Unable to detect file changes on hamlet templates on stack devel for lts-12.5

[jvliwanag]

On a new project initialized with the yesod templates, with the resolver automatically set to lts-12.5, hamlet templates are not watched. That is, running yesod devel fails to rebuild the app on changes to the template files.

Tested on both macos 10.13.6 and Ubuntu 18.04.

What worked however is changing the stack resolver from the picked up lts-12.5 stack resolver to lts-11.20.

Running watched command from stack build --file-watch confirms that the hamlet files are missing when on lts-12.5, but are present on lts-11.20.

[snoyberg]

That's most likely a different in how GHC is reporting the watched files in the two different versions. There should be some .hi-dump files in your .stack-work directory. Can you report whether those files reference your Hamlet files with the two different resolvers?

[jvliwanag]

Looks like they point to the same file, but have the 12.5 has an additional hex string.

11.20 (working auto build)
Path: ./.stack-work/dist/x86_64-osx/Cabal-2.0.1.0/build/src/Handler/Home.dump-hi

addDependentFile "templates/homepage.hamlet"
54086c982e9b4ed881fcb2d9d3c2aa4d
  $trModule :: GHC.Types.Module
  {- HasNoCafRefs, Strictness: m,
     Unfolding: (GHC.Types.Module
                   Handler.Home.$trModule3
                   Handler.Home.$trModule1) -}

12.5 (auto build not working)
Path: ./.stack-work/dist/x86_64-osx/Cabal-2.2.0.1/build/src/Handler/Home.dump-hi

addDependentFile "templates/homepage.hamlet" 64b74188b62bac042119e8a0d26c3289
3886f14f725c6b9c0e89769a9758c7a7
  $trModule :: GHC.Types.Module
  {- HasNoCafRefs, Strictness: m,
     Unfolding: (GHC.Types.Module
                   Handler.Home.$trModule3
                   Handler.Home.$trModule1) -}

[snoyberg]

Good catch, looks like Stack needs to be updated to support that hex. I'm running out for the weekend right now, but a patch along these lines would probably do the trick. But I won't be able to try this out myself until next week:

diff --git a/src/Stack/Package.hs b/src/Stack/Package.hs
index ef986e95..d5ceb779 100644
--- a/src/Stack/Package.hs
+++ b/src/Stack/Package.hs
@@ -1184,8 +1184,9 @@ parseDumpHI dumpHIPath = do
             -- It can be an absolute or relative path.
             mapMaybe
                 (fmap TL.unpack .
-                  (TL.stripSuffix "\"" <=< TL.stripPrefix "\"") .
-                  TL.dropWhileEnd (== '\r') . TLE.decodeUtf8 . CL8.dropWhile (/= '"')) $
+                  TL.stripPrefix "\"" .
+                  -- Starting with GHC 8.4.3, there's a hash following the path
+                  TL.takeWhile (/= '\"') . TLE.decodeUtf8 . CL8.dropWhile (/= '"')) $
             filter ("addDependentFile \"" `CL8.isPrefixOf`) dumpHI
     thDepsResolved <- liftM catMaybes $ forM thDeps $ \x -> do
         mresolved <- liftIO (forgivingAbsence (resolveFile dir x)) >>= rejectMissingFile

[ygale]

Even with versions of stack that include the linked fix, yesod devel still does not detect changes to hamlet files.

In GHC 8.2 and earlier, referenced hamlet files appear as addDependentFile lines in the .dump-hi file. But in GHC 8.4 these lines do not appear. That appears to be the cause of the problem.

[ygale]

I am still experiencing this issue. Perhaps it should be re-opened?

The underlying stack issue is commercialhaskell/stack#4360.