[SR-4288] Modifying object interface makes the compiler compiles every sources again

[swift-ci]

Previous ID	SR-4288
Radar	None
Original Reporter	dalu93 (JIRA User)
Type	Bug

Environment

Macbook Air Early 2015 (8gb RAM, Intel Core i7 2.2Ghz) w macOS Sierra
Xcode 8.2.1 (8C1002)

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, IncrementalBuild
Assignee	None
Priority	Medium

md5: dd88e1f47e62cd975b4086d6e749127c

Issue Description:

Hi,
I noticed that everytime I modify a class/struct/protocol public interface and not the compiler compiles again the whole project from beginning

For example, by just adding a character in a private variable's name triggers this issue.
I would like to give you more informations about it, but I'm not able to get this concrete informations anywhere. I'm just saying so because the compilation takes up to 5 mins everytime I touch these elements, while, by adding a simple print inside a method scope, builds in few seconds (maybe 30 seconds)

[belkadan]

I suspect this is expected behavior today. The compiler only has a very rough idea of what you changed, and so it has to be conservative about recompilation. There're definitely areas to improve here.

cc graydon (JIRA User)