tree-wide: shuffle headers around for about 30s compile time

This didn't really feel so worth it afterwards, but I did untangle a
bunch of stuff that should not have been tangled.

The general gist of this change is that variant bullshit was causing a
bunch of compile time, and it seems like the only way to deal with
variant induced compile time is to keep variant types out of headers.
Explicit template instantiation seems to do nothing for them.

I also seem to have gotten some back-end time improvement from
explicitly instantiating regex, but I don't know why. There is no
corresponding front-end time improvement from it: regex is still at the
top of the sinners list.

**** Templates that took longest to instantiate:
 15231 ms: std::basic_regex<char>::_M_compile (28 times, avg 543 ms)
 15066 ms: std::__detail::_Compiler<std::regex_traits<char>>::_Compiler (28 times, avg 538 ms)
 12571 ms: std::__detail::_Compiler<std::regex_traits<char>>::_M_disjunction (28 times, avg 448 ms)
 12454 ms: std::__detail::_Compiler<std::regex_traits<char>>::_M_alternative (28 times, avg 444 ms)
 12225 ms: std::__detail::_Compiler<std::regex_traits<char>>::_M_term (28 times, avg 436 ms)
 11363 ms: nlohmann::basic_json<>::parse<const char *> (21 times, avg 541 ms)
 10628 ms: nlohmann::basic_json<>::basic_json (109 times, avg 97 ms)
 10134 ms: std::__detail::_Compiler<std::regex_traits<char>>::_M_atom (28 times, avg 361 ms)

Back-end time before messing with the regex:
**** Function sets that took longest to compile / optimize:
  8076 ms: void boost::io::detail::put<$>(boost::io::detail::put_holder<$> cons... (177 times, avg 45 ms)
  4382 ms: std::_Rb_tree<$>::_M_erase(std::_Rb_tree_node<$>*) (1247 times, avg 3 ms)
  3137 ms: boost::stacktrace::detail::to_string_impl_base<boost::stacktrace::de... (137 times, avg 22 ms)
  2896 ms: void boost::io::detail::mk_str<$>(std::__cxx11::basic_string<$>&, ch... (177 times, avg 16 ms)
  2304 ms: std::_Rb_tree<$>::_M_get_insert_hint_unique_pos(std::_Rb_tree_const_... (210 times, avg 10 ms)
  2116 ms: bool std::__detail::_Compiler<$>::_M_expression_term<$>(std::__detai... (112 times, avg 18 ms)
  2051 ms: std::_Rb_tree_iterator<$> std::_Rb_tree<$>::_M_emplace_hint_unique<$... (244 times, avg 8 ms)
  2037 ms: toml::result<$> toml::detail::sequence<$>::invoke<$>(toml::detail::l... (93 times, avg 21 ms)
  1928 ms: std::__detail::_Compiler<$>::_M_quantifier() (28 times, avg 68 ms)
  1859 ms: nlohmann::json_abi_v3_11_3::detail::serializer<$>::dump(nlohmann::js... (41 times, avg 45 ms)
  1824 ms: std::_Function_handler<$>::_M_manager(std::_Any_data&, std::_Any_dat... (973 times, avg 1 ms)
  1810 ms: std::__detail::_BracketMatcher<$>::_BracketMatcher(std::__detail::_B... (112 times, avg 16 ms)
  1793 ms: nix::fetchers::GitInputScheme::fetch(nix::ref<$>, nix::fetchers::Inp... (1 times, avg 1793 ms)
  1759 ms: std::_Rb_tree<$>::_M_get_insert_unique_pos(std::__cxx11::basic_strin... (281 times, avg 6 ms)
  1722 ms: bool nlohmann::json_abi_v3_11_3::detail::parser<$>::sax_parse_intern... (19 times, avg 90 ms)
  1677 ms: boost::io::basic_altstringbuf<$>::overflow(int) (194 times, avg 8 ms)
  1674 ms: std::__cxx11::basic_string<$>::_M_mutate(unsigned long, unsigned lon... (249 times, avg 6 ms)
  1660 ms: std::_Rb_tree_node<$>* std::_Rb_tree<$>::_M_copy<$>(std::_Rb_tree_no... (304 times, avg 5 ms)
  1599 ms: bool nlohmann::json_abi_v3_11_3::detail::parser<$>::sax_parse_intern... (19 times, avg 84 ms)
  1568 ms: void std::__detail::_Compiler<$>::_M_insert_bracket_matcher<$>(bool) (112 times, avg 14 ms)
  1541 ms: std::__shared_ptr<$>::~__shared_ptr() (531 times, avg 2 ms)
  1539 ms: nlohmann::json_abi_v3_11_3::detail::serializer<$>::dump_escaped(std:... (41 times, avg 37 ms)
  1471 ms: void std::__detail::_Compiler<$>::_M_insert_character_class_matcher<... (112 times, avg 13 ms)

After messing with the regex (notice std::__detail::_Compiler vanishes
here, but I don't know why):

