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Add JSON_DELETE_DEPRECATED_FUNCTIONS to delete the deprecated functions

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Defining JSON_DELETE_DEPRECATED_FUNCTIONS to 1 (or the CMake option
JSON_DeleteDeprecatedFunctions) declares every deprecated function as
deleted instead of deprecated, so that code that is not ready for 4.0.0
no longer compiles. A deleted function still takes part in overload
resolution, so from_*(ptr, len) cannot silently bind len to the strict
parameter of from_*(InputType&&, bool); the roadmap now plans to keep
these overloads deleted in 4.0.0 instead of removing them.

The legacy discarded-value comparison is left to its own macro.

Also update the 4.0 roadmap: add JSON_DISABLE_TUPLE_REFERENCE_CONVERSION
and JSON_DELETE_DEPRECATED_FUNCTIONS to the macro table, add the
from_bjdata/from_bon8 (ptr, len) overloads to the deprecated functions,
document the macro in the migration guide, and fix the docs style check
findings (example titles, missing docset entry for JSON_STRICT_BINARY_UTF8).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-10-04 12:54:07 +02:00
parent 4f3f26a1d4
commit 99ae1d0d03
31 changed files with 833 additions and 18 deletions
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docs/mkdocs/docs/api/macros/index.md
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@@ -59,6 +59,11 @@ header. See also the [macro overview page](../../features/macros.md).
- [**JSON_DISABLE_TUPLE_REFERENCE_CONVERSION**](json_disable_tuple_reference_conversion.md) - switch off conversion from a one-element tuple of a JSON reference
- [**JSON_USE_IMPLICIT_CONVERSIONS**](json_use_implicit_conversions.md) - control implicit conversions
## Deprecated functions
- [**JSON_DELETE_DEPRECATED_FUNCTIONS**](json_delete_deprecated_functions.md) - opt in to deleting the deprecated
functions ahead of their removal in version 4.0.0
## Comparison behavior
- [**JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON**](json_use_legacy_discarded_value_comparison.md) -
docs/mkdocs/docs/api/macros/json_delete_deprecated_functions.md
+96
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@@ -0,0 +1,96 @@
# JSON_DELETE_DEPRECATED_FUNCTIONS
```cpp
#define JSON_DELETE_DEPRECATED_FUNCTIONS /* value */
```
When defined to `1`, all [deprecated functions](../../community/roadmap.md#removal-of-deprecated-functions) of the
library are declared as deleted (`= delete`) instead of only being marked as deprecated. Code that still calls one of
them no longer compiles. This way, you can find all calls that need to be replaced before version 4.0.0 removes these
functions; the [migration guide](../../integration/migration_guide.md#replace-deprecated-functions) describes how.
A deleted function, unlike a removed one, still takes part in overload resolution. A call that would select it
therefore fails to compile instead of silently selecting another overload. This matters for the deprecated
`from_*(ptr, len)` overloads of [`from_cbor`](../basic_json/from_cbor.md), [`from_msgpack`](../basic_json/from_msgpack.md),
[`from_ubjson`](../basic_json/from_ubjson.md), [`from_bjdata`](../basic_json/from_bjdata.md),
[`from_bon8`](../basic_json/from_bon8.md), and [`from_bson`](../basic_json/from_bson.md): without them, a call like
`from_cbor(ptr, len)` would compile, read `ptr` as a NUL-terminated string, and convert `len` to the `strict` parameter.
The macro does not affect the deprecated legacy comparison of discarded values, which is controlled by
[`JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON`](json_use_legacy_discarded_value_comparison.md).
## Default definition
The default value is `0` (disabled, the deprecated functions can still be called, and the compiler warns about it).
```cpp
#define JSON_DELETE_DEPRECATED_FUNCTIONS 0
```
## Notes
!!! info "CMake option"
The macro can also be set with the CMake option
[`JSON_DeleteDeprecatedFunctions`](../../integration/cmake.md#json_deletedeprecatedfunctions) (`OFF` by default).
!!! warning "Opt-in only"
This macro must be defined **before** including `<nlohmann/json.hpp>`. Defining it after the include has no
effect. Define it for the whole project to avoid different declarations of the same class in different
translation units.
!!! note "ABI compatibility"
The macro only turns calls that compile into calls that do not; it does not change the layout or the behavior of
any type. Its value is therefore not encoded in the [namespace](../../features/namespace.md).
