_sokol_inited = 1;
       }
     _sapp_call_frame_native();
 }

vlib/builtin/builtin.c.v

@@ -120,12 +120,11 @@ pub fn eprintln(s string) {
 				C.fprintf(C.stderr, c'%.*s\n', s.len, s.str)
 			}
 		} $else {
-			mut n := 0
 			if s.str == 0 {
-				n = C.write(2, c'eprintln(NIL)\n', 14)
+				_ = C.write(2, c'eprintln(NIL)\n', 14)
 			} else {
-				n = C.write(2, s.str, s.len)
-				n = C.write(2, c'\n', 1)
+				_ = C.write(2, s.str, s.len)
+				_ = C.write(2, c'\n', 1)
 			}
 		}
 		C.fflush(C.stderr)
@@ -158,11 +157,10 @@ pub fn eprint(s string) {
 				C.fprintf(C.stderr, c'%.*s', s.len, s.str)
 			}
 		} $else {
-			mut n := 0
 			if s.str == 0 {
-				n = C.write(2, c'eprint(NIL)', 11)
+				_ = C.write(2, c'eprint(NIL)', 11)
 			} else {
-				n = C.write(2, s.str, s.len)
+				_ = C.write(2, s.str, s.len)
 			}
 		}
 		C.fflush(C.stderr)
@@ -172,7 +170,6 @@ pub fn eprint(s string) {
 // print prints a message to stdout. Unlike `println` stdout is not automatically flushed.
 // A call to `flush()` will flush the output buffer to stdout.
 pub fn print(s string) {
-	mut n := 0
 	$if android {
 		C.fprintf(C.stdout, c'%.*s', s.len, s.str)
 	} $else $if ios {
@@ -181,7 +178,7 @@ pub fn print(s string) {
 	} $else $if freestanding {
 		bare_print(s.str, u64(s.len))
 	} $else {
-		n = C.write(1, s.str, s.len)
+		_ = C.write(1, s.str, s.len)
 	}
 }
 
@@ -194,7 +191,6 @@ fn C.asl_log(voidptr, voidptr, int, charptr)
 */
 // println prints a message with a line end, to stdout. stdout is flushed.
 pub fn println(s string) {
-	mut n := 0
 	if s.str == 0 {
 		$if android {
 			C.fprintf(C.stdout, c'println(NIL)\n')
@@ -204,7 +200,7 @@ pub fn println(s string) {
 			bare_print(s.str, u64(s.len))
 			bare_print(c'println(NIL)\n', 13)
 		} $else {
-			n = C.write(1, c'println(NIL)\n', 13)
+			_ = C.write(1, c'println(NIL)\n', 13)
 		}
 		return
 	}
@@ -216,8 +212,8 @@ pub fn println(s string) {
 		bare_print(s.str, u64(s.len))
 		bare_print(c'\n', 1)
 	} $else {
-		n = C.write(1, s.str, s.len)
-		n = C.write(1, c'\n', 1)
+		_ = C.write(1, s.str, s.len)
+		_ = C.write(1, c'\n', 1)
 	}
 }
 

vlib/builtin/builtin_nix.c.v

@@ -145,5 +145,6 @@ fn break_if_debugger_attached() {
 	unsafe {
 		mut ptr := &voidptr(0)
 		*ptr = voidptr(0)
+		_ = ptr
 	}
 }

vlib/os/os_c.v

@@ -740,11 +740,10 @@ pub fn is_link(path string) bool {
 
 // chdir changes the current working directory to the new directory in `path`.
 pub fn chdir(path string) {
-	mut n := 0
 	$if windows {
 		C._wchdir(path.to_wide())
 	} $else {
-		n = C.chdir(&char(path.str))
+		_ = C.chdir(&char(path.str))
 	}
 }
 

vlib/os/process_nix.c.v

@@ -3,12 +3,11 @@ module os
 fn C.setpgid(pid int, pgid int) int
 
 fn (mut p Process) unix_spawn_process() int {
-	mut n := 0
 	mut pipeset := [6]int{}
 	if p.use_stdio_ctl {
-		n = C.pipe(&pipeset[0]) // pipe read end 0 <- 1 pipe write end
-		n = C.pipe(&pipeset[2]) // pipe read end 2 <- 3 pipe write end
-		n = C.pipe(&pipeset[4]) // pipe read end 4 <- 5 pipe write end
+		_ = C.pipe(&pipeset[0]) // pipe read end 0 <- 1 pipe write end
+		_ = C.pipe(&pipeset[2]) // pipe read end 2 <- 3 pipe write end
+		_ = C.pipe(&pipeset[4]) // pipe read end 4 <- 5 pipe write end
 	}
 	pid := fork()
 	if pid != 0 {

