[python] fix TypedDict rendering for template-instantiated models by l0lawrence · Pull Request #11161 · microsoft/typespec

l0lawrence · 2026-07-02T22:16:12Z

Why

PR #10439 enabled TypedDict body-overload generation in the default dpg mode. In real Azure mgmt libraries (e.g. azure-mgmt-netapp), this produced dangling _types.CacheUpdate references that were absent from types.py, causing an AttributeError at import time.

Root cause

Template-instantiated models all share the template's crossLanguageDefinitionId. For example, every Azure.ResourceManager.Foundations.ResourceUpdateModel<T, P> instantiation (CacheUpdate, VolumeUpdate, ActiveDirectoryConfigUpdate, ...) carries clid = Azure.ResourceManager.Foundations.ResourceUpdateModel.

The typeddict_models dedup keyed the dpg-vs-copy pairing on that clid, so it treated genuinely distinct models as duplicates and skipped all but the first one. In netapp, ActiveDirectoryConfigUpdate was seen first, so CacheUpdate was dropped from types.py while still being referenced via _types.CacheUpdate.

Fix

Key the dpg-vs-copy pairing on the model name instead of crossLanguageDefinitionId. The typeddict copy is a shallow copy of the source, so it shares the source's name; distinct template instantiations have distinct names, and model names are unique within a types.py module.
Harden _find_existing_typeddict in preprocess to also match on name (same root cause, tightly coupled).

This keeps TypedDict generation on in dpg mode (intentional per #10439) and just corrects the rendering so referenced TypedDicts actually land in types.py.

pkg-pr-new · 2026-07-02T22:17:52Z

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npm i https://pkg.pr.new/@typespec/http-client-python@11161

commit: 2b469b6

github-actions · 2026-07-02T22:18:59Z

All changed packages have been documented.

✅ @typespec/http-client-python

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`@typespec/http-client-python` - fix ✏️

Fix dangling _types.X references when template-instantiated models (e.g. ResourceUpdateModel<Foo, FooProperties>) share a crossLanguageDefinitionId. The TypedDict deduplication now pairs each model with its own copy by name, so distinct models such as CacheUpdate and VolumeUpdate are all rendered in types.py.,> ,> Also stop emitting unused TypedDicts for response-only models in types.py. Output-only models already render as classes in models/ and are referenced via _models.X, so their TypedDict copies (e.g. GetResponse) were dead code. The set of TypedDicts (and discriminated-base union aliases) rendered in types.py is now the transitive closure of the request-body input models over their base classes, discriminated subtypes and property types. Input body overloads (including spread bodies whose usage lacks the Input flag) are still emitted, and any output-only model reachable from an input model — such as a discriminated subtype or an ARM SystemData property — is kept so no forward reference is left undefined. This fixes a NameError at import time when an output-only union alias (e.g. Dinosaur = Union[TRex]) referenced an excluded subtype, and a pyright reportUndefinedVariable error when an input model referenced an excluded property type (e.g. SystemData).

azure-sdk-automation · 2026-07-02T22:28:33Z

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…models sharing a cross-language id Template-instantiated models such as ResourceUpdateModel<Foo, FooProperties> all carry the template's crossLanguageDefinitionId, so the TypedDict dedup that keyed on it wrongly collapsed distinct models (e.g. CacheUpdate and VolumeUpdate) into one and dropped the rest from types.py, producing dangling _types.X refs. Key the dpg-vs-copy pairing on the model name instead, and harden the preprocess typeddict lookup to also match on name. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

l0lawrence · 2026-07-02T23:44:05Z

I dont think this is a complete solution because the other types of models -> typeddict conversions could fall into the same trap

l0lawrence · 2026-07-02T23:50:00Z

        """Models that should be rendered as TypedDicts (excluding discriminated bases which become unions).

-        When both a dpg model and its typeddict copy exist (same crossLanguageDefinitionId),
+        When both a dpg model and its typeddict copy exist for the same model,


bc crossLangDefId can apply to multiple models if they have the same base type but diff names? I feel like thats a weird case but it does seem like something that is existing in typespec today

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Spread (json) bodies keep the template clid but may be renamed to <Method>Request, so a clid-only lookup could reference the wrong sibling model's TypedDict. Add _find_spread_original which only reuses an original when the choice is unambiguous (name match, or a single clid candidate) and otherwise falls back to the json model itself. Add tests covering non-spread dpg reuse, list-element dpg copies, and spread single/name-match/ambiguous-renamed scenarios. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Response-only models (e.g. GetResponse) already render as classes in models/ and are referenced via _models.*, so emitting a TypedDict copy for them in types.py was dead code never referenced via _types.*. typeddict_models now keeps a model only when it is a typeddict copy (base=typeddict, always an input body overload), is_typed_dict_only (covers full typeddict mode incl. responses), or used as input. Spread request bodies are kept via the base check since tcgc marks their usage Json|Spread without the Input flag. Add is_usage_input helper and tests covering output-only exclusion, input/output inclusion, typeddict-mode inclusion, and the spread-copy (no Input flag) case. Verified across all azure + unbranded generated packages: no dangling _types.* references. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

