Upgrade to hpack 0.20.0 (fixes #3383)

ChangeLog.md

@@ -118,6 +118,9 @@ Other enhancements:
 * Passing non local packages as targets to `stack ghci` will now
   cause them to be used as `-package` args along with package
   hiding.
+* Detect when user changed .cabal file instead of package.yaml. This
+  was implemented upstream in hpack. See
+  [#3383](https://github.com/commercialhaskell/stack/issues/3383).
 
 Bug fixes:
 

package.yaml

@@ -63,7 +63,7 @@ dependencies:
 - hackage-security
 - hashable
 - hastache
-- hpack
+- hpack >= 0.20
 - hpc
 - http-client
 - http-client-tls

src/Stack/Package.hs

@@ -1321,11 +1321,7 @@ hpack pkgDir = do
         config <- view configL
         case configOverrideHpack config of
             HpackBundled -> do
-#if MIN_VERSION_hpack(0,18,0)
-                r <- liftIO $ Hpack.hpackResult (Just $ toFilePath pkgDir)
-#else
-                r <- liftIO $ Hpack.hpackResult (toFilePath pkgDir)
-#endif
+                r <- liftIO $ Hpack.hpackResult (Just $ toFilePath pkgDir) Hpack.NoForce
                 forM_ (Hpack.resultWarnings r) prettyWarnS
                 let cabalFile = styleFile . fromString . Hpack.resultCabalFile $ r
                 case Hpack.resultStatus r of
@@ -1338,6 +1334,13 @@ hpack pkgDir = do
                         , flow "was generated with a newer version of hpack,"
                         , flow "please upgrade and try again."
                         ]
+                    Hpack.ExistingCabalFileWasModifiedManually -> prettyWarnL
+                        [ flow "WARNING: "
+                        , cabalFile
+                        , flow " was modified manually.  Ignoring package.yaml in favor of cabal file."
+                        , flow "If you want to use package.yaml instead of the cabal file, "
+                        , flow "then please delete the cabal file."
+                        ]
             HpackCommand command -> do
                 envOverride <- getMinimalEnvOverride
                 let cmd = Cmd (Just pkgDir) command envOverride []

stack-nightly.yaml

@@ -8,3 +8,4 @@ nix:
 extra-deps:
 - bindings-uname-0.1
 - conduit-extra-1.2.0
+- hpack-0.20.0

stack.yaml

@@ -25,3 +25,4 @@ extra-deps:
 - path-io-1.3.3
 - extra-1.6
 - hsc2hs-0.68.2
+- hpack-0.20.0