## Examples
??? example "Example: default behavior (macro not defined)"
Without the macro, the deprecated overload is called, and the compiler warns about it:
```cpp
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
const std::vector<std::uint8_t> v = {0x82, 0x01, 0x02};
auto j = json::from_cbor(v.data(), v.size());
// warning: 'from_cbor' is deprecated: Since 3.8.0; use from_cbor(ptr, ptr + len)
}
```
??? example "Example: deleted deprecated functions (macro defined to 1)"
With the macro, the call does not compile:
```cpp
#define JSON_DELETE_DEPRECATED_FUNCTIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
const std::vector<std::uint8_t> v = {0x82, 0x01, 0x02};
auto j = json::from_cbor(v.data(), v.size());
// error: call to deleted function 'from_cbor'
}
```
## See also
- [Roadmap: removal of deprecated functions](../../community/roadmap.md#removal-of-deprecated-functions) - the
deprecated functions and the version they were deprecated in
- [Migration guide: replace deprecated functions](../../integration/migration_guide.md#replace-deprecated-functions) -
how to replace each deprecated function
## Version history
- Added in version 3.13.0.
- Planned to be removed in version 4.0.0, which removes the deprecated functions. The deprecated `from_*(ptr, len)`
overloads stay deleted in version 4.0.0.
docs/mkdocs/docs/api/macros/json_disable_tuple_reference_conversion.md
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@@ -112,3 +112,4 @@ The default value is `0` (disabled — existing behavior is preserved).
## Version history
- Added in version 3.13.0.
- Planned to become the default (with the macro removed) in version 4.0.0.
docs/mkdocs/docs/api/macros/json_strict_binary_utf8.md
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@@ -54,7 +54,7 @@ The default value is `0` (disabled, the behavior of version 3.12.0 and earlier i
## Examples
??? example "Default behavior (macro not defined)"
??? example "Example: default behavior (macro not defined)"
Without the macro, the bytes are written unchanged:
@@ -70,7 +70,7 @@ The default value is `0` (disabled, the behavior of version 3.12.0 and earlier i
}
```
??? example "Opt-in check (macro defined to 1)"
??? example "Example: opt-in check (macro defined to 1)"
With the macro, ill-formed UTF-8 is rejected:
docs/mkdocs/docs/api/macros/json_use_implicit_conversions.md
+2 -2
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@@ -44,7 +44,7 @@ By default, implicit conversions are enabled.
## Examples
??? example
??? example "Example: implicit and explicit conversions"
This is an example for an implicit conversion:
@@ -61,7 +61,7 @@ By default, implicit conversions are enabled.
auto s = j.get<std::string>();
```
??? example "Conversion between `basic_json` specializations"
??? example "Example: conversion between `basic_json` specializations"
A `basic_json` specialization with a different string type is also no longer converted implicitly when
`JSON_USE_IMPLICIT_CONVERSIONS` is defined to `0`:
docs/mkdocs/docs/community/roadmap.md
+12 -2
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@@ -64,6 +64,8 @@ The following macros guard changes that are planned to become the default in ver
| [`JSON_PRECISE_STREAM_POSITION`](../api/macros/json_precise_stream_position.md) | `0` | `1`: reading from a stream does not consume the character after a number | – | 3.13.0 |
| [`JSON_STRICT_NUL_HANDLING`](../api/macros/json_strict_nul_handling.md) | `0` | `1`: a NUL byte in the input is a parse error instead of the end of input | [`JSON_StrictNulHandling`](../integration/cmake.md#json_strictnulhandling) | 3.13.0 |
| [`JSON_STRICT_BINARY_UTF8`](../api/macros/json_strict_binary_utf8.md) | `0` | `1`: `to_cbor`, `to_ubjson`, `to_bjdata`, and `to_bson` throw for strings that are not valid UTF-8 by default | [`JSON_StrictBinaryUTF8`](../integration/cmake.md#json_strictbinaryutf8) | 3.13.0 |
| [`JSON_DISABLE_TUPLE_REFERENCE_CONVERSION`](../api/macros/json_disable_tuple_reference_conversion.md) | `0` | `1`: a `basic_json` value can no longer be created from a one-element tuple of a reference to it, such as `std::forward_as_tuple(j)`| [`JSON_DisableTupleReferenceConversion`](../integration/cmake.md#json_disabletuplereferenceconversion) | 3.13.0 |
| [`JSON_DELETE_DEPRECATED_FUNCTIONS`](../api/macros/json_delete_deprecated_functions.md) | `0` | removed: the deprecated functions are removed (see below); the `from_*(ptr, len)` overloads stay deleted | [`JSON_DeleteDeprecatedFunctions`](../integration/cmake.md#json_deletedeprecatedfunctions) | 3.13.0 |
For example, the following makes a 3.x release behave like version 4.0 with respect to these changes:
@@ -75,6 +77,8 @@ For example, the following makes a 3.x release behave like version 4.0 with resp
#define JSON_PRECISE_STREAM_POSITION 1
#define JSON_STRICT_NUL_HANDLING 1
#define JSON_STRICT_BINARY_UTF8 1
#define JSON_DISABLE_TUPLE_REFERENCE_CONVERSION 1
#define JSON_DELETE_DEPRECATED_FUNCTIONS 1
#include <nlohmann/json.hpp>
```
@@ -84,8 +88,13 @@ way to achieve this.
