fix(compiler): Don't crash on WHERE x IN (... UNION ...)

fixes sqlc-dev#2139

internal/compiler/find_params.go

@@ -195,7 +195,7 @@ func (p paramSearch) Visit(node ast.Node) astutils.Visitor {
 		if n.Sel == nil {
 			p.parent = node
 		} else {
-			if sel, ok := n.Sel.(*ast.SelectStmt); ok && sel.FromClause != nil {
+			if sel, ok := n.Sel.(*ast.SelectStmt); ok && sel.FromClause != nil && len(sel.FromClause.Items) > 0 {
 				from := sel.FromClause
 				if schema, ok := from.Items[0].(*ast.RangeVar); ok && schema != nil {
 					p.rangeVar = &ast.RangeVar{

internal/endtoend/testdata/in_union/mysql/query.sql

@@ -0,0 +1,3 @@
+-- name: GetAuthors :many
+SELECT * FROM authors
+WHERE author_id IN (SELECT author_id FROM book1 UNION SELECT author_id FROM book2);

internal/endtoend/testdata/in_union/mysql/schema.sql

@@ -0,0 +1,15 @@
+CREATE TABLE authors (
+  id   int PRIMARY KEY,
+  name text      NOT NULL,
+  bio  text
+);
+CREATE TABLE book1 (
+  author_id  int PRIMARY KEY,
+  name text,
+  FOREIGN KEY (`author_id`) REFERENCES `authors` (`id`) ON DELETE CASCADE
+);
+CREATE TABLE book2 (
+  author_id  int PRIMARY KEY,
+  name text,
+  FOREIGN KEY (`author_id`) REFERENCES `authors` (`id`) ON DELETE CASCADE
+);

internal/endtoend/testdata/in_union/mysql/sqlc.json

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