id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
7548	GHC API dependency analysis is broken	MikolajKonarski		"Sometimes, when a module fails to compile, GHC API invalidates other modules that do not depend on it (the attached example shows that) and sometimes the opposite --- it does not invalidate modules it should (I haven't created a standalone example with that so far). The problem is deterministic, but depends on the order in which targets are added using addSingle.

Generally, it seems if module B imports A, it correctly assumes A does not depend on B, but if B does not import A, it sometimes assumes A must depend on B, even if neither mentions the other. See comments in the example.

To reproduce, compile the example with

ghc --make typecheck-dir.hs -package ghc-7.4.2

create directory ./tmp and run typecheck-dir. You should see that module XXX is needlessly recompiled."	bug	closed	highest	7.8.1	GHC API	7.4.2	duplicate			Linux	x86_64 (amd64)	None/Unknown	Unknown