Allow JSON empty exponent as trailing junk

Revert #251, and instead allow an invalid trailing empty exponent to be
treated as junk data in JSON parsing. Expand the test suite to test this
case, including testing the trailing junk.

include/fast_float/ascii_number.h

@@ -349,7 +349,7 @@ parsed_number_string_t<UC> parse_number_string(UC const *p, UC const * pend, par
       ++p;
     }
     if ((p == pend) || !is_integer(*p)) {
-      if(!(fmt & chars_format::fixed) || (fmt & FASTFLOAT_JSONFMT)) {
+      if(!(fmt & chars_format::fixed)) {
         // We are in error.
         return answer;
       }

tests/json_fmt.cpp

@@ -36,32 +36,55 @@ int main_readme3() {
     return EXIT_SUCCESS;
 }
 
-int main()
-{
-  const std::vector<double> expected{ -0.2, 0.02, 0.002, 1., 0., std::numeric_limits<double>::infinity() };
-  const std::vector<std::string> accept{ "-0.2", "0.02", "0.002", "1e+0000", "0e-2", "inf" };
-  const std::vector<std::string> reject{"-.2", "00.02",    "0.e+1", "00.e+1",
-                                        "1e",  "1e+",      ".25",   "+0.25",
-                                        "inf", "nan(snan)"};
+struct ExpectedResult {
+  double value;
+  std::string junk_chars;
+};
+struct AcceptedValue {
+  std::string input;
+  ExpectedResult expected;
+};
+
+int main() {
+  const std::vector<AcceptedValue> accept{
+      {"-0.2", {-0.2, ""}},
+      {"0.02", {0.02, ""}},
+      {"0.002", {0.002, ""}},
+      {"1e+0000", {1., ""}},
+      {"0e-2", {0., ""}},
+      {"1e", {1., "e"}},
+      {"1e+", {1., "e+"}},
+      {"inf", {std::numeric_limits<double>::infinity(), ""}}};
+  const std::vector<std::string> reject{"-.2", "00.02", "0.e+1", "00.e+1",
+                                        ".25", "+0.25", "inf",   "nan(snan)"};
 
   for (std::size_t i = 0; i < accept.size(); ++i)
   {
-    const auto& f = accept[i];
+    const auto& s = accept[i].input;
+    const auto& expected = accept[i].expected;
     double result;
-    auto answer = fast_float::from_chars(f.data(), f.data() + f.size(), result, fast_float::chars_format::json_or_infnan);
-    if (answer.ec != std::errc() || result != expected[i]) {
-      std::cerr << "json fmt rejected valid json " << f << std::endl;
+    auto answer = fast_float::from_chars(s.data(), s.data() + s.size(), result, fast_float::chars_format::json_or_infnan);
+    if (answer.ec != std::errc()) {
+      std::cerr << "json fmt rejected valid json " << s << std::endl;
+      return EXIT_FAILURE;
+    }
+    if (result != expected.value) {
+      std::cerr << "json fmt gave wrong result " << s << " (expected " << expected.value << " got " << result << ")" << std::endl;
+      return EXIT_FAILURE;
+    }
+    if (std::string(answer.ptr) != expected.junk_chars) {
+      std::cerr << "json fmt has wrong trailing characters " << s << " (expected " << expected.junk_chars << " got " << answer.ptr << ")" << std::endl;
       return EXIT_FAILURE;
     }
   }
 
   for (std::size_t i = 0; i < reject.size(); ++i)
   {
-    const auto& f = reject[i];
+    const auto& s = reject[i];
     double result;
-    auto answer = fast_float::from_chars(f.data(), f.data() + f.size(), result, fast_float::chars_format::json);
+    auto answer = fast_float::from_chars(s.data(), s.data() + s.size(), result, fast_float::chars_format::json);
     if (answer.ec == std::errc()) {
-      std::cerr << "json fmt accepted invalid json " << f << std::endl;
+      std::cerr << "json fmt accepted invalid json " << s << std::endl;
       return EXIT_FAILURE;
     }
   }