Weird heap overflow when compiling a single line of code with recursive type definition.

[Veetaha]

TypeScript Version: typescript@3.4.2, typescript@3.5.0-dev.20190409

Search Terms:

• Heap overflow

Code

type Foo<T> = Extract<{[i in keyof T]: Foo<T[i]>; }[0], 0>;

Expected behavior:
Should print an error for indexing object literal with 0 or using circular references.
Or at least the same behavior as in v3.3.4000:

Output when compiled with `typescript@3.3.4000`

Actual behavior:

NodeJS standard heap crash report: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory

Details

Playground from typescriptlang.com produces in-browser heap memory allocation failure:

Details

Playground Link:

Klick me if you are not afraid of crashing your browser's heap

Related Issues:

• typesafe-joi heap overflow JavaScript heap out of memory when compiling typesafe-joi on v3.4.x #30794
• extremely slow compilation Extremely slow compilation; resolving generics? #30781
• performance degradation since typescript@3.4.1 3.4.1 tsc works 20! times slower than 3.3.4 #30663
• weird stack overflow issue Weird stack overflow when compiling 4-line code with function, untyped variable, operator and spread operator within cycle #30804
• stackoverflow question about heap overflow

[hjkcai]

Great! I think this will be the minimal reproduction of this issue. Thanks a lot!

[ahejlsberg]

The example above produces the expected errors with #30769.

t.ts:1:6 - error TS2456: Type alias 'Foo' circularly references itself.

1 type Foo<T> = Extract<{[i in keyof T]: Foo<T[i]>; }[0], 0>;
       ~~~

t.ts:1:23 - error TS2536: Type '0' cannot be used to index type '{ [i in keyof T]: any; }'.

1 type Foo<T> = Extract<{[i in keyof T]: Foo<T[i]>; }[0], 0>;
                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

t.ts:1:40 - error TS2315: Type 'Foo' is not generic.

1 type Foo<T> = Extract<{[i in keyof T]: Foo<T[i]>; }[0], 0>;
                                         ~~~~~~~~~


Found 3 errors.

[andrewbranch]

Confirmed that this doesn't crash in 3.5.0-rc, although the only error I get is

main.ts:1:23 - error TS2536: Type '0' cannot be used to index type '{ [i in keyof T]: Extract<{ [i in keyof T[i]]: Extract<{ [i in keyof T[i][i]]: Extract<{ [i in keyof T[i][i][i]]: Extract<{ [i in keyof T[i][i][i][i]]: Extract<{ [i in keyof T[i][i][i][i][i]]: Extract<{ [i in keyof T[i][i][i][i][i][i]]: Extract<{ [i in keyof T[i][i][i][i][i][i][i]]: Extract<{ [i in keyof T[i][i][i][i][i][i][i][i]]: Extract<{ [i in keyof T[i][i][i][i][i][i][i][i][i]]: Extract<{ [i in keyof T[i][i][i][i][i][i][i][i][i][i]]: Extract<any[0], 0>; }[0], 0>; }[0], 0>; }[0], 0>; }[0], 0>; }[0], 0>; }[0], 0>; }[0], 0>; }[0], 0>; }[0], 0>; }[0], 0>; }'.

1 type Foo = Extract<{[i in keyof T]: Foo<T[i]>; }[0], 0>;

🤔

[andrewbranch]

Talked to @weswigham and this is probably caused by #31354. I think the new output here is not super desirable, but it's not related to this issue per se. If there are new real-world issues with this code or other conditional types in the RC, a new issue is welcomed.