Use of intersection type leads to extremely slow typecheck times about typescript HOT 9 OPEN

@xixixao Thanks. With npx tsc -diagnostics I see the following:

Files:              289
Lines:            89160
Identifiers:      81591
Symbols:         214861
Types:           207767
Instantiations: 8903666
Memory used:    314029K
I/O read:         0.11s
I/O write:        0.00s
Parse time:       0.53s
Bind time:        0.12s
Check time:      14.37s
Emit time:        0.00s
Total time:      15.03s

The number that catches my eye here is the ~10M type instantiations. That is a very high number, indicative of some expensive type operations in the code base.

Unfortunately, when I compile the code base with the nightly build of the compiler (or the 5.5 beta release) I see a long list of type check errors (but not the long compile times), so I can't really debug the issue further. Looks to me like a conditional type is making a different choice with 5.5, which subsequently causes a lot of tests to error.

If you can update your repo to reproduce the issue with 5.5 beta or the nightly builds I can try to look further.

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A subtype of B
X' = X<A, C>
X'' = X<B, C>
implied that X' subtype of X''
even when X<T, U> = T & U

This is not a valid assumption for arbitrary X. For example, T might be contravariant, or X might even be a conditional type in which case the resulting type relationship is entirely arbitrary.

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It's hard to diagnose an issue without a specific example. Ideally one that fits in the playground, but if not, a repo that can be easily cloned.

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@ahejlsberg appreciate you having a look! This should do the trick in a few seconds:

git clone https://github.com/xixixao/convex-ents --depth 2 -b edgebitfaster repro-convex-ents
cd repro-convex-ents
npm i
cd test
npm i
npx tsc

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@ahejlsberg that looks to be caused by a potential bug in 5.5. I can't again get it to simplify, as it doesn't repro inside an individual module. But the main issue is in setup.testing.ts:

This is caused by EntDefinition not being accepted as a subtype of TableDefinition (which comes from another npm package, and if I inline it the issue goes away):

You can replace setup.testing.ts with:

import {
  TableDefinition,
} from "convex/server";
import { EntDefinition } from "../../src";

const x: EntDefinition = null as any;

function foo(t: TableDefinition) {

}

foo(x);

And you will see the error:

I don't know how to fix this error. TableDefinition is defined as a class, exported as a type. EntDefinition is right now defined as an interface extending TableDefinition. If change it to declare class the error stays the same.

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Looks like you have two competing declarations of TableDefinition with the following paths (on my machine):

C:\tc\repro-convex-ents\test\node_modules\convex\src\server\schema.ts
C:\tc\repro-convex-ents\src\schema.ts

The compiler is pointing this out. We've made some fixes to module resolution in 5.5 so likely that's the cause. I would trust that 5.5 is getting it right, so you probably want to look into that.

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@ahejlsberg So that's because of my funky importing from within test from the parent project, which 5.5 resolution seems to choke on (since I have the dependency installed twice). So fixed that via linking but then the issue no longer repros inside the repo.

But I can still repro it in a separate repo (set up with TS5.5 and the "broken" version of the lib):

git clone https://github.com/xixixao/saas-starter --depth 2 -b repro-ts-issue repro-convex-saas
cd repro-convex-saas
npm i -f
npx tsc -diagnostics

Gives:

Files:              1200
Lines:            197780
Identifiers:      208367
Symbols:          471886
Types:            657241
Instantiations: 17862935
Memory used:     808594K
I/O read:          0.04s
I/O write:         0.00s
Parse time:        0.69s
Bind time:         0.19s
Check time:       13.88s
Emit time:         0.02s
Total time:       14.77s

So back to the high instantiation count.

And from the trace I can see that it's the EntWriter < Ent typecheck in several places that causes this.

The only other thing I noticed is that TS caches the results in tsconfig.tsbuildinfo so it needs to be deleted to observe the full typecheck.

The library source code is on branch stillslowinstarter (vs the much faster version on the parent commit), the diff between them is:

--- a/src/functions.ts
+++ b/src/functions.ts
@@ -2375,7 +2375,15 @@ class PromiseEntWriterImpl<
 declare class EntWriterInstance<
   EntsDataModel extends GenericEntsDataModel,
   Table extends TableNamesInDataModel<EntsDataModel>,
-> extends EntInstance<EntsDataModel, Table> {
+> {
+  edge<Edge extends keyof EntsDataModel[Table]["edges"]>(
+    edge: Edge,
+  ): PromiseEdgeWriter<EntsDataModel, Table, Edge>;
+  edgeX<Edge extends keyof EntsDataModel[Table]["edges"]>(
+    edge: Edge,
+  ): PromiseEdgeWriterOrThrow<EntsDataModel, Table, Edge>;
+  doc(): DocumentByName<EntsDataModel, Table>;
+

(leaving the extends in doesn't help, TS still goes and checks that the edge and edgeX are compatible with the parent class)

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So fixed that via linking but then the issue no longer repros inside the repo.

That may indeed be the fix. I have a hunch your issue is caused by excessive work resulting from structural comparisons of very similar (if not structurally identical) types. That can happen when you have multiple copies of the same library in a single compilation.

But I can still repro it in a separate repo (set up with TS5.5 and the "broken" version of the lib)

What is it that is "broken" here? If it is because you have multiple copies of the same types (and thus excessive work from structural comparisons), then I don't think there's much we can do.

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@ahejlsberg no, I don't I have multiple copies of the same library in the second repro I shared. There's a single flat node_modules with only one copy of convex and convex-ents.

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