Merge pull request #8091 from random-internet-cat/interface-inheritance

Interface inheritance

Changelog.md

@@ -3,6 +3,7 @@
 Language Features:
  * Allow accessing external functions via contract and interface names to obtain their selector.
  * Inline Assembly: Support literals ``true`` and ``false``.
+ * Allow interfaces to inherit from other interfaces
 
 
 Compiler Features:

docs/contracts/interfaces.rst

@@ -8,7 +8,7 @@ Interfaces
 
 Interfaces are similar to abstract contracts, but they cannot have any functions implemented. There are further restrictions:
 
-- They cannot inherit other contracts or interfaces.
+- They cannot inherit from other contracts, but they can inherit from other interfaces.
 - All declared functions must be external.
 - They cannot declare a constructor.
 - They cannot declare state variables.
@@ -37,6 +37,27 @@ they can be overridden. This does not automatically mean that an overriding func
 can be overridden again - this is only possible if the overriding
 function is marked ``virtual``.
 
+Interfaces can inherit from other interfaces. This has the same rules as normal
+inheritance.
+
+::
+
+    pragma solidity >0.6.1 <0.7.0;
+
+    interface ParentA {
+        function test() external returns (uint256);
+    }
+
+    interface ParentB {
+        function test() external returns (uint256);
+    }
+
+    interface SubInterface is ParentA, ParentB {
+        // Must redefine test in order to assert that the parent
+        // meanings are compatible.
+        function test() external override(ParentA, ParentB) returns (uint256);
+    }
+
 Types defined inside interfaces and other contract-like structures
 can be accessed from other contracts: ``Token.TokenType`` or ``Token.Coin``.
 

libsolidity/analysis/TypeChecker.cpp

@@ -237,8 +237,8 @@ void TypeChecker::endVisit(InheritanceSpecifier const& _inheritance)
 	auto base = dynamic_cast<ContractDefinition const*>(&dereference(_inheritance.name()));
 	solAssert(base, "Base contract not available.");
 
-	if (m_scope->isInterface())
-		m_errorReporter.typeError(_inheritance.location(), "Interfaces cannot inherit.");
+	if (m_scope->isInterface() && !base->isInterface())
+		m_errorReporter.typeError(_inheritance.location(), "Interfaces can only inherit from other interfaces.");
 
 	if (base->isLibrary())
 		m_errorReporter.typeError(_inheritance.location(), "Libraries cannot be inherited from.");

test/libsolidity/semanticTests/interface_inheritance_conversions.sol

@@ -0,0 +1,39 @@
+interface Parent {
+    function parentFun() external returns (uint256);
+}
+
+interface SubA is Parent {
+    function subAFun() external returns (uint256);
+}
+
+interface SubB is Parent {
+    function subBFun() external returns (uint256);
+}
+
+contract Impl is SubA, SubB {
+    function parentFun() override external returns (uint256) { return 1; }
+    function subAFun() override external returns (uint256) { return 2; }
+    function subBFun() override external returns (uint256) { return 3; }
+}
+
+contract C {
+    function convertParent() public returns (uint256) {
+        Parent p = new Impl();
+        return p.parentFun();
+    }
+
+    function convertSubA() public returns (uint256, uint256) {
+        SubA sa = new Impl();
+        return (sa.parentFun(), sa.subAFun());
+    }
+
+    function convertSubB() public returns (uint256, uint256) {
+        SubB sb = new Impl();
+        return (sb.parentFun(), sb.subBFun());
+    }
+}
+
+// ----
+// convertParent() -> 1
+// convertSubA() -> 1, 2
+// convertSubB() -> 1, 3

test/libsolidity/syntaxTests/inheritance/interface/contract_base.sol

@@ -0,0 +1,5 @@
+contract C {}
+interface I is C {}
+
+// ----
+// TypeError: (29-30): Interfaces can only inherit from other interfaces.

test/libsolidity/syntaxTests/inheritance/interface/diamond/diamond_no_relist.sol

@@ -0,0 +1,10 @@
+interface Parent {
+    function test() external returns (uint256);
+}
+
+interface SubA is Parent {}
+interface SubB is Parent {}
+
+contract C is SubA, SubB {
+    function test() external override returns (uint256) { return 42; }
+}

test/libsolidity/syntaxTests/inheritance/interface/diamond/diamond_with_relist.sol

@@ -0,0 +1,15 @@
+interface Parent {
+    function test() external returns (uint256);
+}
+
+interface SubA is Parent {
+    function test() external override returns (uint256);
+}
+
+interface SubB is Parent {
+    function test() external override returns (uint256);
+}
+
+contract C is SubA, SubB {
+    function test() external override(SubA, SubB) returns (uint256) { return 42; }
+}

test/libsolidity/syntaxTests/inheritance/interface/implementation/complete.sol

@@ -0,0 +1,17 @@
+interface ParentA {
+    function testA() external returns (uint256);
+}
+
+interface ParentB {
+    function testB() external returns (uint256);
+}
+
+interface Sub is ParentA, ParentB {
+    function testSub() external returns (uint256);
+}
+
+contract SubImpl is Sub {
+    function testA() external override returns (uint256) { return 12; }
+    function testB() external override(ParentB) returns (uint256) { return 42; }
+    function testSub() external override returns (uint256) { return 99; }
+}

test/libsolidity/syntaxTests/inheritance/interface/implementation/partial.sol

@@ -0,0 +1,19 @@
+interface ParentA {
+    function testA() external returns (uint256);
+}
+
+interface ParentB {
+    function testB() external returns (uint256);
+}
+
+interface Sub is ParentA, ParentB {
+    function testSub() external returns (uint256);
+}
+
+contract SubImpl is Sub {
+    function testA() external override returns (uint256) { return 12; }
+    function testSub() external override returns (uint256) { return 99; }
+}
+
+// ----
+// TypeError: (234-407): Contract "SubImpl" should be marked as abstract.

