Merge pull request #10224 from ethereum/strict-literal-to-enum-conversion

[BREAKING] Strict explicit conversion between literals and enums

test/libsolidity/syntaxTests/enums/literal_conversion.sol

@@ -0,0 +1,10 @@
+contract C {
+    enum Test { One, Two }
+    function f() public pure {
+        Test a = Test(0);
+        Test b = Test(1);
+        Test c = Test(type(uint).max);
+        a; b; c;
+    }
+}
+// ----

test/libsolidity/syntaxTests/enums/literal_conversion_error.sol

@@ -0,0 +1,16 @@
+contract C {
+    enum Test { One, Two }
+    function f() public {
+        Test(-1);
+        Test(2);
+        Test(13);
+        Test(5/3);
+        Test(0.5);
+    }
+}
+// ----
+// TypeError 9640: (74-82): Explicit type conversion not allowed from "int_const -1" to "enum C.Test".
+// TypeError 9640: (92-99): Explicit type conversion not allowed from "int_const 2" to "enum C.Test".
+// TypeError 9640: (109-117): Explicit type conversion not allowed from "int_const 13" to "enum C.Test".
+// TypeError 9640: (127-136): Explicit type conversion not allowed from "rational_const 5 / 3" to "enum C.Test".
+// TypeError 9640: (146-155): Explicit type conversion not allowed from "rational_const 1 / 2" to "enum C.Test".