refactor(3p/nix): Apply clang-tidy's readability-* fixes r/788

This applies the readability fixes listed here:

https://clang.llvm.org/extra/clang-tidy/checks/list.html

10 files changed, 122 insertions, 107 deletions

diff --git a/third_party/nix/src/libutil/archive.cc b/third_party/nix/src/libutil/archive.cc
index a316336ec73f..6583dc20b899 100644
--- a/third_party/nix/src/libutil/archive.cc
+++ b/third_party/nix/src/libutil/archive.cc
@@ -40,7 +40,7 @@ const std::string narVersionMagic1 = "nix-archive-1";
 
 static string caseHackSuffix = "~nix~case~hack~";
 
-PathFilter defaultPathFilter = [](const Path&) { return true; };
+PathFilter defaultPathFilter = [](const Path& /*unused*/) { return true; };
 
 static void dumpContents(const Path& path, size_t size, Sink& sink) {
   sink << "contents" << size;
@@ -67,7 +67,7 @@ static void dump(const Path& path, Sink& sink, PathFilter& filter) {
   checkInterrupt();
 
   struct stat st;
-  if (lstat(path.c_str(), &st)) {
+  if (lstat(path.c_str(), &st) != 0) {
     throw SysError(format("getting attributes of path '%1%'") % path);
   }
 
@@ -76,7 +76,7 @@ static void dump(const Path& path, Sink& sink, PathFilter& filter) {
   if (S_ISREG(st.st_mode)) {
     sink << "type"
          << "regular";
-    if (st.st_mode & S_IXUSR) {
+    if ((st.st_mode & S_IXUSR) != 0u) {
       sink << "executable"
            << "";
     }
@@ -167,7 +167,7 @@ static void parseContents(ParseSink& sink, Source& source, const Path& path) {
   unsigned long long left = size;
   std::vector<unsigned char> buf(65536);
 
-  while (left) {
+  while (left != 0u) {
     checkInterrupt();
     auto n = buf.size();
     if ((unsigned long long)n > left) {
@@ -208,7 +208,7 @@ static void parse(ParseSink& sink, Source& source, const Path& path) {
       break;
     }
 
-    else if (s == "type") {
+    if (s == "type") {
       if (type != tpUnknown) {
         throw badArchive("multiple type fields");
       }
@@ -240,14 +240,15 @@ static void parse(ParseSink& sink, Source& source, const Path& path) {
 
     else if (s == "executable" && type == tpRegular) {
       auto s = readString(source);
-      if (s != "") {
+      if (!s.empty()) {
         throw badArchive("executable marker has non-empty value");
       }
       sink.isExecutable();
     }
 
     else if (s == "entry" && type == tpDirectory) {
-      string name, prevName;
+      string name;
+      string prevName;
 
       s = readString(source);
       if (s != "(") {
@@ -261,7 +262,8 @@ static void parse(ParseSink& sink, Source& source, const Path& path) {
 
         if (s == ")") {
           break;
-        } else if (s == "name") {
+        }
+        if (s == "name") {
           name = readString(source);
           if (name.empty() || name == "." || name == ".." ||
               name.find('/') != string::npos ||
@@ -350,7 +352,7 @@ struct RestoreSink : ParseSink {
 
   void preallocateContents(unsigned long long len) override {
 #if HAVE_POSIX_FALLOCATE
-    if (len) {
+    if (len != 0u) {
       errno = posix_fallocate(fd.get(), 0, len);
       /* Note that EINVAL may indicate that the underlying
          filesystem doesn't support preallocation (e.g. on
diff --git a/third_party/nix/src/libutil/args.cc b/third_party/nix/src/libutil/args.cc
index 92343d88e5a3..2b4407480254 100644
--- a/third_party/nix/src/libutil/args.cc
+++ b/third_party/nix/src/libutil/args.cc
@@ -7,9 +7,9 @@ namespace nix {
 Args::FlagMaker Args::mkFlag() { return FlagMaker(*this); }
 
