diff --git a/src/libexpr-c/nix_api_value.cc b/src/libexpr-c/nix_api_value.cc index 3442bf1a1..c58d4fe89 100644 --- a/src/libexpr-c/nix_api_value.cc +++ b/src/libexpr-c/nix_api_value.cc @@ -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) diff --git a/src/libexpr-c/nix_api_value.h b/src/libexpr-c/nix_api_value.h index 2c4e35b66..38fede62b 100644 --- a/src/libexpr-c/nix_api_value.h +++ b/src/libexpr-c/nix_api_value.h @@ -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. diff --git a/src/libexpr-tests/nix_api_value.cc b/src/libexpr-tests/nix_api_value.cc index c74c3258f..830637f3e 100644 --- a/src/libexpr-tests/nix_api_value.cc +++ b/src/libexpr-tests/nix_api_value.cc @@ -185,6 +185,91 @@ TEST_F(nix_api_expr_test, nix_get_list_byidx_large_indices) nix_gc_decref(ctx, intValue); } +TEST_F(nix_api_expr_test, nix_get_list_byidx_lazy) +{ + // Create a list with a throwing lazy element, an already-evaluated int, and a lazy function call + + // 1. Throwing lazy element - create a function application thunk that will throw when forced + nix_value * throwingFn = nix_alloc_value(ctx, state); + nix_value * throwingValue = nix_alloc_value(ctx, state); + + nix_expr_eval_from_string( + ctx, + state, + R"( + _: throw "This should not be evaluated by the lazy accessor" + )", + "", + throwingFn); + assert_ctx_ok(); + + nix_init_apply(ctx, throwingValue, throwingFn, throwingFn); + assert_ctx_ok(); + + // 2. Already evaluated int (not lazy) + nix_value * intValue = nix_alloc_value(ctx, state); + nix_init_int(ctx, intValue, 42); + assert_ctx_ok(); + + // 3. Lazy function application that would compute increment 5 = 6 + nix_value * lazyApply = nix_alloc_value(ctx, state); + nix_value * incrementFn = nix_alloc_value(ctx, state); + nix_value * argFive = nix_alloc_value(ctx, state); + + nix_expr_eval_from_string(ctx, state, "x: x + 1", "", incrementFn); + assert_ctx_ok(); + nix_init_int(ctx, argFive, 5); + + // Create a lazy application: (x: x + 1) 5 + nix_init_apply(ctx, lazyApply, incrementFn, argFive); + assert_ctx_ok(); + + ListBuilder * builder = nix_make_list_builder(ctx, state, 3); + nix_list_builder_insert(ctx, builder, 0, throwingValue); + nix_list_builder_insert(ctx, builder, 1, intValue); + nix_list_builder_insert(ctx, builder, 2, lazyApply); + nix_make_list(ctx, builder, value); + nix_list_builder_free(builder); + + // Test 1: Lazy accessor should return the throwing element without forcing evaluation + nix_value * lazyThrowingElement = nix_get_list_byidx_lazy(ctx, value, state, 0); + assert_ctx_ok(); + ASSERT_NE(nullptr, lazyThrowingElement); + + // Verify the element is still lazy by checking that forcing it throws + nix_value_force(ctx, state, lazyThrowingElement); + assert_ctx_err(); + ASSERT_THAT( + nix_err_msg(nullptr, ctx, nullptr), testing::HasSubstr("This should not be evaluated by the lazy accessor")); + + // Test 2: Lazy accessor should return the already-evaluated int + nix_value * intElement = nix_get_list_byidx_lazy(ctx, value, state, 1); + assert_ctx_ok(); + ASSERT_NE(nullptr, intElement); + ASSERT_EQ(42, nix_get_int(ctx, intElement)); + + // Test 3: Lazy accessor should return the lazy function application without forcing + nix_value * lazyFunctionElement = nix_get_list_byidx_lazy(ctx, value, state, 2); + assert_ctx_ok(); + ASSERT_NE(nullptr, lazyFunctionElement); + + // Force the lazy function application - should compute 5 + 1 = 6 + nix_value_force(ctx, state, lazyFunctionElement); + assert_ctx_ok(); + ASSERT_EQ(6, nix_get_int(ctx, lazyFunctionElement)); + + // Clean up + nix_gc_decref(ctx, throwingFn); + nix_gc_decref(ctx, throwingValue); + nix_gc_decref(ctx, intValue); + nix_gc_decref(ctx, lazyApply); + nix_gc_decref(ctx, incrementFn); + nix_gc_decref(ctx, argFive); + nix_gc_decref(ctx, lazyThrowingElement); + nix_gc_decref(ctx, intElement); + nix_gc_decref(ctx, lazyFunctionElement); +} + TEST_F(nix_api_expr_test, nix_build_and_init_attr_invalid) { ASSERT_EQ(nullptr, nix_get_attr_byname(ctx, nullptr, state, 0)); @@ -299,6 +384,193 @@ TEST_F(nix_api_expr_test, nix_get_attr_byidx_large_indices) free(out_name); } +TEST_F(nix_api_expr_test, nix_get_attr_byname_lazy) +{ + // Create an attribute set with a throwing lazy attribute, an already-evaluated int, and a lazy function call + + // 1. Throwing lazy element - create a function application thunk that will throw when forced + nix_value * throwingFn = nix_alloc_value(ctx, state); + nix_value * throwingValue = nix_alloc_value(ctx, state); + + nix_expr_eval_from_string( + ctx, + state, + R"( + _: throw "This should not be evaluated by the lazy accessor" + )", + "", + throwingFn); + assert_ctx_ok(); + + nix_init_apply(ctx, throwingValue, throwingFn, throwingFn); + assert_ctx_ok(); + + // 2. Already evaluated int (not lazy) + nix_value * intValue = nix_alloc_value(ctx, state); + nix_init_int(ctx, intValue, 42); + assert_ctx_ok(); + + // 3. Lazy function application that would compute increment 7 = 8 + nix_value * lazyApply = nix_alloc_value(ctx, state); + nix_value * incrementFn = nix_alloc_value(ctx, state); + nix_value * argSeven = nix_alloc_value(ctx, state); + + nix_expr_eval_from_string(ctx, state, "x: x + 1", "", incrementFn); + assert_ctx_ok(); + nix_init_int(ctx, argSeven, 7); + + // Create a lazy application: (x: x + 1) 7 + nix_init_apply(ctx, lazyApply, incrementFn, argSeven); + assert_ctx_ok(); + + BindingsBuilder * builder = nix_make_bindings_builder(ctx, state, 3); + nix_bindings_builder_insert(ctx, builder, "throwing", throwingValue); + nix_bindings_builder_insert(ctx, builder, "normal", intValue); + nix_bindings_builder_insert(ctx, builder, "lazy", lazyApply); + nix_make_attrs(ctx, value, builder); + nix_bindings_builder_free(builder); + + // Test 1: Lazy accessor should return the throwing attribute without forcing evaluation + nix_value * lazyThrowingAttr = nix_get_attr_byname_lazy(ctx, value, state, "throwing"); + assert_ctx_ok(); + ASSERT_NE(nullptr, lazyThrowingAttr); + + // Verify the attribute is still lazy by checking that forcing it throws + nix_value_force(ctx, state, lazyThrowingAttr); + assert_ctx_err(); + ASSERT_THAT( + nix_err_msg(nullptr, ctx, nullptr), testing::HasSubstr("This should not be evaluated by the lazy accessor")); + + // Test 2: Lazy accessor should return the already-evaluated int + nix_value * intAttr = nix_get_attr_byname_lazy(ctx, value, state, "normal"); + assert_ctx_ok(); + ASSERT_NE(nullptr, intAttr); + ASSERT_EQ(42, nix_get_int(ctx, intAttr)); + + // Test 3: Lazy accessor should return the lazy function application without forcing + nix_value * lazyFunctionAttr = nix_get_attr_byname_lazy(ctx, value, state, "lazy"); + assert_ctx_ok(); + ASSERT_NE(nullptr, lazyFunctionAttr); + + // Force the lazy function application - should compute 7 + 1 = 8 + nix_value_force(ctx, state, lazyFunctionAttr); + assert_ctx_ok(); + ASSERT_EQ(8, nix_get_int(ctx, lazyFunctionAttr)); + + // Test 4: Missing attribute should return NULL with NIX_ERR_KEY + nix_value * missingAttr = nix_get_attr_byname_lazy(ctx, value, state, "nonexistent"); + ASSERT_EQ(nullptr, missingAttr); + ASSERT_EQ(NIX_ERR_KEY, nix_err_code(ctx)); + + // Clean up + nix_gc_decref(ctx, throwingFn); + nix_gc_decref(ctx, throwingValue); + nix_gc_decref(ctx, intValue); + nix_gc_decref(ctx, lazyApply); + nix_gc_decref(ctx, incrementFn); + nix_gc_decref(ctx, argSeven); + nix_gc_decref(ctx, lazyThrowingAttr); + nix_gc_decref(ctx, intAttr); + nix_gc_decref(ctx, lazyFunctionAttr); +} + +TEST_F(nix_api_expr_test, nix_get_attr_byidx_lazy) +{ + // Create an attribute set with a throwing lazy attribute, an already-evaluated int, and a lazy function call + + // 1. Throwing lazy element - create a function application thunk that will throw when forced + nix_value * throwingFn = nix_alloc_value(ctx, state); + nix_value * throwingValue = nix_alloc_value(ctx, state); + + nix_expr_eval_from_string( + ctx, + state, + R"( + _: throw "This should not be evaluated by the lazy accessor" + )", + "", + throwingFn); + assert_ctx_ok(); + + nix_init_apply(ctx, throwingValue, throwingFn, throwingFn); + assert_ctx_ok(); + + // 2. Already evaluated int (not lazy) + nix_value * intValue = nix_alloc_value(ctx, state); + nix_init_int(ctx, intValue, 99); + assert_ctx_ok(); + + // 3. Lazy function application that would compute increment 10 = 11 + nix_value * lazyApply = nix_alloc_value(ctx, state); + nix_value * incrementFn = nix_alloc_value(ctx, state); + nix_value * argTen = nix_alloc_value(ctx, state); + + nix_expr_eval_from_string(ctx, state, "x: x + 1", "", incrementFn); + assert_ctx_ok(); + nix_init_int(ctx, argTen, 10); + + // Create a lazy application: (x: x + 1) 10 + nix_init_apply(ctx, lazyApply, incrementFn, argTen); + assert_ctx_ok(); + + BindingsBuilder * builder = nix_make_bindings_builder(ctx, state, 3); + nix_bindings_builder_insert(ctx, builder, "a_throwing", throwingValue); + nix_bindings_builder_insert(ctx, builder, "b_normal", intValue); + nix_bindings_builder_insert(ctx, builder, "c_lazy", lazyApply); + nix_make_attrs(ctx, value, builder); + nix_bindings_builder_free(builder); + + // Proper usage: first get the size and gather all attributes into a map + unsigned int attrCount = nix_get_attrs_size(ctx, value); + assert_ctx_ok(); + ASSERT_EQ(3u, attrCount); + + // Gather all attributes into a map (proper contract usage) + std::map attrMap; + const char * name; + + for (unsigned int i = 0; i < attrCount; i++) { + nix_value * attr = nix_get_attr_byidx_lazy(ctx, value, state, i, &name); + assert_ctx_ok(); + ASSERT_NE(nullptr, attr); + attrMap[std::string(name)] = attr; + } + + // Now test the gathered attributes + ASSERT_EQ(3u, attrMap.size()); + ASSERT_TRUE(attrMap.count("a_throwing")); + ASSERT_TRUE(attrMap.count("b_normal")); + ASSERT_TRUE(attrMap.count("c_lazy")); + + // Test 1: Throwing attribute should be lazy + nix_value * throwingAttr = attrMap["a_throwing"]; + nix_value_force(ctx, state, throwingAttr); + assert_ctx_err(); + ASSERT_THAT( + nix_err_msg(nullptr, ctx, nullptr), testing::HasSubstr("This should not be evaluated by the lazy accessor")); + + // Test 2: Normal attribute should be already evaluated + nix_value * normalAttr = attrMap["b_normal"]; + ASSERT_EQ(99, nix_get_int(ctx, normalAttr)); + + // Test 3: Lazy function should compute when forced + nix_value * lazyAttr = attrMap["c_lazy"]; + nix_value_force(ctx, state, lazyAttr); + assert_ctx_ok(); + ASSERT_EQ(11, nix_get_int(ctx, lazyAttr)); + + // Clean up + nix_gc_decref(ctx, throwingFn); + nix_gc_decref(ctx, throwingValue); + nix_gc_decref(ctx, intValue); + nix_gc_decref(ctx, lazyApply); + nix_gc_decref(ctx, incrementFn); + nix_gc_decref(ctx, argTen); + for (auto & pair : attrMap) { + nix_gc_decref(ctx, pair.second); + } +} + TEST_F(nix_api_expr_test, nix_value_init) { // Setup