checker: make map literals have a real type

vlib/builtin/map_test.v

@@ -207,3 +207,45 @@ fn test_delete_size() {
         }
     }
 }
+
+struct Mstruct1 {
+pub mut:
+	mymap map[string]int
+}
+
+struct Mstruct2 {
+pub mut:
+	mymap map[string]f64
+}
+
+struct Mstruct3 {
+pub mut:
+	mymap map[string]u16
+}
+
+fn test_map_assign() {
+	mut a := map[string]f64{}
+	mut b := map[string]int{}
+	mut c := map[string]u16{}
+	a = {
+		'x': 12.4
+		'y': 3
+	}
+	b = {
+		'u': -13
+		'v': 12
+	}
+	c = {
+		's': u16(5)
+		't': 3
+	}
+	d := Mstruct1 {
+		{ 'p': 12 }
+	}
+	e := Mstruct2 {
+		{ 'q': 1.7 }
+	}
+	f := Mstruct3 {
+		{ 'r': u16(6), 's': 5 }
+	}
+}

vlib/v/checker/checker.v

@@ -2515,8 +2515,8 @@ pub fn (mut c Checker) map_init(mut node ast.MapInit) table.Type {
 		return node.typ
 	}
 	// `{'age': 20}`
-	key0_type := c.expr(node.keys[0])
-	val0_type := c.expr(node.vals[0])
+	key0_type := c.table.mktyp(c.expr(node.keys[0]))
+	val0_type := c.table.mktyp(c.expr(node.vals[0]))
 	for i, key in node.keys {
 		key_i := key as ast.StringLiteral
 		for j in 0 .. i {

vlib/v/checker/tests/map_init_wrong_type.out

@@ -0,0 +1,6 @@
+vlib/v/checker/tests/map_init_wrong_type.v:3:10: error: cannot assign `map_string_f64` to `a` of type `map_string_f32` 
+    1 | fn main() {
+    2 |    mut a := map[string]f32{}
+    3 |    a = { 'x': 12.3 }
+      |          ~~~
+    4 | }

vlib/v/checker/tests/map_init_wrong_type.vv

@@ -0,0 +1,4 @@
+fn main() {
+   mut a := map[string]f32{}
+   a = { 'x': 12.3 }
+}