 Args::FlagMaker::~FlagMaker() {
-  assert(flag->longName != "");
+  assert(!flag->longName.empty());
   args.longFlags[flag->longName] = flag;
-  if (flag->shortName) {
+  if (flag->shortName != 0) {
     args.shortFlags[flag->shortName] = flag;
   }
 }
@@ -26,12 +26,12 @@ void Args::parseCmdline(const Strings& _cmdline) {
     /* Expand compound dash options (i.e., `-qlf' -> `-q -l -f',
        `-j3` -> `-j 3`). */
     if (!dashDash && arg.length() > 2 && arg[0] == '-' && arg[1] != '-' &&
-        isalpha(arg[1])) {
+        (isalpha(arg[1]) != 0)) {
       *pos = (string) "-" + arg[1];
       auto next = pos;
       ++next;
       for (unsigned int j = 2; j < arg.length(); j++) {
-        if (isalpha(arg[j])) {
+        if (isalpha(arg[j]) != 0) {
           cmdline.insert(next, (string) "-" + arg[j]);
         } else {
           cmdline.insert(next, string(arg, j));
@@ -74,11 +74,11 @@ void Args::printHelp(const string& programName, std::ostream& out) {
   std::cout << "\n";
 
   auto s = description();
-  if (s != "") {
+  if (!s.empty()) {
     std::cout << "\nSummary: " << s << ".\n";
   }
 
-  if (longFlags.size()) {
+  if (!longFlags.empty() != 0u) {
     std::cout << "\n";
     std::cout << "Flags:\n";
     printFlags(out);
@@ -88,11 +88,11 @@ void Args::printHelp(const string& programName, std::ostream& out) {
 void Args::printFlags(std::ostream& out) {
   Table2 table;
   for (auto& flag : longFlags) {
-    if (hiddenCategories.count(flag.second->category)) {
+    if (hiddenCategories.count(flag.second->category) != 0u) {
       continue;
     }
     table.push_back(std::make_pair(
-        (flag.second->shortName
+        (flag.second->shortName != 0
              ? std::string("-") + flag.second->shortName + ", "
              : "    ") +
             "--" + flag.first + renderLabels(flag.second->labels),
@@ -188,7 +188,7 @@ Strings argvToStrings(int argc, char** argv) {
   Strings args;
   argc--;
   argv++;
-  while (argc--) {
+  while ((argc--) != 0) {
     args.push_back(*argv++);
   }
   return args;
diff --git a/third_party/nix/src/libutil/compression.cc b/third_party/nix/src/libutil/compression.cc
index 851a7f817994..d7084ab7f15d 100644
--- a/third_party/nix/src/libutil/compression.cc
+++ b/third_party/nix/src/libutil/compression.cc
@@ -21,7 +21,7 @@ struct ChunkedCompressionSink : CompressionSink {
 
   void write(const unsigned char* data, size_t len) override {
     const size_t CHUNK_SIZE = sizeof(outbuf) << 2;
-    while (len) {
+    while (len != 0u) {
       size_t n = std::min(CHUNK_SIZE, len);
       writeInternal(data, n);
       data += n;
@@ -68,10 +68,10 @@ struct XzDecompressionSink : CompressionSink {
     strm.next_in = data;
     strm.avail_in = len;
 
-    while (!finished && (!data || strm.avail_in)) {
+    while (!finished && ((data == nullptr) || (strm.avail_in != 0u))) {
       checkInterrupt();
 
-      lzma_ret ret = lzma_code(&strm, data ? LZMA_RUN : LZMA_FINISH);
+      lzma_ret ret = lzma_code(&strm, data != nullptr ? LZMA_RUN : LZMA_FINISH);
       if (ret != LZMA_OK && ret != LZMA_STREAM_END) {
         throw CompressionError("error %d while decompressing xz file", ret);
       }
@@ -116,7 +116,7 @@ struct BzipDecompressionSink : ChunkedCompressionSink {
     strm.next_in = (char*)data;
     strm.avail_in = len;
 
-    while (strm.avail_in) {
+    while (strm.avail_in != 0u) {
       checkInterrupt();
 
       int ret = BZ2_bzDecompress(&strm);
@@ -142,7 +142,7 @@ struct BrotliDecompressionSink : ChunkedCompressionSink {
 
   explicit BrotliDecompressionSink(Sink& nextSink) : nextSink(nextSink) {
     state = BrotliDecoderCreateInstance(nullptr, nullptr, nullptr);
-    if (!state) {
+    if (state == nullptr) {
       throw CompressionError("unable to initialize brotli decoder");
     }
   }
@@ -160,11 +160,11 @@ struct BrotliDecompressionSink : ChunkedCompressionSink {
     uint8_t* next_out = outbuf;
     size_t avail_out = sizeof(outbuf);
 
-    while (!finished && (!data || avail_in)) {
+    while (!finished && ((data == nullptr) || (avail_in != 0u))) {
       checkInterrupt();
 
-      if (!BrotliDecoderDecompressStream(state, &avail_in, &next_in, &avail_out,
-                                         &next_out, nullptr)) {
+      if (BrotliDecoderDecompressStream(state, &avail_in, &next_in, &avail_out,
+                                        &next_out, nullptr) == 0u) {
         throw CompressionError("error while decompressing brotli file");
       }
 
