[SR-305] Simple, legit literal takes exponentially growing compile time.

[dduan]

Previous ID	SR-305
Radar	None
Original Reporter	@dduan
Type	Bug
Status	Resolved
Resolution	Done

Attachment: Download

Additional Detail from JIRA

Votes	6
Component/s	Compiler
Labels	Bug, TypeChecker
Assignee	@jopamer
Priority	Medium

md5: 671f0ac06627b6519c1b4f035d41c57c

Issue Description:

Run swiftc -dump-ast on this file, the compilation will never finish. Removing values gradually from the array and you'll notice that the shorter the expression, the less time it takes.

long.swift

[belkadan]

Dictionary of dictionaries of dictionaries of string-string mappings.

[modocache]

This appears to be a pain point. From https://spin.atomicobject.com/2016/04/26/swift-long-compile-time/:

"Copy the above code into Xcode, press “build,” and go get a coffee. Come back in 12 hours. Yes, the above dictionary literal code takes at least 12 hours to compile. The compilation time grows roughly exponentially with each employee that is added."

A commenter on that article proposes speeding up the compilation by adding a type annotation:

let myCompany: [String: [String: [String: String]]]

Is this the best workaround right now?

[belkadan]

Type annotations are always the first thing to reach for when an expression is taking a long time, yes.

[jopamer]

Fixed in master with 2cdd7d6.