gen: fix mutable map generation (#7251)

TESTS.md

@@ -10,6 +10,7 @@ particularly useful for checking that errors are printed.
 
 Tip: use `v -cc tcc` when compiling tests for speed.
 
+
 ## `v test-compiler`
 
 This builds and tests:

vlib/v/gen/cgen.v

@@ -1235,16 +1235,17 @@ fn (mut g Gen) for_in(it ast.ForInStmt) {
 		idx := g.new_tmp_var()
 		atmp := g.new_tmp_var()
 		atmp_styp := g.typ(it.cond_type)
+		arw_or_pt := if it.cond_type.nr_muls() > 0 { '->' } else { '.' }
 		g.write('$atmp_styp $atmp = ')
 		g.expr(it.cond)
 		g.writeln(';')
-		g.writeln('for (int $idx = 0; $idx < ${atmp}.key_values.len; ++$idx) {')
+		g.writeln('for (int $idx = 0; $idx < $atmp${arw_or_pt}key_values.len; ++$idx) {')
 		// TODO: don't have this check when the map has no deleted elements
-		g.writeln('\tif (!DenseArray_has_index(&${atmp}.key_values, $idx)) {continue;}')
+		g.writeln('\tif (!DenseArray_has_index(&$atmp${arw_or_pt}key_values, $idx)) {continue;}')
 		if it.key_var != '_' {
 			key_styp := g.typ(it.key_type)
 			key := c_name(it.key_var)
-			g.writeln('\t$key_styp $key = /*key*/ *($key_styp*)DenseArray_key(&${atmp}.key_values, $idx);')
+			g.writeln('\t$key_styp $key = /*key*/ *($key_styp*)DenseArray_key(&$atmp${arw_or_pt}key_values, $idx);')
 			// TODO: analyze whether it.key_type has a .clone() method and call .clone() for all types:
 			if it.key_type == table.string_type {
 				g.writeln('\t$key = string_clone($key);')
@@ -1260,7 +1261,7 @@ fn (mut g Gen) for_in(it ast.ForInStmt) {
 				val_styp := g.typ(it.val_type)
 				g.write('\t$val_styp ${c_name(it.val_var)} = (*($val_styp*)')
 			}
-			g.writeln('DenseArray_value(&${atmp}.key_values, $idx));')
+			g.writeln('DenseArray_value(&$atmp${arw_or_pt}key_values, $idx));')
 		}
 		g.stmts(it.stmts)
 		if it.key_type == table.string_type && !g.is_builtin_mod {

vlib/v/tests/map_mut_fn_test.v

@@ -0,0 +1,20 @@
+fn print_all(mut m map[string]string) {
+	for k, v in m {
+		println(k)
+		println(v)
+		m[k] = 'foo'
+	}
+	assert m['test'] == 'foo'
+}
+
+fn test_map_mutable_arg() {
+	mut m := map[string]string{}
+	m['test'] = 'test'
+
+	for k, v in m {
+		println(k)
+		println(v)
+	}
+
+	print_all(mut m)
+}