compiler: fix a bug with mutable array args

compiler/fn.v

@@ -853,7 +853,7 @@ fn (p mut Parser) fn_call_args(f mut Fn) *Fn {
 			p.error(err)
 		}
 		is_interface := p.table.is_interface(arg.typ)
-		// Add & or * before arg?
+		// Add `&` or `*` before an argument?
 		if !is_interface {
 			// Dereference
 			if got.contains('*') && !expected.contains('*') {
@@ -862,11 +862,17 @@ fn (p mut Parser) fn_call_args(f mut Fn) *Fn {
 			// Reference
 			// TODO ptr hacks. DOOM hacks, fix please.
 			if !got.contains('*') && expected.contains('*') && got != 'voidptr' {
+				// Special case for mutable arrays. We can't & function results,
+				// have to use `(array[]){ expr }` hack. 
+				if expected.starts_with('array_') && expected.ends_with('*') { 
+					p.cgen.set_placeholder(ph, '& /*111*/ (array_int[]){') 
+					p.gen('} ') 
+				} 
 				// println('\ne:"$expected" got:"$got"')
-				if ! (expected == 'void*' && got == 'int') &&
+				else if ! (expected == 'void*' && got == 'int') &&
 				! (expected == 'byte*' && got.contains(']byte')) &&
 				! (expected == 'byte*' && got == 'string') {
-					p.cgen.set_placeholder(ph, '& /*11 EXP:"$expected" GOT:"$got" */') 
+					p.cgen.set_placeholder(ph, '& /*112 EXP:"$expected" GOT:"$got" */') 
 				}
 			}
 		}

vlib/builtin/array_test.v

@@ -177,3 +177,15 @@ fn test_fixed() {
 	nums2 := [N]int 
 	assert nums2[N - 1] == 0 
 } 
+
+fn modify (numbers mut []int) {
+        numbers[0] = 777
+}
+
+fn test_mut_slice() { 
+        mut n := [1,2,3]
+        modify(mut n.left(2)) 
+	assert n[0] == 777 
+        println(n)
+}
+