fix(3p/nix): Use SkipEmpty in all calls to absl::StrSplit r/1613

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 26a59482d2427f640893517f1b24dd650a5bd5da, 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>

1 files changed, 12 insertions, 8 deletions

diff --git a/third_party/nix/src/libstore/machines.cc b/third_party/nix/src/libstore/machines.cc
index e5d22c534c36..57c89e06924b 100644
--- a/third_party/nix/src/libstore/machines.cc
+++ b/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(','))
-                 : std::vector<std::string>{settings.thisSystem},
+        isSet(1)
+            ? 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(','))
-                 : std::set<std::string>{},
-        isSet(6) ? absl::StrSplit(tokens[6], absl::ByChar(','))
-                 : std::set<std::string>{},
+        isSet(5)
+            ? absl::StrSplit(tokens[5], absl::ByChar(','), absl::SkipEmpty())
+            : std::set<std::string>{},
+        isSet(6)
+            ? absl::StrSplit(tokens[6], absl::ByChar(','), absl::SkipEmpty())
+            : std::set<std::string>{},
         isSet(7) ? tokens[7] : "");
   }
 }