C API: Add libflake-c (backport #11940)

.github/workflows/ci.yml

@@ -23,7 +23,9 @@ jobs:
     - uses: cachix/install-nix-action@v30
       with:
         # The sandbox would otherwise be disabled by default on Darwin
-        extra_nix_config: "sandbox = true"
+        extra_nix_config: |
+          sandbox = true
+          max-jobs = 1
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
     - uses: cachix/cachix-action@v15
       if: needs.check_secrets.outputs.cachix == 'true'

meson.build

@@ -34,6 +34,7 @@ endif
 subproject('libutil-c')
 subproject('libstore-c')
 subproject('libexpr-c')
+subproject('libflake-c')
 subproject('libmain-c')
 
 # Language Bindings

packaging/components.nix

@@ -49,6 +49,7 @@ in
   nix-expr-tests = callPackage ../src/libexpr-tests/package.nix { };
 
   nix-flake = callPackage ../src/libflake/package.nix { };
+  nix-flake-c = callPackage ../src/libflake-c/package.nix { };
   nix-flake-tests = callPackage ../src/libflake-tests/package.nix { };
 
   nix-main = callPackage ../src/libmain/package.nix { };

packaging/everything.nix

@@ -22,6 +22,7 @@
   nix-expr-tests,
 
   nix-flake,
+  nix-flake-c,
   nix-flake-tests,
 
   nix-main,
@@ -40,6 +41,75 @@
   nix-perl-bindings,
 }:
 
+<<<<<<< HEAD
+=======
+let
+  dev = stdenv.mkDerivation (finalAttrs: {
+    name = "nix-${nix-cli.version}-dev";
+    pname = "nix";
+    version = nix-cli.version;
+    dontUnpack = true;
+    dontBuild = true;
+    libs = map lib.getDev [
+      nix-cmd
+      nix-expr
+      nix-expr-c
+      nix-fetchers
+      nix-flake
+      nix-flake-c
+      nix-main
+      nix-main-c
+      nix-store
+      nix-store-c
+      nix-util
+      nix-util-c
+      nix-perl-bindings
+    ];
+    installPhase = ''
+      mkdir -p $out/nix-support
+      echo $libs >> $out/nix-support/propagated-build-inputs
+    '';
+    passthru = {
+      tests = {
+        pkg-config =
+          testers.hasPkgConfigModules {
+            package = finalAttrs.finalPackage;
+          };
+      };
+
+      # If we were to fully emulate output selection here, we'd confuse the Nix CLIs,
+      # because they rely on `drvPath`.
+      dev = finalAttrs.finalPackage.out;
+
+      libs = throw "`nix.dev.libs` is not meant to be used; use `nix.libs` instead.";
+    };
+    meta = {
+      pkgConfigModules = [
+        "nix-cmd"
+        "nix-expr"
+        "nix-expr-c"
+        "nix-fetchers"
+        "nix-flake"
+        "nix-flake-c"
+        "nix-main"
+        "nix-main-c"
+        "nix-store"
+        "nix-store-c"
+        "nix-util"
+        "nix-util-c"
+      ];
+    };
+  });
+  devdoc = buildEnv {
+    name = "nix-${nix-cli.version}-devdoc";
+    paths = [
+      nix-internal-api-docs
+      nix-external-api-docs
+    ];
+  };
+
+in
+>>>>>>> 4eecf3c20 (Add nix-flake-c, nix_flake_init_global, nix_flake_settings_new)
 (buildEnv {
   name = "nix-${nix-cli.version}";
   paths = [
@@ -124,6 +194,7 @@
         nix-expr
         nix-expr-c
         nix-flake
+        nix-flake-c
         nix-main
         nix-main-c
       ;

src/external-api-docs/doxygen.cfg.in

@@ -40,6 +40,7 @@ GENERATE_LATEX         = NO
 INPUT                  = \
   @src@/src/libutil-c \
   @src@/src/libexpr-c \
+  @src@/src/libflake-c \
   @src@/src/libstore-c \
   @src@/doc/external-api/README.md
 

src/external-api-docs/package.nix

@@ -30,6 +30,7 @@ mkMesonDerivation (finalAttrs: {
       # Source is not compiled, but still must be available for Doxygen
       # to gather comments.
       (cpp ../libexpr-c)
+      (cpp ../libflake-c)
       (cpp ../libstore-c)
       (cpp ../libutil-c)
     ];

src/libexpr-c/nix_api_expr.cc

@@ -6,6 +6,7 @@
 #include "eval-gc.hh"
 #include "globals.hh"
 #include "eval-settings.hh"
+#include "ref.hh"
 
