fix(3p/nix): Use SkipEmpty in all calls to absl::StrSplit

The behavior to return a list containing a single empty string when
provided an empty string is a behavior that absl inherited from legacy
code. However, the behavior expected by legacy code in Nix is the
behavior provided by the SkipEmpty option. Switch all calls to use
SkipEmpty, except for the call already using SkipWhitespace.

See also commit 26a59482d2, with the
partly-prophetic message: "there may be other places we need to
fix this as well."

Change-Id: I6e94856a12cfb1b7e4a3b4e221769ed446648861
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1687
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

third_party/nix/src/libexpr/primops.cc

@@ -620,7 +620,8 @@ static void prim_derivationStrict(EvalState& state, const Pos& pos,
           } else if (i->name == state.sOutputHashMode) {
             handleHashMode(s);
           } else if (i->name == state.sOutputs) {
-            handleOutputs(absl::StrSplit(s, absl::ByAnyChar(" \t\n\r")));
+            handleOutputs(absl::StrSplit(s, absl::ByAnyChar(" \t\n\r"),
+                                         absl::SkipEmpty()));
           }
         }
       }

third_party/nix/src/libexpr/primops/fetchGit.cc

@@ -57,7 +57,7 @@ GitInfo exportGit(ref<Store> store, const std::string& uri,
 
       std::set<std::string> files =
           absl::StrSplit(runProgram("git", true, {"-C", uri, "ls-files", "-z"}),
-                         absl::ByChar('\0'));
+                         absl::ByChar('\0'), absl::SkipEmpty());
 
       PathFilter filter = [&](const Path& p) -> bool {
         assert(absl::StartsWith(p, uri));

third_party/nix/src/libexpr/primops/fetchMercurial.cc

@@ -53,7 +53,7 @@ HgInfo exportMercurial(ref<Store> store, const std::string& uri,
           runProgram("hg", true,
                      {"status", "-R", uri, "--clean", "--modified", "--added",
                       "--no-status", "--print0"}),
-          absl::ByChar('\0'));
+          absl::ByChar('\0'), absl::SkipEmpty());
 
       PathFilter filter = [&](const Path& p) -> bool {
         assert(absl::StartsWith(p, uri));
@@ -129,7 +129,7 @@ HgInfo exportMercurial(ref<Store> store, const std::string& uri,
       absl::StrSplit(runProgram("hg", true,
                                 {"log", "-R", cacheDir, "-r", rev, "--template",
                                  "{node} {rev} {branch}"}),
-                     absl::ByAnyChar(" \t\n\r"));
+                     absl::ByAnyChar(" \t\n\r"), absl::SkipEmpty());
   assert(tokens.size() == 3);
 
   HgInfo hgInfo;

third_party/nix/src/libstore/binary-cache-store.cc

@@ -42,7 +42,8 @@ void BinaryCacheStore::init() {
     upsertFile(cacheInfoFile, "StoreDir: " + storeDir + "\n",
                "text/x-nix-cache-info");
   } else {
-    for (auto& line : absl::StrSplit(*cacheInfo, absl::ByChar('\n'))) {
+    for (auto& line :
+         absl::StrSplit(*cacheInfo, absl::ByChar('\n'), absl::SkipEmpty())) {
       size_t colon = line.find(':');
       if (colon == std::string::npos) {
         continue;

third_party/nix/src/libstore/build.cc

@@ -2485,7 +2485,8 @@ void DerivationGoal::initTmpDir() {
      there is no size constraint). */
   if (!parsedDrv->getStructuredAttrs()) {
     std::set<std::string> passAsFile =
-        absl::StrSplit(get(drv->env, "passAsFile"), absl::ByAnyChar(" \t\n\r"));
+        absl::StrSplit(get(drv->env, "passAsFile"), absl::ByAnyChar(" \t\n\r"),
+                       absl::SkipEmpty());
     for (auto& i : drv->env) {
       if (passAsFile.find(i.first) == passAsFile.end()) {
         env[i.first] = i.second;

