Allow assignments to local variables of mapping types.

test/libsolidity/syntaxTests/types/mapping/assignment_local.sol

@@ -9,7 +9,3 @@ contract test {
     }
 }
 // ----
-// TypeError: (176-177): Mappings cannot be assigned to.
-// TypeError: (192-193): Mappings cannot be assigned to.
-// TypeError: (209-210): Mappings cannot be assigned to.
-// TypeError: (212-213): Mappings cannot be assigned to.

test/libsolidity/syntaxTests/types/mapping/mapping_return_external.sol

@@ -0,0 +1,7 @@
+contract C {
+    function f() external pure returns (mapping(uint=>uint) storage m) {
+    }
+}
+// ----
+// TypeError: (53-82): Type is required to live outside storage.
+// TypeError: (53-82): Internal or recursive type is not allowed for public or external functions.

test/libsolidity/syntaxTests/types/mapping/mapping_return_internal.sol

@@ -0,0 +1,21 @@
+// This should be allowed in a future release.
+contract C {
+    mapping(uint=>uint) m;
+    function f() internal view returns (mapping(uint=>uint) storage) {
+        return m;
+    }
+    function g() private view returns (mapping(uint=>uint) storage) {
+        return m;
+    }
+    function h() internal view returns (mapping(uint=>uint) storage r) {
+        r = m;
+    }
+    function i() private view returns (mapping(uint=>uint) storage r) {
+        (r,r) = (m,m);
+    }
+}
+// ----
+// TypeError: (127-146): Type is required to live outside storage.
+// TypeError: (221-240): Type is required to live outside storage.
+// TypeError: (316-345): Type is required to live outside storage.
+// TypeError: (409-438): Type is required to live outside storage.

test/libsolidity/syntaxTests/types/mapping/mapping_return_public.sol

@@ -0,0 +1,7 @@
+contract C {
+    function f() public pure returns (mapping(uint=>uint) storage m) {
+    }
+}
+// ----
+// TypeError: (51-80): Type is required to live outside storage.
+// TypeError: (51-80): Internal or recursive type is not allowed for public or external functions.