**** Function sets that took longest to compile / optimize:
  8054 ms: void boost::io::detail::put<$>(boost::io::detail::put_holder<$> cons... (177 times, avg 45 ms)
  4313 ms: std::_Rb_tree<$>::_M_erase(std::_Rb_tree_node<$>*) (1217 times, avg 3 ms)
  3259 ms: boost::stacktrace::detail::to_string_impl_base<boost::stacktrace::de... (137 times, avg 23 ms)
  3045 ms: void boost::io::detail::mk_str<$>(std::__cxx11::basic_string<$>&, ch... (177 times, avg 17 ms)
  2314 ms: std::_Rb_tree<$>::_M_get_insert_hint_unique_pos(std::_Rb_tree_const_... (207 times, avg 11 ms)
  1923 ms: std::_Rb_tree_iterator<$> std::_Rb_tree<$>::_M_emplace_hint_unique<$... (216 times, avg 8 ms)
  1817 ms: bool nlohmann::json_abi_v3_11_3::detail::parser<$>::sax_parse_intern... (18 times, avg 100 ms)
  1816 ms: toml::result<$> toml::detail::sequence<$>::invoke<$>(toml::detail::l... (93 times, avg 19 ms)
  1788 ms: nlohmann::json_abi_v3_11_3::detail::serializer<$>::dump(nlohmann::js... (40 times, avg 44 ms)
  1749 ms: std::_Rb_tree<$>::_M_get_insert_unique_pos(std::__cxx11::basic_strin... (278 times, avg 6 ms)
  1724 ms: std::__cxx11::basic_string<$>::_M_mutate(unsigned long, unsigned lon... (248 times, avg 6 ms)
  1697 ms: boost::io::basic_altstringbuf<$>::overflow(int) (194 times, avg 8 ms)
  1684 ms: nix::fetchers::GitInputScheme::fetch(nix::ref<$>, nix::fetchers::Inp... (1 times, avg 1684 ms)
  1680 ms: std::_Rb_tree_node<$>* std::_Rb_tree<$>::_M_copy<$>(std::_Rb_tree_no... (303 times, avg 5 ms)
  1589 ms: bool nlohmann::json_abi_v3_11_3::detail::parser<$>::sax_parse_intern... (18 times, avg 88 ms)
  1483 ms: non-virtual thunk to boost::wrapexcept<$>::~wrapexcept() (181 times, avg 8 ms)
  1447 ms: nlohmann::json_abi_v3_11_3::detail::serializer<$>::dump_escaped(std:... (40 times, avg 36 ms)
  1441 ms: std::__shared_ptr<$>::~__shared_ptr() (496 times, avg 2 ms)
  1420 ms: boost::stacktrace::basic_stacktrace<$>::init(unsigned long, unsigned... (137 times, avg 10 ms)
  1396 ms: boost::basic_format<$>::~basic_format() (194 times, avg 7 ms)
  1290 ms: std::__cxx11::basic_string<$>::_M_replace_cold(char*, unsigned long,... (231 times, avg 5 ms)
  1258 ms: std::vector<$>::~vector() (354 times, avg 3 ms)
  1222 ms: std::__cxx11::basic_string<$>::_M_replace(unsigned long, unsigned lo... (231 times, avg 5 ms)
  1194 ms: std::_Rb_tree<$>::_M_get_insert_hint_unique_pos(std::_Rb_tree_const_... (49 times, avg 24 ms)
  1186 ms: bool tao::pegtl::internal::sor<$>::match<$>(std::integer_sequence<$>... (1 times, avg 1186 ms)
  1149 ms: std::__detail::_Executor<$>::_M_dfs(std::__detail::_Executor<$>::_Ma... (70 times, avg 16 ms)
  1123 ms: toml::detail::sequence<$>::invoke(toml::detail::location&) (69 times, avg 16 ms)
  1110 ms: nlohmann::json_abi_v3_11_3::basic_json<$>::json_value::destroy(nlohm... (55 times, avg 20 ms)
  1079 ms: std::_Function_handler<$>::_M_manager(std::_Any_data&, std::_Any_dat... (541 times, avg 1 ms)
  1033 ms: nlohmann::json_abi_v3_11_3::detail::lexer<$>::scan_number() (20 times, avg 51 ms)

Change-Id: I10af282bcd4fc39c2d3caae3453e599e4639c70b

64 files changed, 190 insertions, 125 deletions

diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index 2450e80c2..3c7af067b 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -1,11 +1,7 @@
-#include <cstdlib>
-#include <cstring>
 #include <algorithm>
 #include <set>
 #include <memory>
-#include <string_view>
 #include <tuple>
-#include <iomanip>
 #if __APPLE__
 #include <sys/time.h>
 #endif
@@ -18,6 +14,7 @@
 #include "build-result.hh"
 #include "store-api.hh"
 #include "derivations.hh"
+#include "strings.hh"
 #include "local-store.hh"
 #include "legacy.hh"
 #include "experimental-features.hh"
diff --git a/src/libcmd/editor-for.cc b/src/libcmd/editor-for.cc
index 67653d9c9..868153e90 100644
--- a/src/libcmd/editor-for.cc
+++ b/src/libcmd/editor-for.cc
@@ -1,6 +1,7 @@
 #include "editor-for.hh"
 #include "environment-variables.hh"
 #include "source-path.hh"
+#include "strings.hh"
 
 namespace nix {
 
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 227cd254a..a87383f7f 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -19,6 +19,7 @@
 #include "gc-small-vector.hh"
 #include "fetch-to-store.hh"
 #include "flake/flakeref.hh"
+#include "exit.hh"
 
 #include <algorithm>
 #include <iostream>
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index eab1f22ef..ba1e4a820 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -12,6 +12,7 @@
 #include "experimental-features.hh"
 #include "search-path.hh"
 #include "repl-exit-status.hh"
+#include "backed-string-view.hh"
 
 #include <map>
 #include <optional>
@@ -791,4 +792,4 @@ static constexpr std::string_view corepkgsPrefix{"/__corepkgs__/"};
 
