Add AST-based SQL transpiler for PostgreSQL to DuckDB conversion

Replace regex-based query rewriting with proper AST-based transpilation
using pg_query_go (PostgreSQL's C parser via CGO). This provides:

- Proper handling of string literals (won't rewrite 'pg_catalog' in strings)
- Type mappings: JSONB→JSON, BYTEA→BLOB, INET→TEXT, etc.
- Function mappings: array_agg→list, string_to_array→string_split, etc.
- Operator compatibility for JSON and regex operators
- ON CONFLICT (upsert) syntax support
- DDL constraint stripping for DuckLake mode
- SET/SHOW command handling with 70+ ignored parameters

The transpiler package applies a pipeline of transforms to the parsed AST:
- PgCatalogTransform: pg_catalog.* references
- TypeMappingTransform: PostgreSQL→DuckDB type conversions
- TypeCastTransform: ::regtype→::VARCHAR
- FunctionTransform: 50+ function mappings
- OperatorTransform: operator compatibility
- VersionTransform: version() replacement
- SetShowTransform: SET/SHOW command syntax
- OnConflictTransform: upsert handling
- DDLTransform: constraint stripping (DuckLake mode)
- PlaceholderTransform: $1→? conversion

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: EDsCODE

CLAUDE.md

@@ -18,10 +18,14 @@ PostgreSQL Client → TLS → Duckgres Server → DuckDB (per-user database)
 - **server/server.go**: Server struct, connection handling, graceful shutdown
 - **server/conn.go**: Client connection handling, query execution, COPY protocol
 - **server/protocol.go**: PostgreSQL wire protocol message encoding/decoding
-- **server/catalog.go**: pg_catalog compatibility (views, functions, query rewriting)
+- **server/catalog.go**: pg_catalog compatibility views and macros initialization
 - **server/types.go**: Type OID mapping between DuckDB and PostgreSQL
 - **server/ratelimit.go**: Rate limiting for brute-force protection
 - **server/tls.go**: Auto-generation of self-signed TLS certificates
+- **transpiler/**: AST-based SQL transpiler (PostgreSQL → DuckDB)
+  - `transpiler.go`: Main API, transform pipeline orchestration
+  - `config.go`: Configuration types (DuckLakeMode, ConvertPlaceholders)
+  - `transform/`: Individual transform implementations
 
 ## PostgreSQL Wire Protocol
 
@@ -41,22 +45,27 @@ The server implements the PostgreSQL v3 protocol:
 ### Extended Query Protocol
 Supports prepared statements (Parse/Bind/Execute) for parameterized queries and binary result formats.
 
-## pg_catalog Compatibility (server/catalog.go)
+## pg_catalog Compatibility
 
 psql and other clients expect PostgreSQL system catalogs. We provide compatibility by:
 
-1. **Creating views** in main schema that mirror pg_catalog tables:
+1. **Creating views** in main schema (server/catalog.go `initPgCatalog()`):
    - `pg_database`, `pg_class_full`, `pg_collation`, `pg_policy`, `pg_roles`
    - `pg_statistic_ext`, `pg_publication`, `pg_publication_rel`, `pg_inherits`, etc.
 
-2. **Creating macros** for PostgreSQL functions:
+2. **Creating macros** for PostgreSQL functions (server/catalog.go):
    - `pg_get_userbyid`, `pg_table_is_visible`, `format_type`, `pg_get_expr`
    - `obj_description`, `col_description`, `pg_get_indexdef`, etc.
 
