[dexhunter]

TL;DR

• Lower the peak memory of input_is_nested_too_deeply, the depth check for variable values.
• Keep one stack frame per nesting level and do not push one tuple per list item.
• tracemalloc peak for a [Int] variable of 50,000 ints: 4,091,392 bytes -> 818,981 bytes, 80.0% less.
• Native tests: PYTHONPATH=src python3 -m pytest tests/execution/test_variables.py -q passed 106 tests.

Refs #317

What & Why

Before, the check pushed one (item, type, depth) tuple per list item onto its stack before it popped any.
The memory for the check grew with the width of the list, about 70 bytes per item.

Now each stack frame holds one nesting level: the values, their type, the depth, and the next index.
The check also stops the walk of a level when the item type is not a list or an input object.
Such items cannot nest, so one depth check covers the full level.

The output stays identical because the check still visits each followed value at the same depth.
Empty lists still add no depth, and values under scalars are still not followed.

Validation

Peak traced memory (tracemalloc) and best time of one call to the check:

Situation	Before	After	Change
[Int], 50,000 ints	3,516,880 bytes, 11.50 ms	112 bytes, 0.0005 ms	memory no longer grows with the list
[Int], 10,000 ints	597,680 bytes, 2.16 ms	112 bytes, 0.0005 ms	memory no longer grows with the list
[[Int]], 500 lists of 100 ints	5,936 bytes, 10.58 ms	176 bytes, 0.23 ms	about 46x less time
[Point], 5,000 input objects	234,608 bytes, 8.59 ms	712 bytes, 7.25 ms	16% less time
Int, one value	128 bytes, 0.0003 ms	88 bytes, 0.0003 ms	no measurable change in time

The last row shows a case where the change does not help, and it shows no slowdown.
The number in the TL;DR is for the full get_variable_values call, so it includes the coerced result.
Measured on CPython 3.12.13, Linux x86-64, AMD EPYC 9R14, on one isolated core.

Script for the first row; run it on the base commit and on this change:

import tracemalloc
from graphql import GraphQLInt, GraphQLList
from graphql.execution.values import input_is_nested_too_deeply

value = list(range(50_000))
tracemalloc.start()
input_is_nested_too_deeply(value, GraphQLList(GraphQLInt))
print(tracemalloc.get_traced_memory()[1])

The complete suite also passed with PYTHONPATH=src python3 -m pytest tests -q: 3,821 passed, 18 skipped.
ruff check, ruff format --check (ruff 0.17.4) and mypy (2.4.1) passed for src/graphql/execution/values.py.

Why this is safe and easy to maintain

The change is small and easy to read: 13 added lines in one private function, with no new imports.
The function keeps its loop, its explicit stack, and its signature.
Behaviour is unchanged, and the returned bool is the same for every value and type.
The tests in tests/execution/test_variables.py cover the depth limit for lists, input objects, and custom scalars.

Scope

This changes Python bookkeeping in a private helper only.
It adds no feature and does not change GraphQL behavior or the public API.

AI assistance

This PR was prepared with AI assistance from Aiden. Candidates were tracked with Weco Observe.

Weco share link: https://dashboard.weco.ai/share/yE6YtGpMB4NV3RCoYfCM3tHnAk6srhv_

[codspeed]

Merging this PR will not alter performance

✅ 20 untouched benchmarks

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_{Comparing dexhunter:perf/nested-input-depth-check-memory (0259ce7) with main (1d505c1)}