 }
 
-#include "eval-inline.hh"
+#include "eval-inline.hh" // IWYU pragma: keep
diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index 52f254813..d16281c39 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -11,6 +11,7 @@
 #include "eval-error.hh"
 #include "pos-idx.hh"
 #include "pos-table.hh"
+#include "strings.hh"
 
 namespace nix {
 
diff --git a/src/libfetchers/fetchers.hh b/src/libfetchers/fetchers.hh
index 40f2b6294..f778908fb 100644
--- a/src/libfetchers/fetchers.hh
+++ b/src/libfetchers/fetchers.hh
@@ -7,6 +7,8 @@
 #include "path.hh"
 #include "attrs.hh"
 #include "url.hh"
+#include "ref.hh"
+#include "strings.hh"
 
 #include <memory>
 
diff --git a/src/libmain/progress-bar.cc b/src/libmain/progress-bar.cc
index f0270df04..cdb15d8c7 100644
--- a/src/libmain/progress-bar.cc
+++ b/src/libmain/progress-bar.cc
@@ -1,8 +1,9 @@
 #include "progress-bar.hh"
+#include "file-system.hh"
 #include "sync.hh"
-#include "store-api.hh"
 #include "names.hh"
 #include "terminal.hh"
+#include "strings.hh"
 
 #include <map>
 #include <thread>
diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index 018e34509..bc9548e09 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -6,6 +6,8 @@
 #include "loggers.hh"
 #include "current-process.hh"
 #include "terminal.hh"
+#include "strings.hh"
+#include "exit.hh"
 
 #include <algorithm>
 #include <exception>
diff --git a/src/libmain/shared.hh b/src/libmain/shared.hh
index d7d872319..b41efe567 100644
--- a/src/libmain/shared.hh
+++ b/src/libmain/shared.hh
@@ -7,12 +7,10 @@
 #include "path.hh"
 #include "derived-path.hh"
 #include "processes.hh"
-#include "exit.hh"
+#include "strings.hh"
 
 #include <signal.h>
 
-#include <locale>
-
 
 namespace nix {
 
diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index fc0569a66..d4197b3df 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -10,6 +10,7 @@
 #include "nar-accessor.hh"
 #include "thread-pool.hh"
 #include "signals.hh"
+#include "strings.hh"
 
 #include <chrono>
 #include <regex>
diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index f2c8ccc5f..3ed3cb6bd 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -9,6 +9,7 @@
 #include "logging-json.hh"
 #include "substitution-goal.hh"
 #include "drv-output-substitution-goal.hh"
+#include "strings.hh"
 
 #include <fstream>
 #include <sys/types.h>
diff --git a/src/libstore/build/entry-points.cc b/src/libstore/build/entry-points.cc
index f52f2876f..1f85881fa 100644
--- a/src/libstore/build/entry-points.cc
+++ b/src/libstore/build/entry-points.cc
@@ -2,6 +2,7 @@
 #include "substitution-goal.hh"
 #include "derivation-goal.hh"
 #include "local-store.hh"
+#include "strings.hh"
 
 namespace nix {
 
diff --git a/src/libstore/build/hook-instance.cc b/src/libstore/build/hook-instance.cc
index d5da80c74..f91a904cc 100644
--- a/src/libstore/build/hook-instance.cc
+++ b/src/libstore/build/hook-instance.cc
@@ -2,6 +2,7 @@
 #include "file-system.hh"
 #include "globals.hh"
 #include "hook-instance.hh"
+#include "strings.hh"
 
 namespace nix {
 
diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index 1571627d6..7553f1e79 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -1,15 +1,12 @@
 #include "local-derivation-goal.hh"
 #include "indirect-root-store.hh"
-#include "hook-instance.hh"
 #include "machines.hh"
 #include "store-api.hh"
 #include "worker.hh"
 #include "builtins.hh"
 #include "builtins/buildenv.hh"
 #include "path-references.hh"
-#include "finally.hh"
 #include "archive.hh"
-#include "compression.hh"
 #include "daemon.hh"
 #include "topo-sort.hh"
 #include "json-utils.hh"
@@ -19,6 +16,7 @@
 #include "child.hh"
 #include "unix-domain-socket.hh"
 #include "mount.hh"
+#include "strings.hh"
 
 #include <regex>
 #include <queue>
diff --git a/src/libstore/builtins/buildenv.cc b/src/libstore/builtins/buildenv.cc
index 61c729d27..9fe5f6660 100644
--- a/src/libstore/builtins/buildenv.cc
+++ b/src/libstore/builtins/buildenv.cc
@@ -1,4 +1,5 @@
 #include "buildenv.hh"
+#include "strings.hh"
 
 #include <sys/stat.h>
 #include <sys/types.h>
diff --git a/src/libstore/builtins/fetchurl.cc b/src/libstore/builtins/fetchurl.cc
index 4049d1c6c..062ecdc14 100644
--- a/src/libstore/builtins/fetchurl.cc
+++ b/src/libstore/builtins/fetchurl.cc
@@ -3,6 +3,7 @@
 #include "store-api.hh"
 #include "archive.hh"
 #include "compression.hh"
+#include "strings.hh"
 
 namespace nix {
 
diff --git a/src/libstore/content-address.cc b/src/libstore/content-address.cc
index 6aa6d598d..dae311609 100644
--- a/src/libstore/content-address.cc
+++ b/src/libstore/content-address.cc
@@ -1,6 +1,7 @@
 #include "args.hh"
 #include "content-address.hh"
 #include "split.hh"
+#include "strings.hh"
 
 namespace nix {
 
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 5ac9cd2ef..a9239197b 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -2,7 +2,7 @@
 #include "monitor-fd.hh"
 #include "worker-protocol.hh"
 #include "worker-protocol-impl.hh"
-#include "build-result.hh"
+#include "build-result.hh" // IWYU pragma: keep
 #include "store-api.hh"
 #include "store-cast.hh"
 #include "gc-store.hh"
@@ -12,6 +12,7 @@
 #include "finally.hh"
 #include "archive.hh"
 #include "derivations.hh"
+#include "strings.hh"
 #include "args.hh"
 
