Fallback function has to be external: backwards-compatible changes.

test/libsolidity/syntaxTests/fallback/default_visibility.sol

@@ -0,0 +1,6 @@
+contract C {
+    // Check that visibility is also enforced for the fallback function.
+    function() {}
+}
+// ----
+// Warning: (90-103): No visibility specified. Defaulting to "public". 

test/libsolidity/syntaxTests/fallback/pure_modifier.sol

@@ -1,6 +1,6 @@
 contract C {
     uint x;
-    function() pure { x = 2; }
+    function() external pure { x = 2; }
 }
 // ----
-// TypeError: (29-55): Fallback function must be payable or non-payable, but is "pure".
+// TypeError: (29-64): Fallback function must be payable or non-payable, but is "pure".

test/libsolidity/syntaxTests/fallback/view_modifier.sol

@@ -1,6 +1,6 @@
 contract C {
     uint x;
-    function() view { x = 2; }
+    function() external view { x = 2; }
 }
 // ----
-// TypeError: (29-55): Fallback function must be payable or non-payable, but is "view".
+// TypeError: (29-64): Fallback function must be payable or non-payable, but is "view".

test/libsolidity/syntaxTests/nameAndTypeResolution/074_fallback_function.sol

@@ -1,4 +1,4 @@
 contract C {
     uint x;
-    function() public { x = 2; }
+    function() external { x = 2; }
 }

test/libsolidity/syntaxTests/nameAndTypeResolution/075_fallback_function_with_arguments.sol

@@ -1,6 +1,6 @@
 contract C {
     uint x;
-    function(uint a) public { x = 2; }
+    function(uint a) external { x = 2; }
 }
 // ----
 // TypeError: (37-45): Fallback function cannot take parameters.

test/libsolidity/syntaxTests/nameAndTypeResolution/076_fallback_function_in_library.sol

@@ -1,5 +1,5 @@
 library C {
-    function() public {}
+    function() external {}
 }
 // ----
-// TypeError: (16-36): Libraries cannot have fallback functions.
+// TypeError: (16-38): Libraries cannot have fallback functions.

test/libsolidity/syntaxTests/nameAndTypeResolution/077_fallback_function_with_return_parameters.sol

@@ -1,5 +1,5 @@
 contract C {
-    function() public returns (uint) { }
+    function() external returns (uint) { }
 }
 // ----
-// TypeError: (43-49): Fallback function cannot return values.
+// TypeError: (45-51): Fallback function cannot return values.

test/libsolidity/syntaxTests/nameAndTypeResolution/078_fallback_function_twice.sol

@@ -1,7 +1,7 @@
 contract C {
     uint x;
-    function() public { x = 2; }
-    function() public { x = 3; }
+    function() external { x = 2; }
+    function() external { x = 3; }
 }
 // ----
-// DeclarationError: (62-90): Only one fallback function is allowed.
+// DeclarationError: (64-94): Only one fallback function is allowed.

test/libsolidity/syntaxTests/nameAndTypeResolution/079_fallback_function_inheritance.sol

@@ -1,7 +1,7 @@
 contract A {
     uint x;
-    function() public { x = 1; }
+    function() external { x = 1; }
 }
 contract C is A {
-    function() public { x = 2; }
+    function() external { x = 2; }
 }

test/libsolidity/syntaxTests/nameAndTypeResolution/196_integer_boolean_or.sol

@@ -1,3 +1,3 @@
-contract test { function() public { uint x = 1; uint y = 2; x || y; } }
+contract test { function() external { uint x = 1; uint y = 2; x || y; } }
 // ----
-// TypeError: (60-66): Operator || not compatible with types uint256 and uint256
+// TypeError: (62-68): Operator || not compatible with types uint256 and uint256

test/libsolidity/syntaxTests/nameAndTypeResolution/197_integer_boolean_and.sol

@@ -1,3 +1,3 @@
-contract test { function() public { uint x = 1; uint y = 2; x && y; } }
+contract test { function() external { uint x = 1; uint y = 2; x && y; } }
 // ----
-// TypeError: (60-66): Operator && not compatible with types uint256 and uint256
+// TypeError: (62-68): Operator && not compatible with types uint256 and uint256

test/libsolidity/syntaxTests/nameAndTypeResolution/198_integer_boolean_not.sol

@@ -1,3 +1,3 @@
-contract test { function() public { uint x = 1; !x; } }
+contract test { function() external { uint x = 1; !x; } }
 // ----
-// TypeError: (48-50): Unary operator ! cannot be applied to type uint256
+// TypeError: (50-52): Unary operator ! cannot be applied to type uint256

test/libsolidity/syntaxTests/nameAndTypeResolution/199_integer_unsigned_exp_signed.sol