vlib/v/cflag/cflags.v

@@ -33,10 +33,10 @@ pub fn (cf &CFlag) eval() string {
 				sparams := remainder[cflag.fexisting_literal.len + 1..].all_before(')')
 				i += sparams.len + cflag.fexisting_literal.len + 1
 				svalues := sparams.replace(',', '\n').split_into_lines().map(it.trim(' \'"'))
-				mut found_spath := ''
+				// mut found_spath := ''
 				for spath in svalues {
 					if os.exists(spath) {
-						found_spath = spath
+						// found_spath = spath
 						value += spath
 						continue cflag_eval_outer_loop
 					}

vlib/v/checker/checker.v

@@ -119,7 +119,7 @@ pub fn (mut c Checker) check_scope_vars(sc &ast.Scope) {
 		match obj {
 			ast.Var {
 				if !c.pref.is_repl {
-					if !obj.is_used && obj.name[0] != `_` {
+					if !obj.is_used && obj.name[0] != `_` && !c.file.is_test {
 						c.warn('unused variable: `$obj.name`', obj.pos)
 					}
 				}
@@ -2570,7 +2570,10 @@ pub fn (mut c Checker) selector_expr(mut selector_expr ast.SelectorExpr) ast.Typ
 	//
 	c.using_new_err_struct = using_new_err_struct_save
 	if typ == ast.void_type_idx {
-		c.error('unknown selector expression', selector_expr.pos)
+		// This means that the variable's value was assigned to an
+		// unknown function or method, so the error was already handled
+		// earlier
+		// c.error('unknown selector expression', selector_expr.pos)
 		return ast.void_type
 	}
 	selector_expr.expr_type = typ
@@ -3644,7 +3647,7 @@ fn (mut c Checker) stmt(node ast.Stmt) {
 fn (mut c Checker) assert_stmt(node ast.AssertStmt) {
 	cur_exp_typ := c.expected_type
 	assert_type := c.check_expr_opt_call(node.expr, c.expr(node.expr))
-	if assert_type != ast.bool_type_idx {
+	if assert_type != ast.bool_type_idx && assert_type != ast.void_type_idx {
 		atype_name := c.table.get_type_symbol(assert_type).name
 		c.error('assert can be used only with `bool` expressions, but found `$atype_name` instead',
 			node.pos)
@@ -4763,7 +4766,7 @@ pub fn (mut c Checker) ident(mut ident ast.Ident) ast.Type {
 				}
 				ast.Var {
 					// incase var was not marked as used yet (vweb tmpl)
-					obj.is_used = true
+					// obj.is_used = true
 					if ident.pos.pos < obj.pos.pos {
 						c.error('undefined variable `$ident.name` (used before declaration)',
 							ident.pos)

vlib/v/checker/tests/array_or_map_assign_err.out

@@ -10,10 +10,10 @@ vlib/v/checker/tests/array_or_map_assign_err.vv:5:5: error: use `array2 = array1
     4 |     mut a3 := []int{}
     5 |     a3 = a1
       |        ^
-    6 |
+    6 | 
     7 |     m1 := {'one': 1}
 vlib/v/checker/tests/array_or_map_assign_err.vv:8:8: error: cannot copy map: call `move` or `clone` method (or use a reference)
-    6 |
+    6 | 
     7 |     m1 := {'one': 1}
     8 |     m2 := m1
       |           ~~
@@ -24,12 +24,12 @@ vlib/v/checker/tests/array_or_map_assign_err.vv:10:7: error: cannot copy map: ca
     9 |     mut m3 := map[string]int{}
    10 |     m3 = m1
       |          ~~
-   11 |
+   11 | 
    12 |     _ = a2
-vlib/v/checker/tests/array_or_map_assign_err.vv:20:8: error: cannot copy map: call `move` or `clone` method (or use a reference)
-   18 |
-   19 | fn foo(mut m map[string]int) {
-   20 |     m2 := m
+vlib/v/checker/tests/array_or_map_assign_err.vv:25:8: error: cannot copy map: call `move` or `clone` method (or use a reference)
+   23 | 
+   24 | fn foo(mut m map[string]int) {
+   25 |     m2 := m
       |           ^
-   21 |     m['foo'] = 100
-   22 |     println(m)
+   26 |     m['foo'] = 100
+   27 |     println(m)

