Revert "Delete and re-add libpqxx-7.7.3 due to weird corruption."

This reverts commit e96515433d.

ext/libpqxx-7.7.3/test/unit/test_pipeline.cxx

@@ -0,0 +1,64 @@
+#include <chrono>
+
+#include <pqxx/pipeline>
+#include <pqxx/transaction>
+
+#include "../test_helpers.hxx"
+
+namespace
+{
+void test_pipeline()
+{
+  pqxx::connection conn;
+  pqxx::work tx{conn};
+
+  // A pipeline grabs transaction focus, blocking regular queries and such.
+  pqxx::pipeline pipe(tx, "test_pipeline_detach");
+  PQXX_CHECK_THROWS(
+    tx.exec("SELECT 1"), std::logic_error,
+    "Pipeline does not block regular queries");
+
+  // Flushing a pipeline relinquishes transaction focus.
+  pipe.flush();
+  auto r{tx.exec("SELECT 2")};
+  PQXX_CHECK_EQUAL(
+    std::size(r), 1, "Wrong query result after flushing pipeline.");
+  PQXX_CHECK_EQUAL(
+    r[0][0].as<int>(), 2, "Query returns wrong data after flushing pipeline.");
+
+  // Inserting a query makes the pipeline grab transaction focus back.
+  auto q{pipe.insert("SELECT 2")};
+  PQXX_CHECK_THROWS(
+    tx.exec("SELECT 3"), std::logic_error,
+    "Pipeline does not block regular queries");
+
+  // Invoking complete() also detaches the pipeline from the transaction.
+  pipe.complete();
+  r = tx.exec("SELECT 4");
+  PQXX_CHECK_EQUAL(std::size(r), 1, "Wrong query result after complete().");
+  PQXX_CHECK_EQUAL(
+    r[0][0].as<int>(), 4, "Query returns wrong data after complete().");
+
+  // The complete() also received any pending query results from the backend.
+  r = pipe.retrieve(q);
+  PQXX_CHECK_EQUAL(std::size(r), 1, "Wrong result from pipeline.");
+  PQXX_CHECK_EQUAL(r[0][0].as<int>(), 2, "Pipeline returned wrong data.");
+
+  // We can cancel while the pipe is empty, and things will still work.
+  pipe.cancel();
+
+  // Issue a query and cancel it.  Measure time to see that we don't really
+  // wait.
+  using clock = std::chrono::steady_clock;
+  auto const start{clock::now()};
+  pipe.retain(0);
+  pipe.insert("pg_sleep(10)");
+  pipe.cancel();
+  auto const finish{clock::now()};
+  auto const seconds{
+    std::chrono::duration_cast<std::chrono::seconds>(finish - start).count()};
+  PQXX_CHECK_LESS(seconds, 5, "Canceling a sleep took suspiciously long.");
+}
+} // namespace
+
+PQXX_REGISTER_TEST(test_pipeline);