Allow leading plus signs when parsing integers.

Author: LTLA

include/eminem/Parser.hpp

@@ -1372,11 +1372,9 @@ class Parser {
     public:
         template<class Input2_>
         ParseInfo<Type_> operator()(Input2_& input, Index overall_line_count) {
-            Type_ val = 0;
-            bool found = false;
-
-            bool negative = (input.get() == '-');
-            if (negative) {
+            char firstchar = input.get();
+            bool negative = (firstchar == '-');
+            if (negative || firstchar == '+') {
                 if (!(input.advance())) {
                     throw std::runtime_error("premature termination of an integer on line " + std::to_string(overall_line_count + 1));
                 }
@@ -1389,6 +1387,8 @@ class Parser {
             constexpr Type_ lower_limit_before_mult = lower_limit / 10;
             constexpr Type_ lower_limit_mod = -(lower_limit % 10);
 
+            Type_ val = 0;
+            bool found = false;
             while (1) {
                 char x = input.get();
                 switch (x) {

tests/src/integer.cpp

@@ -50,7 +50,8 @@ INSTANTIATE_TEST_SUITE_P(
         std::make_tuple<std::string, int, int, std::vector<int> >("1 1 -1\n2 2 -23\n3 3 -456\n4 4 -7890\n", 5, 5, { -1, -23, -456, -7890 }), // negative values
         std::make_tuple<std::string, int, int, std::vector<int> >("12 34 567890", 50, 50, { 567890 }), // no trailing newline
         std::make_tuple<std::string, int, int, std::vector<int> >("12 34 567890   ", 50, 50, { 567890 }), // trailing blank without a trailing newline.
-        std::make_tuple<std::string, int, int, std::vector<int> >("1 1  11  \n2 22   2222\n33 3\t33\t\n44 44 \t4\t \n", 100, 100, { 11, 2222, 33, 4 }) // variable numbers of blanks 
+        std::make_tuple<std::string, int, int, std::vector<int> >("1 1  11  \n2 22   2222\n33 3\t33\t\n44 44 \t4\t \n", 100, 100, { 11, 2222, 33, 4 }), // variable numbers of blanks 
+        std::make_tuple<std::string, int, int, std::vector<int> >("1 1  0111\n2 22 +002\n33 3 033\t\n44 44 +0004\n", 100, 100, { 111, 2, 33, 4 }) // leading zeros and pluses
     )
 );