third_party/nix/src/libstore/builtins/buildenv.cc

@@ -137,7 +137,7 @@ static void addPkg(const Path& pkgDir, int priority) {
   try {
     for (auto p : absl::StrSplit(
              readFile(pkgDir + "/nix-support/propagated-user-env-packages"),
-             absl::ByAnyChar(" \n"))) {
+             absl::ByAnyChar(" \n"), absl::SkipEmpty())) {
       auto pkg = std::string(p);
       if (!done.count(pkg)) {
         postponed.insert(pkg);
@@ -175,8 +175,8 @@ void builtinBuildenv(const BasicDerivation& drv) {
   /* Convert the stuff we get from the environment back into a
    * coherent data type. */
   Packages pkgs;
-  Strings derivations =
+  Strings derivations = absl::StrSplit(
-      absl::StrSplit(getAttr("derivations"), absl::ByAnyChar(" \t\n\r"));
+      getAttr("derivations"), absl::ByAnyChar(" \t\n\r"), absl::SkipEmpty());
   while (!derivations.empty()) {
     /* !!! We're trusting the caller to structure derivations env var correctly
      */

third_party/nix/src/libstore/derivations.cc

@@ -421,7 +421,8 @@ DrvPathWithOutputs parseDrvPathWithOutputs(absl::string_view path) {
 
   return DrvPathWithOutputs(
       path.substr(0, pos),
-      absl::StrSplit(path.substr(pos + 1), absl::ByChar(',')));
+      absl::StrSplit(path.substr(pos + 1), absl::ByChar(','),
+                     absl::SkipEmpty()));
 }
 
 Path makeDrvPathWithOutputs(const Path& drvPath,

third_party/nix/src/libstore/download.cc

@@ -181,7 +181,8 @@ struct CurlDownloader : public Downloader {
                  << "': " << absl::StripAsciiWhitespace(line);
       if (line.compare(0, 5, "HTTP/") == 0) {  // new response starts
         result.etag = "";
-        std::vector<std::string> ss = absl::StrSplit(line, absl::ByChar(' '));
+        std::vector<std::string> ss =
+            absl::StrSplit(line, absl::ByChar(' '), absl::SkipEmpty());
         status = ss.size() >= 2 ? ss[1] : "";
         result.data = std::make_shared<std::string>();
         result.bodySize = 0;
@@ -896,8 +897,8 @@ CachedDownloadResult Downloader::downloadCached(
     storePath = readLink(fileLink);
     store->addTempRoot(storePath);
     if (store->isValidPath(storePath)) {
-      std::vector<std::string> ss =
+      std::vector<std::string> ss = absl::StrSplit(
-          absl::StrSplit(readFile(dataFile), absl::ByChar('\n'));
+          readFile(dataFile), absl::ByChar('\n'), absl::SkipEmpty());
       if (ss.size() >= 3 && ss[0] == url) {
         time_t lastChecked;
         if (absl::SimpleAtoi(ss[2], &lastChecked) &&

third_party/nix/src/libstore/gc.cc

@@ -423,8 +423,8 @@ void LocalStore::findRuntimeRoots(Roots& roots, bool censor) {
 
         try {
           auto mapFile = fmt("/proc/%s/maps", ent->d_name);
-          std::vector<std::string> mapLines =
+          std::vector<std::string> mapLines = absl::StrSplit(
-              absl::StrSplit(readFile(mapFile, true), absl::ByChar('\n'));
+              readFile(mapFile, true), absl::ByChar('\n'), absl::SkipEmpty());
           for (const auto& line : mapLines) {
             auto match = std::smatch{};
             if (std::regex_match(line, match, mapRegex)) {

third_party/nix/src/libstore/globals.cc

@@ -59,14 +59,14 @@ Settings::Settings()
   auto s = getEnv("NIX_REMOTE_SYSTEMS");
   if (!s.empty()) {
     Strings ss;
-    for (auto p : absl::StrSplit(s, absl::ByChar(':'))) {
+    for (auto p : absl::StrSplit(s, absl::ByChar(':'), absl::SkipEmpty())) {
       ss.push_back(absl::StrCat("@", p));
     }
     builders = concatStringsSep(" ", ss);
   }
 