An output-only discriminated base (e.g. Dinosaur = Union[TRex]) was emitted as a union alias in types.py while its subtype TRex was correctly excluded, causing NameError: name 'TRex' is not defined at import time. discriminated_base_models now applies the same input-only predicate as typeddict_models via a shared _renders_as_input_typeddict helper. typeddict_models additionally force-includes any subtype referenced by a rendered (input) discriminated base, so an input base's union alias never references an undefined name even if the subtype's own usage flags would exclude it. Add unit tests: output-only base excluded, input base included with subtypes, and input base force-including an output-only subtype. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Compute the models rendered in types.py as the reachability closure of the request-body input surface over base classes, discriminated subtypes and property types. This keeps output-only models that are referenced by an input model (e.g. an ARM `SystemData` property on `Resource`), fixing a pyright `reportUndefinedVariable` error, while still dropping response-only dead code. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Fixes Python TypedDict rendering/selection in models-mode=dpg when template-instantiated models share a crossLanguageDefinitionId, preventing missing _types.X definitions and import-time crashes in generated SDKs.

Changes:

Adjust TypedDict copy deduplication/matching to key on model name (not crossLanguageDefinitionId) for both preprocessing overload insertion and types.py rendering.
Restrict types.py TypedDict/union-alias emission to the transitive closure of request-body “input surface” models, preventing dead/invalid output-only definitions.
Add targeted unit tests covering shared-CLID template instantiations, spread bodies, and reachability (incl. container element types).

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/http-client-python/tests/unit/test_typeddict.py	Adds regression tests for shared-CLID models and input-surface reachability rules for `types.py`.
packages/http-client-python/tests/unit/test_typeddict_overloads.py	Adds tests ensuring overload preprocessing creates distinct TypedDict copies per model name (including list bodies and spread-body edge cases).
packages/http-client-python/generator/pygen/preprocess/init.py	Updates `_find_existing_typeddict` to also match by `name` and adds `_find_spread_original` to avoid ambiguous shared-CLID cross-references.
packages/http-client-python/generator/pygen/codegen/serializers/types_serializer.py	Switches TypedDict pairing to name-based dedup and introduces input-surface closure filtering for `types.py` emission.
packages/http-client-python/generator/pygen/codegen/models/model_type.py	Adds `is_usage_input` helper used by `types_serializer` filtering logic.
.chronus/changes/python-fix-typeddict-shared-clid-2026-6-2-0-0-0.md	Changelog entry documenting the fix and the new reachability-based emission behavior.

Memoize _types_file_model_names via functools.cached_property so the model-graph reachability walk runs once per TypesSerializer instead of on every access from typeddict_models and discriminated_base_models. self._models is set at construction and never mutated, so per-instance caching is safe and the generated output is unchanged. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

microsoft-github-policy-service Bot added the emitter:client:python Issue for the Python client emitter: @typespec/http-client-python label Jul 2, 2026

l0lawrence force-pushed the python-gate-typeddict-fix branch from 5436bbe to 316d3a2 Compare July 2, 2026 23:16

l0lawrence changed the title ~~[python] gate TypedDict body overloads behind models-mode typeddict~~ [python] fix TypedDict rendering for template-instantiated models sharing a cross-language id Jul 2, 2026

l0lawrence changed the title ~~[python] fix TypedDict rendering for template-instantiated models sharing a cross-language id~~ [python] fix TypedDict rendering for template-instantiated models Jul 2, 2026

l0lawrence commented Jul 2, 2026

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msyyc marked this pull request as ready for review July 3, 2026 02:49

msyyc requested review from ChenxiJiang333, catalinaperalta, iscai-msft, kashifkhan, lmazuel, msyyc, tadelesh and timotheeguerin as code owners July 3, 2026 02:49

msyyc and others added 2 commits July 3, 2026 10:56

fix(http-client-python): reword 'dedup' to satisfy cspell

4cd5332

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Merge branch 'main' into python-gate-typeddict-fix

eef6a19

github-actions Bot mentioned this pull request Jul 3, 2026

[typespec-python] Regenerate tests from microsoft/typespec PR #11161 Azure/azure-sdk-for-python#47826

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msyyc mentioned this pull request Jul 3, 2026

[typespec-python] Regenerate tests from microsoft/typespec PR #11161 (DO NOT MERGE) Azure/azure-sdk-for-python#47827

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msyyc and others added 4 commits July 3, 2026 11:22

msyyc requested a review from Copilot July 3, 2026 06:37

Copilot started reviewing on behalf of msyyc July 3, 2026 06:37 View session

Copilot AI reviewed Jul 3, 2026

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Comment thread packages/http-client-python/generator/pygen/codegen/serializers/types_serializer.py

msyyc approved these changes Jul 3, 2026

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msyyc enabled auto-merge July 3, 2026 08:00

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[python] fix TypedDict rendering for template-instantiated models#11161

[python] fix TypedDict rendering for template-instantiated models#11161
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