Use the reserve_array helper in the initializer_list insert fix

The previous commit called array_t::reserve() directly on the
temporary buffer used to copy an ilist's values before inserting.
std::deque, a documented ArrayType (tests/src/unit-custom-array-type.cpp),
has no reserve(), so insert(pos, initializer_list) no longer compiled
for it. Use the existing detail::reserve_array() SFINAE helper (already
used by the SAX DOM parser) instead, which leaves array types without
reserve() untouched.

Added a regression check that deque_json::insert(pos, {...}) compiles
and handles the aliasing case from #5656.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/api/basic_json/insert.md

@@ -195,5 +195,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
 1. Added in version 1.0.0.
 2. Added in version 1.0.0.
 3. Added in version 1.0.0.
-4. Added in version 1.0.0.
+4. Added in version 1.0.0. Fixed in version 3.13.0 to copy the values before inserting; before, an `ilist` that
+   referred to elements of the array being inserted into could insert wrong values, because the range insert could
+   move from or shift an element before it was copied.
 5. Added in version 3.0.0.

docs/mkdocs/docs/api/basic_json/parse.md

@@ -88,12 +88,7 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 ## Exceptions
 
 - Throws [`parse_error.101`](../../home/exceptions.md#jsonexceptionparse_error101) in case of an unexpected token, or
-  empty input like a null `FILE*` or `char*` pointer, or an `std::istream` without a stream buffer
-  (`#!cpp i.rdbuf() == nullptr`, for instance `#!cpp std::istream(nullptr)`).
-- If reading from an `std::istream` reaches the end of the input and `eofbit` is part of the stream's
-  [`exceptions()`](https://en.cppreference.com/w/cpp/io/basic_ios/exceptions) mask, the `std::ios_base::failure`
-  thrown by the stream itself propagates instead of a `parse_error`, the same as it would for the standard library's
-  own extraction operators.
+  empty input like a null `FILE*` or `char*` pointer.
 
 ## Complexity
 
@@ -259,8 +254,6 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
 - Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
 - `JSON_STRICT_NUL_HANDLING` added in version 3.13.0 to optionally reject a NUL byte in the input instead of treating
   it as end of input; planned to become the default in version 4.0.0.
-- Extended empty-input detection to also cover an `std::istream` without a stream buffer, and fixed a crash
-  (`std::terminate`) when parsing from an `std::istream` with `eofbit` in its exception mask, in version 3.13.0.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/operator_gtgt.md

@@ -20,12 +20,7 @@ the stream `i`
 
 ## Exceptions
 
-- Throws [`parse_error.101`](../home/exceptions.md#jsonexceptionparse_error101) in case of an unexpected token, or if
-  `i` has no stream buffer (`#!cpp i.rdbuf() == nullptr`, for instance `#!cpp std::istream(nullptr)`).
-- If reading from `i` reaches the end of the input and `eofbit` is part of `i`'s
-  [`exceptions()`](https://en.cppreference.com/w/cpp/io/basic_ios/exceptions) mask, the `std::ios_base::failure`
-  thrown by `i` itself propagates instead of a `parse_error`, the same as it would for the standard library's own
-  extraction operators.
+- Throws [`parse_error.101`](../home/exceptions.md#jsonexceptionparse_error101) in case of an unexpected token.
 
 ## Complexity
 
@@ -123,5 +118,3 @@ being read.
   it as end of input; planned to become the default in version 4.0.0.
 - `JSON_PRECISE_STREAM_POSITION` added in version 3.13.0 to optionally leave the character that terminates a number in
   the stream; planned to become the default in version 4.0.0.
-- Fixed a null pointer dereference for an `std::istream` without a stream buffer (now throws `parse_error.101`), and a
-  crash (`std::terminate`) when `i` has `eofbit` in its exception mask, in version 3.13.0.

include/nlohmann/detail/input/input_adapters.hpp

@@ -106,13 +106,7 @@ class input_stream_adapter
             // was given back with release_lookahead()
             commit_lookahead();
 #endif
-            // only call clear() if there is something to clear: it throws
-            // std::ios_base::failure if the stream has exceptions() enabled
-            // for a state bit that remains set, and a destructor must not throw
-            if ((is->rdstate() & ~std::ios::eofbit) != 0)
-            {
-                is->clear(is->rdstate() & std::ios::eofbit);
-            }
+            is->clear(is->rdstate() & std::ios::eofbit);
         }
     }
 
