Re: bug in ghci module loading post 9.12.4?

I tried your reproducer with GHC 9.10.2, 9.12.2 and 9.12.4
and GHCi picked up the changes to BugA every time:

ghci> bug
10
ghci> :r
[1 of 3] Compiling BugA             ( BugA.hs, BugA.o ) [Source file changed]
Ok, three modules reloaded.
ghci> bug
11

Which platform/OS are you building on and how did you obtain
GHC?

On 26/06/23 01:07, Evan Laforge wrote:
>I recently upgraded from ghc 9.2 to 9.6 (I know, I'm slow), and one of
>the things I was looking forward to was better recompilation
>avoidance, that wouldn't be fooled by spurious mtime changes that are
>common with with e.g. git branch switches.  Unfortunately, it seems to
>have gotten buggy at the same time!  I upgraded again to 9.12.4 and it
>looks like it's still buggy.  Either that or I'm doing things wrong
>somehow.  Here's a repro, it requires 3 modules:
>
>% cat >BugA.hs
>module BugA where
>
>x :: Int
>x = 13
>% cat >BugB.hs
>module BugB where
>import qualified BugA
>
>f :: IO ()
>f = print BugA.x
>% cat >BugC.hs
>module BugC where
>import qualified BugB
>
>bug :: IO ()
>bug = BugB.f
>
>% ghci -fobject-code # compile so we can load .o
>GHCi, version 9.12.4: https://www.haskell.org/ghc/  :? for help
>Loaded GHCi configuration from /Users/elaforge/qlib/dotfiles/.ghci
>Prelude> :load BugC
>[1 of 3] Compiling BugA             ( BugA.hs, BugA.o )
>[2 of 3] Compiling BugB             ( BugB.hs, BugB.o )
>[3 of 3] Compiling BugC             ( BugC.hs, BugC.o )
>Ok, three modules loaded.
>Leaving GHCi.
>% ghci
>Prelude> :load BugC
>Ok, three modules loaded.
>Prelude BugC> bug
>13
>
>As expected!  Now go edit BugA.hs, and change 13 to say 14, and save.
>Now reload:
>
>Prelude BugC> :r
>[1 of 3] Compiling BugA             ( BugA.hs, interpreted ) [Source
>file changed]
>Ok, three modules reloaded.
>Prelude BugC> bug
>13
>
>So that's not right!  This will also cause linking errors if something
>was removed, though it's easier to reproduce the stale values.
>
>For my interpretation of what's going on, I believe previously it
>would have also reloaded BugB.  While it has noticed that BugA must be
>reloaded (and switched to bytecode), it hasn't noticed that BugB is in
>the dependency path and should also be reloaded, and possibly winds up
>using stale values inlined into BugB.o.
>
>Is it a bug?
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