@@ -174,7 +174,7 @@ struct BrotliDecompressionSink : ChunkedCompressionSink {
         avail_out = sizeof(outbuf);
       }
 
-      finished = BrotliDecoderIsFinished(state);
+      finished = (BrotliDecoderIsFinished(state) != 0);
     }
   }
 };
@@ -189,9 +189,10 @@ ref<std::string> decompress(const std::string& method, const std::string& in) {
 
 ref<CompressionSink> makeDecompressionSink(const std::string& method,
                                            Sink& nextSink) {
-  if (method == "none" || method == "") {
+  if (method == "none" || method.empty()) {
     return make_ref<NoneSink>(nextSink);
-  } else if (method == "xz") {
+  }
+  if (method == "xz") {
     return make_ref<XzDecompressionSink>(nextSink);
   } else if (method == "bzip2") {
     return make_ref<BzipDecompressionSink>(nextSink);
@@ -260,10 +261,10 @@ struct XzCompressionSink : CompressionSink {
     strm.next_in = data;
     strm.avail_in = len;
 
-    while (!finished && (!data || strm.avail_in)) {
+    while (!finished && ((data == nullptr) || (strm.avail_in != 0u))) {
       checkInterrupt();
 
-      lzma_ret ret = lzma_code(&strm, data ? LZMA_RUN : LZMA_FINISH);
+      lzma_ret ret = lzma_code(&strm, data != nullptr ? LZMA_RUN : LZMA_FINISH);
       if (ret != LZMA_OK && ret != LZMA_STREAM_END) {
         throw CompressionError("error %d while compressing xz file", ret);
       }
@@ -308,10 +309,10 @@ struct BzipCompressionSink : ChunkedCompressionSink {
     strm.next_in = (char*)data;
     strm.avail_in = len;
 
-    while (!finished && (!data || strm.avail_in)) {
+    while (!finished && ((data == nullptr) || (strm.avail_in != 0u))) {
       checkInterrupt();
 
-      int ret = BZ2_bzCompress(&strm, data ? BZ_RUN : BZ_FINISH);
+      int ret = BZ2_bzCompress(&strm, data != nullptr ? BZ_RUN : BZ_FINISH);
       if (ret != BZ_RUN_OK && ret != BZ_FINISH_OK && ret != BZ_STREAM_END) {
         throw CompressionError("error %d while compressing bzip2 file", ret);
       }
@@ -335,7 +336,7 @@ struct BrotliCompressionSink : ChunkedCompressionSink {
 
   explicit BrotliCompressionSink(Sink& nextSink) : nextSink(nextSink) {
     state = BrotliEncoderCreateInstance(nullptr, nullptr, nullptr);
-    if (!state) {
+    if (state == nullptr) {
       throw CompressionError("unable to initialise brotli encoder");
     }
   }
@@ -353,12 +354,14 @@ struct BrotliCompressionSink : ChunkedCompressionSink {
     uint8_t* next_out = outbuf;
     size_t avail_out = sizeof(outbuf);
 
-    while (!finished && (!data || avail_in)) {
+    while (!finished && ((data == nullptr) || (avail_in != 0u))) {
       checkInterrupt();
 
-      if (!BrotliEncoderCompressStream(
-              state, data ? BROTLI_OPERATION_PROCESS : BROTLI_OPERATION_FINISH,
-              &avail_in, &next_in, &avail_out, &next_out, nullptr)) {
+      if (BrotliEncoderCompressStream(state,
+                                      data != nullptr ? BROTLI_OPERATION_PROCESS
+                                                      : BROTLI_OPERATION_FINISH,
+                                      &avail_in, &next_in, &avail_out,
+                                      &next_out, nullptr) == 0) {
         throw CompressionError("error while compressing brotli compression");
       }
 
@@ -368,7 +371,7 @@ struct BrotliCompressionSink : ChunkedCompressionSink {
         avail_out = sizeof(outbuf);
       }
 