vlib/v/checker/tests/array_or_map_assign_err.vv

@@ -14,6 +14,11 @@ fn main() {
 
 	mut m := {'foo':1}
 	foo(mut m)
+
+	_ = a3
+	_ = m1
+	_ = m2
+	_ = m3
 }
 
 fn foo(mut m map[string]int) {

vlib/v/checker/tests/arrow_op_wrong_left_type_err_b.out

@@ -3,4 +3,5 @@ vlib/v/checker/tests/arrow_op_wrong_left_type_err_b.vv:4:8: error: cannot assign
     3 |     mut obj := 9
     4 |     obj = <-ch
       |           ~~
-    5 | }
+    5 |     _ = obj
+    6 | }

vlib/v/checker/tests/arrow_op_wrong_left_type_err_b.vv

@@ -2,4 +2,5 @@ fn main() {
 	ch := chan string{}
 	mut obj := 9
 	obj = <-ch
+	_ = obj
 }

vlib/v/checker/tests/assign_expr_type_err_a.out

@@ -3,4 +3,5 @@ vlib/v/checker/tests/assign_expr_type_err_a.vv:3:2: error: operator <<= not defi
     2 |     mut foo := 0.5
     3 |     foo <<= 1
       |     ~~~
-    4 | }
+    4 |     _ = foo
+    5 | }

vlib/v/checker/tests/assign_expr_type_err_a.vv

@@ -1,4 +1,5 @@
 fn main() {
 	mut foo := 0.5
 	foo <<= 1
-}
+	_ = foo
+}

vlib/v/checker/tests/assign_expr_type_err_b.out

@@ -3,4 +3,5 @@ vlib/v/checker/tests/assign_expr_type_err_b.vv:3:9: error: operator %= not defin
     2 |     mut foo := 10
     3 |     foo %= 'hello'
       |            ~~~~~~~
-    4 | }
+    4 |     _ = foo
+    5 | }

vlib/v/checker/tests/assign_expr_type_err_b.vv

@@ -1,4 +1,5 @@
 fn main() {
 	mut foo := 10
 	foo %= 'hello'
-}
+	_ = foo
+}

vlib/v/checker/tests/assign_expr_type_err_c.out

@@ -3,4 +3,5 @@ vlib/v/checker/tests/assign_expr_type_err_c.vv:3:2: error: operator *= not defin
     2 |     mut foo := 'hello'
     3 |     foo *= 10
       |     ~~~
-    4 | }
+    4 |     _ = foo
+    5 | }

vlib/v/checker/tests/assign_expr_type_err_c.vv

@@ -1,4 +1,5 @@
 fn main() {
 	mut foo := 'hello'
 	foo *= 10
-}
+	_ = foo
+}

vlib/v/checker/tests/assign_expr_type_err_d.out

@@ -3,4 +3,5 @@ vlib/v/checker/tests/assign_expr_type_err_d.vv:3:9: error: operator /= not defin
     2 |     mut foo := 1.5
     3 |     foo /= true
       |            ~~~~
-    4 | }
+    4 |     _ = foo
+    5 | }

vlib/v/checker/tests/assign_expr_type_err_d.vv

@@ -1,4 +1,5 @@
 fn main() {
 	mut foo := 1.5
 	foo /= true
-}
+	_ = foo
+}

vlib/v/checker/tests/assign_expr_type_err_e.out

@@ -3,4 +3,5 @@ vlib/v/checker/tests/assign_expr_type_err_e.vv:3:2: error: operator `-=` not def
     2 |     mut foo := 'hello'
     3 |     foo -= `a`
       |     ~~~
-    4 | }
+    4 |     _ = foo
+    5 | }

vlib/v/checker/tests/assign_expr_type_err_e.vv

@@ -1,4 +1,5 @@
 fn main() {
 	mut foo := 'hello'
 	foo -= `a`
-}
+	_ = foo
+}

vlib/v/checker/tests/assign_expr_type_err_f.out

@@ -3,4 +3,5 @@ vlib/v/checker/tests/assign_expr_type_err_f.vv:3:9: error: invalid right operand
     2 |     mut foo := 10
     3 |     foo -= false
       |            ~~~~~
-    4 | }
+    4 |     _ = foo
+    5 | }

