[BREAKING] Disallow trailing dot not followed by number

Changelog.md

@@ -6,6 +6,7 @@ Breaking Changes:
  * Commandline interface: Require ``-`` if standard input is used as source.
  * General: ``continue`` in a ``do...while`` loop jumps to the condition (it used to jump to the loop body). Warning: this may silently change the semantics of existing code.
  * Type Checker: Disallow arithmetic operations for Boolean variables.
+ * Disallow trailing dots that are not followed by a number.
 
 Language Features:
  * General: Allow appending ``calldata`` keyword to types, to explicitly specify data location for arguments of external functions.

libsolidity/parsing/Scanner.cpp

@@ -768,8 +768,14 @@ Token::Value Scanner::scanNumber(char _charSeen)
 			scanDecimalDigits();  // optional
 			if (m_char == '.')
 			{
+				// A '.' has to be followed by a number.
+				if (m_source.isPastEndOfInput() || !isDecimalDigit(m_source.get(1)))
+				{
+					literal.complete();
+					return Token::Number;
+				}
 				addLiteralCharAndAdvance();
-				scanDecimalDigits();  // optional
+				scanDecimalDigits();
 			}
 		}
 	}

test/libsolidity/SolidityScanner.cpp

@@ -127,6 +127,26 @@ BOOST_AUTO_TEST_CASE(scientific_notation)
 	BOOST_CHECK_EQUAL(scanner.next(), Token::EOS);
 }
 
+BOOST_AUTO_TEST_CASE(trailing_dot)
+{
+	Scanner scanner(CharStream("2.5"));
+	BOOST_CHECK_EQUAL(scanner.currentToken(), Token::Number);
+	BOOST_CHECK_EQUAL(scanner.next(), Token::EOS);
+	scanner.reset(CharStream("2.5e10"), "");
+	BOOST_CHECK_EQUAL(scanner.currentToken(), Token::Number);
+	BOOST_CHECK_EQUAL(scanner.next(), Token::EOS);
+	scanner.reset(CharStream(".5"), "");
+	BOOST_CHECK_EQUAL(scanner.currentToken(), Token::Number);
+	BOOST_CHECK_EQUAL(scanner.next(), Token::EOS);
+	scanner.reset(CharStream(".5e10"), "");
+	BOOST_CHECK_EQUAL(scanner.currentToken(), Token::Number);
+	BOOST_CHECK_EQUAL(scanner.next(), Token::EOS);
+	scanner.reset(CharStream("2."), "");
+	BOOST_CHECK_EQUAL(scanner.currentToken(), Token::Number);
+	BOOST_CHECK_EQUAL(scanner.next(), Token::Period);
+	BOOST_CHECK_EQUAL(scanner.next(), Token::EOS);
+}
+
 BOOST_AUTO_TEST_CASE(negative_numbers)
 {
 	Scanner scanner(CharStream("var x = -.2 + -0x78 + -7.3 + 8.9 + 2e-2;"));

test/libsolidity/syntaxTests/parsing/trailing_dot1.sol

@@ -0,0 +1,7 @@
+contract test {
+	uint256 a = 2.2e10;
+	uint256 b = .5E10;
+	uint256 c = 4.e-2;
+}
+// ----
+// TypeError: (70-73): Member "e" not found or not visible after argument-dependent lookup in int_const 4

test/libsolidity/syntaxTests/parsing/trailing_dot2.sol

@@ -0,0 +1,7 @@
+contract test {
+	uint256 a = 2.2e10;
+	uint256 b = .5E10;
+	uint256 c = 2 + 2.;
+}
+// ----
+// ParserError: (76-77): Expected identifier but got ';'

test/libsolidity/syntaxTests/parsing/trailing_dot3.sol

@@ -0,0 +1,4 @@
+contract test {
+	uint a = 2.
+// ----
+// ParserError: (29-29): Expected identifier but got end of source