Make stream_to accept optional<string_view>. (#597)

Fixes #596.

It'd be nice to support each of `optional`, `shared_ptr`, `unique_ptr`,
and potentially other smart pointer types for each of these string
types.  But doing that without C++20's "concepts" is going to be a
little hairy.

Also switching CircleCI tests to use clang, just because the `debian/unstable` image keeps failing with a warning in gcc's own headers.  Can't reproduce that on my own machine, so I hope it's just a transient that's already fixed in Debian.

.circleci/config.yml

@@ -3,8 +3,7 @@ version: 2
 jobs:
   build:
     docker:
-      - image: debian:testing
-#      - image: postgres:latest
+      - image: debian:unstable
     environment:
       - PGHOST: "/tmp"
     steps:
@@ -14,10 +13,10 @@ jobs:
           command: apt update
       - run:
           name: Install
-          command: apt install -y lsb-release python3 cmake postgresql libpq-dev postgresql-server-dev-all build-essential autoconf dh-autoreconf autoconf-archive automake cppcheck
+          command: apt install -y lsb-release python3 cmake postgresql libpq-dev postgresql-server-dev-all build-essential autoconf dh-autoreconf autoconf-archive automake cppcheck clang
       - run:
           name: Identify
-          command: lsb_release -a && c++ --version
+          command: lsb_release -a && c++ --version && clang++ --version
       - run:
           name: Prepare postgres
           command: |
@@ -35,7 +34,7 @@ jobs:
           command: createdb root
       - run:
           name: Autogen
-          command: NOCONFIGURE=1 ./autogen.sh
+          command: ./autogen.sh
       - run:
           name: Configure
           command: |
@@ -44,7 +43,8 @@ jobs:
                   --enable-maintainer-mode \
                   --enable-audit \
                   --enable-shared --disable-static \
-                  CXXFLAGS=-O3
+                  CXXFLAGS='-O3 -std=c++17' \
+                  CXX=clang++
       - store_artifacts:
           path: config.log
       - run:

config/Makefile.in

@@ -123,7 +123,7 @@ am__can_run_installinfo = \
   esac
 am__tagged_files = $(HEADERS) $(SOURCES) $(TAGS_FILES) $(LISP)
 am__DIST_COMMON = $(srcdir)/Makefile.in compile config.guess \
-	config.sub install-sh ltmain.sh missing mkinstalldirs
+	config.sub depcomp install-sh ltmain.sh missing mkinstalldirs
 DISTFILES = $(DIST_COMMON) $(DIST_SOURCES) $(TEXINFOS) $(EXTRA_DIST)
 ACLOCAL = @ACLOCAL@
 AMTAR = @AMTAR@

include/pqxx/stream_to.hxx

@@ -349,7 +349,6 @@ private:
         // Shrink to fit.  Keep the tab though.
         m_buffer.resize(static_cast<std::size_t>(end - data));
       }
-      // TODO: Also support std::optional<std::string_view> etc. (#596)
       else if constexpr (
         std::is_same_v<Field, std::string> or
         std::is_same_v<Field, std::string_view> or
@@ -359,6 +358,31 @@ private:
         m_field_buf.resize(budget);
         escape_field_to_buffer(f);
       }
+      else if constexpr (
+        std::is_same_v<Field, std::optional<std::string>> or
+        std::is_same_v<Field, std::optional<std::string_view>> or
+        std::is_same_v<Field, std::optional<zview>>)
+      {
+        // Optional string.  It's not null (we checked for that above), so...
+        // Treat like a string.
+        m_field_buf.resize(budget);
+        escape_field_to_buffer(f.value());
+      }
+      // TODO: Support deleter template argument on unique_ptr.
+      else if constexpr (
+        std::is_same_v<Field, std::unique_ptr<std::string>> or
+        std::is_same_v<Field, std::unique_ptr<std::string_view>> or
+        std::is_same_v<Field, std::unique_ptr<zview>> or
+        std::is_same_v<Field, std::shared_ptr<std::string>> or
+        std::is_same_v<Field, std::shared_ptr<std::string_view>> or
+        std::is_same_v<Field, std::shared_ptr<zview>>)
+      {
+        // TODO: Can we generalise this elegantly without Concepts?
+        // Effectively also an optional string.  It's not null (we checked
+        // for that above).
+        m_field_buf.resize(budget);
+        escape_field_to_buffer(*f);
+      }
       else
       {
         // This field needs to be converted to a string, and after that,

test/unit/test_stream_to.cxx

@@ -436,10 +436,60 @@ void test_stream_to_quotes_arguments()
 }
 
 
+void test_stream_to_optionals()
+{
+  pqxx::connection conn;
+  pqxx::work tx{conn};
+
+  tx.exec0("CREATE TEMP TABLE pqxx_strings(key integer, value varchar)");
+
+  auto stream{pqxx::stream_to::table(tx, {"pqxx_strings"}, {"key", "value"})};
+  stream.write_values(1, std::optional<std::string>{});
+  stream.write_values(2, std::optional<std::string_view>{});
+  stream.write_values(3, std::optional<pqxx::zview>{});
+  stream.write_values(4, std::optional<std::string>{"Opt str."});
+  stream.write_values(5, std::optional<std::string_view>{"Opt sv."});
+  stream.write_values(6, std::optional<pqxx::zview>{"Opt zv."});
+
+  stream.write_values(7, std::shared_ptr<std::string>{});
+  stream.write_values(8, std::shared_ptr<std::string_view>{});
+  stream.write_values(9, std::shared_ptr<pqxx::zview>{});
+  stream.write_values(10, std::make_shared<std::string>("Shared str."));
+  stream.write_values(11, std::make_shared<std::string_view>("Shared sv."));
+  stream.write_values(12, std::make_shared<pqxx::zview>("Shared zv."));
+
+  stream.write_values(13, std::unique_ptr<std::string>{});
+  stream.write_values(14, std::unique_ptr<std::string_view>{});
+  stream.write_values(15, std::unique_ptr<pqxx::zview>{});
+  stream.write_values(16, std::make_unique<std::string>("Uq str."));
+  stream.write_values(17, std::make_unique<std::string_view>("Uq sv."));
+  stream.write_values(18, std::make_unique<pqxx::zview>("Uq zv."));
+  stream.complete();
+
+  std::string nulls;
+  for (auto [key] : tx.query<int>(
+         "SELECT key FROM pqxx_strings WHERE value IS NULL ORDER BY key"))
+    nulls += pqxx::to_string(key) + '.';
+  PQXX_CHECK_EQUAL(
+    nulls, "1.2.3.7.8.9.13.14.15.", "Unexpected list of nulls.");
+
+  std::string values;
+  for (auto [value] :
+       tx.query<std::string>("SELECT value FROM pqxx_strings WHERE value IS "
+                             "NOT NULL ORDER BY key"))
+    values += value;
+  PQXX_CHECK_EQUAL(
+    values,
+    "Opt str.Opt sv.Opt zv.Shared str.Shared sv.Shared zv.Uq str.Uq sv.Uq zv.",
+    "Unexpected list of values.");
+}
+
+
 PQXX_REGISTER_TEST(test_stream_to);
 PQXX_REGISTER_TEST(test_container_stream_to);
 PQXX_REGISTER_TEST(test_stream_to_does_nonnull_optional);
 PQXX_REGISTER_TEST(test_stream_to_factory_with_static_columns);
 PQXX_REGISTER_TEST(test_stream_to_factory_with_dynamic_columns);
 PQXX_REGISTER_TEST(test_stream_to_quotes_arguments);
+PQXX_REGISTER_TEST(test_stream_to_optionals);
 } // namespace