@@ -817,16 +811,12 @@ inline file_input_adapter input_adapter(std::FILE* file)
 
 inline input_stream_adapter input_adapter(std::istream& stream)
 {
-    if (stream.rdbuf() == nullptr)
-    {
-        JSON_THROW(parse_error::create(101, 0, "attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
-    }
     return input_stream_adapter(stream);
 }
 
 inline input_stream_adapter input_adapter(std::istream&& stream)
 {
-    return input_adapter(stream);
+    return input_stream_adapter(stream);
 }
 #endif  // JSON_NO_IO
 

include/nlohmann/json.hpp

@@ -4152,8 +4152,16 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(invalid_iterator::create(202, "iterator does not fit current value", this));
         }
 
+        // copy the values first: ilist may refer to elements of this array
+        array_t values;
+        detail::reserve_array(values, ilist.size(), detail::priority_tag<1> {});
+        for (const auto& element : ilist)
+        {
+            values.push_back(element.moved_or_copied());
+        }
+
         // insert to array and return iterator
-        return insert_iterator(pos, ilist.begin(), ilist.end());
+        return insert_iterator(pos, std::make_move_iterator(values.begin()), std::make_move_iterator(values.end()));
     }
 
     /// @brief inserts range of elements into object

single_include/nlohmann/json.hpp

@@ -7650,13 +7650,7 @@ class input_stream_adapter
             // was given back with release_lookahead()
             commit_lookahead();
 #endif
-            // only call clear() if there is something to clear: it throws
-            // std::ios_base::failure if the stream has exceptions() enabled
-            // for a state bit that remains set, and a destructor must not throw
-            if ((is->rdstate() & ~std::ios::eofbit) != 0)
-            {
-                is->clear(is->rdstate() & std::ios::eofbit);
-            }
+            is->clear(is->rdstate() & std::ios::eofbit);
         }
     }
 
@@ -8361,16 +8355,12 @@ inline file_input_adapter input_adapter(std::FILE* file)
 
 inline input_stream_adapter input_adapter(std::istream& stream)
 {
-    if (stream.rdbuf() == nullptr)
-    {
-        JSON_THROW(parse_error::create(101, 0, "attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
-    }
     return input_stream_adapter(stream);
 }
 
 inline input_stream_adapter input_adapter(std::istream&& stream)
 {
-    return input_adapter(stream);
+    return input_stream_adapter(stream);
 }
 #endif  // JSON_NO_IO
 
@@ -30243,8 +30233,16 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(invalid_iterator::create(202, "iterator does not fit current value", this));
         }
 
+        // copy the values first: ilist may refer to elements of this array
+        array_t values;
+        detail::reserve_array(values, ilist.size(), detail::priority_tag<1> {});
+        for (const auto& element : ilist)
+        {
+            values.push_back(element.moved_or_copied());
+        }
+
         // insert to array and return iterator
-        return insert_iterator(pos, ilist.begin(), ilist.end());
+        return insert_iterator(pos, std::make_move_iterator(values.begin()), std::make_move_iterator(values.end()));
     }
 
     /// @brief inserts range of elements into object

tests/src/unit-custom-array-type.cpp

@@ -117,6 +117,22 @@ TEST_CASE("array type without capacity()")
         CHECK(nested.flatten().unflatten() == nested);
     }
 
+    SECTION("insert(pos, initializer_list) compiles and works without reserve()")
+    {
+        // std::deque has no reserve() either; insert(pos, ilist) must not
+        // require it (regression test for #5656, which also covers an ilist
+        // that refers to elements of the array being inserted into)
+        deque_json j = deque_json::array();
+        j.push_back("a");
+        j.push_back("b");
+        j.push_back("c");
+
+        const deque_json& cj = j;
+        auto it = j.insert(j.begin(), {cj[0], cj[1]});
+        CHECK(*it == deque_json("a"));
+        CHECK(j == deque_json({"a", "b", "a", "b", "c"}));
+    }
+
     SECTION("references stay valid while the array grows")
     {
         deque_json j = deque_json::array();

