Use duckdb functions without having to specify the full type signature

Makefile

@@ -46,6 +46,13 @@ COMPILER_FLAGS=-Wno-sign-compare -Wshadow -Wswitch -Wunused-parameter -Wunreacha
 
 override PG_CPPFLAGS += -Iinclude -isystem third_party/duckdb/src/include -isystem third_party/duckdb/third_party/re2 ${COMPILER_FLAGS}
 override PG_CXXFLAGS += -std=c++17 ${DUCKDB_BUILD_CXX_FLAGS} ${COMPILER_FLAGS} -Wno-register
+# Ignore declaration-after-statement warnings in our code. Postgres enforces
+# this because their ancient style guide requires it, but we don't care. It
+# would only apply to C files anyway, and we don't have many of those. The only
+# ones that we do have are vendored in from Postgres (ruleutils), and allowing
+# declarations to be anywhere is even a good thing for those as we can keep our
+# changes to the vendored code in one place.
+override PG_CFLAGS += -Wno-declaration-after-statement
 
 SHLIB_LINK += -Wl,-rpath,$(PG_LIB)/ -lpq -Lthird_party/duckdb/build/$(DUCKDB_BUILD_TYPE)/src -L$(PG_LIB) -lduckdb -lstdc++ -llz4
 

include/pgduckdb/pgduckdb_metadata_cache.hpp

@@ -7,6 +7,9 @@ bool IsExtensionRegistered();
 bool IsDuckdbOnlyFunction(Oid function_oid);
 uint64 CacheVersion();
 Oid ExtensionOid();
+Oid SchemaOid();
+Oid DuckdbRowOid();
+Oid DuckdbUnresolvedTypeOid();
 Oid DuckdbTableAmOid();
 bool IsMotherDuckEnabled();
 bool IsMotherDuckEnabledAnywhere();

include/pgduckdb/pgduckdb_ruleutils.h

@@ -7,3 +7,12 @@ char *pgduckdb_get_tabledef(Oid relation_id);
 bool pgduckdb_is_not_default_expr(Node *node, void *context);
 List *pgduckdb_db_and_schema(const char *postgres_schema_name, bool is_duckdb_table);
 const char *pgduckdb_db_and_schema_string(const char *postgres_schema_name, bool is_duckdb_table);
+bool pgduckdb_is_duckdb_row(Oid type_oid);
+bool pgduckdb_is_unresolved_type(Oid type_oid);
+bool pgduckdb_var_is_duckdb_row(Var *var);
+bool pgduckdb_func_returns_duckdb_row(RangeTblFunction *rtfunc);
+bool pgduckdb_target_list_contains_unresolved_type_or_row(List *target_list);
+Var *pgduckdb_duckdb_row_subscript_var(Expr *expr);
+List *pgduckdb_star_start_vars(List *target_list);
+
+extern bool processed_targetlist;