-  sandboxPaths =
+  sandboxPaths = absl::StrSplit("/bin/sh=" SANDBOX_SHELL,
-      absl::StrSplit("/bin/sh=" SANDBOX_SHELL, absl::ByAnyChar(" \t\n\r"));
+                                absl::ByAnyChar(" \t\n\r"), absl::SkipEmpty());
 }
 
 void loadConfFile() {

third_party/nix/src/libstore/local-store.cc

@@ -468,9 +468,9 @@ static void canonicalisePathMetaData_(const Path& path, uid_t fromUid,
       throw SysError("querying extended attributes of '%s'", path);
     }
 
-    for (auto& eaName :
+    for (auto& eaName : absl::StrSplit(std::string(eaBuf.data(), eaSize),
-         absl::StrSplit(std::string(eaBuf.data(), eaSize),
+                                       absl::ByString(std::string("\000", 1)),
-                        absl::ByString(std::string("\000", 1)))) {
+                                       absl::SkipEmpty())) {
       /* Ignore SELinux security labels since these cannot be
          removed even by root. */
       if (eaName == "security.selinux") {
@@ -702,7 +702,7 @@ void LocalStore::queryPathInfoUncached(
 
       s = (const char*)sqlite3_column_text(state->stmtQueryPathInfo, 6);
       if (s != nullptr) {
-        info->sigs = absl::StrSplit(s, absl::ByChar(' '));
+        info->sigs = absl::StrSplit(s, absl::ByChar(' '), absl::SkipEmpty());
       }
 
       s = (const char*)sqlite3_column_text(state->stmtQueryPathInfo, 7);

third_party/nix/src/libstore/local-store.hh

@@ -97,8 +97,8 @@ class LocalStore : public LocalFSStore {
  public:
   // Hack for build-remote.cc.
   // TODO(tazjin): remove this when we've got gRPC
-  PathSet locksHeld =
+  PathSet locksHeld = absl::StrSplit(
-      absl::StrSplit(getEnv("NIX_HELD_LOCKS"), absl::ByAnyChar(" \t\n\r"));
+      getEnv("NIX_HELD_LOCKS"), absl::ByAnyChar(" \t\n\r"), absl::SkipEmpty());
 
   /* Initialise the local store, upgrading the schema if
      necessary. */

third_party/nix/src/libstore/machines.cc

@@ -52,7 +52,8 @@ bool Machine::mandatoryMet(const std::set<std::string>& features) const {
 }
 
 void parseMachines(const std::string& s, Machines& machines) {
-  for (auto line : absl::StrSplit(s, absl::ByAnyChar("\n;"))) {
+  for (auto line :
+       absl::StrSplit(s, absl::ByAnyChar("\n;"), absl::SkipEmpty())) {
     // Skip empty lines & comments
     line = absl::StripAsciiWhitespace(line);
     if (line.empty() || line[line.find_first_not_of(" \t")] == '#') {
@@ -73,7 +74,7 @@ void parseMachines(const std::string& s, Machines& machines) {
     }
 
     std::vector<std::string> tokens =
-        absl::StrSplit(line, absl::ByAnyChar(" \t\n\r"));
+        absl::StrSplit(line, absl::ByAnyChar(" \t\n\r"), absl::SkipEmpty());
     auto sz = tokens.size();
     if (sz < 1) {
       throw FormatError("bad machine specification '%s'", line);
@@ -86,14 +87,17 @@ void parseMachines(const std::string& s, Machines& machines) {
     // TODO(tazjin): what???
     machines.emplace_back(
         tokens[0],
-        isSet(1) ? absl::StrSplit(tokens[1], absl::ByChar(','))
+        isSet(1)
-                 : std::vector<std::string>{settings.thisSystem},
+            ? absl::StrSplit(tokens[1], absl::ByChar(','), absl::SkipEmpty())
+            : std::vector<std::string>{settings.thisSystem},
         isSet(2) ? tokens[2] : "", isSet(3) ? std::stoull(tokens[3]) : 1LL,
         isSet(4) ? std::stoull(tokens[4]) : 1LL,
-        isSet(5) ? absl::StrSplit(tokens[5], absl::ByChar(','))
+        isSet(5)
-                 : std::set<std::string>{},
+            ? absl::StrSplit(tokens[5], absl::ByChar(','), absl::SkipEmpty())
-        isSet(6) ? absl::StrSplit(tokens[6], absl::ByChar(','))
+            : std::set<std::string>{},
-                 : std::set<std::string>{},
+        isSet(6)
+            ? absl::StrSplit(tokens[6], absl::ByChar(','), absl::SkipEmpty())
+            : std::set<std::string>{},
         isSet(7) ? tokens[7] : "");
   }
 }

