feat: propagate GEOMETRY CRS through PostGIS in both directions

src/include/postgres_binary_writer.hpp

@@ -10,6 +10,7 @@
 
 #include "duckdb.hpp"
 #include "duckdb/common/types/interval.hpp"
+#include "duckdb/common/types/geometry_crs.hpp"
 #include "duckdb/common/serializer/memory_stream.hpp"
 #include "postgres_conversion.hpp"
 
@@ -29,7 +30,7 @@
 		} else if (sizeof(T) == sizeof(uint32_t)) {
 			return htonl(val);
 		} else if (sizeof(T) == sizeof(uint64_t)) {
 			return htonll(val);
 		} else {
 			D_ASSERT(0);
 			return val;
@@ -207,6 +208,44 @@
 		stream.WriteData(const_data_ptr_cast(str_data), str_size);
 	}
 
+	//! Write GEOMETRY to PostGIS. If the type carries CRS metadata, writes EWKB
+	//! (WKB with SRID) so PostGIS receives the correct SRID.
+	void WriteGeometry(string_t value, const LogicalType &type) {
+		if (!GeoType::HasCRS(type)) {
+			WriteRawBlob(value);
+			return;
+		}
+		auto &crs = GeoType::GetCRS(type);
+
+		// Extract SRID from CRS identifier (e.g., "EPSG:4326" → 4326)
+		auto &id = crs.GetIdentifier();
+		auto colon = id.find(':');
+		if (colon == string::npos) {
+			WriteRawBlob(value);
+			return;
+		}
+		int32_t srid;
+		try {
+			srid = std::stoi(id.substr(colon + 1));
+		} catch (...) {
+			WriteRawBlob(value);
+			return;
+		}
+
+		// Write EWKB: WKB with SRID flag set on the type field + 4-byte SRID inserted.
+		// [byte_order:1] [type|0x20000000:4] [srid:4] [coordinates...]
+		auto wkb_size = value.GetSize();
+		auto wkb_data = const_data_ptr_cast(value.GetData());
+		WriteRawInteger<int32_t>(NumericCast<int32_t>(wkb_size + 4));
+		stream.WriteData(wkb_data, 1); // byte order
+		uint32_t wkb_type;
+		memcpy(&wkb_type, wkb_data + 1, 4);
+		wkb_type |= 0x20000000;
+		stream.WriteData(const_data_ptr_cast(reinterpret_cast<const uint8_t *>(&wkb_type)), 4); // type + SRID flag
+		stream.WriteData(const_data_ptr_cast(reinterpret_cast<const uint8_t *>(&srid)), 4); // SRID (LE, matching WKB)
+		stream.WriteData(wkb_data + 5, wkb_size - 5);                                       // rest of payload
+	}
+
 	void WriteVarchar(string_t value) {
 		auto str_size = value.GetSize();
 		auto str_data = value.GetData();
@@ -354,7 +393,7 @@
 		}
 		case LogicalTypeId::GEOMETRY: {
 			auto data = FlatVector::GetData<string_t>(col)[r];
-			WriteRawBlob(data);
+			WriteGeometry(data, type);
 			break;
 		}
 		case LogicalTypeId::ENUM: {

src/postgres_utils.cpp

@@ -2,6 +2,7 @@
 #include "storage/postgres_schema_entry.hpp"
 #include "storage/postgres_transaction.hpp"
 #include "postgres_type_oids.hpp"
+#include "duckdb/common/types/geometry_crs.hpp"
 
 namespace duckdb {
 
@@ -20,6 +21,26 @@ PGconn *PostgresUtils::PGConnect(const string &dsn, const string &attach_path) {
 }
 
 string PostgresUtils::TypeToString(const LogicalType &input) {
+	// Handle GEOMETRY('EPSG:N') first: the CRS-bearing GEOMETRY type can have
+	// an alias of "GEOMETRY", which would otherwise short-circuit the alias
+	// branch below and emit an untyped `geometry` column (typmod -1).  When
+	// CRS is present, emit a typmod-bearing PostGIS column type so the SRID
+	// survives a CREATE TABLE round trip; otherwise fall through.
+	if (input.id() == LogicalTypeId::GEOMETRY && GeoType::HasCRS(input)) {
+		auto &crs = GeoType::GetCRS(input);
+		auto &id = crs.GetIdentifier();
+		auto colon = id.find(':');
+		if (colon != string::npos) {
+			try {
+				int32_t srid = std::stoi(id.substr(colon + 1));
+				if (srid > 0) {
+					return "geometry(Geometry, " + std::to_string(srid) + ")";
+				}
+			} catch (...) {
+				// fall through to plain GEOMETRY
+			}
+		}
+	}
 	if (input.HasAlias()) {
 		return input.GetAlias();
 	}
@@ -147,6 +168,20 @@ LogicalType PostgresUtils::TypeToLogicalType(optional_ptr<PostgresTransaction> t
 		postgres_type.info = PostgresTypeAnnotation::JSONB;
 		return LogicalType::VARCHAR;
 	} else if (pgtypename == "geometry") {
+		// PostGIS encodes the column-level SRID in the type modifier of
+		// `geometry(TYPE, SRID)` columns. The bit layout is:
+		//   bits  0    : has-M
+		//   bits  1    : has-Z
+		//   bits  2-7  : geometry type code (POINT=1, LINESTRING=2, ...)
+		//   bits  8-29 : SRID
+		// Untyped `geometry` columns carry typmod -1 and we fall back to
+		// plain GEOMETRY (no CRS), matching the previous behavior.
+		if (type_info.type_modifier > 0) {
+			int32_t srid = static_cast<int32_t>((static_cast<uint32_t>(type_info.type_modifier) & 0x0FFFFF00u) >> 8);
+			if (srid > 0) {
+				return LogicalType::GEOMETRY("EPSG:" + std::to_string(srid));
+			}
+		}
 		return LogicalType::GEOMETRY();
 	} else if (pgtypename == "date") {
 		return LogicalType::DATE;
@@ -261,7 +296,11 @@ LogicalType PostgresUtils::ToPostgresType(const LogicalType &input) {
 	case LogicalTypeId::HUGEINT:
 		return LogicalType::DOUBLE;
 	case LogicalTypeId::GEOMETRY:
-		return LogicalType::GEOMETRY();
+		// Preserve CRS metadata so downstream TypeToString can emit a typmod-
+		// bearing PostGIS column type and the SRID survives a CREATE TABLE
+		// AS round trip.  Returning a CRS-less GEOMETRY here strips the CRS
+		// before it ever reaches the schema-emission path.
+		return input;
 	default:
 		return LogicalType::VARCHAR;
 	}