@@ -1,3 +1,3 @@
-contract test { function() public { uint x = 3; int y = -4; x ** y; } }
+contract test { function() external { uint x = 3; int y = -4; x ** y; } }
 // ----
-// TypeError: (60-66): Operator ** not compatible with types uint256 and int256
+// TypeError: (62-68): Operator ** not compatible with types uint256 and int256

test/libsolidity/syntaxTests/nameAndTypeResolution/200_integer_signed_exp_unsigned.sol

@@ -1,3 +1,3 @@
-contract test { function() public { uint x = 3; int y = -4; y ** x; } }
+contract test { function() external { uint x = 3; int y = -4; y ** x; } }
 // ----
-// TypeError: (60-66): Operator ** not compatible with types int256 and uint256
+// TypeError: (62-68): Operator ** not compatible with types int256 and uint256

test/libsolidity/syntaxTests/nameAndTypeResolution/201_integer_signed_exp_signed.sol

@@ -1,3 +1,3 @@
-contract test { function() public { int x = -3; int y = -4; x ** y; } }
+contract test { function() external { int x = -3; int y = -4; x ** y; } }
 // ----
-// TypeError: (60-66): Operator ** not compatible with types int256 and int256
+// TypeError: (62-68): Operator ** not compatible with types int256 and int256

test/libsolidity/syntaxTests/nameAndTypeResolution/202_bytes_reference_compare_operators.sol

@@ -1,3 +1,3 @@
-contract test { bytes a; bytes b; function() public { a == b; } }
+contract test { bytes a; bytes b; function() external { a == b; } }
 // ----
-// TypeError: (54-60): Operator == not compatible with types bytes storage ref and bytes storage ref
+// TypeError: (56-62): Operator == not compatible with types bytes storage ref and bytes storage ref

test/libsolidity/syntaxTests/nameAndTypeResolution/203_struct_reference_compare_operators.sol

@@ -1,3 +1,10 @@
-contract test { struct s {uint a;} s x; s y; function() public { x == y; } }
+contract test {
+  struct s {uint a;}
+  s x;
+  s y;
+  function() external {
+    x == y;
+  }
+}
 // ----
-// TypeError: (65-71): Operator == not compatible with types struct test.s storage ref and struct test.s storage ref
+// TypeError: (79-85): Operator == not compatible with types struct test.s storage ref and struct test.s storage ref

test/libsolidity/syntaxTests/nameAndTypeResolution/415_interface_functions.sol

@@ -1,9 +1,5 @@
 interface I {
-    function();
-    function f();
+    function() external;
+    function f() external;
 }
 // ----
-// Warning: (18-29): Functions in interfaces should be declared external.
-// Warning: (34-47): Functions in interfaces should be declared external.
-// Warning: (18-29): No visibility specified. Defaulting to "public". In interfaces it defaults to external.
-// Warning: (34-47): No visibility specified. Defaulting to "public". In interfaces it defaults to external.

test/libsolidity/syntaxTests/nameAndTypeResolution/424_using_interface_complex.sol

@@ -1,17 +1,11 @@
 interface I {
     event A();
-    function f();
-    function g();
-    function();
+    function f() external;
+    function g() external;
+    function() external;
 }
 contract C is I {
     function f() public {
     }
 }
 // ----
-// Warning: (33-46): Functions in interfaces should be declared external.
-// Warning: (51-64): Functions in interfaces should be declared external.
-// Warning: (69-80): Functions in interfaces should be declared external.
-// Warning: (33-46): No visibility specified. Defaulting to "public". In interfaces it defaults to external.
-// Warning: (51-64): No visibility specified. Defaulting to "public". In interfaces it defaults to external.
-// Warning: (69-80): No visibility specified. Defaulting to "public". In interfaces it defaults to external.

test/libsolidity/syntaxTests/nameAndTypeResolution/463_error_transfer_non_payable_fallback.sol

@@ -2,16 +2,16 @@
 // because A's fallback function is not payable.
 
 contract A {
-    function() public {}
+    function() external {}
 }
 
 contract B {
     A a;
 
