Test :iter with MySQL and SQLite

An :iter query in the wrap_errors, emit_prepared_queries and sqlc_slice
cases for MySQL and SQLite, and a runtime test in the SQLite authors
example, covering the stdlib template against a live database.

queryCodeStdExec no longer starts with a newline when it rewrites a
query for sqlc.slice, which left a blank line inside :iter methods.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: sgielen

examples/authors/sqlite/db_test.go

@@ -5,6 +5,8 @@ package authors
 import (
 	"context"
 	"database/sql"
+	"errors"
+	"slices"
 	"testing"
 
 	"github.com/sqlc-dev/sqlc/internal/sqltest"
@@ -46,3 +48,66 @@ func TestAuthors(t *testing.T) {
 	}
 	t.Log(fetchedAuthor)
 }
+
+func TestIterAuthors(t *testing.T) {
+	sdb, cleanup := sqltest.SQLite(t, []string{"schema.sql"})
+	defer sdb.Close()
+	defer cleanup()
+
+	ctx := context.Background()
+	db := New(sdb)
+
+	for _, name := range []string{"Rob Pike", "Brian Kernighan", "Ken Thompson"} {
+		if _, err := db.CreateAuthor(ctx, CreateAuthorParams{Name: name}); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	// the query only runs once the iterator is ranged over
+	authors, ferr := db.IterAuthors(ctx)
+	if inUse := sdb.Stats().InUse; inUse != 0 {
+		t.Fatalf("%d connections in use before ranging, want 0", inUse)
+	}
+	var names []string
+	for author := range authors {
+		names = append(names, author.Name)
+	}
+	if err := ferr(); err != nil {
+		t.Fatal(err)
+	}
+	if want := []string{"Brian Kernighan", "Ken Thompson", "Rob Pike"}; !slices.Equal(names, want) {
+		t.Fatalf("got %v, want %v", names, want)
+	}
+
+	// the iterator is single-use: ranging over it again yields nothing and
+	// reports an error
+	for author := range authors {
+		t.Errorf("second range yielded %v", author)
+	}
+	if err := ferr(); err == nil {
+		t.Error("ranging twice reported no error")
+	}
+
+	// breaking out of the loop early releases the connection
+	authors, ferr = db.IterAuthors(ctx)
+	for range authors {
+		break
+	}
+	if err := ferr(); err != nil {
+		t.Fatal(err)
+	}
+	if inUse := sdb.Stats().InUse; inUse != 0 {
+		t.Errorf("%d connections in use after breaking out, want 0", inUse)
+	}
+
+	// a query that fails reports its error through the returned func
+	cctx, cancel := context.WithCancel(ctx)
+	cancel()
+	authors, ferr = db.IterAuthors(cctx)
+	for author := range authors {
+		t.Errorf("cancelled query yielded %v", author)
+	}
+	if err := ferr(); !errors.Is(err, context.Canceled) {
+		t.Errorf("got error %v, want context.Canceled", err)
+	}
+}

examples/authors/sqlite/query.sql

@@ -16,3 +16,7 @@ INSERT INTO authors (
 /* name: DeleteAuthor :exec */
 DELETE FROM authors
 WHERE id = ?;
+
+/* name: IterAuthors :iter */
+SELECT * FROM authors
+ORDER BY name;

examples/authors/sqlite/query.sql.go

@@ -164,7 +164,7 @@ func (q *Queries) {{.MethodName}}(ctx context.Context, {{ dbarg }} {{.Arg.Pair}}
 {{end}}
 
 {{define "queryCodeStdExec"}}
-    {{- if .Arg.HasSqlcSlices }}
+    {{- if .Arg.HasSqlcSlices -}}
         query := {{.ConstantName}}
         var queryParams []any
         {{- if .Arg.Struct }}

internal/codegen/golang/templates/stdlib/queryCode.tmpl

@@ -4,6 +4,9 @@ SELECT first_name, id, last_name FROM users WHERE id = sqlc.arg('target_id');
 /* name: ListUsers :many */
 SELECT first_name, last_name FROM users;
 
+/* name: IterUsers :iter */
+SELECT first_name, last_name FROM users;
+
 /* name: InsertNewUser :exec */
 INSERT INTO users (first_name, last_name) VALUES (?, ?);
 

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

@@ -3,6 +3,11 @@ SELECT name FROM foo
 WHERE name = sqlc.arg(slug)
   AND id IN (sqlc.slice(favourites));
 
+/* name: FuncParamIdentIter :iter */
+SELECT name FROM foo
+WHERE name = sqlc.arg(slug)
+  AND id IN (sqlc.slice(favourites));
+
 /* name: FuncParamString :many */
 SELECT name FROM foo
 WHERE name = sqlc.arg('slug')