 #include <sstream>
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index 7f41e6865..93baa9f20 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -3,11 +3,12 @@
 #include "store-api.hh"
 #include "globals.hh"
 #include "types.hh"
-#include "split.hh"
 #include "common-protocol.hh"
 #include "common-protocol-impl.hh"
-#include "fs-accessor.hh"
 #include "json-utils.hh"
+#include "strings.hh"
+#include "backed-string-view.hh"
+
 #include <boost/container/small_vector.hpp>
 #include <nlohmann/json.hpp>
 
diff --git a/src/libstore/derived-path.hh b/src/libstore/derived-path.hh
index c96e0df67..b75415aec 100644
--- a/src/libstore/derived-path.hh
+++ b/src/libstore/derived-path.hh
@@ -5,6 +5,7 @@
 #include "path.hh"
 #include "outputs-spec.hh"
 #include "comparator.hh"
+#include "ref.hh"
 
 #include <variant>
 
diff --git a/src/libstore/filetransfer.cc b/src/libstore/filetransfer.cc
index 11c8a755c..f3e8a5312 100644
--- a/src/libstore/filetransfer.cc
+++ b/src/libstore/filetransfer.cc
@@ -5,6 +5,7 @@
 #include "s3.hh"
 #include "signals.hh"
 #include "compression.hh"
+#include "strings.hh"
 
 #if ENABLE_S3
 #include <aws/core/client/ClientConfiguration.h>
diff --git a/src/libstore/filetransfer.hh b/src/libstore/filetransfer.hh
index b2ee66312..4352cb81b 100644
--- a/src/libstore/filetransfer.hh
+++ b/src/libstore/filetransfer.hh
@@ -2,6 +2,7 @@
 ///@file
 
 #include "box_ptr.hh"
+#include "ref.hh"
 #include "logging.hh"
 #include "serialise.hh"
 #include "types.hh"
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index 7b4a12dc9..d5903d01e 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -5,6 +5,7 @@
 #include "signals.hh"
 #include "finally.hh"
 #include "unix-domain-socket.hh"
+#include "strings.hh"
 
 #include <queue>
 #include <regex>
diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index 9e2d65a1c..4433b411d 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -9,6 +9,7 @@
 #include "path-with-outputs.hh"
 #include "ssh.hh"
 #include "ssh-store.hh"
+#include "strings.hh"
 #include "derivations.hh"
 
 namespace nix {
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 4c8e2ea2f..49991e38a 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -10,6 +10,7 @@
 #include "signals.hh"
 #include "finally.hh"
 #include "compression.hh"
+#include "strings.hh"
 
 #include <algorithm>
 #include <cstring>
diff --git a/src/libstore/lock.hh b/src/libstore/lock.hh
index 1c268e1fb..ac5ff061b 100644
--- a/src/libstore/lock.hh
+++ b/src/libstore/lock.hh
@@ -1,11 +1,10 @@
 #pragma once
 ///@file
 
-#include "types.hh"
-
-#include <optional>
+#include <memory>
 
 #include <sys/types.h>
+#include <vector>
 
 namespace nix {
 
diff --git a/src/libstore/machines.hh b/src/libstore/machines.hh
index 8516409d4..56d9bed30 100644
--- a/src/libstore/machines.hh
+++ b/src/libstore/machines.hh
@@ -1,7 +1,9 @@
 #pragma once
 ///@file
 
-#include "types.hh"
+#include "ref.hh"
+#include <set>
+#include <vector>
 
 namespace nix {
 
diff --git a/src/libstore/make-content-addressed.cc b/src/libstore/make-content-addressed.cc
index abb6e9889..0c592ce22 100644
--- a/src/libstore/make-content-addressed.cc
+++ b/src/libstore/make-content-addressed.cc
@@ -1,5 +1,6 @@
 #include "make-content-addressed.hh"
 #include "references.hh"
+#include "strings.hh"
 
 namespace nix {
 
diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
index a63a28482..7ea7c189a 100644
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -1,12 +1,12 @@
 #include "derivations.hh"
 #include "parsed-derivations.hh"
 #include "globals.hh"
-#include "local-store.hh"
 #include "store-api.hh"
 #include "thread-pool.hh"
 #include "topo-sort.hh"
 #include "closure.hh"
 #include "filetransfer.hh"
+#include "strings.hh"
 
 namespace nix {
 
diff --git a/src/libstore/nar-accessor.hh b/src/libstore/nar-accessor.hh
index 5e19bd3c7..4299daf1b 100644
--- a/src/libstore/nar-accessor.hh
+++ b/src/libstore/nar-accessor.hh
@@ -1,10 +1,12 @@
 #pragma once
 ///@file
 
+#include "fs-accessor.hh"
+#include "ref.hh"
+
 #include <functional>
 
 #include <nlohmann/json_fwd.hpp>
-#include "fs-accessor.hh"
 
 namespace nix {
 
diff --git a/src/libstore/nar-info-disk-cache.cc b/src/libstore/nar-info-disk-cache.cc
index 5c0bb17b9..c83a8fbfb 100644
--- a/src/libstore/nar-info-disk-cache.cc
+++ b/src/libstore/nar-info-disk-cache.cc
@@ -4,6 +4,7 @@
 #include "sqlite.hh"
 #include "globals.hh"
 #include "users.hh"
+#include "strings.hh"
 