vlib/v/checker/tests/assign_expr_type_err_f.vv

@@ -1,4 +1,5 @@
 fn main() {
 	mut foo := 10
 	foo -= false
-}
+	_ = foo
+}

vlib/v/checker/tests/assign_expr_type_err_g.out

@@ -3,4 +3,5 @@ vlib/v/checker/tests/assign_expr_type_err_g.vv:3:2: error: operator `+=` not def
     2 |     mut foo := true
     3 |     foo += false
       |     ~~~
-    4 | }
+    4 |     _ = foo
+    5 | }

vlib/v/checker/tests/assign_expr_type_err_g.vv

@@ -1,4 +1,5 @@
 fn main() {
 	mut foo := true
 	foo += false
-}
+	_ = foo
+}

vlib/v/checker/tests/assign_expr_type_err_h.out

@@ -3,4 +3,5 @@ vlib/v/checker/tests/assign_expr_type_err_h.vv:3:9: error: invalid right operand
     2 |     mut foo := 'hello'
     3 |     foo += false
       |            ~~~~~
-    4 | }
+    4 |     _ = foo
+    5 | }

vlib/v/checker/tests/assign_expr_type_err_h.vv

@@ -1,4 +1,5 @@
 fn main() {
 	mut foo := 'hello'
 	foo += false
-}
+	_ = foo
+}

vlib/v/checker/tests/assign_expr_type_err_i.out

@@ -1,6 +1,7 @@
 vlib/v/checker/tests/assign_expr_type_err_i.vv:3:9: error: invalid right operand: f64 += string
     1 | fn main() {
     2 |     mut foo := 1.5
-    3 |     foo += 'hello' 
+    3 |     foo += 'hello'
       |            ~~~~~~~
-    4 | }
+    4 |     _ = foo
+    5 | }

vlib/v/checker/tests/assign_expr_type_err_i.vv

@@ -1,4 +1,5 @@
 fn main() {
 	mut foo := 1.5
-	foo += 'hello' 
-}
+	foo += 'hello'
+	_ = foo
+}

vlib/v/checker/tests/assign_expr_unresolved_variables_err_chain.out

@@ -1,13 +1,13 @@
-vlib/v/checker/tests/assign_expr_unresolved_variables_err_chain.vv:2:7: error: undefined variable `b` (used before declaration) 
+vlib/v/checker/tests/assign_expr_unresolved_variables_err_chain.vv:2:7: error: undefined variable `b` (used before declaration)
     1 | fn main() {
     2 |     a := b
       |          ^
     3 |     b := c
     4 |     c := a
-vlib/v/checker/tests/assign_expr_unresolved_variables_err_chain.vv:3:7: error: undefined variable `c` (used before declaration) 
+vlib/v/checker/tests/assign_expr_unresolved_variables_err_chain.vv:3:7: error: undefined variable `c` (used before declaration)
     1 | fn main() {
     2 |     a := b
     3 |     b := c
       |          ^
     4 |     c := a
-    5 | }
+    5 |     _ = a

vlib/v/checker/tests/assign_expr_unresolved_variables_err_chain.vv

@@ -2,4 +2,7 @@ fn main() {
 	a := b
 	b := c
 	c := a
+	_ = a
+	_ = b
+	_ = c
 }

vlib/v/checker/tests/assign_sumtype_err.out

@@ -3,4 +3,5 @@ vlib/v/checker/tests/assign_sumtype_err.vv:13:9: error: cannot assign to `decl`:
    12 |     mut decl := Decl{}
    13 |     decl = stmt
       |            ~~~~
-   14 | }
+   14 |     _ = decl
+   15 | }

vlib/v/checker/tests/assign_sumtype_err.vv

@@ -11,4 +11,5 @@ fn main() {
 	stmt := Stmt(Decl{})
 	mut decl := Decl{}
 	decl = stmt
-}
+	_ = decl
+}

vlib/v/checker/tests/enum_as_int_err.out

@@ -11,10 +11,11 @@ vlib/v/checker/tests/enum_as_int_err.vv:10:8: error: cannot assign to `foo`: exp
    10 |     foo = Color.red
       |           ~~~~~~~~~
    11 |     println(color == 0)
-   12 | }
+   12 |     _ = foo
 vlib/v/checker/tests/enum_as_int_err.vv:11:10: error: infix expr: cannot use `int literal` (right expression) as `Color`
     9 |     color = 1
    10 |     foo = Color.red
    11 |     println(color == 0)
       |             ~~~~~~~~~~
-   12 | }
+   12 |     _ = foo
+   13 | }

vlib/v/checker/tests/enum_as_int_err.vv

@@ -9,4 +9,5 @@ fn main() {
 	color = 1
 	foo = Color.red
 	println(color == 0)
+	_ = foo
 }