-3. **Query rewriting** to replace PostgreSQL-specific syntax:
-   - `pg_catalog.pg_class` → `pg_class_full`
-   - `OPERATOR(pg_catalog.~)` → `~`
-   - `::pg_catalog.regtype` → `::VARCHAR`
+3. **AST-based SQL transpilation** (transpiler/ package):
+   The transpiler parses PostgreSQL SQL into an AST using pg_query_go (PostgreSQL's C parser),
+   applies transforms, and deparses back to DuckDB-compatible SQL. Transforms include:
+   - **PgCatalogTransform**: `pg_catalog.pg_class` → `pg_class_full`, strips schema prefix from functions
+   - **TypeCastTransform**: `::pg_catalog.regtype` → `::VARCHAR`
+   - **VersionTransform**: `version()` → PostgreSQL-compatible version string
+   - **SetShowTransform**: Converts SET/SHOW commands, marks ignored parameters
+   - **DDLTransform**: (DuckLake mode) Strips PRIMARY KEY, UNIQUE, REFERENCES, SERIAL types
+   - **PlaceholderTransform**: Counts $1, $2 parameters for prepared statements
 
 ## COPY Protocol (server/conn.go)
 
@@ -95,12 +104,17 @@ PGPASSWORD=postgres psql "host=127.0.0.1 port=35437 user=postgres sslmode=requir
 
 ### Adding a new pg_catalog view
 1. Add view creation SQL in `initPgCatalog()` in `catalog.go`
-2. Add regex pattern to rewrite `pg_catalog.viewname` to `viewname`
-3. Add the replacement in `rewritePgCatalogQuery()`
+2. If the view needs query rewriting (e.g., `pg_catalog.viewname` → `viewname`):
+   - Add mapping in `transpiler/transform/pgcatalog.go` in `pgCatalogViewMappings`
 
 ### Adding a new PostgreSQL function
 1. Add `CREATE MACRO` in the `functions` slice in `initPgCatalog()`
-2. Add function name to `pgCatalogFunctions` slice for query rewriting
+2. The transpiler automatically strips `pg_catalog.` prefix from function calls
+
+### Adding a new transform
+1. Create a new file in `transpiler/transform/` implementing the `Transform` interface
+2. Register the transform in `transpiler/transpiler.go` `New()` function
+3. Add tests in `transpiler/transpiler_test.go`
 
 ### Adding protocol support
 1. Add message type constant in `protocol.go`
@@ -110,6 +124,7 @@ PGPASSWORD=postgres psql "host=127.0.0.1 port=35437 user=postgres sslmode=requir
 ## Dependencies
 
 - `github.com/duckdb/duckdb-go/v2` - DuckDB Go driver
+- `github.com/pganalyze/pg_query_go/v6` - PostgreSQL SQL parser (CGO, uses libpg_query)
 - `gopkg.in/yaml.v3` - YAML config parsing
 
 ## Known Limitations

go.mod

@@ -24,6 +24,7 @@ require (
 	github.com/klauspost/compress v1.18.0 // indirect
 	github.com/klauspost/cpuid/v2 v2.3.0 // indirect
 	github.com/lib/pq v1.10.9 // indirect
+	github.com/pganalyze/pg_query_go/v6 v6.1.0 // indirect
 	github.com/pierrec/lz4/v4 v4.1.22 // indirect
 	github.com/zeebo/xxh3 v1.0.2 // indirect
 	golang.org/x/exp v0.0.0-20250408133849-7e4ce0ab07d0 // indirect
@@ -32,4 +33,5 @@ require (
 	golang.org/x/sys v0.35.0 // indirect
 	golang.org/x/tools v0.36.0 // indirect
 	golang.org/x/xerrors v0.0.0-20240903120638-7835f813f4da // indirect
+	google.golang.org/protobuf v1.36.8 // indirect
 )

