fix(client): restore OmitOpts default type to improve type-checking performance

[nfl1ryxditimo12]

Fixes #29011

Problem

After upgrading from Prisma 6 to 7, type checking on our production codebase (406 models, ~9,300-line schema) became effectively unusable — tsc --noEmit ran for over 2 minutes and tsgo timed out at 3 minutes, whereas it completed in ~9 seconds on v6.

I traced this down to a single line change.

Root Cause

In #28375, the default value of the OmitOpts generic parameter on the PrismaClient interface was changed from Prisma.PrismaClientOptions['omit'] to undefined:

 export interface PrismaClient<
   in LogOpts extends Prisma.LogLevel = never,
-  in out OmitOpts extends Prisma.PrismaClientOptions['omit'] = Prisma.PrismaClientOptions['omit'],
+  in out OmitOpts extends Prisma.PrismaClientOptions['omit'] = undefined,
   in out ExtArgs extends runtime.Types.Extensions.InternalArgs = runtime.Types.Extensions.DefaultArgs
 > {

This reverts the optimization from #27777 (ORM-850). The change looks unintentional — #28375 was focused on removing the library engine and doesn't mention any reason for touching the OmitOpts default.

Why this causes the regression

When OmitOpts defaults to undefined, every model delegate gets instantiated with { omit: undefined }. Since undefined is structurally distinct from the constraint type (GlobalOmitConfig | undefined), TypeScript can't reuse cached type instantiations — it re-evaluates the full generic chain for every model x every operation.

When the default matches the constraint (= Prisma.PrismaClientOptions['omit']), TypeScript can short-circuit the structural comparison and reuse a single cached instantiation. This is exactly how #27777 was designed to work.

Benchmark

406 models, ~9,300-line schema. Using tsgo --extendedDiagnostics:

Metric	= undefined (current)	= PrismaClientOptions['omit'] (this fix)	Improvement
Type Instantiations	32,823,262	2,650,891	12.4x
Types	6,385,830	1,162,723	5.5x
Memory	4,610 MB	2,193 MB	2.1x
Check time	16.97s	2.47s	6.9x

Full project type check (pnpm check:type):

Tool	Before	After
tsgo	>3min (timeout)	7.7s
tsc v5.9.2	OOM / >2min	9.0s

I can't share the production schema (proprietary), but the numbers in #29011 from other reporters are consistent with what I'm seeing — ~30M instantiations on v7 vs ~8M on v6.

Changes

One-line fix in packages/client-generator-ts/src/TSClient/PrismaClient.ts — restores the original default from #27777.

Note that ClientFile.ts already uses Prisma.PrismaClientOptions['omit'] as the default for the public-facing export type, so this just aligns the internal interface with it.

Type safety

PrismaClientOptions['omit'] resolves to GlobalOmitConfig | undefined (since omit is optional), which is a superset of undefined — so this is not a breaking change. The constructor's OmitOpts default is also unaffected. No runtime behavior changes.

[coderabbitai]

Walkthrough

The PrismaClient interface generic parameter OmitOpts default value is changed from undefined to Prisma.PrismaClientOptions['omit']. This updates the inferred type when PrismaClient is instantiated without an explicit generic argument.

Changes

PrismaClient Generic Parameter Update

Layer / File(s)	Summary
PrismaClient OmitOpts generic default packages/client-generator-ts/src/TSClient/PrismaClient.ts	The OmitOpts generic parameter default is changed from undefined to Prisma.PrismaClientOptions['omit'], aligning the default constraint with the actual type constraint bound.

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🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description is directly related to the changeset, providing detailed context about the performance regression, root cause analysis, and benchmarks supporting the one-line fix.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title accurately describes the main change: restoring the OmitOpts default type parameter to improve type-checking performance in the client.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

✨ Simplify code

• Create PR with simplified code

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[aqrln]

Thanks so much, this looks good and works well. CI failures are unrelated, I'll fix them separately.

[clemens]

@aqrln Any plans on a 7.8.1/7.9.0 release soon(ish)? I was so used to your bi-weekly release cycles that 2 months since the last release now feel like an eternity…

[aqrln]

@clemens yes, we're planning a release this week.

[aqrln]

@clemens apologies for the unplanned delay, release is still coming soon

[SagnikPradhanPearSuite]

Hey @aqrln, do we have any timeline for when 7.9.0 will be released? We've been using the dev-13 version locally to improve our editors experience at work, and we're just waiting for the stable release so the rest of the team can start using it as well.

Thanks

[StefanWerW]

We are also waiting for the release. We are patching prisma locally, and is not the best workflow. This PR is super important for large schema. Can we not have this as a quick patch 7.8.1?