Add plugins to make Nix more extensible.

All plugins in plugin-files will be dlopened, allowing them to
statically construct instances of the various Register* types Nix
supports.

Author: shlevy

.gitignore

@@ -38,6 +38,7 @@ perl/Makefile.config
 /scripts/nix-copy-closure
 /scripts/nix-reduce-build
 /scripts/nix-http-export.cgi
+/scripts/nix-profile-daemon.sh
 
 # /src/libexpr/
 /src/libexpr/lexer-tab.cc

Makefile

@@ -24,7 +24,8 @@ makefiles = \
   misc/launchd/local.mk \
   misc/upstart/local.mk \
   doc/manual/local.mk \
-  tests/local.mk
+  tests/local.mk \
+  tests/plugins/local.mk
 
 GLOBAL_CXXFLAGS += -std=c++14 -g -Wall -include config.h
 

doc/manual/command-ref/conf-file.xml

@@ -742,6 +742,33 @@ builtins.fetchurl {
   </varlistentry>
 
 
+  <varlistentry xml:id="conf-plugin-files">
+    <term><literal>plugin-files</literal></term>
+    <listitem>
+      <para>
+        A list of plugin files to be loaded by Nix. Each of these
+        files will be dlopened by Nix, allowing them to affect
+        execution through static initialization. In particular, these
+        plugins may construct static instances of RegisterPrimOp to
+        add new primops to the expression language,
+        RegisterStoreImplementation to add new store implementations,
+        and RegisterCommand to add new subcommands to the
+        <literal>nix</literal> command. See the constructors for those
+        types for more details.
+      </para>
+      <para>
+	Since these files are loaded into the same address space as
+        Nix itself, they must be DSOs compatible with the instance of
+        Nix running at the time (i.e. compiled against the same
+        headers, not linked to any incompatible libraries). They
+        should not be linked to any Nix libs directly, as those will
+        be available already at load time.
+      </para>
+    </listitem>
+
+  </varlistentry>
+
+
 </variablelist>
 
 </para>

doc/manual/release-notes/rl-2.0.xml

@@ -389,6 +389,13 @@ configureFlags = "--prefix=${placeholder "out"} --includedir=${placeholder "dev"
     </para>
   </listitem>
 
+  <listitem>
+    <para>
+      Nix can now be extended with plugins. See the documentation of
+      the 'plugin-files' option for more details.
+    </para>
+  </listitem>
+
 </itemizedlist>
 
 <para>Some features were removed:</para>

mk/libraries.mk

@@ -45,6 +45,11 @@ endif
 # - $(1)_INSTALL_DIR: the directory where the library will be
 #   installed.  Defaults to $(libdir).
 #
+# - $(1)_EXCLUDE_FROM_LIBRARY_LIST: if defined, the library will not
+#   be automatically marked as a dependency of the top-level all
+#   target andwill not be listed in the make help output. This is
+#   useful for libraries built solely for testing, for example.
+#
 # - BUILD_SHARED_LIBS: if equal to ‘1’, a dynamic library will be
 #   built, otherwise a static library.
 define build-library
@@ -149,7 +154,9 @@ define build-library
   $(1)_DEPS := $$(foreach fn, $$($(1)_OBJS), $$(call filename-to-dep, $$(fn)))
   -include $$($(1)_DEPS)
 
+  ifndef $(1)_EXCLUDE_FROM_LIBRARY_LIST
   libs-list += $$($(1)_PATH)
+  endif
   clean-files += $$(_d)/*.a $$(_d)/*.$(SO_EXT) $$(_d)/*.o $$(_d)/.*.dep $$($(1)_DEPS) $$($(1)_OBJS)
   dist-files += $$(_srcs)
 endef

src/build-remote/build-remote.cc

@@ -64,6 +64,8 @@ int main (int argc, char * * argv)
 
         settings.maxBuildJobs.set("1"); // hack to make tests with local?root= work
 
+        initPlugins();
+
         auto store = openStore().cast<LocalStore>();
 
         /* It would be more appropriate to use $XDG_RUNTIME_DIR, since

src/libmain/shared.hh

@@ -22,6 +22,7 @@ public:
 
 int handleExceptions(const string & programName, std::function<void()> fun);
 
+/* Don't forget to call initPlugins() after settings are initialized! */
 void initNix();
 
 void parseCmdLine(int argc, char * * argv,

src/libstore/globals.cc

@@ -6,6 +6,7 @@
 #include <algorithm>
 #include <map>
 #include <thread>
+#include <dlfcn.h>
 
 
 namespace nix {
@@ -137,4 +138,18 @@ void MaxBuildJobsSetting::set(const std::string & str)
         throw UsageError("configuration setting '%s' should be 'auto' or an integer", name);
 }
 
+
+void initPlugins()
+{
+    for (const auto & pluginFile : settings.pluginFiles.get()) {
+        /* handle is purposefully leaked as there may be state in the
+           DSO needed by the action of the plugin. */
+        void *handle =
+            dlopen(pluginFile.c_str(), RTLD_LAZY | RTLD_LOCAL);
+        if (!handle)
+            throw Error(format("could not dynamically open plugin file '%1%': %2%") % pluginFile % dlerror());
+    }
+}
+
+
 }

src/libstore/globals.hh

@@ -367,12 +367,19 @@ public:
 
     Setting<Strings> allowedUris{this, {}, "allowed-uris",
         "Prefixes of URIs that builtin functions such as fetchurl and fetchGit are allowed to fetch."};
+
+    Setting<Paths> pluginFiles{this, {}, "plugin-files",
+        "Plugins to dynamically load at nix initialization time."};
 };
 
 
 // FIXME: don't use a global variable.
 extern Settings settings;
 
+/* This should be called after settings are initialized, but before
+   anything else */
+void initPlugins();
+
 
 extern const string nixVersion;
 

src/libstore/local.mk

@@ -9,6 +9,9 @@ libstore_SOURCES := $(wildcard $(d)/*.cc)
 libstore_LIBS = libutil libformat
 
 libstore_LDFLAGS = $(SQLITE3_LIBS) -lbz2 $(LIBCURL_LIBS) $(SODIUM_LIBS) -pthread
+ifneq ($(OS), FreeBSD)
+ libstore_LDFLAGS += -ldl
+endif
 
 libstore_FILES = sandbox-defaults.sb sandbox-minimal.sb sandbox-network.sb