vlib/v/checker/tests/error_with_unicode.out

@@ -1,5 +1,5 @@
 vlib/v/checker/tests/error_with_unicode.vv:5:17: error: cannot use `int literal` as `string` in argument 2 to `f1`
-    3 |
+    3 | 
     4 | fn main() {
     5 |     f1('🐀🐈', 0)
       |                ^
@@ -46,10 +46,11 @@ vlib/v/checker/tests/error_with_unicode.vv:12:6: error: cannot assign to `n`: ex
    12 |     n = '한글'
       |         ~~~~~~
    13 |     n = 'Кириллица'
-   14 | }
+   14 |     _ = n
 vlib/v/checker/tests/error_with_unicode.vv:13:6: error: cannot assign to `n`: expected `int`, not `string`
    11 |     n = '繁體字'
    12 |     n = '한글'
    13 |     n = 'Кириллица'
       |         ~~~~~~~~~~~
-   14 | }
+   14 |     _ = n
+   15 | }

vlib/v/checker/tests/error_with_unicode.vv

@@ -11,4 +11,5 @@ fn main() {
 	n = '繁體字'
 	n = '한글'
 	n = 'Кириллица'
+	_ = n
 }

vlib/v/checker/tests/fixed_array_conv.out

@@ -11,31 +11,31 @@ vlib/v/checker/tests/fixed_array_conv.vv:5:4: error: mismatched types `&int` and
     5 | ip = arr
       |    ^
     6 | _ = &int(arr)
-    7 |
+    7 | _ = p
 vlib/v/checker/tests/fixed_array_conv.vv:6:6: error: cannot cast a fixed array (use e.g. `&arr[0]` instead)
     4 | mut ip := &int(0)
     5 | ip = arr
     6 | _ = &int(arr)
       |      ~~~~~~~~
-    7 |
-    8 | unsafe {
-vlib/v/checker/tests/fixed_array_conv.vv:9:13: error: cannot use `[2]int` as `voidptr` in argument 1 to `memdup`
-    7 |
-    8 | unsafe {
-    9 |     _ = memdup(arr, 1)
+    7 | _ = p
+    8 | _ = ip
+vlib/v/checker/tests/fixed_array_conv.vv:11:13: error: cannot use `[2]int` as `voidptr` in argument 1 to `memdup`
+    9 | 
+   10 | unsafe {
+   11 |     _ = memdup(arr, 1)
       |                ~~~
-   10 |     _ = tos(arr, 1)
-   11 |     fn (p &int){}(arr)
-vlib/v/checker/tests/fixed_array_conv.vv:10:10: error: cannot use `[2]int` as `&byte` in argument 1 to `tos`
-    8 | unsafe {
-    9 |     _ = memdup(arr, 1)
-   10 |     _ = tos(arr, 1)
+   12 |     _ = tos(arr, 1)
+   13 |     fn (p &int){}(arr)
+vlib/v/checker/tests/fixed_array_conv.vv:12:10: error: cannot use `[2]int` as `&byte` in argument 1 to `tos`
+   10 | unsafe {
+   11 |     _ = memdup(arr, 1)
+   12 |     _ = tos(arr, 1)
       |             ~~~
-   11 |     fn (p &int){}(arr)
-   12 | }
-vlib/v/checker/tests/fixed_array_conv.vv:11:16: error: cannot use `[2]int` as `&int` in argument 1 to `anon`
-    9 |     _ = memdup(arr, 1)
-   10 |     _ = tos(arr, 1)
-   11 |     fn (p &int){}(arr)
+   13 |     fn (p &int){}(arr)
+   14 | }
+vlib/v/checker/tests/fixed_array_conv.vv:13:16: error: cannot use `[2]int` as `&int` in argument 1 to `anon`
+   11 |     _ = memdup(arr, 1)
+   12 |     _ = tos(arr, 1)
+   13 |     fn (p &int){}(arr)
       |                   ~~~
-   12 | }
+   14 | }

vlib/v/checker/tests/fixed_array_conv.vv

@@ -4,6 +4,8 @@ p = arr
 mut ip := &int(0)
 ip = arr
 _ = &int(arr)
+_ = p
+_ = ip
 
 unsafe {
 	_ = memdup(arr, 1)

