Add more tests for strings with unicode (escapes)

test/libsolidity/semanticTests/strings/unicode_escapes.sol

@@ -0,0 +1,22 @@
+contract C {
+    function oneByteUTF8() public pure returns (string memory) {
+        return "aaa\u0024aaa"; // usdollar
+    }
+
+    function twoBytesUTF8() public pure returns (string memory) {
+        return "aaa\u00A2aaa"; // cent
+    }
+
+    function threeBytesUTF8() public pure returns (string memory) {
+        return "aaa\u20ACaaa"; // euro
+    }
+
+    function combined() public pure returns (string memory) {
+        return "\u0024\u00A2\u20AC";
+    }
+}
+// ----
+// oneByteUTF8() -> 0x20, 7, "aaa$aaa"
+// twoBytesUTF8() -> 0x20, 8, "aaa\xc2\xa2aaa"
+// threeBytesUTF8() -> 0x20, 9, "aaa\xe2\x82\xacaaa"
+// combined() -> 0x20, 6, "$\xc2\xa2\xe2\x82\xac"

test/libsolidity/semanticTests/strings/unicode_string.sol

@@ -0,0 +1,7 @@
+contract C {
+    function f() public pure returns (string memory) {
+        return "😃, 😭, and 😈";
+    }
+}
+// ----
+// f() -> 0x20, 0x14, "\xf0\x9f\x98\x83, \xf0\x9f\x98\xad, and \xf0\x9f\x98\x88"

test/libsolidity/syntaxTests/string/invalid_utf8_hex_string.sol

@@ -0,0 +1,5 @@
+contract C {
+    string s = hex"a000";
+}
+// ----
+// TypeError 7407: (28-37): Type literal_string (contains invalid UTF-8 sequence at position 0) is not implicitly convertible to expected type string storage ref.

test/libsolidity/syntaxTests/string/invalid_utf8_in_bytes.sol

@@ -0,0 +1,6 @@
+contract C {
+    bytes b1 = "\xa0\x00";
+    bytes32 b2 = "\xa0\x00";
+    bytes b3 = hex"a000";
+}
+// ----

test/libsolidity/syntaxTests/string/string_unicode.sol

@@ -0,0 +1,6 @@
+contract test {
+    function f() public pure returns (string memory) {
+        return "😃, 😭, and 😈";
+    }
+}
+// ----

test/libsolidity/syntaxTests/string/unicode_escape_literals.sol

@@ -1,5 +1,4 @@
 contract test {
-
     function oneByteUTF8() public pure returns (bytes32) {
         bytes32 usdollar = "aaa\u0024aaa";
         return usdollar;
@@ -15,17 +14,8 @@ contract test {
         return  eur;
     }
 
-    function together() public pure returns (bytes32) {
+    function combined() public pure returns (bytes32) {
         bytes32 res = "\u0024\u00A2\u20AC";
         return res;
     }
-
-    // this function returns an invalid unicode character
-    function invalidLiteral() public pure returns(bytes32) {
-        bytes32 invalid = "\u00xx";
-        return invalid;
-    }
-
 }
-// ----
-// ParserError 8936: (678-681): Invalid escape sequence.

test/libsolidity/syntaxTests/string/unicode_escape_literals_invalid_codepoint.sol

@@ -0,0 +1,7 @@
+contract test {
+    function f() public pure returns (string memory) {
+        return "\xc1";
+    }
+}
+// ----
+// TypeError 6359: (86-92): Return argument type literal_string (contains invalid UTF-8 sequence at position 0) is not implicitly convertible to expected type (type of first return variable) string memory.

test/libsolidity/syntaxTests/string/unicode_escape_literals_invalid_format.sol

@@ -0,0 +1,10 @@
+contract test {
+    // this function returns an invalid unicode character
+    function invalidLiteral() public pure returns (bytes32) {
+        bytes32 invalid = "\u00xx";
+        return invalid;
+    }
+
+}
+// ----
+// ParserError 8936: (162-165): Invalid escape sequence.