feat(engine): add -println / -printfln with OS line ending

xff/engine/evaluate.cc

@@ -47,6 +47,11 @@
 namespace xff::engine {
 namespace {
 
+// The OS-native line terminator used by -println/-printfln (xff extensions).
+// LF today; a Windows build would select "\r\n". Centralized so both actions
+// agree and the platform choice lives in one place.
+constexpr std::string_view kOsLineEnding = "\n";
+
 bool Fnmatch(std::string_view pattern, std::string_view text, int flags) {
   return ::fnmatch(std::string(pattern).c_str(), std::string(text).c_str(), flags) == 0;
 }
@@ -441,6 +446,16 @@ bool EvaluatePredicate(const parser::Expr& expr, EvalContext& ctx) {
     }
     return true;
   }
+  if (name == "-println") {
+    emit(absl::StrCat(visit.path, kOsLineEnding));  // xff: -print with the OS line ending
+    return true;
+  }
+  if (name == "-printfln") {
+    if (has_arg) {  // xff: -printf plus the OS line ending appended
+      emit(absl::StrCat(FormatPrintf(expr.args.front(), visit), kOsLineEnding));
+    }
+    return true;
+  }
   if (name == "-delete") {
     static_cast<void>(fs.Remove(visit.path));  // failures set a nonzero exit; wired in the exit-code work
     return true;

xff/engine/evaluate_test.cc

@@ -341,6 +341,19 @@ TEST_F(EvaluateTest, PrintfExpandsDirectivesAndEscapes) {
   EXPECT_THAT(emitted_, Eq("%\t3"));
 }
 
+TEST_F(EvaluateTest, PrintlnAndPrintflnAppendOsLineEnding) {
+  vfs::Metadata md;
+  md.type = vfs::FileType::kRegular;
+  md.size = 42;
+  const Visit visit{.path = "a/b/c.txt", .name = "c.txt", .depth = 2, .metadata = md};
+  // -println: -print with the OS line ending (LF on this platform).
+  EXPECT_TRUE(Match({"-println"}, visit));
+  EXPECT_THAT(emitted_, Eq("a/b/c.txt\n"));
+  // -printfln: -printf plus a trailing OS line ending the format need not carry.
+  EXPECT_TRUE(Match({"-printfln", "%f|%s"}, visit));
+  EXPECT_THAT(emitted_, Eq("c.txt|42\n"));
+}
+
 TEST_F(EvaluateTest, ExecFieldsGatesNamedPlaceholderSubstitution) {
   vfs::Metadata md;
   const Visit visit = MakeVisit("a/b/f.txt", "f.txt", vfs::FileType::kRegular, md);

xff/registry/registry.cc

@@ -68,6 +68,8 @@ constexpr std::array kDescriptors = std::to_array<Descriptor>({
     {.name = "-print", .kind = Kind::kAction, .arity = 0},
     {.name = "-print0", .kind = Kind::kAction, .arity = 0},
     {.name = "-printf", .kind = Kind::kAction, .arity = 1},
+    {.name = "-println", .kind = Kind::kAction, .arity = 0},    // xff: -print with the OS line ending
+    {.name = "-printfln", .kind = Kind::kAction, .arity = 1},   // xff: -printf + the OS line ending
     {.name = "-delete", .kind = Kind::kAction, .arity = 0},
     {.name = "-prune", .kind = Kind::kAction, .arity = 0},
     {.name = "-quit", .kind = Kind::kAction, .arity = 0},