Merge pull request #10335 from ethereum/fixMappingConversion

[Sol->Yul] Fix mapping conversion.

libsolidity/codegen/YulUtilFunctions.cpp

@@ -3072,6 +3072,12 @@ string YulUtilFunctions::conversionFunction(Type const& _from, Type const& _to)
 				solAssert(false, "Invalid conversion from " + _from.canonicalName() + " to " + _to.canonicalName());
 			break;
 		}
+		case Type::Category::Mapping:
+		{
+			solAssert(_from == _to, "");
+			body = "converted := value";
+			break;
+		}
 		default:
 			solAssert(false, "Invalid conversion from " + _from.canonicalName() + " to " + _to.canonicalName());
 		}

test/libsolidity/semanticTests/variables/mapping_local_tuple_assignment.sol

@@ -12,5 +12,7 @@ contract test {
         return (m1[1], m1[2], m2[1], m2[2]);
     }
 }
+// ====
+// compileViaYul: also
 // ----
 // f() -> 42, 0, 0, 21