third_party/nix/src/libstore/nar-info-disk-cache.cc

@@ -232,14 +232,15 @@ class NarInfoDiskCacheImpl final : public NarInfoDiskCache {
           auto hash_ = Hash::deserialize(queryNAR.getStr(6));
           narInfo->narHash = Hash::unwrap_throw(hash_);
           narInfo->narSize = queryNAR.getInt(7);
-          for (auto r : absl::StrSplit(queryNAR.getStr(8), absl::ByChar(' '))) {
+          for (auto r : absl::StrSplit(queryNAR.getStr(8), absl::ByChar(' '),
+                                       absl::SkipEmpty())) {
             narInfo->references.insert(absl::StrCat(cache.storeDir, "/", r));
           }
           if (!queryNAR.isNull(9)) {
             narInfo->deriver = cache.storeDir + "/" + queryNAR.getStr(9);
           }
-          for (auto& sig :
+          for (auto& sig : absl::StrSplit(
-               absl::StrSplit(queryNAR.getStr(10), absl::ByChar(' '))) {
+                   queryNAR.getStr(10), absl::ByChar(' '), absl::SkipEmpty())) {
             narInfo->sigs.insert(std::string(sig));
           }
           narInfo->ca = queryNAR.getStr(11);

third_party/nix/src/libstore/nar-info.cc

@@ -62,7 +62,8 @@ NarInfo::NarInfo(const Store& store, const std::string& s,
         corrupt();
       }
     } else if (name == "References") {
-      std::vector<std::string> refs = absl::StrSplit(value, absl::ByChar(' '));
+      std::vector<std::string> refs =
+          absl::StrSplit(value, absl::ByChar(' '), absl::SkipEmpty());
       if (!references.empty()) {
         corrupt();
       }

third_party/nix/src/libstore/parsed-derivations.cc

@@ -88,7 +88,8 @@ std::optional<Strings> ParsedDerivation::getStringsAttr(
     if (i == drv.env.end()) {
       return {};
     }
-    return absl::StrSplit(i->second, absl::ByAnyChar(" \t\n\r"));
+    return absl::StrSplit(i->second, absl::ByAnyChar(" \t\n\r"),
+                          absl::SkipEmpty());
   }
 }
 

third_party/nix/src/libstore/ssh.cc

@@ -22,7 +22,8 @@ SSHMaster::SSHMaster(const std::string& host, std::string keyFile,
 
 void SSHMaster::addCommonSSHOpts(Strings& args) {
   for (auto& i :
-       absl::StrSplit(getEnv("NIX_SSHOPTS"), absl::ByAnyChar(" \t\n\r"))) {
+       absl::StrSplit(getEnv("NIX_SSHOPTS"), absl::ByAnyChar(" \t\n\r"),
+                      absl::SkipEmpty())) {
     args.push_back(std::string(i));
   }
   if (!keyFile.empty()) {

third_party/nix/src/libstore/store-api.cc

@@ -960,7 +960,8 @@ std::pair<std::string, Store::Params> splitUriAndParams(
   Store::Params params;
   auto q = uri.find('?');
   if (q != std::string::npos) {
-    Strings parts = absl::StrSplit(uri.substr(q + 1), absl::ByChar('&'));
+    Strings parts =
+        absl::StrSplit(uri.substr(q + 1), absl::ByChar('&'), absl::SkipEmpty());
     for (const auto& s : parts) {
       auto e = s.find('=');
       if (e != std::string::npos) {

