Fix seg fault parsing invalid exponents

Add error message when exponents are incomplete,
for example 5e and 5.e

CHANGES.current

@@ -7,6 +7,9 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.0.0 (in progress)
 ===========================
 
+2018-01-14: wsfulton
+            Fix issue #1172. Seg fault parsing invalid exponents in the preprocessor.
+
 2018-01-12: Liryna
             [C#] Patch #1128. Add ToArray function to std::vector wrappers.
 

Examples/test-suite/errors/cpp_invalid_exponents1.i

@@ -0,0 +1,4 @@
+%module xxx
+
+void bad(double nn = 5e);
+

Examples/test-suite/errors/cpp_invalid_exponents1.stderr

@@ -0,0 +1,2 @@
+cpp_invalid_exponents1.i:3: Error: Exponent does not have any digits
+cpp_invalid_exponents1.i:3: Error: Syntax error in input(1).

Examples/test-suite/errors/cpp_invalid_exponents2.i

@@ -0,0 +1,4 @@
+%module xxx
+
+void bad(double nn = 6.6e);
+

Examples/test-suite/errors/cpp_invalid_exponents2.stderr

@@ -0,0 +1,2 @@
+cpp_invalid_exponents2.i:3: Error: Exponent does not have any digits
+cpp_invalid_exponents2.i:3: Error: Syntax error in input(1).

Examples/test-suite/errors/pp_invalid_exponents.i

@@ -0,0 +1,7 @@
+%module xxx
+
+#if 123e
+#endif
+
+#if 456.e
+#endif

Examples/test-suite/errors/pp_invalid_exponents.stderr

@@ -0,0 +1,6 @@
+:EOF: Error: Exponent does not have any digits
+pp_invalid_exponents.i:3: Warning 202: Could not evaluate expression '123e'
+pp_invalid_exponents.i:3: Warning 202: Error: 'Syntax error'
+:EOF: Error: Exponent does not have any digits
+pp_invalid_exponents.i:6: Warning 202: Could not evaluate expression '456.e'
+pp_invalid_exponents.i:6: Warning 202: Error: 'Syntax error'

Source/Swig/scanner.c

@@ -1118,27 +1118,29 @@ static int look(Scanner *s) {
       break;
     case 82:
       if ((c = nextchar(s)) == 0) {
-	retract(s, 1);
+	Swig_error(cparse_file, cparse_start_line, "Exponent does not have any digits\n");
-	return SWIG_TOKEN_INT;
+	return SWIG_TOKEN_ERROR;
       }
       if ((isdigit(c)) || (c == '-') || (c == '+'))
 	state = 86;
       else {
 	retract(s, 2);
-	return (SWIG_TOKEN_INT);
+	Swig_error(cparse_file, cparse_start_line, "Exponent does not have any digits\n");
+	return SWIG_TOKEN_ERROR;
       }
       break;
     case 820:
       /* Like case 82, but we've seen a decimal point. */
       if ((c = nextchar(s)) == 0) {
-	retract(s, 1);
+	Swig_error(cparse_file, cparse_start_line, "Exponent does not have any digits\n");
-	return SWIG_TOKEN_DOUBLE;
+	return SWIG_TOKEN_ERROR;
       }
       if ((isdigit(c)) || (c == '-') || (c == '+'))
 	state = 86;
       else {
 	retract(s, 2);
-	return (SWIG_TOKEN_DOUBLE);
+	Swig_error(cparse_file, cparse_start_line, "Exponent does not have any digits\n");
+	return SWIG_TOKEN_ERROR;
       }
       break;
     case 83: