use diagnostic positions in exceptions

docs/examples/diagnostic_positions_exception.cpp

@@ -0,0 +1,29 @@
+#include <iostream>
+
+#define JSON_DIAGNOSTIC_POSITIONS 1
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+/* Demonstration of type error exception with diagnostic postions support enabled */
+int main()
+{
+    //Invalid json string - housenumber type must be int instead of string
+    std::string json_invalid_string = R"(
+    {
+        "address": {
+            "street": "Fake Street",
+            "housenumber": "1"
+        }
+    }
+    )";
+    json j = json::parse(json_invalid_string);
+    try
+    {
+        int housenumber = j["address"]["housenumber"];
+    }
+    catch (const json::exception& e)
+    {
+        std::cout << e.what() << '\n';
+    }
+}

docs/examples/diagnostic_positions_exception.output

@@ -0,0 +1 @@
+[json.exception.type_error.302] (bytes 92-95) type must be number, but is string

docs/examples/diagnostics_extended_positions.cpp

@@ -0,0 +1,30 @@
+#include <iostream>
+
+#define JSON_DIAGNOSTICS 1
+#define JSON_DIAGNOSTIC_POSITIONS 1
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+/* Demonstration of type error exception with diagnostic postions support enabled */
+int main()
+{
+    //Invalid json string - housenumber type must be int instead of string
+    std::string json_invalid_string = R"(
+    {
+        "address": {
+            "street": "Fake Street",
+            "housenumber": "1"
+        }
+    }
+    )";
+    json j = json::parse(json_invalid_string);
+    try
+    {
+        int housenumber = j["address"]["housenumber"];
+    }
+    catch (const json::exception& e)
+    {
+        std::cout << e.what() << '\n';
+    }
+}

docs/examples/diagnostics_extended_positions.output

@@ -0,0 +1 @@
+[json.exception.type_error.302] (/address/housenumber) (bytes 92-95) type must be number, but is string

docs/mkdocs/docs/api/macros/json_diagnostic_positions.md

@@ -54,8 +54,33 @@ When the macro is not defined, the library will define it to its default value.
     ```
     --8<-- "examples/diagnostic_positions.output"
     ```
-
     The output shows the start/end positions of all the objects and fields in the JSON string.
 
+??? example "Example 2: using extended diagnostics with positions enabled in exceptions"
+
+    ```cpp
+    --8<-- "examples/diagnostics_extended_positions.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/diagnostics_extended_positions.output"
+    ```
+        The output shows the exception with diagnostic path info and start/end positions.
+
+??? example "Example 3: using only diagnostic positions in exceptions"
+
+    ```cpp
+    --8<-- "examples/diagnostic_positions_exception.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/diagnostic_positions_exception.output"
+    ```    
+        The output shows the exception with start/end positions only.
+
 ## Version history
 

include/nlohmann/detail/exceptions.hpp

@@ -131,16 +131,30 @@ class exception : public std::exception
         {
             return concat(a, '/', detail::escape(b));
         });
-        return concat('(', str, ") ");
+
+        return concat('(', str, ") ") + get_byte_positions(leaf_element);
 #else
-        static_cast<void>(leaf_element);
-        return "";
+        return get_byte_positions(leaf_element);
 #endif
     }
 
   private:
     /// an exception object as storage for error messages
     std::runtime_error m;
+    template<typename BasicJsonType>
+    static std::string get_byte_positions(const BasicJsonType* leaf_element)
+    {
+#if JSON_DIAGNOSTIC_POSITIONS
+        if ((leaf_element->start_pos() != std::string::npos) && (leaf_element->end_pos() != std::string::npos))
+        {
+            return concat('(', "bytes ", std::to_string(leaf_element->start_pos()), "-", std::to_string(leaf_element->end_pos()), ") ");
+        }
+        return "";
+#else
+        static_cast<void>(leaf_element);
+        return "";
+#endif
+    }
 };
 
