Fix using for with explicit reference types.

Changelog.md

@@ -13,6 +13,7 @@ Bugfixes:
  * SMTChecker: Fix internal error when encoding tuples of tuples.
  * SMTChecker: Fix aliasing soundness after pushing to an array pointer.
  * Type system: Fix internal compiler error on calling externally a function that returns variables with calldata location.
+ * Type system: Fix bug where a bound function was not found if ``using for`` is applied to explicit reference types.
 
 ### 0.6.9 (2020-06-04)
 

libsolidity/ast/Types.cpp

@@ -356,10 +356,18 @@ MemberList::MemberMap Type::boundFunctions(Type const& _type, ContractDefinition
 	for (ContractDefinition const* contract: _scope.annotation().linearizedBaseContracts)
 		for (UsingForDirective const* ufd: contract->usingForDirectives())
 		{
-			if (ufd->typeName() && _type != *TypeProvider::withLocationIfReference(
-				typeLocation,
-				ufd->typeName()->annotation().type
-			))
+			// Convert both types to pointers for comparison to see if the `using for`
+			// directive applies.
+			// Further down, we check more detailed for each function if `_type` is
+			// convertible to the function parameter type.
+			if (ufd->typeName() &&
+				*TypeProvider::withLocationIfReference(typeLocation, &_type, true) !=
+				*TypeProvider::withLocationIfReference(
+					typeLocation,
+					ufd->typeName()->annotation().type,
+					true
+				)
+			)
 				continue;
 			auto const& library = dynamic_cast<ContractDefinition const&>(
 				*ufd->libraryName().annotation().referencedDeclaration

test/libsolidity/semanticTests/libraries/using_for_storage_structs.sol

@@ -0,0 +1,25 @@
+struct Struct { uint x; }
+
+library L {
+    function f(Struct storage _x) internal view returns (uint256) {
+      return _x.x;
+    }
+}
+
+contract C {
+  using L for Struct;
+
+  Struct s;
+
+  function h(Struct storage _s) internal view returns (uint) {
+    // _s is pointer
+    return _s.f();
+  }
+  function g() public returns (uint, uint) {
+    s.x = 7;
+    // s is reference
+    return (s.f(), h(s));
+  }
+}
+// ----
+// g() -> 7, 7