-      finished = BrotliEncoderIsFinished(state);
+      finished = (BrotliEncoderIsFinished(state) != 0);
     }
   }
 };
@@ -377,7 +380,8 @@ ref<CompressionSink> makeCompressionSink(const std::string& method,
                                          Sink& nextSink, const bool parallel) {
   if (method == "none") {
     return make_ref<NoneSink>(nextSink);
-  } else if (method == "xz") {
+  }
+  if (method == "xz") {
     return make_ref<XzCompressionSink>(nextSink, parallel);
   } else if (method == "bzip2") {
     return make_ref<BzipCompressionSink>(nextSink);
diff --git a/third_party/nix/src/libutil/config.cc b/third_party/nix/src/libutil/config.cc
index 56f0c8c3e7cd..ef47c167ed49 100644
--- a/third_party/nix/src/libutil/config.cc
+++ b/third_party/nix/src/libutil/config.cc
@@ -303,7 +303,7 @@ template class BaseSetting<Strings>;
 template class BaseSetting<StringSet>;
 
 void PathSetting::set(const std::string& str) {
-  if (str == "") {
+  if (str.empty()) {
     if (allowEmpty) {
       value = "";
     } else {
@@ -356,7 +356,7 @@ GlobalConfig globalConfig;
 GlobalConfig::ConfigRegistrations* GlobalConfig::configRegistrations;
 
 GlobalConfig::Register::Register(Config* config) {
-  if (!configRegistrations) {
+  if (configRegistrations == nullptr) {
     configRegistrations = new ConfigRegistrations;
   }
   configRegistrations->emplace_back(config);
diff --git a/third_party/nix/src/libutil/hash.cc b/third_party/nix/src/libutil/hash.cc
index e33c76cc9093..81d8628e972b 100644
--- a/third_party/nix/src/libutil/hash.cc
+++ b/third_party/nix/src/libutil/hash.cc
@@ -193,7 +193,7 @@ Hash::Hash(const std::string& s, HashType type) : type(type) {
       if (i < hashSize - 1) {
         hash[i + 1] |= digit >> (8 - j);
       } else {
-        if (digit >> (8 - j)) {
+        if ((digit >> (8 - j)) != 0) {
           throw BadHash("invalid base-32 hash '%s'", s);
         }
       }
@@ -280,7 +280,7 @@ Hash hashFile(HashType ht, const Path& path) {
 
   std::vector<unsigned char> buf(8192);
   ssize_t n;
-  while ((n = read(fd.get(), buf.data(), buf.size()))) {
+  while ((n = read(fd.get(), buf.data(), buf.size())) != 0) {
     checkInterrupt();
     if (n == -1) {
       throw SysError(format("reading file '%1%'") % path);
@@ -341,7 +341,8 @@ Hash compressHash(const Hash& hash, unsigned int newSize) {
 HashType parseHashType(const string& s) {
   if (s == "md5") {
     return htMD5;
-  } else if (s == "sha1") {
+  }
+  if (s == "sha1") {
     return htSHA1;
   } else if (s == "sha256") {
     return htSHA256;
@@ -355,7 +356,8 @@ HashType parseHashType(const string& s) {
 string printHashType(HashType ht) {
   if (ht == htMD5) {
     return "md5";
-  } else if (ht == htSHA1) {
+  }
+  if (ht == htSHA1) {
     return "sha1";
   } else if (ht == htSHA256) {
     return "sha256";
diff --git a/third_party/nix/src/libutil/json.cc b/third_party/nix/src/libutil/json.cc
index c5f52ae8ef3f..218fc264ba50 100644
--- a/third_party/nix/src/libutil/json.cc
+++ b/third_party/nix/src/libutil/json.cc
@@ -27,7 +27,7 @@ void toJSON(std::ostream& str, const char* start, const char* end) {
 }
 
 void toJSON(std::ostream& str, const char* s) {
-  if (!s) {
+  if (s == nullptr) {
     str << "null";
   } else {
     toJSON(str, s, s + strlen(s));
@@ -91,7 +91,7 @@ JSONWriter::JSONWriter(std::ostream& str, bool indent)
 JSONWriter::JSONWriter(JSONState* state) : state(state) { state->stack++; }
 
 JSONWriter::~JSONWriter() {
-  if (state) {
+  if (state != nullptr) {
     assertActive();
     state->stack--;
     if (state->stack == 0) {
@@ -150,7 +150,7 @@ void JSONObject::open() {
 }
 
 JSONObject::~JSONObject() {
-  if (state) {
+  if (state != nullptr) {
     state->depth--;
     if (state->indent && !first) {
       indent();
diff --git a/third_party/nix/src/libutil/serialise.cc b/third_party/nix/src/libutil/serialise.cc
index 0d9b069a2887..4b12367196f1 100644
--- a/third_party/nix/src/libutil/serialise.cc
+++ b/third_party/nix/src/libutil/serialise.cc
@@ -16,7 +16,7 @@ void BufferedSink::operator()(const unsigned char* data, size_t len) {
     buffer = decltype(buffer)(new unsigned char[bufSize]);
   }
 