 #include "nix_api_expr.h"
 #include "nix_api_expr_internal.h"
@@ -18,6 +19,29 @@
 #  include <mutex>
 #endif
 
+/**
+ * @brief Allocate and initialize using self-reference
+ *
+ * This allows a brace initializer to reference the object being constructed.
+ *
+ * @warning Use with care, as the pointer points to an object that is not fully constructed yet.
+ *
+ * @tparam T Type to allocate
+ * @tparam F A function type for `init`, taking a T* and returning the initializer for T
+ * @param init Function that takes a T* and returns the initializer for T
+ * @return Pointer to allocated and initialized object
+ */
+template <typename T, typename F>
+static T * unsafe_new_with_self(F && init)
+{
+    // Allocate
+    void * p = ::operator new(
+        sizeof(T),
+        static_cast<std::align_val_t>(alignof(T)));
+    // Initialize with placement new
+    return new (p) T(init(static_cast<T *>(p)));
+}
+
 nix_err nix_libexpr_init(nix_c_context * context)
 {
     if (context)
@@ -93,7 +117,42 @@ nix_err nix_value_force_deep(nix_c_context * context, EvalState * state, nix_val
     NIXC_CATCH_ERRS
 }
 
-EvalState * nix_state_create(nix_c_context * context, const char ** lookupPath_c, Store * store)
+nix_eval_state_builder * nix_eval_state_builder_new(nix_c_context * context, Store * store)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        return unsafe_new_with_self<nix_eval_state_builder>([&](auto * self) {
+            return nix_eval_state_builder{
+                .store = nix::ref<nix::Store>(store->ptr),
+                .settings = nix::EvalSettings{/* &bool */ self->readOnlyMode},
+                .fetchSettings = nix::fetchers::Settings{},
+                .readOnlyMode = true,
+            };
+        });
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+void nix_eval_state_builder_free(nix_eval_state_builder * builder)
+{
+    delete builder;
+}
+
+nix_err nix_eval_state_builder_load(nix_c_context * context, nix_eval_state_builder * builder)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        // TODO: load in one go?
+        builder->settings.readOnlyMode = nix::settings.readOnlyMode;
+        loadConfFile(builder->settings);
+        loadConfFile(builder->fetchSettings);
+    }
+    NIXC_CATCH_ERRS
+}
+
+nix_err nix_eval_state_builder_set_lookup_path(nix_c_context * context, nix_eval_state_builder * builder, const char ** lookupPath_c)
 {
     if (context)
         context->last_err_code = NIX_OK;
@@ -102,28 +161,47 @@ EvalState * nix_state_create(nix_c_context * context, const char ** lookupPath_c
         if (lookupPath_c != nullptr)
             for (size_t i = 0; lookupPath_c[i] != nullptr; i++)
                 lookupPath.push_back(lookupPath_c[i]);
+        builder->lookupPath = nix::LookupPath::parse(lookupPath);
+    }
+    NIXC_CATCH_ERRS
+}
 
-        void * p = ::operator new(
-            sizeof(EvalState),
-            static_cast<std::align_val_t>(alignof(EvalState)));
-        auto * p2 = static_cast<EvalState *>(p);
-        new (p) EvalState {
-            .fetchSettings = nix::fetchers::Settings{},
-            .settings = nix::EvalSettings{
-                nix::settings.readOnlyMode,
-            },
-            .state = nix::EvalState(
-                nix::LookupPath::parse(lookupPath),
-                store->ptr,
-                p2->fetchSettings,
-                p2->settings),
-        };
-        loadConfFile(p2->settings);
-        return p2;
+EvalState * nix_eval_state_build(nix_c_context * context, nix_eval_state_builder * builder)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        return unsafe_new_with_self<EvalState>([&](auto * self) {
+            return EvalState{
+                .fetchSettings = std::move(builder->fetchSettings),
+                .settings = std::move(builder->settings),
+                .state = nix::EvalState(
+                    builder->lookupPath,
+                    builder->store,
+                    self->fetchSettings,
+                    self->settings),
+            };
+        });
     }
     NIXC_CATCH_ERRS_NULL
 }
 
