cgen: fix iteration over `shared` map (#9763)

vlib/v/gen/c/cgen.v

@@ -1538,7 +1538,10 @@ fn (mut g Gen) for_in_stmt(node ast.ForInStmt) {
 			g.expr(node.cond)
 			g.writeln(';')
 		}
-		arw_or_pt := if node.cond_type.is_ptr() { '->' } else { '.' }
+		mut arw_or_pt := if node.cond_type.is_ptr() { '->' } else { '.' }
+		if node.cond_type.has_flag(.shared_f) {
+			arw_or_pt = '->val.'
+		}
 		idx := g.new_tmp_var()
 		map_len := g.new_tmp_var()
 		g.empty_line = true

vlib/v/tests/shared_map_test.v

@@ -82,3 +82,76 @@ fn new_map() map[string]f64 {
 	}
 	return m
 }
+
+fn test_shared_array_iteration() {
+	shared a := [12.75, -0.125, 17]
+	mut n0 := 0
+	mut n1 := 0
+	mut n2 := 0
+	rlock a {
+		for i, val in a {
+			match i {
+				1 {
+					assert val == -0.125
+					n1++
+					// check for order, too:
+					assert n0 == 1
+				}
+				0 {
+					assert val == 12.75
+					n0++
+				}
+				2 {
+					assert val == 17.0
+					n2++
+					assert n1 == 1
+				}
+				else {
+					// this should not happen
+					assert false
+				}
+			}
+		}
+	}
+	// make sure we have iterated over each of the 3 keys exactly once
+	assert n0 == 1
+	assert n1 == 1
+	assert n2 == 1
+}
+
+fn test_shared_map_iteration() {
+	shared m := map{
+		'qwe': 12.75
+		'rtz': -0.125
+		'k':   17
+	}
+	mut n0 := 0
+	mut n1 := 0
+	mut n2 := 0
+	rlock m {
+		for k, val in m {
+			match k {
+				'rtz' {
+					assert val == -0.125
+					n0++
+				}
+				'qwe' {
+					assert val == 12.75
+					n1++
+				}
+				'k' {
+					assert val == 17.0
+					n2++
+				}
+				else {
+					// this should not happen
+					assert false
+				}
+			}
+		}
+	}
+	// make sure we have iterated over each of the 3 keys exactly once
+	assert n0 == 1
+	assert n1 == 1
+	assert n2 == 1
+}