GHC recompiles unchanged hs-boot files

A.hs:

module A where

import B

f = someError

A.hs-boot:

module A where

B.hs:

module B where

import {-# SOURCE #-} A

$ ghc-7.10.3 --make A.hs
[1 of 3] Compiling A[boot]          ( A.hs-boot, A.o-boot )
[2 of 3] Compiling B                ( B.hs, B.o )
[3 of 3] Compiling A                ( A.hs, A.o )

A.hs:5:5: Not in scope: ‘someError’


$ ghc-7.10.3 --make A.hs
[1 of 3] Compiling A[boot]          ( A.hs-boot, A.o-boot )
[3 of 3] Compiling A                ( A.hs, A.o )

A.hs:5:5: Not in scope: ‘someError’

Why does ghc --make recompile B.hs-boot?

Note that recompilation avoidance does work when using ghc -c:

$ ghc -c A.hs-boot
compilation IS NOT required

(found while trying to reduce the testcase for #11532 (closed), which contains 644 .hs and 642 .hs-boot files)

Trac metadata

Trac field	Value
Version	7.10.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Driver
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	ezyang
Operating system
Architecture