vlib/v/checker/tests/fn_var.out

@@ -14,10 +14,10 @@ vlib/v/checker/tests/fn_var.vv:4:5: error: cannot assign to `p`: expected `&fn (
     3 | mut p := &f
     4 | p = &[f]
       |     ^
-    5 | i := 0
-    6 | println(i)
-vlib/v/checker/tests/fn_var.vv:7:31: error: undefined ident: `i`
-    5 | i := 0
-    6 | println(i)
-    7 | f = fn(mut a []int) { println(i) }
+    5 | _ = p
+    6 | i := 0
+vlib/v/checker/tests/fn_var.vv:8:31: error: undefined ident: `i`
+    6 | i := 0
+    7 | println(i)
+    8 | f = fn(mut a []int) { println(i) }
       |                               ^

vlib/v/checker/tests/fn_var.vv

@@ -2,6 +2,7 @@ mut f := fn(i int) byte {}
 f = 4
 mut p := &f
 p = &[f]
+_ = p
 i := 0
 println(i)
 f = fn(mut a []int) { println(i) }

vlib/v/checker/tests/immutable_var.out

@@ -3,4 +3,5 @@ vlib/v/checker/tests/immutable_var.vv:3:2: error: `a` is immutable, declare it w
     2 |     a := 1
     3 |     a = 2
       |     ^
-    4 | }
+    4 |     _ = a
+    5 | }

vlib/v/checker/tests/immutable_var.vv

@@ -1,4 +1,5 @@
 fn main() {
 	a := 1
 	a = 2
+	_ = a
 }

vlib/v/checker/tests/map_init_wrong_type.out

@@ -11,10 +11,11 @@ vlib/v/checker/tests/map_init_wrong_type.vv:4:17: error: invalid map key: expect
     4 |    _ = {2:0 3:0 "hi":0}
       |                 ~~~~
     5 |    _ = {2:0 3:`@` 4:0}
-    6 | }
+    6 |   _ = a
 vlib/v/checker/tests/map_init_wrong_type.vv:5:15: error: invalid map value: expected `int`, not `rune`
     3 |    a = { 'x': 12.3 }
     4 |    _ = {2:0 3:0 "hi":0}
     5 |    _ = {2:0 3:`@` 4:0}
       |               ~~~
-    6 | }
+    6 |   _ = a
+    7 | }

vlib/v/checker/tests/map_init_wrong_type.vv

@@ -3,4 +3,5 @@ fn main() {
    a = { 'x': 12.3 }
    _ = {2:0 3:0 "hi":0}
    _ = {2:0 3:`@` 4:0}
+  _ = a
 }

vlib/v/checker/tests/method_op_err.out

@@ -46,25 +46,24 @@ vlib/v/checker/tests/method_op_err.vv:34:13: error: mismatched types `User` and
    34 |     println(User{3, 4} < Foo{3, 4})
       |             ~~~~~~~~~~~~~~~~~~~~~~
    35 |     mut u := User{3, 4}
-   36 |     u += 12
-vlib/v/checker/tests/method_op_err.vv:36:10: error: cannot assign to `u`: expected `User`, not `int literal`
-   34 |     println(User{3, 4} < Foo{3, 4})
+   36 |    _ = u
+vlib/v/checker/tests/method_op_err.vv:37:10: error: cannot assign to `u`: expected `User`, not `int literal`
    35 |     mut u := User{3, 4}
-   36 |     u += 12
+   36 |    _ = u
+   37 |     u += 12
       |          ~~
-   37 |     u %= User{1, 3}
-   38 |     u += User{2, 3}
-vlib/v/checker/tests/method_op_err.vv:37:5: error: operator %= not defined on left operand type `User`
-   35 |     mut u := User{3, 4}
-   36 |     u += 12
-   37 |     u %= User{1, 3}
+   38 |     u %= User{1, 3}
+   39 |     u += User{2, 3}
+vlib/v/checker/tests/method_op_err.vv:38:5: error: operator %= not defined on left operand type `User`
+   36 |    _ = u
+   37 |     u += 12
+   38 |     u %= User{1, 3}
       |     ^
-   38 |     u += User{2, 3} 
-   39 | }
-vlib/v/checker/tests/method_op_err.vv:38:7: error: operator `+` must return `User` to be used as an assignment operator
-   36 |     u += 12
-   37 |     u %= User{1, 3}
-   38 |     u += User{2, 3} 
+   39 |     u += User{2, 3}
+   40 | }
+vlib/v/checker/tests/method_op_err.vv:39:7: error: operator `+` must return `User` to be used as an assignment operator
+   37 |     u += 12
+   38 |     u %= User{1, 3}
+   39 |     u += User{2, 3}
       |       ~~
-   39 | }
-
+   40 | }