third_party/nix/src/libutil/config.cc

@@ -262,7 +262,7 @@ void BaseSetting<bool>::convertToArg(Args& args, const std::string& category) {
 
 template <>
 void BaseSetting<Strings>::set(const std::string& str) {
-  value = absl::StrSplit(str, absl::ByAnyChar(" \t\n\r"));
+  value = absl::StrSplit(str, absl::ByAnyChar(" \t\n\r"), absl::SkipEmpty());
 }
 
 template <>
@@ -280,7 +280,7 @@ void BaseSetting<Strings>::toJSON(JSONPlaceholder& out) {
 
 template <>
 void BaseSetting<StringSet>::set(const std::string& str) {
-  value = absl::StrSplit(str, absl::ByAnyChar(" \t\n\r"));
+  value = absl::StrSplit(str, absl::ByAnyChar(" \t\n\r"), absl::SkipEmpty());
 }
 
 template <>

third_party/nix/src/libutil/util.cc

@@ -547,7 +547,7 @@ std::vector<Path> getConfigDirs() {
   Path configHome = getConfigDir();
   std::string configDirs = getEnv("XDG_CONFIG_DIRS");
   std::vector<std::string> result =
-      absl::StrSplit(configDirs, absl::ByChar(':'));
+      absl::StrSplit(configDirs, absl::ByChar(':'), absl::SkipEmpty());
   result.insert(result.begin(), configHome);
   return result;
 }

third_party/nix/src/nix-build/nix-build.cc

@@ -114,7 +114,8 @@ static void _main(int argc, char** argv) {
       !std::regex_search(argv[1], std::regex("nix-shell"))) {
     script = argv[1];
     try {
-      Strings lines = absl::StrSplit(readFile(script), absl::ByChar('\n'));
+      Strings lines = absl::StrSplit(readFile(script), absl::ByChar('\n'),
+                                     absl::SkipEmpty());
       if (std::regex_search(lines.front(), std::regex("^#!"))) {
         lines.pop_front();
         inShebang = true;
@@ -443,8 +444,9 @@ static void _main(int argc, char** argv) {
     env["NIX_STORE"] = store->storeDir;
     env["NIX_BUILD_CORES"] = std::to_string(settings.buildCores);
 
-    StringSet passAsFile = absl::StrSplit(get(drv.env, "passAsFile", ""),
+    StringSet passAsFile =
-                                          absl::ByAnyChar(" \t\n\r"));
+        absl::StrSplit(get(drv.env, "passAsFile", ""),
+                       absl::ByAnyChar(" \t\n\r"), absl::SkipEmpty());
 
     bool keepTmp = false;
     int fileNr = 0;

third_party/nix/src/nix-channel/nix-channel.cc

@@ -26,14 +26,15 @@ static void readChannels() {
   auto channelsFile = readFile(channelsList);
 
   std::vector<std::string> lines =
-      absl::StrSplit(channelsFile, absl::ByChar('\n'));
+      absl::StrSplit(channelsFile, absl::ByChar('\n'), absl::SkipEmpty());
 
   for (auto& line : lines) {
     line = absl::StripTrailingAsciiWhitespace(line);
     if (std::regex_search(line, std::regex("^\\s*\\#"))) {
       continue;
     }
-    std::vector<std::string> split = absl::StrSplit(line, absl::ByChar(' '));
+    std::vector<std::string> split =
+        absl::StrSplit(line, absl::ByChar(' '), absl::SkipEmpty());
     auto url = std::regex_replace(split[0], std::regex("/*$"), "");
     auto name = split.size() > 1 ? split[1] : baseNameOf(url);
     channels[name] = url;

third_party/nix/src/nix-daemon/nix-daemon-legacy.cc

@@ -533,7 +533,8 @@ static void performOp(TunnelLogger* logger, const ref<Store>& store,
             trusted.insert(s);
           }
           Strings subs;
-          Strings ss = absl::StrSplit(value, absl::ByAnyChar(" \t\n\r"));
+          Strings ss = absl::StrSplit(value, absl::ByAnyChar(" \t\n\r"),
+                                      absl::SkipEmpty());
           for (auto& s : ss) {
             if (trusted.count(s) != 0u) {
               subs.push_back(s);

third_party/nix/src/nix/doctor.cc

@@ -48,7 +48,8 @@ struct CmdDoctor final : StoreCommand {
   static bool checkNixInPath() {
     PathSet dirs;
 
