duckdb: make JSON a type of its own

DuckDB's catalog lists JSON as a spelling of VARCHAR, so the seed made it
an alias and a JSON column came out as string. But DuckDB keeps JSON
apart: typeof() reports it as JSON, and duckdb-go decodes a JSON value
into whatever the document holds, which only any can receive.

goldeneye now asks typeof() for each alias, and seeds a spelling that
DuckDB reports by its own name as a type that stands on the logical type.
For JSON that is the base varchar. The DuckDB Go mapper scans JSON into
any and binds a JSON parameter from its text as a string. A new
duckdb_json case covers columns, parameters and json_extract, and its
generated code was run against DuckDB.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KRHPAjUHm5bE8noT5ut2C5

Author: claude

docs/reference/language-support.md

@@ -15,9 +15,9 @@ Spanner and SQL Server, with the types their drivers hand back:
 [go-sql-spanner](https://github.com/googleapis/go-sql-spanner) and
 [go-mssqldb](https://github.com/microsoft/go-mssqldb). DuckDB enums and SQL
 Server alias types are not yet resolved and come out as `any`; ClickHouse
-enums are strings. DuckDB reports a JSON column as the VARCHAR it aliases, so
-it comes out as `string`, and a query reads a JSON object or array by casting
-it to VARCHAR.
+enums are strings. A DuckDB JSON column comes out as `any`, holding the value
+the driver decodes the document into, and a JSON parameter is passed as its
+text.
 
 ## Community language support
 

internal/codegen/golang/duckdb_type.go

@@ -19,9 +19,8 @@ import (
 // parameter as a map. An ENUM is reported by the name it was created with,
 // which the catalog does not yet carry, so it maps to any until it does.
 // JSON comes back decoded, as whatever value the document holds, which
-// only any holds; the catalog reports it as the VARCHAR it aliases, so it
-// maps to string, and a query reads a JSON object or array as text by
-// casting it to VARCHAR.
+// only any holds, and is bound from its text, so a JSON parameter is a
+// string.
 func duckdbType(req *plugin.GenerateRequest, options *opts.Options, col *plugin.Column, param bool) string {
 	t, nullable := columnType(col)
 	if param {
@@ -128,6 +127,12 @@ func duckdbGoType(options *opts.Options, t *plugin.TypeExpr, nullable bool, plac
 	case "varchar", "char", "bpchar", "text", "string":
 		return null("string", "sql.NullString")
 
+	case "json":
+		if place == duckdbParam {
+			return null("string", "sql.NullString")
+		}
+		return "any"
+
 	case "bit", "bitstring":
 		return driver("duckdb.Bit", "")
 

internal/endtoend/testdata/analyze_types/duckdb/stdout.json

@@ -230,7 +230,7 @@
       {
         "name": "doc",
         "type": {
-          "name": "varchar",
+          "name": "json",
           "nullable": true
         },
         "table": "things"

internal/endtoend/testdata/core_types/duckdb/go/models.go

@@ -0,0 +1,3 @@
+{
+  "contexts": ["base"]
+}

internal/endtoend/testdata/duckdb_json/duckdb/exec.json

@@ -0,0 +1,15 @@
+-- name: CreateEvent :exec
+INSERT INTO events (id, payload, meta) VALUES ($1, $2, $3);
+
+-- name: GetEvent :one
+SELECT id, payload, meta FROM events WHERE id = $1;
+
+-- name: EventKind :one
+SELECT json_extract(payload, '$.kind') AS kind, json_extract_string(payload, '$.kind') AS kind_text
+FROM events WHERE id = $1;
+
+-- name: EventsByPayload :many
+SELECT id FROM events WHERE payload = $1;
+
+-- name: PayloadText :one
+SELECT CAST(payload AS VARCHAR) AS payload_text FROM events WHERE id = $1;

internal/endtoend/testdata/duckdb_json/duckdb/go/db.go

@@ -0,0 +1,5 @@
+CREATE TABLE events (
+  id INTEGER PRIMARY KEY,
+  payload JSON NOT NULL,
+  meta JSON
+);