vlib/v/checker/tests/method_op_err.vv

@@ -33,7 +33,8 @@ fn main() {
     println(User{3, 2} < User{2, 4})
     println(User{3, 4} < Foo{3, 4})
     mut u := User{3, 4}
+   _ = u
     u += 12
     u %= User{1, 3}
-    u += User{2, 3} 
+    u += User{2, 3}
 }

vlib/v/checker/tests/ptr_assign.out

@@ -3,3 +3,4 @@ vlib/v/checker/tests/ptr_assign.vv:3:5: error: cannot assign to `p`: expected `&
     2 | mut p := &v
     3 | p = 4
       |     ^
+    4 | _ = p

vlib/v/checker/tests/ptr_assign.vv

@@ -1,3 +1,4 @@
 mut v := 43
 mut p := &v
 p = 4
+_ = p

vlib/v/checker/tests/struct_assigned_to_pointer_to_struct.out

@@ -4,10 +4,11 @@ vlib/v/checker/tests/struct_assigned_to_pointer_to_struct.vv:5:4: error: mismatc
     5 |     f = { x: 223344 }
       |       ^
     6 |     f = Foo{ x: 20 }
-    7 | }
+    7 |     _ = f
 vlib/v/checker/tests/struct_assigned_to_pointer_to_struct.vv:6:4: error: mismatched types `&Foo` and `Foo`
     4 |     mut f := &Foo{ 10 }
     5 |     f = { x: 223344 }
     6 |     f = Foo{ x: 20 }
       |       ^
-    7 | }
+    7 |     _ = f
+    8 | }

vlib/v/checker/tests/struct_assigned_to_pointer_to_struct.vv

@@ -4,4 +4,5 @@ fn main() {
 	mut f := &Foo{ 10 }
 	f = { x: 223344 }
 	f = Foo{ x: 20 }
+	_ = f
 }

vlib/v/checker/tests/sum.out

@@ -13,7 +13,7 @@ vlib/v/checker/tests/sum.vv:6:8: error: cannot cast non-sum type `int` using `as
     7 | }
     8 |
 vlib/v/checker/tests/sum.vv:10:7: error: cannot cast `rune` to `Var`
-    8 |
+    8 | 
     9 | fn sum() {
    10 |     _ := Var(`J`)
       |          ~~~~~~~~
@@ -24,4 +24,5 @@ vlib/v/checker/tests/sum.vv:12:7: error: cannot assign to `s2`: expected `Var`,
    11 |     mut s2 := Var('')
    12 |     s2 = true
       |          ~~~~
-   13 | }
+   13 |     _ = s2
+   14 | }

vlib/v/checker/tests/sum.vv

@@ -10,4 +10,5 @@ fn sum() {
 	_ := Var(`J`)
 	mut s2 := Var('')
 	s2 = true
+	_ = s2
 }

vlib/v/checker/tests/sum_type_assign_non_variant_err.out

@@ -3,4 +3,5 @@ vlib/v/checker/tests/sum_type_assign_non_variant_err.vv:11:6: error: cannot assi
    10 |     mut w := Stmt(AnotherThing{})
    11 |     w = IfExpr{}
       |         ~~~~~~~~
-   12 | }
+   12 |     _ = w
+   13 | }

vlib/v/checker/tests/sum_type_assign_non_variant_err.vv

@@ -9,4 +9,5 @@ struct AnotherThing {}
 fn main() {
     mut w := Stmt(AnotherThing{})
 	w = IfExpr{}
+	_ = w
 }

vlib/v/checker/tests/var_used_before_declaration.out

@@ -1,6 +1,6 @@
-vlib/v/checker/tests/var_used_before_declaration.vv:2:13: error: undefined variable `x` (used before declaration) 
+vlib/v/checker/tests/var_used_before_declaration.vv:2:13: error: undefined variable `x` (used before declaration)
     1 | fn main() {
     2 |     println(x)
       |             ^
     3 |     x := 'hello v'
-    4 | }
+    4 |    _ = x

vlib/v/checker/tests/var_used_before_declaration.vv

@@ -1,4 +1,5 @@
 fn main() {
     println(x)
     x := 'hello v'
-}
+   _ = x
+}

vlib/v/checker/tests/void_fn_as_value.vv

@@ -5,4 +5,5 @@ fn main() {
 	a += x('a','b')
 	mut b := 'abcdef'
 	_ = b
+	_ = a
 }