### Removal of deprecated functions
Version 4.0 will remove all deprecated functions. Compiling with deprecation warnings enabled shows which of them your
code still uses. The [migration guide](../integration/migration_guide.md#replace-deprecated-functions) shows how to
replace each of them.
code still uses. Defining [`JSON_DELETE_DEPRECATED_FUNCTIONS`](../api/macros/json_delete_deprecated_functions.md) to
`1` turns these warnings into errors, as the deprecated functions are then deleted. The
[migration guide](../integration/migration_guide.md#replace-deprecated-functions) shows how to replace each of them.
The `from_*` overloads taking a pointer and a length are not removed in version 4.0, but stay deleted. Without them, a
call like `from_cbor(ptr, len)` would still compile: it would read `ptr` as a NUL-terminated string and convert `len`
to the `strict` parameter.
| Deprecated | Since | Migration |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------|----------------------------------------------------------------------------------|
@@ -97,6 +106,7 @@ replace each of them.
| [`json_pointer::operator string_t`](../api/json_pointer/operator_string_t.md) | 3.11.0 | [JSON Pointers](../integration/migration_guide.md#json-pointers) |
| [`json_pointer`](../api/json_pointer/index.md) with a `basic_json` type as template argument, and the overloads of `value`, `contains`, `operator[]`, and `at` accepting such a pointer | 3.11.0 | [JSON Pointers](../integration/migration_guide.md#json-pointers) |
| Comparing a [`json_pointer`](../api/json_pointer/index.md) with a string via [`operator==`](../api/json_pointer/operator_eq.md) or [`operator!=`](../api/json_pointer/operator_ne.md) | 3.11.2 | [JSON Pointers](../integration/migration_guide.md#json-pointers) |
| [`from_bjdata`](../api/basic_json/from_bjdata.md) and [`from_bon8`](../api/basic_json/from_bon8.md) with `(ptr, len)` | 3.13.0 | [Parsing](../integration/migration_guide.md#parsing) |
The deprecated legacy comparison of discarded values is controlled by a macro and therefore listed in the table above.
docs/mkdocs/docs/features/macros.md
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@@ -23,6 +23,17 @@ This macro overrides [`#!cpp catch`](https://en.cppreference.com/w/cpp/language/
See [full documentation of `JSON_CATCH_USER(exception)`](../api/macros/json_throw_user.md).
## `JSON_DELETE_DEPRECATED_FUNCTIONS`
When defined to `1`, all deprecated functions are declared as deleted instead of only being marked as deprecated, so
code that still calls them no longer compiles. This way, you can find all calls that need to be replaced before version
4.0.0 removes these functions.
The macro can also be set with the CMake option
[`JSON_DeleteDeprecatedFunctions`](../integration/cmake.md#json_deletedeprecatedfunctions) (`OFF` by default).
See [full documentation of `JSON_DELETE_DEPRECATED_FUNCTIONS`](../api/macros/json_delete_deprecated_functions.md).
## `JSON_DIAGNOSTICS`
This macro enables extended diagnostics for exception messages. Possible values are `1` to enable or `0` to disable
@@ -86,7 +97,8 @@ See [full documentation of `JSON_DISABLE_ENUM_SERIALIZATION`](../api/macros/json
## `JSON_DISABLE_TUPLE_REFERENCE_CONVERSION`
When defined to `1`, a JSON value can no longer be created from a one-element `std::tuple` holding a reference to a JSON
value, such as the result of `std::forward_as_tuple(j)`. This lets `std::tuple` convert such tuples element-wise.
value, such as the result of `std::forward_as_tuple(j)`. This lets `std::tuple` convert such tuples element-wise. This
is planned to become the default in version 4.0.0.