-  while (len) {
+  while (len != 0u) {
     /* Optimisation: bypass the buffer if the data exceeds the
        buffer size. */
     if (bufPos + len >= bufSize) {
@@ -81,7 +81,7 @@ void FdSink::write(const unsigned char* data, size_t len) {
 bool FdSink::good() { return _good; }
 
 void Source::operator()(unsigned char* data, size_t len) {
-  while (len) {
+  while (len != 0u) {
     size_t n = read(data, len);
     data += n;
     len -= n;
@@ -108,7 +108,7 @@ size_t BufferedSource::read(unsigned char* data, size_t len) {
     buffer = decltype(buffer)(new unsigned char[bufSize]);
   }
 
-  if (!bufPosIn) {
+  if (bufPosIn == 0u) {
     bufPosIn = readUnbuffered(buffer.get(), bufSize);
   }
 
@@ -177,7 +177,7 @@ std::unique_ptr<Source> sinkToSource(std::function<void(Sink&)> fun,
       if (!coro) {
         coro = coro_t::pull_type([&](coro_t::push_type& yield) {
           LambdaSink sink([&](const unsigned char* data, size_t len) {
-            if (len) {
+            if (len != 0u) {
               yield(std::string((const char*)data, len));
             }
           });
@@ -210,7 +210,7 @@ std::unique_ptr<Source> sinkToSource(std::function<void(Sink&)> fun,
 }
 
 void writePadding(size_t len, Sink& sink) {
-  if (len % 8) {
+  if ((len % 8) != 0u) {
     unsigned char zero[8];
     memset(zero, 0, sizeof(zero));
     sink(zero, 8 - (len % 8));
@@ -247,12 +247,12 @@ Sink& operator<<(Sink& sink, const StringSet& s) {
 }
 
 void readPadding(size_t len, Source& source) {
-  if (len % 8) {
+  if ((len % 8) != 0u) {
     unsigned char zero[8];
     size_t n = 8 - (len % 8);
     source(zero, n);
     for (unsigned int i = 0; i < n; i++) {
-      if (zero[i]) {
+      if (zero[i] != 0u) {
         throw SerialisationError("non-zero padding");
       }
     }
diff --git a/third_party/nix/src/libutil/thread-pool.cc b/third_party/nix/src/libutil/thread-pool.cc
index d0042c6df195..879de446c294 100644
--- a/third_party/nix/src/libutil/thread-pool.cc
+++ b/third_party/nix/src/libutil/thread-pool.cc
@@ -8,9 +8,9 @@ namespace nix {
 ThreadPool::ThreadPool(size_t _maxThreads) : maxThreads(_maxThreads) {
   restoreAffinity();  // FIXME
 
-  if (!maxThreads) {
+  if (maxThreads == 0u) {
     maxThreads = std::thread::hardware_concurrency();
-    if (!maxThreads) {
+    if (maxThreads == 0u) {
       maxThreads = 1;
     }
   }
@@ -111,8 +111,8 @@ void ThreadPool::doWork(bool mainThread) {
             try {
               std::rethrow_exception(exc);
             } catch (std::exception& e) {
-              if (!dynamic_cast<Interrupted*>(&e) &&
-                  !dynamic_cast<ThreadPoolShutDown*>(&e)) {
+              if ((dynamic_cast<Interrupted*>(&e) == nullptr) &&
+                  (dynamic_cast<ThreadPoolShutDown*>(&e) == nullptr)) {
                 ignoreException();
               }
             } catch (...) {
@@ -135,7 +135,7 @@ void ThreadPool::doWork(bool mainThread) {
         /* If there are no active or pending items, and the
            main thread is running process(), then no new items
            can be added. So exit. */
-        if (!state->active && state->draining) {
+        if ((state->active == 0u) && state->draining) {
           quit = true;
           work.notify_all();
           return;
diff --git a/third_party/nix/src/libutil/util.cc b/third_party/nix/src/libutil/util.cc
index a4e382f12ebe..21da06b8ab1e 100644
--- a/third_party/nix/src/libutil/util.cc
+++ b/third_party/nix/src/libutil/util.cc
@@ -35,7 +35,7 @@
 #include <sys/prctl.h>
 #endif
 
-extern char** environ __attribute__((weak));
+__attribute__((weak));
 
 namespace nix {
 
@@ -53,15 +53,15 @@ std::string SysError::addErrno(const std::string& s) {
 
 string getEnv(const string& key, const string& def) {
   char* value = getenv(key.c_str());
-  return value ? string(value) : def;
+  return value != nullptr ? string(value) : def;
 }
 
 std::map<std::string, std::string> getEnv() {
   std::map<std::string, std::string> env;
-  for (size_t i = 0; environ[i]; ++i) {
+  for (size_t i = 0; environ[i] != nullptr; ++i) {
     auto s = environ[i];
     auto eq = strchr(s, '=');
-    if (!eq) {
+    if (eq == nullptr) {
       // invalid env, just keep going
       continue;
     }
@@ -85,7 +85,7 @@ void replaceEnv(std::map<std::string, std::string> newEnv) {
 
