Fix mypy arg-type errors in generated discriminated union encoders#175
Merged
darshkpatel merged 1 commit intomainfrom Mar 5, 2026
Merged
Fix mypy arg-type errors in generated discriminated union encoders#175darshkpatel merged 1 commit intomainfrom
darshkpatel merged 1 commit intomainfrom
Conversation
The codegen for discriminated union TypedDict encoders generates a ternary chain where mypy can't narrow the union type through key-based conditions. Instead of suppressing with `# type: ignore[arg-type]`, use `cast()` to explicitly narrow the type to the correct variant after the discriminator check. This preserves type safety in the generated code. Affects both the single-variant and multi-variant discriminator code paths.
ef9a192 to
8c0a0f3
Compare
jackyzha0
approved these changes
Mar 5, 2026
darshkpatel
added a commit
that referenced
this pull request
Mar 5, 2026
Why === Follow-up to #175. The discriminator field in a discriminated union may be `NotRequired` in the TypedDict. Direct key access (`x["shapeType"]`) triggers pyright's `reportTypedDictNotRequiredAccess` error. This broke the pid2 codegen CI when the scribe schema added discriminated union variants where the discriminator field is optional. What changed ============ Use `x.get("key")` instead of `x["key"]` for discriminator checks in the generated ternary chain. This is safe because a missing key returns `None`, which won't match any discriminator value and falls through to the next branch. Test plan ========= - All 64 tests pass - Updated snapshot for `test_unknown_enum` - Tested end-to-end against the pid2 schema from ai-infra — codegen, mypy, and pyright all pass ~ written by Zerg 👾
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Why
The codegen for discriminated union TypedDict encoders produces ternary chains like:
mypy can't narrow union types through these ternary conditions, so it flags every encoder call as receiving the wrong type (
arg-type).This broke the pid2 codegen CI when new discriminated union variants were added to a schema.
What changed
Use
cast()to explicitly narrow the type to the correct variant after the discriminator check, instead of suppressing with# type: ignore[arg-type]. This preserves type safety in the generated code.Before:
After:
Affects both the single-variant and multi-variant discriminator code paths.
Test plan
CI