Regression - default initializer of {} ruins type intersected with object

[DanielRosenwasser]

export interface BarProps {
    barProp?: string;
}

export interface FooProps {
    fooProps?: BarProps & object;
}

declare const foo: FooProps;
const { fooProps = {} } = foo;

fooProps.barProp;
//       ~~~~~~~
// error! Property 'barProp' does not exist on type '{}'.

[DanielRosenwasser]

@typescript-bot bisect good v4.7.3 bad main

[DanielRosenwasser]

Forgot to add strictNullChecks, but it shouldn't matter.

[typescript-bot]

The change between v4.7.3 and main occurred at 5aa0053.

[typescript-bot]

👋 Hi, I'm the Repro bot. I can help narrow down and track compiler bugs across releases! This comment reflects the current state of the repro in the issue body running against the nightly TypeScript.

---

Issue body code block by @DanielRosenwasser

‼️ Exception: Error - Did not find a source file for /home/runner/work/TypeScript/TypeScript/index.ts

Error: Did not find a source file for /home/runner/work/TypeScript/TypeScript/index.ts
    at Object.updateFile (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:6876:15)
    at _loop3 (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:1738:9)
    at twoslasher (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:1744:17)
    at /home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:777:44
    at runTwoslashRequests (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:744:56)
    at run (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:2169:75)
    at runMicrotasks (<anonymous>)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)

Historical Information

Version	Reproduction Outputs	Time
4.3.2, 4.4.2, 4.5.2, 4.6.2, 4.7.2	👍 Compiled	⚠️ Way slower

[fatcerberus]

The change between v4.7.3 and main occurred at 5aa0053.

That’s the second time it’s done that…

[weswigham]

methinks the twoslasher is broken with latest TS - the bug workbench does the same thing.

[DanielRosenwasser]

First repros on [email protected]

Merge list on May 27th is https://github.com/microsoft/TypeScript/pulls?q=is%3Apr+merged%3A2022-05-27+is%3Aclosed

Likely introduced by #49119

[ahejlsberg]

Yup, this is caused by #49119. It modified simpleTypeRelatedTo to consider {} a supertype of object in the strictSubtypeRelation. But really that should only be true for a non-fresh {}. In other words, we want fresh {} <: object <: {} in the strict subtype relation (i.e. fresh {} is a subtype of object which is a subtype of {}).

Also, for some reason we remove object literal freshness from the source side when relating to an intersection on the target side. Lost in history as to why, removing it doesn't change any baselines.

In combination, those two changes fix the issue. I will put up a PR.

[DanielRosenwasser]

In other words, we want {} <: object <: fresh {} in the strict subtype relation.

You mean the reverse, right?

fresh {} ≤ object ≤ {}

[ahejlsberg]

@DanielRosenwasser Argh, yes. I always read <: as is-supertype-of because it looks like an inheritance tree on its side. But you're right, it should be the other way around. I'll correct it.

[DanielRosenwasser]

GitHub now lets you do Mermaid diagrams. This should make it easier to read 😄

graph BT;
    emptyObject("{}");
    nonPrimitive("object");
    freshEmptyObject("fresh {}");
    freshEmptyObject --> nonPrimitive --> emptyObject;

Loading

[fatcerberus]

Mermaid diagrams

I've never heard this term before.

Also, on @ahejlsberg's note, I've personally always felt like the arrows in inheritance diagrams go in the wrong direction (cause <- effect is weird), so I find fresh {} ≤ object ≤ {} to actually be easier to read.

[RyanCavanaugh]

It's super weird because I want class arrows to go one way but subtyping arrows to go the other way. Human brains are a mess.