 #include <sqlite3.h>
 #include <nlohmann/json.hpp>
diff --git a/src/libstore/nar-info.cc b/src/libstore/nar-info.cc
index e557b4677..0434873df 100644
--- a/src/libstore/nar-info.cc
+++ b/src/libstore/nar-info.cc
@@ -1,4 +1,4 @@
-#include "globals.hh"
+#include "strings.hh"
 #include "nar-info.hh"
 #include "store-api.hh"
 
diff --git a/src/libstore/optimise-store.cc b/src/libstore/optimise-store.cc
index 9c871b78f..c60e5a85d 100644
--- a/src/libstore/optimise-store.cc
+++ b/src/libstore/optimise-store.cc
@@ -1,6 +1,7 @@
 #include "local-store.hh"
 #include "globals.hh"
 #include "signals.hh"
+#include "strings.hh"
 
 #include <cstring>
 #include <sys/types.h>
diff --git a/src/libstore/parsed-derivations.cc b/src/libstore/parsed-derivations.cc
index 992a79c6e..1b2ec914d 100644
--- a/src/libstore/parsed-derivations.cc
+++ b/src/libstore/parsed-derivations.cc
@@ -1,4 +1,5 @@
 #include "parsed-derivations.hh"
+#include "strings.hh"
 
 #include <nlohmann/json.hpp>
 #include <regex>
diff --git a/src/libstore/path-info.cc b/src/libstore/path-info.cc
index 4dc2823ce..54519a867 100644
--- a/src/libstore/path-info.cc
+++ b/src/libstore/path-info.cc
@@ -1,5 +1,6 @@
 #include "path-info.hh"
 #include "store-api.hh"
+#include "strings.hh"
 
 namespace nix {
 
diff --git a/src/libstore/path-with-outputs.cc b/src/libstore/path-with-outputs.cc
index af6837370..c49531acb 100644
--- a/src/libstore/path-with-outputs.cc
+++ b/src/libstore/path-with-outputs.cc
@@ -1,7 +1,6 @@
 #include "path-with-outputs.hh"
 #include "store-api.hh"
-
-#include <regex>
+#include "strings.hh"
 
 namespace nix {
 
diff --git a/src/libstore/platform/darwin.cc b/src/libstore/platform/darwin.cc
index 078753bff..956fb1e9b 100644
--- a/src/libstore/platform/darwin.cc
+++ b/src/libstore/platform/darwin.cc
@@ -2,6 +2,7 @@
 #include "signals.hh"
 #include "platform/darwin.hh"
 #include "regex.hh"
+#include "strings.hh"
 
 #include <sys/proc_info.h>
 #include <sys/sysctl.h>
diff --git a/src/libstore/platform/linux.cc b/src/libstore/platform/linux.cc
index f22fbe58f..486d71885 100644
--- a/src/libstore/platform/linux.cc
+++ b/src/libstore/platform/linux.cc
@@ -5,6 +5,7 @@
 #include "signals.hh"
 #include "platform/linux.hh"
 #include "regex.hh"
+#include "strings.hh"
 
 #include <grp.h>
 #include <regex>
diff --git a/src/libstore/profiles.cc b/src/libstore/profiles.cc
index e8b88693d..d88a3b9fe 100644
--- a/src/libstore/profiles.cc
+++ b/src/libstore/profiles.cc
@@ -1,12 +1,11 @@
 #include "profiles.hh"
-#include "store-api.hh"
 #include "local-fs-store.hh"
 #include "users.hh"
+#include "strings.hh"
 
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
-#include <errno.h>
 #include <stdio.h>
 
 
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 36223051b..1f94ca03f 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -15,6 +15,8 @@
 #include "finally.hh"
 #include "logging.hh"
 #include "filetransfer.hh"
+#include "strings.hh"
+
 #include <nlohmann/json.hpp>
 
 namespace nix {
@@ -64,7 +66,7 @@ void RemoteStore::initConnection(Connection & conn)
 {
     /* Send the magic greeting, check for the reply. */
     try {
-        conn.from.endOfFileError = "Nix daemon disconnected unexpectedly (maybe it crashed?)";
+        conn.from.specialEndOfFileError = "Nix daemon disconnected unexpectedly (maybe it crashed?)";
         conn.to << WORKER_MAGIC_1;
         conn.to.flush();
 
diff --git a/src/libstore/s3-binary-cache-store.cc b/src/libstore/s3-binary-cache-store.cc
index 921a2e556..b50084860 100644
--- a/src/libstore/s3-binary-cache-store.cc
+++ b/src/libstore/s3-binary-cache-store.cc
@@ -7,6 +7,7 @@
 #include "globals.hh"
 #include "compression.hh"
 #include "filetransfer.hh"
+#include "strings.hh"
 
