wrap up the new mut check

CHANGELOG.md

@@ -3,6 +3,7 @@
 - @ for escaping keywords (e.g. `struct Foo { @type string }`). 
 - Windows Unicode fixes (V can now work with non-ASCII paths etc on Windows). 
 - Fix mutable args bugs + don't allow primitive arguments to be modified.  
+- Declaring a mutable variable and never modifying it results in a compilation error.
 
 
 ## V 0.1.16 

examples/tetris/tetris.v

@@ -226,7 +226,7 @@ fn (g mut Game) delete_completed_line(y int) {
 	for yy := y - 1; yy >= 1; yy-- {
 		for x := 1; x <= FieldWidth; x++ {
 			mut a := g.field[yy + 1]
-			mut b := g.field[yy]
+			b := g.field[yy]
 			a[x] = b[x]
 		}
 	}

vlib/builtin/array_test.v

@@ -109,7 +109,7 @@ fn test_repeat() {
 		assert aa[9] == f32(1.1)
 	}
 	{
-		mut aa := [f64(1.1) ; 10]
+		aa := [f64(1.1) ; 10]
 		assert aa[0] == f64(1.1)
 		assert aa[5] == f64(1.1)
 		assert aa[9] == f64(1.1)

vlib/builtin/string_test.v

@@ -141,7 +141,7 @@ fn test_clone() {
 	a += 'a'
 	a += 'a'
 	b := a
-	mut c := a.clone()
+	c := a.clone()
 	assert c == a
 	assert c == 'aaa'
 	assert b == 'aaa'

vlib/math/stats_test.v

@@ -256,4 +256,5 @@ fn test_passing_empty() {
 	assert stats.min(data) == f64(0)
 	assert stats.max(data) == f64(0)
 	assert stats.range(data) == f64(0)
+}