dtslint changes output type based on $ExpectType values

[marekdedic]

Hi,
I'm looking at commit 886607f and trying to get the tests to pass by modifying Line 379.

Currently I get the error:

ERROR: 380:1  expect  TypeScript@4.9 expected type to be:
  Page | Post
got:
  Page<"edit"> | Post<"edit">

however, if I change the expected value to be the returned value, I get

ERROR: 380:1  expect  TypeScript@4.9 expected type to be:
  Page<"edit"> | Post<"edit">
got:
  Page | Post

so it seems like dtslint can't decide whether it wants the type parameter ("edit" is actually the default value) or not.

[marekdedic]

I managed to track the issue down to

DefinitelyTyped-tools/packages/dtslint/src/rules/expectRule.ts

Lines 414 to 420 in 15d48f4

	const actual = type
	? checker.typeToString(type, /*enclosingDeclaration*/ undefined, ts.TypeFormatFlags.NoTruncation)
	: "";
	if (!expected.split(/\s*\|\|\s*/).some((s) => actual === s || matchReadonlyArray(actual, s))) {
	unmetExpectations.push({ node, expected, actual });
	}

So... it seems TypeScript itself is changing the type output based on the surroundings?

[marekdedic]

Possibly related:

• Discrepancy when typeToString when enclosingDeclaration is undefined vs defined. TypeScript#43988
• When test with dtslint, it shows a loop expect type. DefinitelyTyped/DefinitelyTyped#38888

[marekdedic]

Ok, I'm dumb, the 2 errors were on different TS versions.