fix(codegen): no spurious lib/pq import for MySQL with sqlc.narg + sqlc.slice (#3783)

Problem
-------
A MySQL query that references the same named parameter as both a regular
argument (e.g. `sqlc.narg('x') IS NULL`) and a `sqlc.slice('x')`
expansion produced Go code that imports `github.com/lib/pq` even
though the import is unused — the runtime path expands the slice
in-place via the `/*SLICE:...*/?` placeholder and never calls
`pq.Array`.

Root cause
----------
The two references generate two `goColumn` entries with the same
name and type; only the slice variant carries the `IsSqlcSlice` flag.
The non-slice duplicate field still satisfies the `[]T && !sqlc.slice`
condition in `sliceScan()` inside `internal/codegen/golang/imports.go`,
which causes `lib/pq` to be added to the import set. The struct
itself is rendered through `UniqueFields` so only one field is
emitted, but the import-bookkeeping pass sees both.

Fix
---
In `sliceScan()`, collect the names of all fields carrying
`IsSqlcSlice` first, then skip any field whose name matches one of
those when deciding whether to require `lib/pq`. The duplicate is
already handled by the slice-expansion code path and does not need
`pq.Array`.

Tests
-----
- New endtoend fixture `mysql_slice_narg_no_pq_3783/mysql` mirrors
  the issue's repro; golden files confirm no `lib/pq` import in the
  generated code.
- Full `internal/endtoend` TestReplay suite passes.
- `go test ./internal/codegen/... ./internal/compiler/... ./internal/sql/...` clean.

What does NOT change
--------------------
- Postgres / pgx output is unaffected (the field-name filter only
  suppresses lib/pq when a sqlc.slice with the same name exists, and
  pgx never went through the lib/pq branch anyway).
- MySQL queries that use `sqlc.slice` alone, or a plain `[]T`
  argument, are unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: luongs3

internal/codegen/golang/imports.go

@@ -376,7 +376,24 @@ func (i *importer) queryImports(filename string) fileImports {
 			}
 			if !q.Arg.isEmpty() {
 				if q.Arg.IsStruct() {
+					// A single named parameter referenced as both a regular
+					// argument (e.g. `sqlc.narg(x) IS NULL`) and as a
+					// `sqlc.slice('x')` produces two struct fields sharing
+					// the same name and type, but only the slice variant
+					// carries the IsSqlcSlice flag. The non-slice duplicate
+					// must not be counted as a `[]T` arg requiring lib/pq,
+					// because the generated code expands the slice in-place
+					// via `/*SLICE:...*/?` and never calls pq.Array on it.
+					sqlcSliceNames := map[string]struct{}{}
 					for _, f := range q.Arg.Struct.Fields {
+						if f.HasSqlcSlice() {
+							sqlcSliceNames[f.Name] = struct{}{}
+						}
+					}
+					for _, f := range q.Arg.Struct.Fields {
+						if _, ok := sqlcSliceNames[f.Name]; ok {
+							continue
+						}
 						if strings.HasPrefix(f.Type, "[]") && f.Type != "[]byte" && !f.HasSqlcSlice() {
 							return true
 						}

internal/endtoend/testdata/mysql_slice_narg_no_pq_3783/mysql/go/db.go

@@ -0,0 +1,10 @@
+-- https://github.com/sqlc-dev/sqlc/issues/3783
+-- name: CausesPgToBeImported :many
+SELECT
+    id AS author_id,
+    name AS author_name,
+    bio AS author_bio
+FROM
+    authors
+WHERE
+    (sqlc.narg('author_ids') IS NULL OR id IN (sqlc.slice('author_ids')));

internal/endtoend/testdata/mysql_slice_narg_no_pq_3783/mysql/go/models.go

@@ -0,0 +1,5 @@
+CREATE TABLE authors (
+  id   BIGINT  NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  name text    NOT NULL,
+  bio  text
+);

internal/endtoend/testdata/mysql_slice_narg_no_pq_3783/mysql/go/query.sql.go

@@ -0,0 +1,12 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "engine": "mysql",
+      "path": "go",
+      "name": "querytest",
+      "schema": "schema.sql",
+      "queries": "query.sql"
+    }
+  ]
+}