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Improve checked json casting (#10087)

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This introduces new utility functions to get elements from JSON — in an ergonomic way and with nice error messages if the expected type does not match.

Co-authored-by: John Ericson <John.Ericson@Obsidian.Systems>
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HaeNoe 2024-04-03 20:04:00 +02:00 • committed by GitHub
parent bf86b939f8
commit 50cb14fcf9
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11 changed files with 315 additions and 69 deletions
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31
src/libutil/json-utils.hh
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@ -3,6 +3,9 @@
#include <nlohmann/json.hpp>
#include <list>
#include <nlohmann/json_fwd.hpp>
#include "types.hh"
namespace nix {
@ -11,26 +14,30 @@ const nlohmann::json * get(const nlohmann::json & map, const std::string & key);
nlohmann::json * get(nlohmann::json & map, const std::string & key);
/**
* Get the value of a json object at a key safely, failing
* with a Nix Error if the key does not exist.
* Get the value of a json object at a key safely, failing with a nice
* error if the key does not exist.
*
* Use instead of nlohmann::json::at() to avoid ugly exceptions.
*
* _Does not check whether `map` is an object_, use `ensureType` for that.
*/
const nlohmann::json & valueAt(
const nlohmann::json & map,
const nlohmann::json::object_t & map,
const std::string & key);
std::optional<nlohmann::json> optionalValueAt(const nlohmann::json & value, const std::string & key);
/**
* Ensure the type of a json object is what you expect, failing
* with a Nix Error if it isn't.
*
* Use before type conversions and element access to avoid ugly exceptions.
* Downcast the json object, failing with a nice error if the conversion fails.
* See https://json.nlohmann.me/features/types/
*/
const nlohmann::json & ensureType(
const nlohmann::json & value,
nlohmann::json::value_type expectedType);
std::optional<nlohmann::json> getNullable(const nlohmann::json & value);
const nlohmann::json::object_t & getObject(const nlohmann::json & value);
const nlohmann::json::array_t & getArray(const nlohmann::json & value);
const nlohmann::json::string_t & getString(const nlohmann::json & value);
const nlohmann::json::number_integer_t & getInteger(const nlohmann::json & value);
const nlohmann::json::boolean_t & getBoolean(const nlohmann::json & value);
Strings getStringList(const nlohmann::json & value);
StringMap getStringMap(const nlohmann::json & value);
StringSet getStringSet(const nlohmann::json & value);
/**
* For `adl_serializer<std::optional<T>>` below, we need to track what