Add initial PG18 support (#788)

Things that this does to make PG18 work:

- Add a bunch of `#if PG_VERSION_NUM` cases for function calls with
  additional/fewer arguments.
- Refactor explain logic to a separate file in `src/pg` because they
  require include new different headers.
- Adds a wrapper to handle differences in C locale checking across
  versions
- Use `TupleDescAttr` instead of manually indexing into the `attrs`
  array. PG18 doesn't use this attrs array anymore.
- Start using `PG_MODULE_MAGIC_EXT`, it's easy and allows people to
  inspect the version of the shared library.

Author: JelteF

.github/workflows/build_and_test.yaml

@@ -52,6 +52,8 @@ jobs:
           type: ReleaseStatic
         - version: REL_17_STABLE
           type: Debug
+        - version: REL_18_BETA1
+          type: Release
 
         # Not enabled for now (waiting for April 2025 code freeze)
         # - version: master

Makefile.global

@@ -7,7 +7,7 @@ $(error Minimum version of PostgreSQL required is $(PG_MIN_VER) (but have $(PG_V
 endif
 
 # If you want to test with an unsupported PG version you can pass a different value to make
-PG_MAX_VER ?= 17
+PG_MAX_VER ?= 18
 ifeq ($(shell expr "$(PG_MAX_VER)" \>=  "$(PG_VER)"), 0)
 $(error Maximum supported version of PostgreSQL is $(PG_MAX_VER) (but have $(PG_VER)))
 endif

include/pgduckdb/pg/declarations.hpp

@@ -90,4 +90,6 @@ struct Plan;
 struct FuncExpr;
 
 typedef struct FunctionCallInfoBaseData *FunctionCallInfo;
+
+struct ExplainState;
 }

include/pgduckdb/pg/explain.hpp

@@ -0,0 +1,10 @@
+#include "pgduckdb/pg/declarations.hpp"
+#include "duckdb/common/enums/explain_format.hpp"
+
+namespace pgduckdb::pg {
+void ExplainPropertyText(const char *qlabel, const char *value, ExplainState *es);
+
+duckdb::ExplainFormat DuckdbExplainFormat(ExplainState *es);
+
+bool IsExplainAnalyze(ExplainState *es);
+} // namespace pgduckdb::pg

include/pgduckdb/pg/locale.hpp

@@ -0,0 +1,5 @@
+#include "pgduckdb/pg/declarations.hpp"
+
+namespace pgduckdb::pg {
+bool IsCLocale(Oid collation_id);
+}

include/pgduckdb/vendor/pg_ruleutils.h

@@ -43,6 +43,13 @@ extern List *pgduckdb_set_deparse_context_plan(List *dpcontext,
 									  struct Plan *plan, List *ancestors);
 extern List *pgduckdb_select_rtable_names_for_explain(List *rtable,
 											 Bitmapset *rels_used);
+#if PG_VERSION_NUM >= 180000
+extern char *get_window_frame_options_for_explain(int frameOptions,
+												  Node *startOffset,
+												  Node *endOffset,
+												  List *dpcontext,
+												  bool forceprefix);
+#endif
 extern char *pgduckdb_generate_collation_name(Oid collid);
 extern char *pgduckdb_generate_opclass_name(Oid opclass);
 extern char *pgduckdb_get_range_partbound_string(List *bound_datums);

src/pg/explain.cpp

@@ -0,0 +1,33 @@
+#include "pgduckdb/pg/explain.hpp"
+#include "pgduckdb/pgduckdb_utils.hpp"
+
+extern "C" {
+#include "postgres.h"
+
+#if PG_VERSION_NUM >= 180000
+#include "commands/explain_format.h"
+#include "commands/explain_state.h"
+#else
+#include "commands/explain.h"
+#endif
+}
+
+namespace pgduckdb::pg {
+void
+ExplainPropertyText(const char *qlabel, const char *value, ExplainState *es) {
+	PostgresFunctionGuard(::ExplainPropertyText, qlabel, value, es);
+}
+
+duckdb::ExplainFormat
+DuckdbExplainFormat(ExplainState *es) {
+	if (es->format == EXPLAIN_FORMAT_JSON)
+		return duckdb::ExplainFormat::JSON;
+
+	return duckdb::ExplainFormat::DEFAULT;
+}
+
+bool
+IsExplainAnalyze(ExplainState *es) {
+	return es->analyze;
+}
+} // namespace pgduckdb::pg

src/pg/locale.cpp

@@ -0,0 +1,32 @@
+#include "pgduckdb/pg/locale.hpp"
+
+extern "C" {
+#include "postgres.h"
+}
+
+/*
+ * Needs to be done outside of 'extern "C"' block AND before including
+ * pg_locale.h. Otherwise you get many compilation errors about templates being
+ * used in C linkage. It also needs to be done after including postgres.h,
+ * because otherwise USE_ICU does not exist.
+ */
+#ifdef USE_ICU
+#include <unicode/ucol.h>
+#endif
+
+extern "C" {
+#include "utils/pg_locale.h"
+}
+
+namespace pgduckdb::pg {
+
+bool
+IsCLocale(Oid collation_id) {
+#if PG_VERSION_NUM >= 180000
+	return pg_newlocale_from_collation(collation_id)->collate_is_c;
+#else
+	return lc_ctype_is_c(collation_id);
+#endif
+}
+
+} // namespace pgduckdb::pg

src/pg/relations.cpp

@@ -56,7 +56,7 @@ GetAttName(const Form_pg_attribute att) {
 
 Form_pg_attribute
 GetAttr(const TupleDesc tupleDesc, int i) {
-	return &tupleDesc->attrs[i];
+	return TupleDescAttr(tupleDesc, i);
 }
 
 bool

src/pgduckdb.cpp

@@ -13,7 +13,12 @@ extern "C" {
 #include "pgduckdb/pgduckdb_xact.hpp"
 
 extern "C" {
+
+#ifdef PG_MODULE_MAGIC_EXT
+PG_MODULE_MAGIC_EXT(.name = "pg_duckdb", .version = "1.0.0");
+#else
 PG_MODULE_MAGIC;
+#endif
 
 void
 _PG_init(void) {