See [full documentation of `JSON_DISABLE_TUPLE_REFERENCE_CONVERSION`](../api/macros/json_disable_tuple_reference_conversion.md).
docs/mkdocs/docs/integration/cmake.md
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@@ -132,6 +132,12 @@ Build the unit tests when [`BUILD_TESTING`](https://cmake.org/cmake/help/latest/
Enable CI build targets. The exact targets are used during the several CI steps and are subject to change without notice. This option is `OFF` by default.
### `JSON_DeleteDeprecatedFunctions`
Delete the deprecated functions instead of only deprecating them by defining the macro
[`JSON_DELETE_DEPRECATED_FUNCTIONS`](../api/macros/json_delete_deprecated_functions.md). This option is `OFF` by
default.
### `JSON_Diagnostics`
Enable [extended diagnostic messages](../home/exceptions.md#extended-diagnostic-messages) by defining macro [`JSON_DIAGNOSTICS`](../api/macros/json_diagnostics.md). This option is `OFF` by default.
docs/mkdocs/docs/integration/migration_guide.md
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@@ -14,6 +14,13 @@ deprecations are annotated with
[`HEDLEY_DEPRECATED_FOR`](https://nemequ.github.io/hedley/api-reference.html#HEDLEY_DEPRECATED_FOR) to report which
function to use instead.
!!! tip "Find all calls of deprecated functions"
Define [`JSON_DELETE_DEPRECATED_FUNCTIONS`](../api/macros/json_delete_deprecated_functions.md) to `1` (or set the
CMake option [`JSON_DeleteDeprecatedFunctions`](cmake.md#json_deletedeprecatedfunctions)) to delete all deprecated
functions. Every remaining call then fails to compile, even if deprecation warnings are disabled, so your code is
ready for version 4.0.0 once it compiles with the macro.
### Parsing
- Function `friend std::istream& operator<<(basic_json&, std::istream&)` is deprecated since 3.0.0. Please use
@@ -41,8 +48,10 @@ function to use instead.
[`from_ubjson`](../api/basic_json/from_ubjson.md), and [`from_bson`](../api/basic_json/from_bson.md)) via initializer
lists is deprecated since 3.8.0. Instead, pass two iterators; for instance, call `from_cbor(ptr, ptr+len)` instead of
`from_cbor({ptr, len})`. Likewise, passing a pointer and a length as two separate arguments to `from_cbor`,
`from_msgpack`, `from_ubjson`, and `from_bson` is deprecated since 3.8.0; call `from_cbor(ptr, ptr+len)` instead of
`from_cbor(ptr, len)`.
`from_msgpack`, `from_ubjson`, and `from_bson` is deprecated since 3.8.0, and to
[`from_bjdata`](../api/basic_json/from_bjdata.md) and [`from_bon8`](../api/basic_json/from_bon8.md) since 3.13.0; call
`from_cbor(ptr, ptr+len)` instead of `from_cbor(ptr, len)`. These overloads will not be removed in version 4.0.0, but
deleted, so a call like `from_cbor(ptr, len)` cannot compile and convert `len` to the `strict` parameter.
=== "Deprecated"
docs/mkdocs/mkdocs.yml
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@@ -292,6 +292,7 @@ nav:
- 'JSON_BRACE_INIT_COPY_SEMANTICS': api/macros/json_brace_init_copy_semantics.md
- 'JSON_CATCH_USER, JSON_THROW_USER, JSON_TRY_USER': api/macros/json_throw_user.md
- 'JSON_DIAGNOSTICS': api/macros/json_diagnostics.md
- 'JSON_DELETE_DEPRECATED_FUNCTIONS': api/macros/json_delete_deprecated_functions.md
- 'JSON_DIAGNOSTIC_POSITIONS': api/macros/json_diagnostic_positions.md
- 'JSON_DISABLE_ENUM_SERIALIZATION': api/macros/json_disable_enum_serialization.md
- 'JSON_DISABLE_TUPLE_REFERENCE_CONVERSION': api/macros/json_disable_tuple_reference_conversion.md