 Path absPath(Path path, Path dir) {
   if (path[0] != '/') {
-    if (dir == "") {
+    if (dir.empty()) {
 #ifdef __GNU__
       /* GNU (aka. GNU/Hurd) doesn't have any limitation on path
          lengths and doesn't define `PATH_MAX'.  */
@@ -93,7 +93,7 @@ Path absPath(Path path, Path dir) {
       if (buf == NULL)
 #else
       char buf[PATH_MAX];
-      if (!getcwd(buf, sizeof(buf))) {
+      if (getcwd(buf, sizeof(buf)) == nullptr) {
 #endif
         throw SysError("cannot get cwd");
     }
@@ -108,7 +108,7 @@ return canonPath(path);
 }  // namespace nix
 
 Path canonPath(const Path& path, bool resolveSymlinks) {
-  assert(path != "");
+  assert(!path.empty());
 
   string s;
 
@@ -116,12 +116,14 @@ Path canonPath(const Path& path, bool resolveSymlinks) {
     throw Error(format("not an absolute path: '%1%'") % path);
   }
 
-  string::const_iterator i = path.begin(), end = path.end();
+  string::const_iterator i = path.begin();
+  string::const_iterator end = path.end();
   string temp;
 
   /* Count the number of times we follow a symlink and stop at some
      arbitrary (but high) limit to prevent infinite loops. */
-  unsigned int followCount = 0, maxFollow = 1024;
+  unsigned int followCount = 0;
+  unsigned int maxFollow = 1024;
 
   while (true) {
     /* Skip slashes. */
@@ -210,7 +212,7 @@ bool isDirOrInDir(const Path& path, const Path& dir) {
 
 struct stat lstat(const Path& path) {
   struct stat st;
-  if (lstat(path.c_str(), &st)) {
+  if (lstat(path.c_str(), &st) != 0) {
     throw SysError(format("getting status of '%1%'") % path);
   }
   return st;
@@ -220,7 +222,7 @@ bool pathExists(const Path& path) {
   int res;
   struct stat st;
   res = lstat(path.c_str(), &st);
-  if (!res) {
+  if (res == 0) {
     return true;
   }
   if (errno != ENOENT && errno != ENOTDIR) {
@@ -238,9 +240,9 @@ Path readLink(const Path& path) {
     if (rlSize == -1) {
       if (errno == EINVAL) {
         throw Error("'%1%' is not a symlink", path);
-      } else {
-        throw SysError("reading symbolic link '%1%'", path);
       }
+      throw SysError("reading symbolic link '%1%'", path);
+
     } else if (rlSize < bufSize) {
       return string(buf.data(), rlSize);
     }
@@ -436,9 +438,8 @@ static Path tempName(Path tmpRoot, const Path& prefix, bool includePid,
   if (includePid) {
     return (format("%1%/%2%-%3%-%4%") % tmpRoot % prefix % getpid() % counter++)
         .str();
-  } else {
-    return (format("%1%/%2%-%3%") % tmpRoot % prefix % counter++).str();
   }
+  return (format("%1%/%2%-%3%") % tmpRoot % prefix % counter++).str();
 }
 
 Path createTempDir(const Path& tmpRoot, const Path& prefix, bool includePid,
@@ -473,7 +474,7 @@ Path createTempDir(const Path& tmpRoot, const Path& prefix, bool includePid,
 
 std::string getUserName() {
   auto pw = getpwuid(geteuid());
-  std::string name = pw ? pw->pw_name : getEnv("USER", "");
+  std::string name = pw != nullptr ? pw->pw_name : getEnv("USER", "");
   if (name.empty()) {
     throw Error("cannot figure out user name");
   }
@@ -487,7 +488,7 @@ static Lazy<Path> getHome2([]() {
     struct passwd pwbuf;
     struct passwd* pw;
     if (getpwuid_r(geteuid(), &pwbuf, buf.data(), buf.size(), &pw) != 0 ||
-        !pw || !pw->pw_dir || !pw->pw_dir[0]) {
+        (pw == nullptr) || (pw->pw_dir == nullptr) || (pw->pw_dir[0] == 0)) {
       throw Error("cannot determine user's home directory");
     }
     homeDir = pw->pw_dir;
@@ -557,7 +558,7 @@ Paths createDirs(const Path& path) {
 }
 