test/libsolidity/syntaxTests/inheritance/interface/linearization/invalid/lists_a.sol

@@ -0,0 +1,8 @@
+interface ParentA {}
+interface ParentB {}
+interface Sub is ParentA, ParentB {}
+
+contract ListsA is Sub, ParentA {}
+
+// ----
+// TypeError: (80-114): Linearization of inheritance graph impossible

test/libsolidity/syntaxTests/inheritance/interface/linearization/invalid/lists_b.sol

@@ -0,0 +1,8 @@
+interface ParentA {}
+interface ParentB {}
+interface Sub is ParentA, ParentB {}
+
+contract ListsB is Sub, ParentB {}
+
+// ----
+// TypeError: (80-114): Linearization of inheritance graph impossible

test/libsolidity/syntaxTests/inheritance/interface/linearization/invalid/lists_both.sol

@@ -0,0 +1,8 @@
+interface ParentA {}
+interface ParentB {}
+interface Sub is ParentA, ParentB {}
+
+contract ListsBoth is Sub, ParentA, ParentB {}
+
+// ----
+// TypeError: (80-126): Linearization of inheritance graph impossible

test/libsolidity/syntaxTests/inheritance/interface/linearization/valid.sol

@@ -0,0 +1,7 @@
+interface ParentA {}
+interface ParentB {}
+interface Sub is ParentA, ParentB {}
+
+contract ListsA is ParentA, Sub {}
+contract ListsB is ParentB, Sub {}
+contract ListsBoth is ParentA, ParentB, Sub {}

test/libsolidity/syntaxTests/inheritance/interface/multiple_parents.sol

@@ -0,0 +1,15 @@
+interface SuperA {
+    function test() external returns (uint256);
+    function testA() external returns (int128);
+}
+
+interface SuperB {
+    function test() external returns (uint256);
+    function testB() external returns (int256);
+}
+
+interface Sub is SuperA, SuperB {
+}
+
+// ----
+// TypeError: (236-271): Derived contract must override function "test". Two or more base classes define function with same name and parameter types.

test/libsolidity/syntaxTests/inheritance/interface/overrides_multiple.sol

@@ -0,0 +1,31 @@
+interface SuperA {
+    function test1() external returns (uint256);
+    function test2() external returns (uint256);
+    function test3() external returns (uint256);
+    function test4() external returns (uint256);
+    function test5() external returns (uint256);
+}
+
+interface SuperB {
+    function test1() external returns (uint256);
+    function test2() external returns (uint256);
+    function test3() external returns (uint256);
+    function test4() external returns (uint256);
+    function test5() external returns (uint256);
+}
+
+interface Sub is SuperA, SuperB {
+    function test1() external returns (uint256);
+    function test2() external override returns (uint256);
+    function test3() external override(SuperA) returns (uint256);
+    function test4() external override(SuperB) returns (uint256);
+    function test5() external override(SuperA, SuperB) returns (uint256);
+}
+
+// ----
+// TypeError: (572-616): Overriding function is missing "override" specifier.
+// TypeError: (572-616): Overriding function is missing "override" specifier.
+// TypeError: (572-616): Function needs to specify overridden contracts "SuperA" and "SuperB".
+// TypeError: (647-655): Function needs to specify overridden contracts "SuperA" and "SuperB".
+// TypeError: (705-721): Function needs to specify overridden contract "SuperB".
+// TypeError: (771-787): Function needs to specify overridden contract "SuperA".

test/libsolidity/syntaxTests/inheritance/interface/overrides_single.sol

@@ -0,0 +1,14 @@
+interface Super {
+    function test1() external returns (uint256);
+    function test2() external returns (uint256);
+    function test3() external returns (uint256);
+}
+
+interface Sub is Super {
+    function test1() external returns (uint256);
+    function test2() external override returns (uint256);
+    function test3() external override(Super) returns (uint256);
+}
+
+// ----
+// TypeError: (197-241): Overriding function is missing "override" specifier.

test/libsolidity/syntaxTests/inheritance/interface/single_parent.sol

@@ -0,0 +1,5 @@
+interface Super {
+    function test() external returns (uint256);
+}
+
+interface Sub is Super {}

test/libsolidity/syntaxTests/nameAndTypeResolution/418_interface_inheritance.sol

@@ -2,5 +2,3 @@ interface A {
 }
 interface I is A {
 }
-// ----
-// TypeError: (31-32): Interfaces cannot inherit.