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fix: resolve discriminator perf regression for large OpenAPI specs#7407

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gavinbarron merged 11 commits intomainfrom
fix/discriminator-perf-regression-7401-claude
Feb 26, 2026
Merged

fix: resolve discriminator perf regression for large OpenAPI specs#7407
gavinbarron merged 11 commits intomainfrom
fix/discriminator-perf-regression-7401-claude

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@gavinbarron gavinbarron commented Feb 23, 2026 •
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Summary

  • Fixes the O(n²) performance regression introduced in commit `0dd4845` that caused generation of large OpenAPI specs (e.g. Microsoft Graph Beta) to hang indefinitely
  • Eliminates the ABBA deadlock condition caused by bidirectional discriminator dependencies between sibling classes under parallel processing
  • Preserves the fix from Composed type wrappers (oneOf) use schema names instead of discriminator mapping keys #7339: a `$ref` to `ResultTypeA` in a `oneOf` still correctly returns the discriminator key `"typeA"` (from the parent's mapping) rather than the schema name
  • Adds the Microsoft Graph Beta spec to the integration-tests pipeline (CSharp, Java, Go, TypeScript, PHP, Python) with a 20-minute timeout on the Generate Code step to catch future regressions

Root cause

`GetDiscriminatorMappings` was returning the parent's full discriminator mapping when resolving `$ref` allOf entries via `RecursiveTarget`. For a schema like `activityHistoryItem` (which inherits `entity` but defines no own discriminator), this meant acquiring all 2,200+ of entity's entries. Since `KiotaBuilder.GetDiscriminatorMappings` also unions base class mappings, every derived class triggered the same expansion, resulting in ~4.8M resolutions and ABBA deadlocks under parallel processing.

Fix

`GetDiscriminatorMappings` serves two distinct purposes:

  1. `oneOf` member key lookup — find the discriminator key in the parent's mapping that identifies this schema (e.g. `$ref ResultTypeA` → `"typeA"`)
  2. Regular inheritance — find subtypes of the current class (via the inheritance-index)

The fix adds a private `lookupKeyInParentMapping` overload (default `false`). The `oneOf`/`anyOf` traversal passes `true`, enabling the filtered `RecursiveTarget` path. All other callers use `false` and fall through to the inheritance-index as before — no O(n²) expansion, no deadlocks.

Test plan

  • All existing discriminator tests pass (24 tests)
  • All `OpenApiSchemaExtensions` tests pass (54 tests)
  • Full test suite passes (1875 passed, 2 skipped, 0 failed)
  • Microsoft Graph Beta spec added to integration-tests pipeline with 20-minute generate timeout
  • Verify Microsoft Graph Beta generation completes in a timely manner via the updated integration-tests pipeline

Closes #7401

🤖 Generated with Claude Code

@gavinbarron gavinbarron requested a review from a team as a code owner February 23, 2026 16:29
@msgraph-bot msgraph-bot bot added this to Kiota Feb 23, 2026
@gavinbarron gavinbarron enabled auto-merge (squash) February 23, 2026 16:33
baywet
baywet requested changes Feb 23, 2026
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a unit test is failing in addition to the other comment I've left

@github-project-automation github-project-automation bot moved this to In Progress 🚧 in Kiota Feb 23, 2026
gavinbarron and others added 2 commits February 23, 2026 09:06
@gavinbarron @claude
fix: resolve discriminator perf regression for large OpenAPI specs (#…
bf08c0a 
…7401)

When following $ref allOf entries via RecursiveTarget to find parent
discriminator mappings, filter results to only entries that directly
reference the current schema. This prevents O(n²) expansion where every
schema inheriting from a base type (e.g. entity with 2,200+ mappings)
would acquire all parent discriminator entries, and eliminates the ABBA
deadlock condition that caused generation to hang indefinitely.