vlib/v/gen/c/fn.v

@@ -1033,7 +1033,7 @@ fn (mut g Gen) autofree_call_postgen(node_pos int) {
 					// this means this tmp expr var has already been freed
 					continue
 				}
-				obj.is_used = true
+				obj.is_used = true // TODO bug? sets all vars is_used to true
 				g.autofree_variable(obj)
 				// g.nr_vars_to_free--
 			}

vlib/v/parser/parser.v

@@ -1947,7 +1947,14 @@ pub fn (mut p Parser) name_expr() ast.Expr {
 		opt := if p.tok.lit == 'r' { '`r` (raw string)' } else { '`c` (c string)' }
 		return p.error('cannot use $opt with `byte` and `rune`')
 	}
-	known_var := p.mark_var_as_used(p.tok.lit)
+	// Make sure that the var is not marked as used in assignments: `x = 1`, `x += 2` etc
+	// but only when it's actually used (e.g. `println(x)`)
+	known_var := if p.peek_tok.kind.is_assign() {
+		p.scope.known_var(p.tok.lit)
+	} else {
+		p.mark_var_as_used(p.tok.lit)
+	}
+	// Handle modules
 	mut is_mod_cast := false
 	if p.peek_tok.kind == .dot && !known_var && (language != .v || p.known_import(p.tok.lit)
 		|| p.mod.all_after_last('.') == p.tok.lit) {

vlib/v/parser/tests/prefix_first.out

@@ -4,14 +4,14 @@ vlib/v/parser/tests/prefix_first.vv:15:3: warning: move infix `-` operator befor
    15 |         -1
       |         ^
    16 |     } else {1}
-   17 | }
-vlib/v/parser/tests/prefix_first.vv:26:3: warning: move infix `&` operator before new line (if infix intended) or use brackets for a prefix expression
-   24 |     _ = opt() or {
-   25 |         _ = 1
-   26 |         &v
+   17 |     _ = p
+vlib/v/parser/tests/prefix_first.vv:27:3: warning: move infix `&` operator before new line (if infix intended) or use brackets for a prefix expression
+   25 |     _ = opt() or {
+   26 |         _ = 1
+   27 |         &v
       |         ^
-   27 |     }
-   28 | }
+   28 |     }
+   29 | }
 vlib/v/parser/tests/prefix_first.vv:13:6: error: `if` expression requires an expression as the last statement of every branch
    11 | 
    12 |     // later this should compile correctly
@@ -19,10 +19,10 @@ vlib/v/parser/tests/prefix_first.vv:13:6: error: `if` expression requires an exp
       |         ~~~~~~~
    14 |         v = 1
    15 |         -1
-vlib/v/parser/tests/prefix_first.vv:24:12: error: last statement in the `or {}` block should be an expression of type `&int` or exit parent scope
-   22 |     // later this should compile correctly
-   23 |     v := 3
-   24 |     _ = opt() or {
+vlib/v/parser/tests/prefix_first.vv:25:12: error: last statement in the `or {}` block should be an expression of type `&int` or exit parent scope
+   23 |     // later this should compile correctly
+   24 |     v := 3
+   25 |     _ = opt() or {
       |               ~~~~
-   25 |         _ = 1
-   26 |         &v
+   26 |         _ = 1
+   27 |         &v

vlib/v/parser/tests/prefix_first.vv

@@ -14,6 +14,7 @@ fn test_prefix() {
 		v = 1
 		-1
 	} else {1}
+	_ = p
 }
 
 fn opt() ?&int {return none}

vlib/v/parser/tests/unnecessary_mut.vv

@@ -3,4 +3,5 @@ fn main() {
 	if mut x == 0 {
 		println(true)
 	}
+	_ = x
 }

vlib/v/pref/default.v

@@ -93,7 +93,7 @@ pub fn (mut p Preferences) fill_with_defaults() {
 	}
 	p.find_cc_if_cross_compiling()
 	p.ccompiler_type = cc_from_string(p.ccompiler)
-	p.is_test = p.path.ends_with('_test.v') || p.path.ends_with('_test.vv')
+	p.is_test = p.path.ends_with('_test.v') || p.path.ends_with('.vv') || p.path.ends_with('.vv')
 		|| p.path.all_before_last('.v').all_before_last('.').ends_with('_test')
 	p.is_vsh = p.path.ends_with('.vsh')
 	p.is_script = p.is_vsh || p.path.ends_with('.v') || p.path.ends_with('.vv')