From f5f975a48c4d32e23e6ee732c495a91f166f5532 Mon Sep 17 00:00:00 2001
From: Florian Albrechtskirchinger <falbrechtskirchinger@gmail.com>
Date: Tue, 5 Apr 2022 14:57:10 +0200
Subject: [PATCH] Allow comparing different json_pointers

---
 include/nlohmann/detail/json_pointer.hpp | 33 +++++++++++++++++-------
 single_include/nlohmann/json.hpp         | 33 +++++++++++++++++-------
 test/src/unit-json_pointer.cpp           | 14 ++++++++++
 3 files changed, 60 insertions(+), 20 deletions(-)

diff --git a/include/nlohmann/detail/json_pointer.hpp b/include/nlohmann/detail/json_pointer.hpp
index a9b208dfd4..f94f3bdf9a 100644
--- a/include/nlohmann/detail/json_pointer.hpp
+++ b/include/nlohmann/detail/json_pointer.hpp
@@ -836,11 +836,10 @@ class json_pointer
 
     @exceptionsafety No-throw guarantee: this function never throws exceptions.
     */
-    friend bool operator==(json_pointer const& lhs,
-                           json_pointer const& rhs) noexcept
-    {
-        return lhs.reference_tokens == rhs.reference_tokens;
-    }
+    template<typename RefStringTypeLhs, typename RefStringTypeRhs>
+    // NOLINTNEXTLINE(readability-redundant-declaration)
+    friend bool operator==(json_pointer<RefStringTypeLhs> const& lhs,
+                           json_pointer<RefStringTypeRhs> const& rhs) noexcept;
 
     /*!
     @brief compares two JSON pointers for inequality
@@ -853,13 +852,27 @@ class json_pointer
 
     @exceptionsafety No-throw guarantee: this function never throws exceptions.
     */
-    friend bool operator!=(json_pointer const& lhs,
-                           json_pointer const& rhs) noexcept
-    {
-        return !(lhs == rhs);
-    }
+    template<typename RefStringTypeLhs, typename RefStringTypeRhs>
+    // NOLINTNEXTLINE(readability-redundant-declaration)
+    friend bool operator!=(json_pointer<RefStringTypeLhs> const& lhs,
+                           json_pointer<RefStringTypeRhs> const& rhs) noexcept;
 
     /// the reference tokens
     std::vector<string_t> reference_tokens;
 };
+
+// functions cannot be defined inside class due to ODR violations
+template<typename RefStringTypeLhs, typename RefStringTypeRhs>
+inline bool operator==(json_pointer<RefStringTypeLhs> const& lhs,
+                       json_pointer<RefStringTypeRhs> const& rhs) noexcept
+{
+    return lhs.reference_tokens == rhs.reference_tokens;
+}
+
+template<typename RefStringTypeLhs, typename RefStringTypeRhs>
+inline bool operator!=(json_pointer<RefStringTypeLhs> const& lhs,
+                       json_pointer<RefStringTypeRhs> const& rhs) noexcept
+{
+    return !(lhs == rhs);
+}
 }  // namespace nlohmann
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 56d02b7f07..5df8554a66 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -13301,11 +13301,10 @@ class json_pointer
 
     @exceptionsafety No-throw guarantee: this function never throws exceptions.
     */
-    friend bool operator==(json_pointer const& lhs,
-                           json_pointer const& rhs) noexcept
-    {
-        return lhs.reference_tokens == rhs.reference_tokens;
-    }
+    template<typename RefStringTypeLhs, typename RefStringTypeRhs>
+    // NOLINTNEXTLINE(readability-redundant-declaration)
+    friend bool operator==(json_pointer<RefStringTypeLhs> const& lhs,
+                           json_pointer<RefStringTypeRhs> const& rhs) noexcept;
 
     /*!
     @brief compares two JSON pointers for inequality
@@ -13318,15 +13317,29 @@ class json_pointer
 
     @exceptionsafety No-throw guarantee: this function never throws exceptions.
     */
-    friend bool operator!=(json_pointer const& lhs,
-                           json_pointer const& rhs) noexcept
-    {
-        return !(lhs == rhs);
-    }
+    template<typename RefStringTypeLhs, typename RefStringTypeRhs>
+    // NOLINTNEXTLINE(readability-redundant-declaration)
+    friend bool operator!=(json_pointer<RefStringTypeLhs> const& lhs,
+                           json_pointer<RefStringTypeRhs> const& rhs) noexcept;
 
     /// the reference tokens
     std::vector<string_t> reference_tokens;
 };
+
+// functions cannot be defined inside class due to ODR violations
+template<typename RefStringTypeLhs, typename RefStringTypeRhs>
+inline bool operator==(json_pointer<RefStringTypeLhs> const& lhs,
+                       json_pointer<RefStringTypeRhs> const& rhs) noexcept
+{
+    return lhs.reference_tokens == rhs.reference_tokens;
+}
+
+template<typename RefStringTypeLhs, typename RefStringTypeRhs>
+inline bool operator!=(json_pointer<RefStringTypeLhs> const& lhs,
+                       json_pointer<RefStringTypeRhs> const& rhs) noexcept
+{
+    return !(lhs == rhs);
+}
 }  // namespace nlohmann
 
 // #include <nlohmann/detail/json_ref.hpp>
diff --git a/test/src/unit-json_pointer.cpp b/test/src/unit-json_pointer.cpp
index 7b73807923..7ec157db33 100644
--- a/test/src/unit-json_pointer.cpp
+++ b/test/src/unit-json_pointer.cpp
@@ -661,6 +661,15 @@ TEST_CASE("JSON pointers")
         CHECK(ptr.to_string() == "/object/~1");
     }
 
+    SECTION("equality comparison")
+    {
+        auto ptr1 = json::json_pointer("/foo/bar");
+        auto ptr2 = json::json_pointer("/foo/bar");
+
+        CHECK(ptr1 == ptr2);
+        CHECK_FALSE(ptr1 != ptr2);
+    }
+
     SECTION("backwards compatibility and mixing")
     {
         json j = R"(
@@ -695,5 +704,10 @@ TEST_CASE("JSON pointers")
 
         CHECK(j.value(ptr, "x") == j.value(ptr_j, "x"));
         CHECK(j.value(ptr, "x") == j.value(ptr_oj, "x"));
+
+        CHECK(ptr == ptr_j);
+        CHECK(ptr == ptr_oj);
+        CHECK_FALSE(ptr != ptr_j);
+        CHECK_FALSE(ptr != ptr_oj);
     }
 }