 #include <aws/core/Aws.h>
 #include <aws/core/VersionConfig.h>
diff --git a/src/libstore/ssh-store.cc b/src/libstore/ssh-store.cc
index 94c0b7237..fb60326c1 100644
--- a/src/libstore/ssh-store.cc
+++ b/src/libstore/ssh-store.cc
@@ -1,13 +1,11 @@
 #include "ssh-store.hh"
 #include "store-api.hh"
-#include "local-fs-store.hh"
 #include "remote-store.hh"
 #include "remote-store-connection.hh"
-#include "remote-fs-accessor.hh"
-#include "archive.hh"
 #include "worker-protocol.hh"
 #include "pool.hh"
 #include "ssh.hh"
+#include "strings.hh"
 
 namespace nix {
 
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index f921956e8..cb0604233 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -5,10 +5,10 @@
 #include "nar-info-disk-cache.hh"
 #include "thread-pool.hh"
 #include "url.hh"
-#include "references.hh"
 #include "archive.hh"
-#include "remote-store.hh"
+#include "uds-remote-store.hh"
 #include "signals.hh"
+#include "strings.hh"
 // FIXME this should not be here, see TODO below on
 // `addMultipleToStore`.
 #include "worker-protocol.hh"
diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index 1342e7c6a..edcab23ac 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -1,10 +1,11 @@
 #include "args.hh"
 #include "args/root.hh"
 #include "hash.hh"
-#include "json-utils.hh"
+#include "strings.hh"
+#include "json-utils.hh" // IWYU pragma: keep (instances)
 #include "environment-variables.hh"
 
-#include "experimental-features-json.hh"
+#include "experimental-features-json.hh" // IWYU pragma: keep (instances)
 #include "logging.hh"
 
 #include <glob.h>
diff --git a/src/libutil/args.hh b/src/libutil/args.hh
index 5fdbaba7e..e2bac6415 100644
--- a/src/libutil/args.hh
+++ b/src/libutil/args.hh
@@ -3,6 +3,8 @@
 
 #include "experimental-features.hh"
 #include "types.hh"
+#include "ref.hh"
+
 #include <functional>
 #include <map>
 #include <memory>
diff --git a/src/libutil/backed-string-view.hh b/src/libutil/backed-string-view.hh
new file mode 100644
index 000000000..96136331c
--- /dev/null
+++ b/src/libutil/backed-string-view.hh
@@ -0,0 +1,69 @@
+#pragma once
+/// @file String view that can be either owned or borrowed.
+#include <variant>
+#include <string>
+#include <string_view>
+
+/**
+ * This wants to be a little bit like rust's Cow type.
+ * Some parts of the evaluator benefit greatly from being able to reuse
+ * existing allocations for strings, but have to be able to also use
+ * newly allocated storage for values.
+ *
+ * We do not define implicit conversions, even with ref qualifiers,
+ * since those can easily become ambiguous to the reader and can degrade
+ * into copying behaviour we want to avoid.
+ */
+class BackedStringView {
+private:
+    std::variant<std::string, std::string_view> data;
+
+    /**
+     * Needed to introduce a temporary since operator-> must return
+     * a pointer. Without this we'd need to store the view object
+     * even when we already own a string.
+     */
+    class Ptr {
+    private:
+        std::string_view view;
+    public:
+        Ptr(std::string_view view): view(view) {}
+        const std::string_view * operator->() const { return &view; }
+    };
+
+public:
+    BackedStringView(std::string && s): data(std::move(s)) {}
+    BackedStringView(std::string_view sv): data(sv) {}
+    template<size_t N>
+    BackedStringView(const char (& lit)[N]): data(std::string_view(lit)) {}
+
+    BackedStringView(const BackedStringView &) = delete;
+    BackedStringView & operator=(const BackedStringView &) = delete;
+
+    /**
+     * We only want move operations defined since the sole purpose of
+     * this type is to avoid copies.
+     */
+    BackedStringView(BackedStringView && other) = default;
+    BackedStringView & operator=(BackedStringView && other) = default;
+
+    bool isOwned() const
+    {
+        return std::holds_alternative<std::string>(data);
+    }
+
+    std::string toOwned() &&
+    {
+        return isOwned()
+            ? std::move(std::get<std::string>(data))
+            : std::string(std::get<std::string_view>(data));
+    }
+
+    std::string_view operator*() const
+    {
+        return isOwned()
+            ? std::get<std::string>(data)
+            : std::get<std::string_view>(data);
+    }
+    Ptr operator->() const { return Ptr(**this); }
+};
diff --git a/src/libutil/error.cc b/src/libutil/error.cc
index e5d6a9fa8..a7cbfbfd0 100644
--- a/src/libutil/error.cc
+++ b/src/libutil/error.cc
@@ -3,6 +3,7 @@
 #include "logging.hh"
 #include "position.hh"
 #include "terminal.hh"
+#include "strings.hh"
 
 #include <iostream>
 #include <optional>
diff --git a/src/libutil/file-system.cc b/src/libutil/file-system.cc
index 631cf076b..1d266067e 100644
--- a/src/libutil/file-system.cc
+++ b/src/libutil/file-system.cc
@@ -10,6 +10,7 @@
 #include "logging.hh"
 #include "serialise.hh"
 #include "signals.hh"
+#include "strings.hh"
 #include "types.hh"
 #include "users.hh"
 
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index f05d4aa98..d383e9802 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -10,6 +10,7 @@
 #include "charptr-cast.hh"
 #include "logging.hh"
 #include "split.hh"
+#include "strings.hh"
 
