fix(json_render): add json render unittest & optimized Number formatter.

Author: 张峰

include/util/json_renderer.hpp

@@ -47,20 +47,12 @@ template <typename Out> struct Renderer
 
     void operator()(const Number &number)
     {
+        // we don't want to print NaN or Infinity
+        BOOST_ASSERT(std::isfinite(number.value));
         // `fmt::memory_buffer` stores first 500 bytes in the object itself(i.e. on stack in this
         // case) and then grows using heap if needed
         fmt::memory_buffer buffer;
-        fmt::format_to(std::back_inserter(buffer), FMT_COMPILE("{}"), number.value);
-
-        // Truncate to 10 decimal places
-        size_t decimalpos = std::find(buffer.begin(), buffer.end(), '.') - buffer.begin();
-        if (buffer.size() > (decimalpos + 10))
-        {
-            buffer.clear();
-            fmt::format_to(std::back_inserter(buffer), FMT_COMPILE("{0:.10f}"), number.value);
-
-            // buffer.resize(decimalpos + 10);
-        }
+        fmt::format_to(std::back_inserter(buffer), FMT_COMPILE("{:.10g}"), number.value);
 
         write(buffer.data(), buffer.size());
     }

unit_tests/util/json_render.cpp

@@ -27,4 +27,11 @@ BOOST_AUTO_TEST_CASE(integer)
     BOOST_CHECK_EQUAL(str, "42");
 }
 
+BOOST_AUTO_TEST_CASE(test_json_issue_6531) {
+    std::string output;
+    osrm::util::json::Renderer<std::string> renderer(output);
+    renderer(0.0000000000017114087924596788);
+    BOOST_CHECK_EQUAL(output, "1.711408792e-12");
+}
+
 BOOST_AUTO_TEST_SUITE_END()