another map bug fix + fix some warnings

compiler/main.v

@@ -193,6 +193,7 @@ fn (v mut V) compile() {
 #include <signal.h>
 #include <stdarg.h> // for va_list 
 #include <inttypes.h>  // int64_t etc 
+#include <string.h> // memcpy 
 
 #define STRUCT_DEFAULT_VALUE {}
 #define EMPTY_STRUCT_DECLARATION

compiler/parser.v

@@ -2309,19 +2309,17 @@ fn format_str(str string) string {
 }
 
 fn (p mut Parser) string_expr() {
-	// println('.str EXPR')
 	str := p.lit
 	// No ${}, just return a simple string
 	if p.peek() != .dollar {
 		p.fgen('\'$str\'')
-		// println('before format: "$str"')
 		f := format_str(str)
-		// println('after format: "$str"')
+		// `C.puts('hi')` => `puts("hi");` 
 		if p.calling_c || (p.pref.translated && p.mod == 'main') {
 			p.gen('"$f"')
 		}
 		else {
-			p.gen('tos2("$f")') 
+			p.gen('tos2((byte*)"$f")') 
 		}
 		p.next()
 		return
@@ -2388,7 +2386,7 @@ fn (p mut Parser) string_expr() {
 	}
 	if complex_inter {
 		p.fgen('}') 
-} 
+	} 
 	p.fgen('\'') 
 	// println("hello %d", num) optimization.
 	if p.cgen.nogen {

vlib/builtin/map.v

@@ -143,11 +143,10 @@ fn (m map) bs(query string, start, end int, out voidptr) {
 */ 
 
 fn (m mut map) preorder_keys(node &Node) { 
-	if node.is_empty {
+	if !node.is_empty {
-		return 
-	} 
 	m._keys[m.key_i] = node.key 
 	m.key_i++ 
+	} 
 	if !isnil(node.left) { 
 		m.preorder_keys(node.left) 
 	} 

vlib/builtin/map_test.v

@@ -38,8 +38,10 @@ fn test_map() {
 	assert keys[1] == 'hello' 
 	m.delete('hi') 
 	assert m.size == 1 
+
 	assert m['hi'] == 0
 	assert m.keys().len == 1 
+	assert m.keys()[0] == 'hello' 
 	//// 
 	mut users := map[string]User{} 
 	users['1'] = User{'Peter'}