Check objects and call arguments as Jinja2 does (0197, 0206)

[rmorozov]

Requested by Ruslan · project thread

Before: cycler(1, 2)|truncate rendered empty. namespace(a=1)|urlencode gave a=1. {% set a, b = {'x': 1, 'y': 2} %} took the items named a and b, so both were empty. A number of calls that Python rejects also rendered: range(stop=2), ['a']|map('upper', 1), ns|attr('a', 'b'), ns|attr(1), joiner('a')('x'), lipsum(namespace()) and 1 is eq(b=1).

After: each of these behaves as in Jinja2 3.1.6. The tuple assignment unpacks the dict's keys (xy), and every other call raises the TypeError Python raises.

The changes:

• truncate on a value that is not a string follows do_truncate. A value with no len() raises (None, a bool, a number, an object). A short list or dict comes back as itself. A long one fails where Python's string code fails. end must have a len(), and an undefined checks length >= len(end) too.
• urlencode quotes the repr of an object such as namespace().
• Tuple assignment from a dict unpacks its keys. A host object (a reflected struct or another GenericMap) keeps the old by-name extension, because Python could not unpack it at all.
• range rejects keyword arguments.
• lipsum checks that n is an integer, and checks min and max when it makes a paragraph.
• The objects' methods reject arguments: joiner's call and cycler's next() and reset().
• attr takes one positional argument, and it must be a string. default= stays a keyword-only Jinja2C++ extension.
• map reports the named filter's argument error at the first item.
• The comparison tests (eq, lt, …) reject keyword arguments.

Deliberate divergences:

• tests.select_unread_extra_arg is now a deliberate divergence under 0101. select stays eager, which is the same model as filters.select_single_pass.
• range() with no arguments still renders empty, as before.

Filed 0212 for what 0197 could not reach:

• An object used as a dict key. Jinja2 accepts it, but the 0197 brief expected a TypeError. It is pinned by the corpus case globals.object_dict_key.
• An object passed through a user callable.
• JSON-bound objects, which still unpack by name. This needs a public-API flag to tell them apart from reflected structs.

How: the corpus lines for 0197 and 0206 are deleted from test/parity/divergences/. New corpus cases cover each behaviour that had none. Unit tests that encoded the old behaviour were updated:

• In forloop_test.cpp, the range keyword rows are gone.
• SetTest.Tuple1AssignmentTest now expects the keys.
• A new reflected-struct case pins the by-name extension.

Roles: verifier (1 round, which found 1 blocking issue: a missing include flagged by clang-tidy, fixed). Its non-blocking findings were fixed here (truncate end/undefined, lipsum(0)) or filed in 0212. scripts/preflight.sh --perf is clean; the worst benchmark moved +1.58% (Render/strings). Red pushes: none yet.

---

Generated by Claude Code