Deprecate the --upgrade-cabal flag (fixes #4070)

ChangeLog.md

@@ -14,6 +14,12 @@ Behavior changes:
 * `stack build` will now announce when sublibraries of a package are being
   build, in the same way executables, tests, benchmarks and libraries are
   announced
+* The `--upgrade-cabal` option to `stack setup` has been
+  deprecated. This feature no longer works with GHC 8.2 and
+  later. Furthermore, the reason for this flag originally being
+  implemented was drastically lessened once Stack started using the
+  snapshot's `Cabal` library for custom setups. See:
+  [#4070](https://github.com/commercialhaskell/stack/issues/4070).
 
 Other enhancements:
 

doc/GUIDE.md

@@ -1787,10 +1787,6 @@ users. Here's a quick rundown:
 * `stack upgrade` will build a new version of stack from source.
     * `--git` is a convenient way to get the most recent version from master for
       those testing and living on the bleeding edge.
-* `stack setup --upgrade-cabal` can install a newer version of the Cabal
-  library, used for performing actual builds. You shouldn't generally do this,
-  since new Cabal versions may introduce incompatibilities with package sets,
-  but it can be useful if you're trying to test a specific bugfix.
 * `stack ls snapshots` will list all the local snapshots by
   default. You can also view the remote snapshots using `stack ls
   snapshots remote`. It also supports option for viewing only lts

src/Stack/Setup.hs

@@ -684,7 +684,8 @@ upgradeCabal :: (HasConfig env, HasGHCVariant env)
              -> UpgradeTo
              -> RIO env ()
 upgradeCabal wc upgradeTo = do
-    logInfo "Manipulating the global Cabal is only for debugging purposes"
+    logWarn "Using deprecated --upgrade-cabal feature, this is not recommended"
+    logWarn "Manipulating the global Cabal is only for debugging purposes"
     let name = $(mkPackageName "Cabal")
     rmap <- resolvePackages Nothing mempty (Set.singleton name)
     installed <- getCabalPkgVer wc
@@ -717,6 +718,10 @@ doCabalInstall :: (HasConfig env, HasGHCVariant env)
                -> Version
                -> RIO env ()
 doCabalInstall wc installed wantedVersion = do
+    when (wantedVersion >= $(mkVersion "2.2")) $ do
+        logWarn "--upgrade-cabal will almost certainly fail for Cabal 2.2 or later"
+        logWarn "See: https://github.com/commercialhaskell/stack/issues/4070"
+        logWarn "Valiantly attempting to build it anyway, but I know this is doomed"
     withSystemTempDir "stack-cabal-upgrade" $ \tmpdir -> do
         logInfo $
             "Installing Cabal-" <>

src/Stack/SetupCmd.hs

@@ -63,7 +63,7 @@ cabalUpgradeParser = Specific <$> version' <|> latestParser
          <> OA.help "Install a specific version of Cabal" )
         latestParser = OA.flag' Latest (
             OA.long "upgrade-cabal"
-         <> OA.help "Install latest version of Cabal globally" )
+         <> OA.help "DEPRECATED Install latest version of Cabal globally" )
 
 setupParser :: OA.Parser SetupCmdOpts
 setupParser = SetupCmdOpts