-    for (auto& dir : absl::StrSplit(getEnv("PATH"), absl::ByChar(':'))) {
+    for (auto& dir :
+         absl::StrSplit(getEnv("PATH"), absl::ByChar(':'), absl::SkipEmpty())) {
       if (pathExists(absl::StrCat(dir, "/nix-env"))) {
         dirs.insert(dirOf(canonPath(absl::StrCat(dir, "/nix-env"), true)));
       }
@@ -71,7 +72,8 @@ struct CmdDoctor final : StoreCommand {
   static bool checkProfileRoots(const ref<Store>& store) {
     PathSet dirs;
 
-    for (auto dir : absl::StrSplit(getEnv("PATH"), absl::ByChar(':'))) {
+    for (auto dir :
+         absl::StrSplit(getEnv("PATH"), absl::ByChar(':'), absl::SkipEmpty())) {
       Path profileDir = dirOf(dir);
       try {
         Path userEnv = canonPath(profileDir, true);

third_party/nix/src/nix/edit.cc

@@ -55,7 +55,8 @@ struct CmdEdit final : InstallableCommand {
 
     auto editor = getEnv("EDITOR", "cat");
 
-    Strings args = absl::StrSplit(editor, absl::ByAnyChar(" \t\n\r"));
+    Strings args =
+        absl::StrSplit(editor, absl::ByAnyChar(" \t\n\r"), absl::SkipEmpty());
 
     if (editor.find("emacs") != std::string::npos ||
         editor.find("nano") != std::string::npos ||

third_party/nix/src/nix/run.cc

@@ -123,7 +123,8 @@ struct CmdRun final : InstallablesCommand {
       todo.push(path);
     }
 
-    Strings unixPath = absl::StrSplit(getEnv("PATH"), absl::ByChar(':'));
+    Strings unixPath =
+        absl::StrSplit(getEnv("PATH"), absl::ByChar(':'), absl::SkipEmpty());
 
     while (!todo.empty()) {
       Path path = todo.front();
@@ -137,7 +138,8 @@ struct CmdRun final : InstallablesCommand {
       auto propPath = path + "/nix-support/propagated-user-env-packages";
       if (accessor->stat(propPath).type == FSAccessor::tRegular) {
         for (auto p :
-             absl::StrSplit(readFile(propPath), absl::ByAnyChar(" \t\n\r"))) {
+             absl::StrSplit(readFile(propPath), absl::ByAnyChar(" \t\n\r"),
+                            absl::SkipEmpty())) {
           todo.push(std::string(p));
         }
       }

third_party/nix/src/nix/upgrade-nix.cc

@@ -103,7 +103,8 @@ struct CmdUpgradeNix final : MixDryRun, StoreCommand {
   static Path getProfileDir(const ref<Store>& store) {
     Path where;
 
-    for (auto& dir : absl::StrSplit(getEnv("PATH"), absl::ByChar(':'))) {
+    for (auto& dir :
+         absl::StrSplit(getEnv("PATH"), absl::ByChar(':'), absl::SkipEmpty())) {
       if (pathExists(absl::StrCat(dir, "/nix-env"))) {
         where = dir;
         break;

third_party/nix/src/tests/language-tests.cc

@@ -80,7 +80,8 @@ std::string TestNameFor(
     const testing::TestParamInfo<std::filesystem::path>& info) {
   std::string name;
 
-  for (auto part : absl::StrSplit(info.param.stem().string(), '-')) {
+  for (auto part :
+       absl::StrSplit(info.param.stem().string(), '-', absl::SkipEmpty())) {
     std::string part_owned(part);
     part_owned[0] = absl::ascii_toupper(part_owned[0]);
     absl::StrAppend(&name, part_owned);