 #include <sys/types.h>
 #include <sys/stat.h>
diff --git a/src/libutil/meson.build b/src/libutil/meson.build
index e7f986363..6566f7f46 100644
--- a/src/libutil/meson.build
+++ b/src/libutil/meson.build
@@ -53,6 +53,7 @@ libutil_headers = files(
   'archive.hh',
   'args/root.hh',
   'args.hh',
+  'backed-string-view.hh',
   'box_ptr.hh',
   'canon-path.hh',
   'cgroup.hh',
diff --git a/src/libutil/processes.cc b/src/libutil/processes.cc
index 61e1ad556..eec592221 100644
--- a/src/libutil/processes.cc
+++ b/src/libutil/processes.cc
@@ -3,6 +3,7 @@
 #include "finally.hh"
 #include "logging.hh"
 #include "processes.hh"
+#include "strings.hh"
 #include "serialise.hh"
 #include "signals.hh"
 
diff --git a/src/libutil/regex.cc b/src/libutil/regex.cc
index a9e6c6bee..a12d13550 100644
--- a/src/libutil/regex.cc
+++ b/src/libutil/regex.cc
@@ -1,6 +1,9 @@
 #include <string>
 #include <regex>
 
+// Declared as extern in precompiled-headers.hh
+template class std::basic_regex<char>;
+
 namespace nix::regex {
 std::string quoteRegexChars(const std::string & raw)
 {
diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index 4eda1b7e7..f509fedff 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -9,6 +9,21 @@
 
 namespace nix {
 
+namespace {
+/**
+ * Convert a little-endian integer to host order.
+ */
+template<typename T>
+T readLittleEndian(unsigned char * p)
+{
+    T x = 0;
+    for (size_t i = 0; i < sizeof(x); ++i, ++p) {
+        x |= ((T) *p) << (i * 8);
+    }
+    return x;
+}
+}
+
 template<typename T>
 T readNum(Source & source)
 {
@@ -152,7 +167,7 @@ size_t FdSource::readUnbuffered(char * data, size_t len)
         n = ::read(fd, data, len);
     } while (n == -1 && errno == EINTR);
     if (n == -1) { _good = false; throw SysError("reading from file"); }
-    if (n == 0) { _good = false; throw EndOfFile(std::string(*endOfFileError)); }
+    if (n == 0) { _good = false; throw EndOfFile(endOfFileError()); }
     read += n;
     return n;
 }
@@ -163,6 +178,11 @@ bool FdSource::good()
     return _good;
 }
 
+std::string FdSource::endOfFileError() const
+{
+    return specialEndOfFileError.has_value() ? *specialEndOfFileError : "unexpected end-of-file";
+}
+
 
 size_t StringSource::read(char * data, size_t len)
 {
diff --git a/src/libutil/serialise.hh b/src/libutil/serialise.hh
index 9ad8018d0..612658b2d 100644
--- a/src/libutil/serialise.hh
+++ b/src/libutil/serialise.hh
@@ -1,12 +1,10 @@
 #pragma once
 ///@file
 
-#include <concepts>
 #include <memory>
 
 #include "charptr-cast.hh"
 #include "generator.hh"
-#include "strings.hh"
 #include "types.hh"
 #include "file-descriptor.hh"
 
@@ -153,7 +151,10 @@ struct FdSource : BufferedSource
 {
     int fd;
     size_t read = 0;
-    BackedStringView endOfFileError{"unexpected end-of-file"};
+    /** Defaults to "unexpected end-of-file" */
+    std::optional<std::string> specialEndOfFileError;
+
+    std::string endOfFileError() const;
 
     FdSource() : fd(-1) { }
     FdSource(int fd) : fd(fd) { }
diff --git a/src/libutil/source-path.cc b/src/libutil/source-path.cc
index cfaac20c0..782005ef1 100644
--- a/src/libutil/source-path.cc
+++ b/src/libutil/source-path.cc
@@ -1,4 +1,5 @@
 #include "source-path.hh"
+#include "strings.hh"
 
 namespace nix {
 
diff --git a/src/libutil/strings.hh b/src/libutil/strings.hh
index 7330e2063..ebafab9ad 100644
--- a/src/libutil/strings.hh
+++ b/src/libutil/strings.hh
@@ -165,19 +165,6 @@ std::optional<N> string2Float(const std::string_view s);
 
 
 /**
- * Convert a little-endian integer to host order.
- */
-template<typename T>
-T readLittleEndian(unsigned char * p)
-{
-    T x = 0;
-    for (size_t i = 0; i < sizeof(x); ++i, ++p) {
-        x |= ((T) *p) << (i * 8);
-    }
-    return x;
-}
-
-/**
  * Convert a string to lower case.
  */
 std::string toLower(const std::string & s);
diff --git a/src/libutil/types.hh b/src/libutil/types.hh
index 13cb062fb..66c41fe59 100644
--- a/src/libutil/types.hh
+++ b/src/libutil/types.hh
@@ -1,17 +1,15 @@
 #pragma once
 ///@file
 
-#include "ref.hh"
-
 #include <list>
 #include <optional>
 #include <set>
 #include <string>
-#include <limits>
+#include <string_view>
 #include <map>
-#include <variant>
 #include <vector>
 #include <span>
+#include <stdint.h> // IWYU pragma: keep (this is used literally everywhere)
 
 namespace nix {
 
@@ -166,70 +164,4 @@ constexpr auto enumerate(T && iterable)
 template<class... Ts> struct overloaded : Ts... { using Ts::operator()...; };
 template<class... Ts> overloaded(Ts...) -> overloaded<Ts...>;
 
