fix(duckdb): rewrite sqlc.arg and @name to native placeholders

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

@@ -0,0 +1,5 @@
+{
+  "command": "analyze",
+  "args": ["--dialect", "duckdb", "--schema", "schema.sql", "query.sql"],
+  "contexts": ["base"]
+}

internal/endtoend/testdata/analyze_slice_rejected/duckdb/query.sql

@@ -0,0 +1,2 @@
+-- name: ByIDs :many
+SELECT id, name FROM items WHERE id IN (sqlc.slice(ids));

internal/endtoend/testdata/analyze_slice_rejected/duckdb/schema.sql

@@ -0,0 +1 @@
+CREATE TABLE items (id INTEGER NOT NULL, name VARCHAR NOT NULL);

internal/endtoend/testdata/analyze_slice_rejected/duckdb/stderr.txt

@@ -0,0 +1 @@
+Error: error parsing queries: query.sql:2:41: sqlc.slice is not supported by this engine; bind a list parameter instead

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

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

internal/endtoend/testdata/duckdb_named_params/duckdb/query.sql

@@ -0,0 +1,11 @@
+-- name: ByID :many
+SELECT id, name FROM items WHERE id = sqlc.arg(want_id);
+
+-- name: ByNullableID :many
+SELECT id, name FROM items WHERE id = sqlc.narg(want_id);
+
+-- name: ByAt :many
+SELECT id, name FROM items WHERE id = @want_id;
+
+-- name: Range :many
+SELECT id, name FROM items WHERE id > sqlc.arg(min_id) AND id < sqlc.arg(max_id);

internal/endtoend/testdata/duckdb_named_params/duckdb/schema.sql

@@ -0,0 +1 @@
+CREATE TABLE items (id INTEGER NOT NULL, name VARCHAR NOT NULL);

internal/endtoend/testdata/duckdb_named_params/duckdb/sqlc.yaml

@@ -0,0 +1,10 @@
+version: "2"
+sql:
+  - engine: "duckdb"
+    schema: "schema.sql"
+    queries: "query.sql"
+    gen:
+      go:
+        package: "querytest"
+        out: "go"
+        sql_package: "database/sql"

internal/sql/preprocess/CLAUDE.md

@@ -20,6 +20,7 @@ Native placeholders by dialect:
 | postgresql | `$1` | sqlc syntax |
 | mysql | `?` | user variable, left alone |
 | sqlite | `?1` | sqlc syntax |
+| duckdb | `$1` | sqlc syntax; `sqlc.slice` is rejected |
 
 GoogleSQL and ClickHouse are deliberately absent. They handle their own
 parameter syntax, so `File` returns their source unchanged and sqlc syntax is

internal/sql/preprocess/dialect.go

@@ -61,6 +61,12 @@ type Dialect struct {
 	// identifiers. It decides the case of a parameter named by a bare
 	// reference, e.g. sqlc.arg(FooBar).
 	FoldIdentifier bool
+
+	// NoSlice reports whether sqlc.slice is rejected. A dialect that numbers
+	// its parameters ($1) binds a list as one value, and the Go code that
+	// sqlc.slice generates only expands "?" placeholders, so it would bind
+	// the first element and return wrong rows without an error.
+	NoSlice bool
 }
 
 var dialects = map[config.Engine]Dialect{
@@ -88,6 +94,15 @@ var dialects = map[config.Engine]Dialect{
 		Backtick:  true,
 		Backslash: true,
 	},
+	// DuckDB binds with $1 like PostgreSQL and accepts $$ ... $$ strings. A
+	// bare ? is left to the engine, as it was before DuckDB had an entry.
+	config.EngineDuckDB: {
+		Style:        StyleDollar,
+		AtSign:       true,
+		DollarQuote:  true,
+		DollarNumber: true,
+		NoSlice:      true,
+	},
 	// ClickHouse binds with an unnumbered ?, like MySQL, and its identifiers
 	// keep their case.
 	config.EngineClickHouse: {

internal/sql/preprocess/scan.go

@@ -112,6 +112,13 @@ func (l *lexer) sqlcCall(start, afterSqlc int) (occurrence, int, bool) {
 	case "narg":
 		occ.kind = kindNarg
 	case "slice":
+		if l.d.NoSlice {
+			occ.err = &sqlerr.Error{
+				Message:  "sqlc.slice is not supported by this engine; bind a list parameter instead",
+				Location: start,
+			}
+			return occ, occ.end, true
+		}
 		occ.kind = kindSlice
 	case "embed":
 		occ.kind = kindEmbed