+EvalState * nix_state_create(nix_c_context * context, const char ** lookupPath_c, Store * store)
+{
+    auto builder = nix_eval_state_builder_new(context, store);
+    if (builder == nullptr)
+        return nullptr;
+
+    if (nix_eval_state_builder_load(context, builder) != NIX_OK)
+        return nullptr;
+
+    if (nix_eval_state_builder_set_lookup_path(context, builder, lookupPath_c)
+            != NIX_OK)
+        return nullptr;
+
+    return nix_eval_state_build(context, builder);
+}
+
 void nix_state_free(EvalState * state)
 {
     delete state;

src/libexpr-c/nix_api_expr.h

@@ -30,6 +30,11 @@ extern "C" {
 // cffi start
 
 // Type definitions
+/**
+ * @brief Builder for EvalState
+ */
+typedef struct nix_eval_state_builder nix_eval_state_builder;
+
 /**
  * @brief Represents a state of the Nix language evaluator.
  *
@@ -174,12 +179,70 @@ nix_err nix_value_force(nix_c_context * context, EvalState * state, nix_value *
 nix_err nix_value_force_deep(nix_c_context * context, EvalState * state, nix_value * value);
 
 /**
- * @brief Create a new Nix language evaluator state.
+ * @brief Create a new nix_eval_state_builder
+ *
+ * The settings are initialized to their default value.
+ * Values can be sourced elsewhere with nix_eval_state_builder_load.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] store The Nix store to use.
+ * @return A new nix_eval_state_builder or NULL on failure.
+ */
+nix_eval_state_builder * nix_eval_state_builder_new(nix_c_context * context, Store * store);
+
+/**
+ * @brief Read settings from the ambient environment
+ *
+ * Settings are sourced from environment variables and configuration files,
+ * as documented in the Nix manual.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[out] builder The builder to modify.
+ * @return NIX_OK if successful, an error code otherwise.
+ */
+nix_err nix_eval_state_builder_load(nix_c_context * context, nix_eval_state_builder * builder);
+
+/**
+ * @brief Set the lookup path for `<...>` expressions
+ *
+ * @param[in] context Optional, stores error information
+ * @param[in] builder The builder to modify.
+ * @param[in] lookupPath Null-terminated array of strings corresponding to entries in NIX_PATH.
+ */
+nix_err nix_eval_state_builder_set_lookup_path(
+    nix_c_context * context, nix_eval_state_builder * builder, const char ** lookupPath);
+
+/**
+ * @brief Create a new Nix language evaluator state
+ *
+ * Remember to nix_eval_state_builder_free after building the state.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] builder The builder to use and free
+ * @return A new Nix state or NULL on failure.
+ * @see nix_eval_state_builder_new, nix_eval_state_builder_free
+ */
+EvalState * nix_eval_state_build(nix_c_context * context, nix_eval_state_builder * builder);
+
+/**
+ * @brief Free a nix_eval_state_builder
+ *
+ * Does not fail.
+ *
+ * @param[in] builder The builder to free.
+ */
+void nix_eval_state_builder_free(nix_eval_state_builder * builder);
+
+/**
+ * @brief Create a new Nix language evaluator state
+ *
+ * For more control, use nix_eval_state_builder
  *
  * @param[out] context Optional, stores error information
  * @param[in] lookupPath Null-terminated array of strings corresponding to entries in NIX_PATH.
  * @param[in] store The Nix store to use.
  * @return A new Nix state or NULL on failure.
+ * @see nix_state_builder_new
  */
 EvalState * nix_state_create(nix_c_context * context, const char ** lookupPath, Store * store);
 

src/libexpr-c/nix_api_expr_internal.h

@@ -6,6 +6,17 @@
 #include "eval-settings.hh"
 #include "attr-set.hh"
 #include "nix_api_value.h"
+#include "search-path.hh"
+
+struct nix_eval_state_builder
+{
+    nix::ref<nix::Store> store;
+    nix::EvalSettings settings;
+    nix::fetchers::Settings fetchSettings;
+    nix::LookupPath lookupPath;
+    // TODO: make an EvalSettings setting own this instead?
+    bool readOnlyMode;
+};
 
 struct EvalState
 {

src/libexpr-c/nix_api_value.h

@@ -214,7 +214,7 @@ nix_get_string(nix_c_context * context, const nix_value * value, nix_get_string_
 /** @brief Get path as string
  * @param[out] context Optional, stores error information
  * @param[in] value Nix value to inspect
- * @return string
+ * @return string, if the type is NIX_TYPE_PATH
  * @return NULL in case of error.
  */
 const char * nix_get_path_string(nix_c_context * context, const nix_value * value);