Massive slowdown in compiling complicated union types

[Arnavion]

This is the same code as what originally prompted #2997

While it isn't crashing because of infinite loops any more, it has become very slow with 1.7. If I pause it in the debugger I see the following stack repeating many times.

inferFromTypes [tsc.js] Line 15334  JavaScript
inferFromTypes [tsc.js] Line 15314  JavaScript
inferFromTypes [tsc.js] Line 15301  JavaScript
inferFromProperties [tsc.js] Line 15350 JavaScript
inferFromTypes [tsc.js] Line 15334  JavaScript
inferFromTypes [tsc.js] Line 15314  JavaScript
inferFromTypes [tsc.js] Line 15301  JavaScript
inferFromIndexTypes [tsc.js] Line 15380 JavaScript
inferFromTypes [tsc.js] Line 15337  JavaScript
inferFromProperties [tsc.js] Line 15350 JavaScript

Reduced test case:

class Module {
    public members: { [name: string]: FFunction | Property };
}

class Namespace {
    public members: { [name: string]: Class | Enum };
}

class Class {
    public parent: Module | Namespace;

    public members: { [name: string]: Property | FFunction };
}

class Interface {
    public members: { [name: string]: Property | FFunction };
}

class FFunction {
    public parent: Module | Namespace | Class | Interface; // (1)
}

class Property {
    public parent: Module | Namespace | Class | Interface; // (2)
}

class Enum {
    public parent: Module | Namespace;

    public members: EnumMember[];
}

class EnumMember {
    public parent: Enum;
}

var members: (Property | FFunction)[];
members.map(member => "");

Compile with tsc foo.ts on node 4.2.2 x64 on Windows 7.

This takes ~18s on my machine. If I remove Module from the union type at (1), it drops to ~12s. Removing Module at (2) drops it to ~6s. And so on.

The original code is at https://github.com/Arnavion/libjass/blob/82f3706/build/typescript/ast.ts which has a much more complicated forest of types. It's been compiling for 5 minutes now, whereas it took ~2s with 1.6

[vladima]

@Arnavion can you give a try to typescript@next. Seems that this issue is already fixed in master. I can confirm that it takes 17.50 s on my machine to compile your sample using release-1.7, however on master it takes only 0.71 s

[Arnavion]

Yes, looks like it. The original code also takes ~2s with next, same as 1.6.

[Arnavion]

Can the fix be backported to 1.7 or do I skip it and wait for 1.8?

[mhegazy]

depends on the fix. @vladima do you know what is going on?

[vladima]

yes: #5738. If source and target types are unions or intersections then removing matching constituents from source and target sides significantly reduces amount of types that participate in type inference. I think it should be safe to backport this fix to 1.7

[Arnavion]

Yes, cherry-picking that PR onto 1.7 fixes the issue (and introduces #5861 but that's a minor annoyance in comparison).

[mhegazy]

@Arnavion is there a chance you can move to typescript@next directly?

[Arnavion]

If you're asking because you don't want to backport it, that's fine. I have no problem staying with 1.6 until 1.8 is released. :)

[mhegazy]

I am asking to figure out the logistics, porting it and publishing an npm is easy, but we will need to publish a VS 2012, VS 2015, and sublime text plugin updates and that all adds up.