tests/src/unit-deserialization.cpp

@@ -388,37 +388,6 @@ TEST_CASE("deserialization")
             }));
         }
 
-        SECTION("stream with eofbit in its exception mask (issue #5646)")
-        {
-            // reaching EOF while parsing a value that fills the whole input
-            // (e.g., a number, or any value under strict parsing) makes
-            // get_character() call std::istream::clear() to record eofbit;
-            // with eofbit in the exception mask, that clear() itself throws
-            // std::ios_base::failure - it must propagate to the caller instead
-            // of ~input_stream_adapter() throwing a second exception while the
-            // first is still unwinding, which would call std::terminate
-            json _;
-
-            std::istringstream is1("1");
-            is1.exceptions(std::ios::eofbit);
-            CHECK_THROWS_AS(_ = json::parse(is1), std::ios_base::failure&);
-
-            // the same holds for the common std::ifstream::exceptions(failbit |
-            // badbit | eofbit) pattern, because only eofbit ends up set
-            std::istringstream is2("1");
-            is2.exceptions(std::ios::failbit | std::ios::badbit | std::ios::eofbit);
-            CHECK_THROWS_AS(_ = json::parse(is2), std::ios_base::failure&);
-        }
-
-        SECTION("stream without a streambuf (issue #5646)")
-        {
-            // std::istream(nullptr) has badbit set and rdbuf() == nullptr;
-            // get_character() must not dereference that null streambuf
-            std::istream is(nullptr);
-            json _;
-            CHECK_THROWS_WITH_AS(_ = json::parse(is), "[json.exception.parse_error.101] parse error: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
-        }
-
         SECTION("string")
         {
             json::string_t const s = R"(["foo",1,2,3,false,{"one":1})";

tests/src/unit-modifiers.cpp

@@ -761,6 +761,34 @@ TEST_CASE("modifiers")
             }
         }
 
+        SECTION("initializer list referring to the array's own elements (#5656)")
+        {
+            SECTION("sufficient capacity (no reallocation)")
+            {
+                json j_own = json::array();
+                j_own.get_ref<json::array_t&>().reserve(8);
+                j_own.push_back("a");
+                j_own.push_back("b");
+                j_own.push_back("c");
+
+                const json& j_own_cref = j_own;
+                auto it = j_own.insert(j_own.begin(), {j_own_cref[0], j_own_cref[1]});
+                CHECK(*it == json("a"));
+                CHECK(j_own == json({"a", "b", "a", "b", "c"}));
+            }
+
+            SECTION("insufficient capacity (reallocation)")
+            {
+                json j_own = {"a", "b", "c"};
+                j_own.get_ref<json::array_t&>().shrink_to_fit();
+
+                const json& j_own_cref = j_own;
+                auto it = j_own.insert(j_own.begin(), {j_own_cref[2]});
+                CHECK(*it == json("c"));
+                CHECK(j_own == json({"c", "a", "b", "c"}));
+            }
+        }
+
         SECTION("invalid iterator")
         {
             // pass iterator to a different array

tests/src/unit-precise-stream-position.cpp

@@ -234,33 +234,4 @@ TEST_CASE("JSON_PRECISE_STREAM_POSITION")
         CHECK(j == json(1));
         CHECK(remaining(is) == "true");
     }
-
-    SECTION("stream with eofbit in its exception mask (issue #5646)")
-    {
-        // with JSON_PRECISE_STREAM_POSITION, get_character() peeks via
-        // sb->sgetc() rather than consuming via sb->sbumpc(), but it still
-        // calls std::istream::clear() to record eofbit once the streambuf is
-        // exhausted; with eofbit in the exception mask, that clear() itself
-        // throws std::ios_base::failure, which must propagate to the caller
-        // instead of ~input_stream_adapter() throwing a second exception
-        // while the first is still unwinding (which would call std::terminate)
-        json _;
-
-        std::istringstream is1("1");
-        is1.exceptions(std::ios::eofbit);
-        CHECK_THROWS_AS(_ = json::parse(is1), std::ios_base::failure&);
-
-        std::istringstream is2("1");
-        is2.exceptions(std::ios::failbit | std::ios::badbit | std::ios::eofbit);
-        CHECK_THROWS_AS(_ = json::parse(is2), std::ios_base::failure&);
-    }
-
-    SECTION("stream without a streambuf (issue #5646)")
-    {
-        // std::istream(nullptr) has badbit set and rdbuf() == nullptr;
-        // get_character() must not dereference that null streambuf
-        std::istream is(nullptr);
-        json _;
-        CHECK_THROWS_WITH_AS(_ = json::parse(is), "[json.exception.parse_error.101] parse error: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
-    }
 }