 /// @brief exception indicating a parse error

single_include/nlohmann/json.hpp

@@ -4534,16 +4534,30 @@ class exception : public std::exception
         {
             return concat(a, '/', detail::escape(b));
         });
-        return concat('(', str, ") ");
+
+        return concat('(', str, ") ") + get_byte_positions(leaf_element);
 #else
-        static_cast<void>(leaf_element);
-        return "";
+        return get_byte_positions(leaf_element);
 #endif
     }
 
   private:
     /// an exception object as storage for error messages
     std::runtime_error m;
+    template<typename BasicJsonType>
+    static std::string get_byte_positions(const BasicJsonType* leaf_element)
+    {
+#if JSON_DIAGNOSTIC_POSITIONS
+        if ((leaf_element->start_pos() != std::string::npos) && (leaf_element->end_pos() != std::string::npos))
+        {
+            return concat('(', "bytes ", std::to_string(leaf_element->start_pos()), "-", std::to_string(leaf_element->end_pos()), ") ");
+        }
+        return "";
+#else
+        static_cast<void>(leaf_element);
+        return "";
+#endif
+    }
 };
 
 /// @brief exception indicating a parse error

tests/src/unit-json_patch.cpp

@@ -60,14 +60,20 @@ TEST_CASE("JSON patch")
             json const doc2 = R"({ "q": { "bar": 2 } })"_json;
 
             // because "a" does not exist.
+#if JSON_DIAGNOSTIC_POSITIONS
+            CHECK_THROWS_WITH_AS(doc2.patch(patch1), "[json.exception.out_of_range.403] (bytes 0-21) key 'a' not found", json::out_of_range&);
+#else
             CHECK_THROWS_WITH_AS(doc2.patch(patch1), "[json.exception.out_of_range.403] key 'a' not found", json::out_of_range&);
+#endif
 
             json const doc3 = R"({ "a": {} })"_json;
             json const patch2 = R"([{ "op": "add", "path": "/a/b/c", "value": 1 }])"_json;
 
             // should cause an error because "b" does not exist in doc3
 #if JSON_DIAGNOSTICS
             CHECK_THROWS_WITH_AS(doc3.patch(patch2), "[json.exception.out_of_range.403] (/a) key 'b' not found", json::out_of_range&);
+#elif JSON_DIAGNOSTIC_POSITIONS
+            CHECK_THROWS_WITH_AS(doc3.patch(patch2), "[json.exception.out_of_range.403] (bytes 7-9) key 'b' not found", json::out_of_range&);
 #else
             CHECK_THROWS_WITH_AS(doc3.patch(patch2), "[json.exception.out_of_range.403] key 'b' not found", json::out_of_range&);
 #endif
@@ -333,6 +339,8 @@ TEST_CASE("JSON patch")
             CHECK_THROWS_AS(doc.patch(patch), json::other_error&);
 #if JSON_DIAGNOSTICS
             CHECK_THROWS_WITH_STD_STR(doc.patch(patch), "[json.exception.other_error.501] (/0) unsuccessful: " + patch[0].dump());
+#elif JSON_DIAGNOSTIC_POSITIONS
+            CHECK_THROWS_WITH_STD_STR(doc.patch(patch), "[json.exception.other_error.501] (bytes 47-95) unsuccessful: " + patch[0].dump());
 #else
             CHECK_THROWS_WITH_STD_STR(doc.patch(patch), "[json.exception.other_error.501] unsuccessful: " + patch[0].dump());
 #endif
@@ -417,8 +425,11 @@ TEST_CASE("JSON patch")
             // applied), because the "add" operation's target location that
             // references neither the root of the document, nor a member of
             // an existing object, nor a member of an existing array.
-
+#if JSON_DIAGNOSTIC_POSITIONS
+            CHECK_THROWS_WITH_AS(doc.patch(patch), "[json.exception.out_of_range.403] (bytes 21-37) key 'baz' not found", json::out_of_range&);
+#else
             CHECK_THROWS_WITH_AS(doc.patch(patch), "[json.exception.out_of_range.403] key 'baz' not found", json::out_of_range&);
+#endif
         }
 