 void createSymlink(const Path& target, const Path& link) {
-  if (symlink(target.c_str(), link.c_str())) {
+  if (symlink(target.c_str(), link.c_str()) != 0) {
     throw SysError(format("creating symlink from '%1%' to '%2%'") % link %
                    target);
   }
@@ -585,7 +586,7 @@ void replaceSymlink(const Path& target, const Path& link) {
 }
 
 void readFull(int fd, unsigned char* buf, size_t count) {
-  while (count) {
+  while (count != 0u) {
     checkInterrupt();
     ssize_t res = read(fd, (char*)buf, count);
     if (res == -1) {
@@ -604,7 +605,7 @@ void readFull(int fd, unsigned char* buf, size_t count) {
 
 void writeFull(int fd, const unsigned char* buf, size_t count,
                bool allowInterrupts) {
-  while (count) {
+  while (count != 0u) {
     if (allowInterrupts) {
       checkInterrupt();
     }
@@ -989,11 +990,12 @@ void runProgram2(const RunOptions& options) {
   }
 
   /* Create a pipe. */
-  Pipe out, in;
-  if (options.standardOut) {
+  Pipe out;
+  Pipe in;
+  if (options.standardOut != nullptr) {
     out.create();
   }
-  if (source) {
+  if (source != nullptr) {
     in.create();
   }
 
@@ -1011,7 +1013,7 @@ void runProgram2(const RunOptions& options) {
         if (options.environment) {
           replaceEnv(*options.environment);
         }
-        if (options.standardOut &&
+        if ((options.standardOut != nullptr) &&
             dup2(out.writeSide.get(), STDOUT_FILENO) == -1) {
           throw SysError("dupping stdout");
         }
@@ -1020,7 +1022,8 @@ void runProgram2(const RunOptions& options) {
             throw SysError("cannot dup stdout into stderr");
           }
         }
-        if (source && dup2(in.readSide.get(), STDIN_FILENO) == -1) {
+        if ((source != nullptr) &&
+            dup2(in.readSide.get(), STDIN_FILENO) == -1) {
           throw SysError("dupping stdin");
         }
 
@@ -1065,7 +1068,7 @@ void runProgram2(const RunOptions& options) {
     }
   });
 
-  if (source) {
+  if (source != nullptr) {
     in.readSide = -1;
     writerThread = std::thread([&]() {
       try {
@@ -1087,7 +1090,7 @@ void runProgram2(const RunOptions& options) {
     });
   }
 
-  if (options.standardOut) {
+  if (options.standardOut != nullptr) {
     drainFD(out.readSide.get(), *options.standardOut);
   }
 
@@ -1095,11 +1098,11 @@ void runProgram2(const RunOptions& options) {
   int status = pid.wait();
 
   /* Wait for the writer thread to finish. */
-  if (source) {
+  if (source != nullptr) {
     promise.get_future().get();
   }
 
-  if (status) {
+  if (status != 0) {
     throw ExecError(status, fmt("program '%1%' %2%", options.program,
                                 statusToString(status)));
   }
@@ -1110,7 +1113,7 @@ void closeMostFDs(const set<int>& exceptions) {
   try {
     for (auto& s : readDirectory("/proc/self/fd")) {
       auto fd = std::stoi(s.name);
-      if (!exceptions.count(fd)) {
+      if (exceptions.count(fd) == 0u) {
         DLOG(INFO) << "closing leaked FD " << fd;
         close(fd);
       }
@@ -1123,7 +1126,7 @@ void closeMostFDs(const set<int>& exceptions) {
   int maxFD = 0;
   maxFD = sysconf(_SC_OPEN_MAX);
   for (int fd = 0; fd < maxFD; ++fd) {
-    if (!exceptions.count(fd)) {
+    if (exceptions.count(fd) == 0u) {
       close(fd);
     } /* ignore result */
   }
@@ -1150,7 +1153,7 @@ void _interrupted() {
   /* Block user interrupts while an exception is being handled.
      Throwing an exception while another exception is being handled
      kills the program! */
-  if (!interruptThrown && !std::uncaught_exceptions()) {
+  if (!interruptThrown && (std::uncaught_exceptions() == 0)) {
     interruptThrown = true;
     throw Interrupted("interrupted by the user");
   }
@@ -1182,7 +1185,7 @@ template vector<string> tokenizeString(const string& s,
 string concatStringsSep(const string& sep, const Strings& ss) {
   string s;
   for (auto& i : ss) {
-    if (s.size() != 0) {
+    if (!s.empty()) {
       s += sep;
     }
     s += i;
@@ -1193,7 +1196,7 @@ string concatStringsSep(const string& sep, const Strings& ss) {
 string concatStringsSep(const string& sep, const StringSet& ss) {
   string s;
   for (auto& i : ss) {
-    if (s.size() != 0) {
+    if (!s.empty()) {
       s += sep;
     }
     s += i;
@@ -1233,7 +1236,8 @@ string statusToString(int status) {
   if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
     if (WIFEXITED(status)) {
       return (format("failed with exit code %1%") % WEXITSTATUS(status)).str();
-    } else if (WIFSIGNALED(status)) {
+    }
+    if (WIFSIGNALED(status)) {
       int sig = WTERMSIG(status);
 #if HAVE_STRSIGNAL
       const char* description = strsignal(sig);
@@ -1294,7 +1298,8 @@ void ignoreException() {
 
