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C API: Add lazy attribute value and list item accessors

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This commit is contained in:
Robert Hensing 2025-09-19 23:06:51 +02:00
parent 7c553a30a9
commit 3d777eb37f
3 changed files with 382 additions and 2 deletions
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62
src/libexpr-c/nix_api_value.cc
View file

@ -339,6 +339,26 @@ nix_value * nix_get_list_byidx(nix_c_context * context, const nix_value * value,
NIXC_CATCH_ERRS_NULL
}
nix_value *
nix_get_list_byidx_lazy(nix_c_context * context, const nix_value * value, EvalState * state, unsigned int ix)
{
if (context)
context->last_err_code = NIX_OK;
try {
auto & v = check_value_in(value);
assert(v.type() == nix::nList);
if (ix >= v.listSize()) {
nix_set_err_msg(context, NIX_ERR_KEY, "list index out of bounds");
return nullptr;
}
auto * p = v.listView()[ix];
nix_gc_incref(nullptr, p);
// Note: intentionally NOT calling forceValue() to keep the element lazy
return as_nix_value_ptr(p);
}
NIXC_CATCH_ERRS_NULL
}
nix_value * nix_get_attr_byname(nix_c_context * context, const nix_value * value, EvalState * state, const char * name)
{
if (context)
@ -359,6 +379,27 @@ nix_value * nix_get_attr_byname(nix_c_context * context, const nix_value * value
NIXC_CATCH_ERRS_NULL
}
nix_value *
nix_get_attr_byname_lazy(nix_c_context * context, const nix_value * value, EvalState * state, const char * name)
{
if (context)
context->last_err_code = NIX_OK;
try {
auto & v = check_value_in(value);
assert(v.type() == nix::nAttrs);
nix::Symbol s = state->state.symbols.create(name);
auto attr = v.attrs()->get(s);
if (attr) {
nix_gc_incref(nullptr, attr->value);
// Note: intentionally NOT calling forceValue() to keep the attribute lazy
return as_nix_value_ptr(attr->value);
}
nix_set_err_msg(context, NIX_ERR_KEY, "missing attribute");
return nullptr;
}
NIXC_CATCH_ERRS_NULL
}
bool nix_has_attr_byname(nix_c_context * context, const nix_value * value, EvalState * state, const char * name)
{
if (context)
@ -406,6 +447,27 @@ nix_get_attr_byidx(nix_c_context * context, nix_value * value, EvalState * state
NIXC_CATCH_ERRS_NULL
}
nix_value * nix_get_attr_byidx_lazy(
nix_c_context * context, nix_value * value, EvalState * state, unsigned int i, const char ** name)
{
if (context)
context->last_err_code = NIX_OK;
try {
auto & v = check_value_in(value);
collapse_attrset_layer_chain_if_needed(v, state);
if (i >= v.attrs()->size()) {
nix_set_err_msg(context, NIX_ERR_KEY, "attribute index out of bounds (Nix C API contract violation)");
return nullptr;
}
const nix::Attr & a = (*v.attrs())[i];
*name = state->state.symbols[a.name].c_str();
nix_gc_incref(nullptr, a.value);
// Note: intentionally NOT calling forceValue() to keep the attribute lazy
return as_nix_value_ptr(a.value);
}
NIXC_CATCH_ERRS_NULL
}
const char * nix_get_attr_name_byidx(nix_c_context * context, nix_value * value, EvalState * state, unsigned int i)
{
if (context)

50
src/libexpr-c/nix_api_value.h
View file

@ -265,10 +265,25 @@ ExternalValue * nix_get_external(nix_c_context * context, nix_value * value);
*/
nix_value * nix_get_list_byidx(nix_c_context * context, const nix_value * value, EvalState * state, unsigned int ix);
/** @brief Get an attr by name
/** @brief Get the ix'th element of a list without forcing evaluation of the element
*
* Returns the list element without forcing its evaluation, allowing access to lazy values.
* The list value itself must already be evaluated.
*
* Owned by the GC. Use nix_gc_decref when you're done with the pointer
* @param[out] context Optional, stores error information
* @param[in] value Nix value to inspect (must be an evaluated list)
* @param[in] state nix evaluator state
* @param[in] ix list element to get
* @return value, NULL in case of errors
*/
nix_value *
nix_get_list_byidx_lazy(nix_c_context * context, const nix_value * value, EvalState * state, unsigned int ix);
/** @brief Get an attr by name
*
* Use nix_gc_decref when you're done with the pointer
* @param[out] context Optional, stores error information
* @param[in] value Nix value to inspect
* @param[in] state nix evaluator state
* @param[in] name attribute name
@ -276,6 +291,21 @@ nix_value * nix_get_list_byidx(nix_c_context * context, const nix_value * value,
*/
nix_value * nix_get_attr_byname(nix_c_context * context, const nix_value * value, EvalState * state, const char * name);
/** @brief Get an attribute value by attribute name, without forcing evaluation of the attribute's value
*
* Returns the attribute value without forcing its evaluation, allowing access to lazy values.
* The attribute set value itself must already be evaluated.
*
* Use nix_gc_decref when you're done with the pointer
* @param[out] context Optional, stores error information
* @param[in] value Nix value to inspect (must be an evaluated attribute set)
* @param[in] state nix evaluator state
* @param[in] name attribute name
* @return value, NULL in case of errors
*/
nix_value *
nix_get_attr_byname_lazy(nix_c_context * context, const nix_value * value, EvalState * state, const char * name);
/** @brief Check if an attribute name exists on a value
* @param[out] context Optional, stores error information
* @param[in] value Nix value to inspect
@ -289,7 +319,7 @@ bool nix_has_attr_byname(nix_c_context * context, const nix_value * value, EvalS
*
* Also gives you the name.
*
* Owned by the GC. Use nix_gc_decref when you're done with the pointer
* Use nix_gc_decref when you're done with the pointer
* @param[out] context Optional, stores error information
* @param[in] value Nix value to inspect
* @param[in] state nix evaluator state
@ -300,6 +330,22 @@ bool nix_has_attr_byname(nix_c_context * context, const nix_value * value, EvalS
nix_value *
nix_get_attr_byidx(nix_c_context * context, nix_value * value, EvalState * state, unsigned int i, const char ** name);
/** @brief Get an attribute by index in the sorted bindings, without forcing evaluation of the attribute's value
*
* Also gives you the name. Returns the attribute value without forcing its evaluation, allowing access to lazy values.
* The attribute set value itself must already be evaluated.
*
* Use nix_gc_decref when you're done with the pointer
* @param[out] context Optional, stores error information
* @param[in] value Nix value to inspect (must be an evaluated attribute set)
* @param[in] state nix evaluator state
* @param[in] i attribute index
* @param[out] name will store a pointer to the attribute name
* @return value, NULL in case of errors
*/
nix_value * nix_get_attr_byidx_lazy(
nix_c_context * context, nix_value * value, EvalState * state, unsigned int i, const char ** name);
/** @brief Get an attribute name by index in the sorted bindings
*
* Returns the attribute name without forcing evaluation of the attribute's value.