gc: Find roots using libproc on Darwin

Previously, the garbage collector found runtime roots on Darwin by
shelling out to `lsof -n -w -F n` then parsing the result.
However, this requires an lsof binary and can be extremely slow.

The official Apple lsof returns in a reasonable amount of time,
about 250ms in my tests, but the lsof packaged in nixpkgs is quite slow,
taking about 40 seconds to run the command.

Using libproc directly is about the same speed as Apple lsof,
and allows us to reënable several tests that were disabled on Darwin.

Change-Id: Ifa0adda7984e13c15535693baba835aae79a3577

3 files changed, 29 insertions, 0 deletions

diff --git a/src/libutil/meson.build b/src/libutil/meson.build
index 11bf97ee7..069798a6f 100644
--- a/src/libutil/meson.build
+++ b/src/libutil/meson.build
@@ -22,6 +22,7 @@ libutil_sources = files(
   'position.cc',
   'print-elided.cc',
   'references.cc',
+  'regex.cc',
   'serialise.cc',
   'shlex.cc',
   'signals.cc',
@@ -77,6 +78,7 @@ libutil_headers = files(
   'ref.hh',
   'references.hh',
   'regex-combinators.hh',
+  'regex.hh',
   'repair-flag.hh',
   'serialise.hh',
   'shlex.hh',
diff --git a/src/libutil/regex.cc b/src/libutil/regex.cc
new file mode 100644
index 000000000..a9e6c6bee
--- /dev/null
+++ b/src/libutil/regex.cc
@@ -0,0 +1,16 @@
+#include <string>
+#include <regex>
+
+namespace nix::regex {
+std::string quoteRegexChars(const std::string & raw)
+{
+    static auto specialRegex = std::regex(R"([.^$\\*+?()\[\]{}|])");
+    return std::regex_replace(raw, specialRegex, R"(\$&)");
+}
+
+std::regex storePathRegex(const std::string & storeDir)
+{
+    return std::regex(quoteRegexChars(storeDir) + R"(/[0-9a-z]+[0-9a-zA-Z\+\-\._\?=]*)");
+}
+
+}
diff --git a/src/libutil/regex.hh b/src/libutil/regex.hh
new file mode 100644
index 000000000..744a7d54a
--- /dev/null
+++ b/src/libutil/regex.hh
@@ -0,0 +1,11 @@
+#pragma once
+///@file
+
+#include <string>
+#include <regex>
+
+namespace nix::regex {
+std::string quoteRegexChars(const std::string & raw);
+
+std::regex storePathRegex(const std::string & storeDir);
+}