-    function() public {
+    function() external {
         a.transfer(100);
     }
 }
 // ----
-// Warning: (209-219): Using contract member "transfer" inherited from the address type is deprecated. Convert the contract to "address" type to access the member, for example use "address(contract).transfer" instead.
-// TypeError: (209-219): Value transfer to a contract without a payable fallback function.
+// Warning: (213-223): Using contract member "transfer" inherited from the address type is deprecated. Convert the contract to "address" type to access the member, for example use "address(contract).transfer" instead.
+// TypeError: (213-223): Value transfer to a contract without a payable fallback function.

test/libsolidity/syntaxTests/nameAndTypeResolution/464_error_transfer_no_fallback.sol

@@ -6,10 +6,10 @@ contract A {}
 contract B {
     A a;
 
-    function() public {
+    function() external {
         a.transfer(100);
     }
 }
 // ----
-// Warning: (190-200): Using contract member "transfer" inherited from the address type is deprecated. Convert the contract to "address" type to access the member, for example use "address(contract).transfer" instead.
-// TypeError: (190-200): Value transfer to a contract without a payable fallback function.
+// Warning: (192-202): Using contract member "transfer" inherited from the address type is deprecated. Convert the contract to "address" type to access the member, for example use "address(contract).transfer" instead.
+// TypeError: (192-202): Value transfer to a contract without a payable fallback function.

test/libsolidity/syntaxTests/nameAndTypeResolution/465_error_send_non_payable_fallback.sol

@@ -2,16 +2,16 @@
 // because A does not have a payable fallback function.
 
 contract A {
-    function() public {}
+    function() external {}
 }
 
 contract B {
     A a;
 
-    function() public {
+    function() external {
         require(a.send(100));
     }
 }
 // ----
-// Warning: (220-226): Using contract member "send" inherited from the address type is deprecated. Convert the contract to "address" type to access the member, for example use "address(contract).send" instead.
-// TypeError: (220-226): Value transfer to a contract without a payable fallback function.
+// Warning: (224-230): Using contract member "send" inherited from the address type is deprecated. Convert the contract to "address" type to access the member, for example use "address(contract).send" instead.
+// TypeError: (224-230): Value transfer to a contract without a payable fallback function.

test/libsolidity/syntaxTests/nameAndTypeResolution/466_does_not_error_transfer_payable_fallback.sol

@@ -2,15 +2,15 @@
 // because A does not have a payable fallback function.
 
 contract A {
-    function() payable public {}
+    function() payable external {}
 }
 
 contract B {
     A a;
 
-    function() public {
+    function() external {
         a.transfer(100);
     }
 }
 // ----
-// Warning: (224-234): Using contract member "transfer" inherited from the address type is deprecated. Convert the contract to "address" type to access the member, for example use "address(contract).transfer" instead.
+// Warning: (228-238): Using contract member "transfer" inherited from the address type is deprecated. Convert the contract to "address" type to access the member, for example use "address(contract).transfer" instead.

test/libsolidity/syntaxTests/nameAndTypeResolution/467_does_not_error_transfer_regular_function.sol

@@ -5,7 +5,7 @@ contract A {
 contract B {
     A a;
 
-    function() public {
+    function() external {
         a.transfer();
     }
 }

test/libsolidity/syntaxTests/nameAndTypeResolution/526_fallback_marked_external.sol

@@ -0,0 +1,3 @@
+contract C {
+    function () external { }
+}

test/libsolidity/syntaxTests/nameAndTypeResolution/527_fallback_marked_internal.sol

@@ -0,0 +1,4 @@
+contract C {
+    function () internal { }
+}
+// ----

test/libsolidity/syntaxTests/nameAndTypeResolution/528_fallback_marked_private.sol

@@ -0,0 +1,4 @@
+contract C {
+    function () private { }
+}
+// ----

test/libsolidity/syntaxTests/nameAndTypeResolution/529_fallback_marked_public.sol

@@ -0,0 +1,4 @@
+contract C {
+    function () public { }
+}
+// ----

test/libsolidity/syntaxTests/parsing/fallback_function.sol

@@ -1,5 +1,4 @@
 contract c {
-    function() { }
+    function() external { }
 }
 // ----
-// Warning: (17-31): No visibility specified. Defaulting to "public". 

test/libsolidity/syntaxTests/viewPureChecker/builtin_functions.sol

@@ -14,5 +14,5 @@ contract C {
         assert(true);
         x; y; z;
     }
-    function() payable public {}
+    function() payable external {}
 }