 std::string filterANSIEscapes(const std::string& s, bool filterAll,
                               unsigned int width) {
-  std::string t, e;
+  std::string t;
+  std::string e;
   size_t w = 0;
   auto i = s.begin();
 
@@ -1333,7 +1338,7 @@ std::string filterANSIEscapes(const std::string& s, bool filterAll,
       i++;
       t += ' ';
       w++;
-      while (w < (size_t)width && w % 8) {
+      while (w < (size_t)width && ((w % 8) != 0u)) {
         t += ' ';
         w++;
       }
@@ -1357,7 +1362,8 @@ static char base64Chars[] =
 
 string base64Encode(const string& s) {
   string res;
-  int data = 0, nbits = 0;
+  int data = 0;
+  int nbits = 0;
 
   for (char c : s) {
     data = data << 8 | (unsigned char)c;
@@ -1368,10 +1374,10 @@ string base64Encode(const string& s) {
     }
   }
 
-  if (nbits) {
+  if (nbits != 0) {
     res.push_back(base64Chars[data << (6 - nbits) & 0x3f]);
   }
-  while (res.size() % 4) {
+  while ((res.size() % 4) != 0u) {
     res.push_back('=');
   }
 
@@ -1391,7 +1397,8 @@ string base64Decode(const string& s) {
   }
 
   string res;
-  unsigned int d = 0, bits = 0;
+  unsigned int d = 0;
+  unsigned int bits = 0;
 
   for (char c : s) {
     if (c == '=') {
@@ -1478,7 +1485,7 @@ static sigset_t savedSignalMask;
 void startSignalHandlerThread() {
   updateWindowSize();
 
-  if (sigprocmask(SIG_BLOCK, nullptr, &savedSignalMask)) {
+  if (sigprocmask(SIG_BLOCK, nullptr, &savedSignalMask) != 0) {
     throw SysError("quering signal mask");
   }
 
@@ -1489,7 +1496,7 @@ void startSignalHandlerThread() {
   sigaddset(&set, SIGHUP);
   sigaddset(&set, SIGPIPE);
   sigaddset(&set, SIGWINCH);
-  if (pthread_sigmask(SIG_BLOCK, &set, nullptr)) {
+  if (pthread_sigmask(SIG_BLOCK, &set, nullptr) != 0) {
     throw SysError("blocking signals");
   }
 
@@ -1497,7 +1504,7 @@ void startSignalHandlerThread() {
 }
 
 void restoreSignals() {
-  if (sigprocmask(SIG_SETMASK, &savedSignalMask, nullptr)) {
+  if (sigprocmask(SIG_SETMASK, &savedSignalMask, nullptr) != 0) {
     throw SysError("restoring signals");
   }
 }
diff --git a/third_party/nix/src/libutil/util.hh b/third_party/nix/src/libutil/util.hh
index 2439b3da5373..737c4aa77f7a 100644
--- a/third_party/nix/src/libutil/util.hh
+++ b/third_party/nix/src/libutil/util.hh
@@ -188,10 +188,10 @@ class AutoCloseFD {
   AutoCloseFD();
   AutoCloseFD(int fd);
   AutoCloseFD(const AutoCloseFD& fd) = delete;
-  AutoCloseFD(AutoCloseFD&& fd);
+  AutoCloseFD(AutoCloseFD&& that);
   ~AutoCloseFD();
   AutoCloseFD& operator=(const AutoCloseFD& fd) = delete;
-  AutoCloseFD& operator=(AutoCloseFD&& fd);
+  AutoCloseFD& operator=(AutoCloseFD&& that);
   int get() const;
   explicit operator bool() const;
   int release();