-
-
-/**
- * This wants to be a little bit like rust's Cow type.
- * Some parts of the evaluator benefit greatly from being able to reuse
- * existing allocations for strings, but have to be able to also use
- * newly allocated storage for values.
- *
- * We do not define implicit conversions, even with ref qualifiers,
- * since those can easily become ambiguous to the reader and can degrade
- * into copying behaviour we want to avoid.
- */
-class BackedStringView {
-private:
-    std::variant<std::string, std::string_view> data;
-
-    /**
-     * Needed to introduce a temporary since operator-> must return
-     * a pointer. Without this we'd need to store the view object
-     * even when we already own a string.
-     */
-    class Ptr {
-    private:
-        std::string_view view;
-    public:
-        Ptr(std::string_view view): view(view) {}
-        const std::string_view * operator->() const { return &view; }
-    };
-
-public:
-    BackedStringView(std::string && s): data(std::move(s)) {}
-    BackedStringView(std::string_view sv): data(sv) {}
-    template<size_t N>
-    BackedStringView(const char (& lit)[N]): data(std::string_view(lit)) {}
-
-    BackedStringView(const BackedStringView &) = delete;
-    BackedStringView & operator=(const BackedStringView &) = delete;
-
-    /**
-     * We only want move operations defined since the sole purpose of
-     * this type is to avoid copies.
-     */
-    BackedStringView(BackedStringView && other) = default;
-    BackedStringView & operator=(BackedStringView && other) = default;
-
-    bool isOwned() const
-    {
-        return std::holds_alternative<std::string>(data);
-    }
-
-    std::string toOwned() &&
-    {
-        return isOwned()
-            ? std::move(std::get<std::string>(data))
-            : std::string(std::get<std::string_view>(data));
-    }
-
-    std::string_view operator*() const
-    {
-        return isOwned()
-            ? std::get<std::string>(data)
-            : std::get<std::string_view>(data);
-    }
-    Ptr operator->() const { return Ptr(**this); }
-};
-
 }
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index 5762b0644..bc43aa7b1 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -1,6 +1,7 @@
 #include "archive.hh"
 #include "derivations.hh"
 #include "dotgraph.hh"
+#include "exit.hh"
 #include "globals.hh"
 #include "build-result.hh"
 #include "store-cast.hh"
@@ -17,7 +18,6 @@
 
 #include <iostream>
 #include <algorithm>
-#include <cstdio>
 
 #include <sys/types.h>
 #include <sys/stat.h>
diff --git a/src/nix/doctor.cc b/src/nix/doctor.cc
index 4e1cfe8c0..17db3f764 100644
--- a/src/nix/doctor.cc
+++ b/src/nix/doctor.cc
@@ -7,6 +7,7 @@
 #include "store-api.hh"
 #include "local-fs-store.hh"
 #include "worker-protocol.hh"
+#include "exit.hh"
 
 using namespace nix;
 
diff --git a/src/nix/verify.cc b/src/nix/verify.cc
index 8783d4e04..d4ab352f4 100644
--- a/src/nix/verify.cc
+++ b/src/nix/verify.cc
@@ -1,10 +1,9 @@
 #include "command.hh"
 #include "shared.hh"
 #include "store-api.hh"
-#include "sync.hh"
 #include "thread-pool.hh"
 #include "signals.hh"
-#include "references.hh"
+#include "exit.hh"
 
 #include <atomic>
 
diff --git a/src/pch/precompiled-headers.hh b/src/pch/precompiled-headers.hh
index f52f1cab8..c417d27db 100644
--- a/src/pch/precompiled-headers.hh
+++ b/src/pch/precompiled-headers.hh
@@ -58,3 +58,19 @@
 #include <unistd.h>
 
 #include <nlohmann/json.hpp>
+
+// This stuff is here to force the compiler to actually apply the extern
+// template directives in all compilation units. To borrow a term, under
+// complex microarchitectural conditions, clang ignores the extern template
+// declaration, as revealed in the profile.
+//
+// In most cases, extern template works fine in the header itself. We don't
+// have any idea why this happens.
+
+// Here because of all the regexes everywhere (it is infeasible to block instantiation everywhere)
+// For some reason this does not actually prevent the instantiation of
+// regex::_M_compile, and the regex compiler (my interpretation of what this is
+// supposed to do is make the template bits out-of-line), but it *does* prevent
+// a bunch of codegen of regex stuff, which seems to save about 30s on-cpu.
+// Instantiated in libutil/regex.cc.
+extern template class std::basic_regex<char>;
diff --git a/tests/unit/libstore/derivation.cc b/tests/unit/libstore/derivation.cc
index f6401a095..21e141693 100644
--- a/tests/unit/libstore/derivation.cc
+++ b/tests/unit/libstore/derivation.cc
@@ -1,8 +1,8 @@
 #include <nlohmann/json.hpp>
 #include <gtest/gtest.h>
 
-#include "experimental-features.hh"
 #include "derivations.hh"
+#include "strings.hh"
 
 #include "tests/libstore.hh"
 #include "tests/characterization.hh"
diff --git a/tests/unit/libstore/protocol.hh b/tests/unit/libstore/protocol.hh
index 059b4d91c..8212959f0 100644
--- a/tests/unit/libstore/protocol.hh
+++ b/tests/unit/libstore/protocol.hh
@@ -1,6 +1,7 @@
 #include <nlohmann/json.hpp>
 #include <gtest/gtest.h>
 
+#include "strings.hh"
 #include "tests/libstore.hh"
 #include "tests/characterization.hh"
 
diff --git a/tests/unit/libutil/references.cc b/tests/unit/libutil/references.cc
index a914e6c70..ef7111e9c 100644
--- a/tests/unit/libutil/references.cc
+++ b/tests/unit/libutil/references.cc
@@ -1,4 +1,5 @@
 #include "references.hh"
+#include "strings.hh"
 #include <gtest/gtest.h>
 
 namespace nix {