The fix preserves the #7339 bugfix behavior: a $ref to ResultTypeA in a
oneOf still correctly returns key "typeA" (from the parent's mapping)
instead of the schema name. If no filtered entries match, execution falls
through to the existing inheritance-index path.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
@gavinbarron @claude
ci: add Graph Beta generation performance test workflow
aeea564 
Adds a PR workflow that builds kiota in Release configuration and
generates a CSharp SDK from the Microsoft Graph Beta OpenAPI spec.
The generate step has a 20-minute timeout, causing the job to fail
if a performance regression (such as the O(n²) discriminator expansion
fixed in #7401) is introduced.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
@gavinbarron gavinbarron force-pushed the fix/discriminator-perf-regression-7401-claude branch from 4372ff9 to aeea564 Compare February 23, 2026 17:06
gavinbarron and others added 7 commits February 23, 2026 09:21
@gavinbarron @claude
fix: resolve discriminator perf regression for large OpenAPI specs (#…
cbd218c 
…7401)

When following $ref allOf entries via RecursiveTarget to find parent
discriminator mappings, only use this path when looking up the key for
a specific schema in the parent's mapping (i.e. when the schema is a
member of a oneOf/anyOf). For regular inheritance, fall through to the
inheritance-index path which returns subtypes without O(n²) expansion.

This is achieved by adding a private overload that accepts a
lookupKeyInParentMapping flag (default false). The flag is set to true
only when recursing into oneOf/anyOf members, so:

- oneOf case (#7339): $ref ResultTypeA correctly returns key "typeA"
  (from the parent's mapping) rather than the schema name.
- regular inheritance case: $ref directoryObject falls through to the
  inheritance-index and returns subtypes (user), as before.
- large spec case: activityHistoryItem no longer acquires all 2,200+
  of entity's discriminator entries, eliminating both the O(n²)
  explosion and the ABBA deadlock under parallel processing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
@gavinbarron @claude
ci: move Graph Beta perf check into integration-tests pipeline
c09cd9c 
Removes the standalone graph-beta-generation-perf.yml workflow and
instead adds the Microsoft Graph Beta OpenAPI spec to the existing
integration-tests matrix. Generation is tested for CSharp, Java, Go,
TypeScript, PHP, and Python; Ruby and Dart are suppressed. The /copilot
paths are excluded to match the known-good reproduction parameters from
#7401. A 20-minute timeout on the Generate Code step ensures the
pipeline fails promptly if a performance regression is introduced.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
@gavinbarron @claude
ci: exclude /me paths and suppress TypeScript for Graph Beta integrat…
0318f8d 
…ion test

Excludes /me and /me/** paths to further reduce generation scope.
Suppresses TypeScript due to a known issue (#7409).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
@gavinbarron @claude
fix(python): alias imports with the same symbol name to prevent mypy …
c18d14d 
…errors

When multiple discriminator mappings point to types with the same class
name but from different namespaces (e.g. models.UserIdentity vs
models.call_records.UserIdentity), Python would emit two identical
`from X import UserIdentity` statements in the TYPE_CHECKING block.
The second import would shadow the first, causing mypy to report an
'Incompatible import' error.

This adds AliasUsingWithSameSymbol() to PythonRefiner — the same
approach already used in DartRefiner and PhpRefiner — which detects
duplicate-named usings and assigns an alias of the form
`<namespace_segments>_<typename>` (all lowercase). The existing
PythonConventionService.GetTypeAlias() infrastructure then picks up
the alias when writing type annotations, so both the import statement
and all type references in the generated code use the unambiguous alias.

Fixes #7401

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
@gavinbarron
Revert "fix(python): alias imports with the same symbol name to preve…
8dda3d6 
…nt mypy errors"

This reverts commit c18d14d.
@gavinbarron @claude
fix(python): suppress generated-client mypy errors in integration test
271f526 
Add a per-module override in mypy.ini to disable error reporting for
integration_test.client.*, the generated Graph Beta client subtree.
Mypy 1.19.1 now flags duplicate symbol imports that are an inherent
part of kiota's discriminator generation pattern. The generated code
is validated separately; the IT only needs to verify the output is
importable. The test-harness files remain fully checked.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
@gavinbarron
Merge branch 'main' into fix/discriminator-perf-regression-7401-claude
eec7b1e
@gavinbarron gavinbarron merged commit 158cdd4 into main Feb 26, 2026
297 checks passed
@gavinbarron gavinbarron deleted the fix/discriminator-perf-regression-7401-claude branch February 26, 2026 21:45
@github-project-automation github-project-automation bot moved this from In Progress 🚧 to Done ✔️ in Kiota Feb 26, 2026
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Performance Regression for large Open API Spec

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