enforce interface-functions to be external-declared

- libsolidity: Enforce interface-functions must be external-declared.
- Changelog adapted to reflect changes wrt. functions in interfaces.
- test: Adjustments according to prior interface-function changes.
- tests: Adapting SolidityEndToEndTest to interface-function change.
- docs: Adapted documentation to interface-function change.

2 files changed, 2 insertions, 2 deletions

diff --git a/test/libsolidity/syntaxTests/constructor/interface_constructor_new.sol b/test/libsolidity/syntaxTests/constructor/interface_constructor_new.sol
index 2cab1851..87585a62 100644
--- a/test/libsolidity/syntaxTests/constructor/interface_constructor_new.sol
+++ b/test/libsolidity/syntaxTests/constructor/interface_constructor_new.sol
@@ -2,6 +2,6 @@ interface I {
 	constructor() public;
 }
 // ----
-// Warning: (15-36): Functions in interfaces should be declared external.
+// TypeError: (15-36): Functions in interfaces must be declared external.
 // TypeError: (15-36): Constructor cannot be defined in interfaces.
 // TypeError: (15-36): Constructor must be implemented if declared.
diff --git a/test/libsolidity/syntaxTests/constructor/interface_constructor_old.sol b/test/libsolidity/syntaxTests/constructor/interface_constructor_old.sol
index 313d4345..2c029f4d 100644
--- a/test/libsolidity/syntaxTests/constructor/interface_constructor_old.sol
+++ b/test/libsolidity/syntaxTests/constructor/interface_constructor_old.sol
@@ -3,6 +3,6 @@ interface I {
 }
 // ----
 // Warning: (15-35): Defining constructors as functions with the same name as the contract is deprecated. Use "constructor(...) { ... }" instead.
-// Warning: (15-35): Functions in interfaces should be declared external.
+// TypeError: (15-35): Functions in interfaces must be declared external.
 // TypeError: (15-35): Constructor cannot be defined in interfaces.
 // TypeError: (15-35): Constructor must be implemented if declared.