go.sum

@@ -28,10 +28,12 @@ github.com/go-viper/mapstructure/v2 v2.4.0 h1:EBsztssimR/CONLSZZ04E8qAkxNYq4Qp9L
 github.com/go-viper/mapstructure/v2 v2.4.0/go.mod h1:oJDH3BJKyqBA2TXFhDsKDGDTlndYOZ6rGS0BRZIxGhM=
 github.com/goccy/go-json v0.10.5 h1:Fq85nIqj+gXn/S5ahsiTlK3TmC85qgirsdTP/+DeaC4=
 github.com/goccy/go-json v0.10.5/go.mod h1:oq7eo15ShAhp70Anwd5lgX2pLfOS3QCiwU/PULtXL6M=
+github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
 github.com/golang/snappy v1.0.0 h1:Oy607GVXHs7RtbggtPBnr2RmDArIsAefDwvrdWvRhGs=
 github.com/golang/snappy v1.0.0/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEWrmP2Q=
 github.com/google/flatbuffers v25.2.10+incompatible h1:F3vclr7C3HpB1k9mxCGRMXq6FdUalZ6H/pNX4FP1v0Q=
 github.com/google/flatbuffers v25.2.10+incompatible/go.mod h1:1AeVuKshWv4vARoZatz6mlQ0JxURH0Kv5+zNeJKJCa8=
+github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
@@ -48,6 +50,8 @@ github.com/minio/asm2plan9s v0.0.0-20200509001527-cdd76441f9d8 h1:AMFGa4R4MiIpsp
 github.com/minio/asm2plan9s v0.0.0-20200509001527-cdd76441f9d8/go.mod h1:mC1jAcsrzbxHt8iiaC+zU4b1ylILSosueou12R++wfY=
 github.com/minio/c2goasm v0.0.0-20190812172519-36a3d3bbc4f3 h1:+n/aFZefKZp7spd8DFdX7uMikMLXX4oubIzJF4kv/wI=
 github.com/minio/c2goasm v0.0.0-20190812172519-36a3d3bbc4f3/go.mod h1:RagcQ7I8IeTMnF8JTXieKnO4Z6JCsikNEzj0DwauVzE=
+github.com/pganalyze/pg_query_go/v6 v6.1.0 h1:jG5ZLhcVgL1FAw4C/0VNQaVmX1SUJx71wBGdtTtBvls=
+github.com/pganalyze/pg_query_go/v6 v6.1.0/go.mod h1:nvTHIuoud6e1SfrUaFwHqT0i4b5Nr+1rPWVds3B5+50=
 github.com/pierrec/lz4/v4 v4.1.22 h1:cKFw6uJDK+/gfw5BcDL0JL5aBsAFdsIT18eRtLj7VIU=
 github.com/pierrec/lz4/v4 v4.1.22/go.mod h1:gZWDp/Ze/IJXGXf23ltt2EXimqmTUXEy0GFuRQyBid4=
 github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 h1:Jamvg5psRIccs7FGNTlIRMkT8wgtp5eCXdBlqhYGL6U=
@@ -68,10 +72,15 @@ golang.org/x/sys v0.35.0 h1:vz1N37gP5bs89s7He8XuIYXpyY0+QlsKmzipCbUtyxI=
 golang.org/x/sys v0.35.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
 golang.org/x/tools v0.36.0 h1:kWS0uv/zsvHEle1LbV5LE8QujrxB3wfQyxHfhOk0Qkg=
 golang.org/x/tools v0.36.0/go.mod h1:WBDiHKJK8YgLHlcQPYQzNCkUxUypCaa5ZegCVutKm+s=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20240903120638-7835f813f4da h1:noIWHXmPHxILtqtCOPIhSt0ABwskkZKjD3bXGnZGpNY=
 golang.org/x/xerrors v0.0.0-20240903120638-7835f813f4da/go.mod h1:NDW/Ps6MPRej6fsCIbMTohpP40sJ/P/vI1MoTEGwX90=
 gonum.org/v1/gonum v0.16.0 h1:5+ul4Swaf3ESvrOnidPp4GZbzf0mxVQpDCYUQE7OJfk=
 gonum.org/v1/gonum v0.16.0/go.mod h1:fef3am4MQ93R2HHpKnLk4/Tbh/s0+wqD5nfa6Pnwy4E=
+google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp09yW+WbY/TyQbw=
+google.golang.org/protobuf v1.31.0/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqwMG9pJV4I=
+google.golang.org/protobuf v1.36.8 h1:xHScyCOEuuwZEc6UtSOvPbAT4zRh0xcNRYekJwfqyMc=
+google.golang.org/protobuf v1.36.8/go.mod h1:fuxRtAxBytpl4zzqUh6/eyUujkJdNiuEkXntxiD/uRU=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=