sql/catalog: Fix comparison of pg_catalog types

internal/endtoend/testdata/ddl_create_func_exists/query.sql

@@ -0,0 +1,5 @@
+CREATE FUNCTION f(x TIMESTAMPTZ) RETURNS void AS '' LANGUAGE sql;
+CREATE FUNCTION f(x timestamp with time zone) RETURNS void AS '' LANGUAGE sql;
+
+-- name: F :one
+SELECT f(1);

internal/endtoend/testdata/ddl_create_func_exists/sqlc.json

@@ -0,0 +1,11 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "name": "querytest",
+      "schema": "query.sql",
+      "queries": "query.sql"
+    }
+  ]
+}

internal/endtoend/testdata/ddl_create_func_exists/stderr.txt

@@ -0,0 +1,2 @@
+# package querytest
+query.sql:1:1: relation "f" already exists

internal/sql/catalog/catalog.go

@@ -92,7 +92,17 @@ func sameType(a, b *ast.TypeName) bool {
 	if a.Catalog != b.Catalog {
 		return false
 	}
-	if a.Schema != b.Schema {
+	// The pg_catalog schema is searched by default, so take that into
+	// account when comparing schemas
+	aSchema := a.Schema
+	bSchema := b.Schema
+	if aSchema == "pg_catalog" {
+		aSchema = ""
+	}
+	if bSchema == "pg_catalog" {
+		bSchema = ""
+	}
+	if aSchema != bSchema {
 		return false
 	}
 	if a.Name != b.Name {