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.

.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
 

src/nix-build/nix-build.cc

@@ -232,6 +232,8 @@ void mainWrapped(int argc, char * * argv)
 
  myArgs.parseCmdline(args);
 
+ initPlugins();
+
  if (packages && fromArgs)
  throw UsageError("'-p' and '-E' are mutually exclusive");
 

src/nix-channel/nix-channel.cc

@@ -213,6 +213,9 @@ int main(int argc, char ** argv)
  }
  return true;
  });
+
+ initPlugins();
+
  switch (cmd) {
  case cNone:
  throw UsageError("no command specified");

src/nix-collect-garbage/nix-collect-garbage.cc

@@ -77,6 +77,8 @@ int main(int argc, char * * argv)
  return true;
  });
 
+ initPlugins();
+
  auto profilesDir = settings.nixStateDir + "/profiles";
  if (removeOld) removeOldGenerations(profilesDir);
 

src/nix-copy-closure/nix-copy-closure.cc

@@ -44,6 +44,8 @@ int main(int argc, char ** argv)
  return true;
  });
 
+ initPlugins();
+
  if (sshHost.empty())
  throw UsageError("no host name specified");
 

src/nix-daemon/nix-daemon.cc

@@ -1060,6 +1060,8 @@ int main(int argc, char * * argv)
  return true;
  });
 
+ initPlugins();
+
  if (stdio) {
  if (getStoreType() == tDaemon) {
  /* Forward on this connection to the real daemon */

src/nix-env/nix-env.cc

@@ -1393,6 +1393,8 @@ int main(int argc, char * * argv)
 
  myArgs.parseCmdline(argvToStrings(argc, argv));
 
+ initPlugins();
+
  if (!op) throw UsageError("no operation specified");
 
  auto store = openStore();

src/nix-instantiate/nix-instantiate.cc

@@ -151,6 +151,8 @@ int main(int argc, char * * argv)
 
  myArgs.parseCmdline(argvToStrings(argc, argv));
 
+ initPlugins();
+
  if (evalOnly && !wantsReadWrite)
  settings.readOnlyMode = true;
 

src/nix-prefetch-url/nix-prefetch-url.cc

@@ -89,6 +89,8 @@ int main(int argc, char * * argv)
 
  myArgs.parseCmdline(argvToStrings(argc, argv));
 
+ initPlugins();
+
  if (args.size() > 2)
  throw UsageError("too many arguments");
 

src/nix-store/nix-store.cc

@@ -1052,6 +1052,8 @@ int main(int argc, char * * argv)
  return true;
  });
 
+ initPlugins();
+
  if (!op) throw UsageError("no operation specified");
 
  if (op != opDump && op != opRestore) /* !!! hack */

src/nix/main.cc

@@ -92,6 +92,8 @@ void mainWrapped(int argc, char * * argv)
 
  args.parseCmdline(argvToStrings(argc, argv));
 
+ initPlugins();
+
  if (!args.command) args.showHelpAndExit();
 
  Finally f([]() { stopProgressBar(); });

tests/local.mk

@@ -22,7 +22,8 @@ nix_tests = \
  run.sh \
  brotli.sh \
  pure-eval.sh \
- check.sh
+ check.sh \
+ plugins.sh
  # parallel.sh
 
 install-tests += $(foreach x, $(nix_tests), tests/$(x))
@@ -31,4 +32,4 @@ tests-environment = NIX_REMOTE= $(bash) -e
 
 clean-files += $(d)/common.sh
 
-installcheck: $(d)/common.sh
+installcheck: $(d)/common.sh $(d)/plugins/plugintest.so

tests/plugins.sh

@@ -0,0 +1,7 @@
+source common.sh
+
+set -o pipefail
+
+res=$(nix eval '(builtins.constNull true)' --option plugin-files $PWD/plugins/plugintest.so)
+
+[ "$res"x = "nullx" ]

tests/plugins/local.mk

@@ -0,0 +1,9 @@
+libraries += plugintest
+
+plugintest_DIR := $(d)
+
+plugintest_SOURCES := $(d)/plugintest.cc
+
+plugintest_ALLOW_UNDEFINED := 1
+
+plugintest_EXCLUDE_FROM_LIBRARY_LIST := 1

tests/plugins/plugintest.cc

@@ -0,0 +1,10 @@
+#include "primops.hh"
+
+using namespace nix;
+
+static void prim_constNull (EvalState & state, const Pos & pos, Value ** args, Value & v)
+{
+ mkNull(v);
+}
+
+static RegisterPrimOp r("constNull", 1, prim_constNull);