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.

24 files changed, 122 insertions, 3 deletions

diff --git a/.gitignore b/.gitignore
index ce22fa007..0a9599378 100644
--- a/.gitignore
+++ b/.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
diff --git a/Makefile b/Makefile
index 5d8e990cc..c867823fc 100644
--- a/Makefile
+++ b/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
 
diff --git a/doc/manual/command-ref/conf-file.xml b/doc/manual/command-ref/conf-file.xml
index fff7994f2..cede6db3c 100644
--- a/doc/manual/command-ref/conf-file.xml
+++ b/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>
diff --git a/doc/manual/release-notes/rl-2.0.xml b/doc/manual/release-notes/rl-2.0.xml
index 32cdb1d0c..effd2e39d 100644
--- a/doc/manual/release-notes/rl-2.0.xml
+++ b/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>
diff --git a/mk/libraries.mk b/mk/libraries.mk
index 3cd7a5310..14c95fa91 100644
--- a/mk/libraries.mk
+++ b/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
diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index df579729a..50eb6b29e 100644
--- a/src/build-remote/build-remote.cc
+++ b/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
diff --git a/src/libmain/shared.hh b/src/libmain/shared.hh
index 1dcc4f0ac..8e4861232 100644
--- a/src/libmain/shared.hh
+++ b/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,
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index d3c96ddd6..21ab0e629 100644
--- a/src/libstore/globals.cc
+++ b/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());
+    }
+}
+
+
 }
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index 20ac8fe4e..508084d08 100644
--- a/src/libstore/globals.hh
+++ b/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;
 
diff --git a/src/libstore/local.mk b/src/libstore/local.mk
index 50c46ce6f..239356aee 100644
--- a/src/libstore/local.mk
+++ b/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
 
diff --git a/src/nix-build/nix-build.cc b/src/nix-build/nix-build.cc
index 1581c282c..99f773451 100755
--- a/src/nix-build/nix-build.cc
+++ b/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");
 
diff --git a/src/nix-channel/nix-channel.cc b/src/nix-channel/nix-channel.cc
index 370f216ab..ec9a7174e 100755
--- a/src/nix-channel/nix-channel.cc
+++ b/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");
diff --git a/src/nix-collect-garbage/nix-collect-garbage.cc b/src/nix-collect-garbage/nix-collect-garbage.cc
index cc663a969..37fe22f48 100644
--- a/src/nix-collect-garbage/nix-collect-garbage.cc
+++ b/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);
 
diff --git a/src/nix-copy-closure/nix-copy-closure.cc b/src/nix-copy-closure/nix-copy-closure.cc
index 861fc2e5c..dfb1b8fc5 100755
--- a/src/nix-copy-closure/nix-copy-closure.cc
+++ b/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");
 
diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
index d3a8ebbdd..890bffa19 100644
--- a/src/nix-daemon/nix-daemon.cc
+++ b/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 */
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index 016caf6d2..97e66cbd9 100644
--- a/src/nix-env/nix-env.cc
+++ b/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();
diff --git a/src/nix-instantiate/nix-instantiate.cc b/src/nix-instantiate/nix-instantiate.cc
index e05040a42..dd262bea0 100644
--- a/src/nix-instantiate/nix-instantiate.cc
+++ b/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;
 
diff --git a/src/nix-prefetch-url/nix-prefetch-url.cc b/src/nix-prefetch-url/nix-prefetch-url.cc
index fef3eaa45..fa7ee2545 100644
--- a/src/nix-prefetch-url/nix-prefetch-url.cc
+++ b/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");
 
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index 4fc3421c0..efef7f15c 100644
--- a/src/nix-store/nix-store.cc
+++ b/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 */
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 8f6bbe8f5..bb107ec7d 100644
--- a/src/nix/main.cc
+++ b/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(); });
diff --git a/tests/local.mk b/tests/local.mk
index e90b9f7da..51bc09dd4 100644
--- a/tests/local.mk
+++ b/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 $(d)/plugins/plugintest.so
diff --git a/tests/plugins.sh b/tests/plugins.sh
new file mode 100644
index 000000000..6d18d1da0
--- /dev/null
+++ b/tests/plugins.sh
@@ -0,0 +1,7 @@
+source common.sh
+
+set -o pipefail
+
+res=$(nix eval '(builtins.constNull true)' --option plugin-files $PWD/plugins/plugintest.so)
+
+[ "$res"x = "nullx" ]
diff --git a/tests/plugins/local.mk b/tests/plugins/local.mk
new file mode 100644
index 000000000..a5f19b087
--- /dev/null
+++ b/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
diff --git a/tests/plugins/plugintest.cc b/tests/plugins/plugintest.cc
new file mode 100644
index 000000000..f788c4814
--- /dev/null
+++ b/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);