         // A.13. Invalid JSON Patch Document
@@ -476,6 +487,8 @@ TEST_CASE("JSON patch")
             CHECK_THROWS_AS(doc.patch(patch), json::other_error&);
 #if JSON_DIAGNOSTICS
             CHECK_THROWS_WITH_STD_STR(doc.patch(patch), "[json.exception.other_error.501] (/0) unsuccessful: " + patch[0].dump());
+#elif JSON_DIAGNOSTIC_POSITIONS
+            CHECK_THROWS_WITH_STD_STR(doc.patch(patch), "[json.exception.other_error.501] (bytes 47-92) unsuccessful: " + patch[0].dump());
 #else
             CHECK_THROWS_WITH_STD_STR(doc.patch(patch), "[json.exception.other_error.501] unsuccessful: " + patch[0].dump());
 #endif
@@ -1205,6 +1218,8 @@ TEST_CASE("JSON patch")
                 CHECK_THROWS_AS(doc.patch(patch), json::other_error&);
 #if JSON_DIAGNOSTICS
                 CHECK_THROWS_WITH_STD_STR(doc.patch(patch), "[json.exception.other_error.501] (/0) unsuccessful: " + patch[0].dump());
+#elif JSON_DIAGNOSTIC_POSITIONS
+                CHECK_THROWS_WITH_STD_STR(doc.patch(patch), "[json.exception.other_error.501] (bytes 47-117) unsuccessful: " + patch[0].dump());
 #else
                 CHECK_THROWS_WITH_STD_STR(doc.patch(patch), "[json.exception.other_error.501] unsuccessful: " + patch[0].dump());
 #endif

tests/src/unit-json_pointer.cpp

@@ -203,11 +203,15 @@ TEST_CASE("JSON pointers")
             // escaped access
             CHECK(j[json::json_pointer("/a~1b")] == j["a/b"]);
             CHECK(j[json::json_pointer("/m~0n")] == j["m~n"]);
-
+#if JSON_DIAGNOSTIC_POSITIONS
+            // unescaped access
+            CHECK_THROWS_WITH_AS(j.at(json::json_pointer("/a/b")),
+                                 "[json.exception.out_of_range.403] (bytes 13-297) key 'a' not found", json::out_of_range&);
+#else
             // unescaped access
             CHECK_THROWS_WITH_AS(j.at(json::json_pointer("/a/b")),
                                  "[json.exception.out_of_range.403] key 'a' not found", json::out_of_range&);
-
+#endif
             // unresolved access
             const json j_primitive = 1;
             CHECK_THROWS_WITH_AS(j_primitive["/foo"_json_pointer],

tests/src/unit-regression1.cpp

@@ -1400,14 +1400,24 @@ TEST_CASE("regression tests 1")
         auto p1 = R"([{"op": "move",
                        "from": "/one/two/three",
                        "path": "/a/b/c"}])"_json;
+#if JSON_DIAGNOSTIC_POSITIONS
+        CHECK_THROWS_WITH_AS(model.patch(p1),
+                             "[json.exception.out_of_range.403] (bytes 0-158) key 'a' not found", json::out_of_range&);
+#else
         CHECK_THROWS_WITH_AS(model.patch(p1),
                              "[json.exception.out_of_range.403] key 'a' not found", json::out_of_range&);
+#endif
 
         auto p2 = R"([{"op": "copy",
                        "from": "/one/two/three",
                        "path": "/a/b/c"}])"_json;
+#if JSON_DIAGNOSTIC_POSITIONS
+        CHECK_THROWS_WITH_AS(model.patch(p2),
+                             "[json.exception.out_of_range.403] (bytes 0-158) key 'a' not found", json::out_of_range&);
+#else
         CHECK_THROWS_WITH_AS(model.patch(p2),
                              "[json.exception.out_of_range.403] key 'a' not found", json::out_of_range&);
+#endif
     }
 
     SECTION("issue #961 - incorrect parsing of indefinite length CBOR strings")