Allow ${pkgroot} prefix.

Cabal/Distribution/Make.hs

@@ -146,6 +146,8 @@ copyAction flags args = do
   let destArgs = case fromFlag $ copyDest flags of
         NoCopyDest      -> ["install"]
         CopyTo path     -> ["copy", "destdir=" ++ path]
+        CopyToDb _      -> error "CopyToDb not supported via Make"
+
   rawSystemExit (fromFlag $ copyVerbosity flags) "make" destArgs
 
 installAction :: InstallFlags -> [String] -> IO ()

Cabal/Distribution/Simple.hs

@@ -742,7 +742,7 @@ defaultInstallHook :: PackageDescription -> LocalBuildInfo
 defaultInstallHook pkg_descr localbuildinfo _ flags = do
   let copyFlags = defaultCopyFlags {
                       copyDistPref   = installDistPref flags,
-                      copyDest       = toFlag NoCopyDest,
+                      copyDest       = installDest     flags,
                       copyVerbosity  = installVerbosity flags
                   }
   install pkg_descr localbuildinfo copyFlags

Cabal/Distribution/Simple/Configure.hs

@@ -747,9 +747,25 @@ configure (pkg_descr0, pbi) cfg = do
     let dirs = absoluteInstallDirs pkg_descr lbi NoCopyDest
         relative = prefixRelativeInstallDirs (packageId pkg_descr) lbi
 
-    unless (isAbsolute (prefix dirs)) $ die' verbosity $
+    -- PKGROOT: allowing ${pkgroot} to be passed as --prefix to
+    -- cabal configure, is only a hidden option. It allows packages
+    -- to be relocatable with their package database.  This however
+    -- breaks when the Paths_* or other includes are used that
+    -- contain hard coded paths. This is still an open TODO.
+    --
+    -- Allowing ${pkgroot} here, however requires less custom hooks
+    -- in scripts that *really* want ${pkgroot}. See haskell/cabal/#4872
+    unless (isAbsolute (prefix dirs)
+           || "${pkgroot}" `isPrefixOf` prefix dirs) $ die' verbosity $
         "expected an absolute directory name for --prefix: " ++ prefix dirs
 
+    when ("${pkgroot}" `isPrefixOf` prefix dirs) $
+      warn verbosity $ "Using ${pkgroot} in prefix " ++ prefix dirs
+                    ++ " will not work if you rely on the Path_* module "
+                    ++ " or other hard coded paths.  Cabal does not yet "
+                    ++ " support fully  relocatable builds! "
+                    ++ " See #462 #2302 #2994 #3305 #3473 #3586 #3909 #4097 #4291 #4872"
+
     info verbosity $ "Using " ++ display currentCabalId
                   ++ " compiled by " ++ display currentCompilerId
     info verbosity $ "Using compiler: " ++ showCompilerId comp

Cabal/Distribution/Simple/InstallDirs.hs

@@ -59,7 +59,8 @@ import Distribution.Text
 import System.Directory (getAppUserDataDirectory)
 import System.FilePath
   ( (</>), isPathSeparator
-  , pathSeparator, dropDrive )
+  , pathSeparator, dropDrive
+  , takeDirectory )
 
 #ifdef mingw32_HOST_OS
 import qualified Prelude
@@ -287,19 +288,29 @@ absoluteInstallDirs :: PackageIdentifier
 absoluteInstallDirs pkgId libname compilerId copydest platform dirs =
     (case copydest of
        CopyTo destdir -> fmap ((destdir </>) . dropDrive)
+       CopyToDb dbdir -> fmap (substPrefix "${pkgroot}" (takeDirectory dbdir))
        _              -> id)
   . appendSubdirs (</>)
   . fmap fromPathTemplate
   $ substituteInstallDirTemplates env dirs
   where
     env = initialPathTemplateEnv pkgId libname compilerId platform
+    substPrefix pre root path
+      | pre `isPrefixOf` path = root ++ drop (length pre) path
+      | otherwise             = path
 
 
 -- |The location prefix for the /copy/ command.
 data CopyDest
   = NoCopyDest
   | CopyTo FilePath
-  deriving (Eq, Show)
+  | CopyToDb FilePath
+  -- ^ when using the ${pkgroot} as prefix. The CopyToDb will
+  --   adjust the paths to be relative to the provided package
+  --   database when copying / installing.
+  deriving (Eq, Show, Generic)
+
+instance Binary CopyDest
 
 -- | Check which of the paths are relative to the installation $prefix.
 --

Cabal/Distribution/Simple/Setup.hs

@@ -950,19 +950,35 @@ copyCommand = CommandUI
       ]
   , commandDefaultFlags = defaultCopyFlags
   , commandOptions      = \showOrParseArgs ->
-      [optionVerbosity copyVerbosity (\v flags -> flags { copyVerbosity = v })
+      (filter ((`notElem` ["target-package-db"])
+        . optionName)) $ copyOptions showOrParseArgs
+}
 
-      ,optionDistPref
-         copyDistPref (\d flags -> flags { copyDistPref = d })
-         showOrParseArgs
+copyOptions ::  ShowOrParseArgs -> [OptionField CopyFlags]
+copyOptions showOrParseArgs =
+  [optionVerbosity copyVerbosity (\v flags -> flags { copyVerbosity = v })
 
-      ,option "" ["destdir"]
-         "directory to copy files to, prepended to installation directories"
-         copyDest (\v flags -> flags { copyDest = v })
-         (reqArg "DIR" (succeedReadE (Flag . CopyTo))
-                       (\f -> case f of Flag (CopyTo p) -> [p]; _ -> []))
-      ]
-  }
+  ,optionDistPref
+    copyDistPref (\d flags -> flags { copyDistPref = d })
+    showOrParseArgs
+
+  ,option "" ["destdir"]
+    "directory to copy files to, prepended to installation directories"
+    copyDest (\v flags -> case copyDest flags of
+                 Flag (CopyToDb _) -> error "Use either 'destdir' or 'target-package-db'."
+                 _ -> flags { copyDest = v })
+    (reqArg "DIR" (succeedReadE (Flag . CopyTo))
+      (\f -> case f of Flag (CopyTo p) -> [p]; _ -> []))
+
+  ,option "" ["target-package-db"]
+    "package database to copy files into. Required when using ${pkgroot} prefix."
+    copyDest (\v flags -> case copyDest flags of
+                 NoFlag -> flags { copyDest = v }
+                 Flag NoCopyDest -> flags { copyDest = v }
+                 _ -> error "Use either 'destdir' or 'target-package-db'.")
+    (reqArg "DATABASE" (succeedReadE (Flag . CopyToDb))
+      (\f -> case f of Flag (CopyToDb p) -> [p]; _ -> []))
+  ]
 
 emptyCopyFlags :: CopyFlags
 emptyCopyFlags = mempty
@@ -981,6 +997,7 @@ instance Semigroup CopyFlags where
 -- | Flags to @install@: (package db, verbosity)
 data InstallFlags = InstallFlags {
     installPackageDB :: Flag PackageDB,
+    installDest      :: Flag CopyDest,
     installDistPref  :: Flag FilePath,
     installUseWrapper :: Flag Bool,
     installInPlace    :: Flag Bool,
@@ -991,6 +1008,7 @@ data InstallFlags = InstallFlags {
 defaultInstallFlags :: InstallFlags
 defaultInstallFlags  = InstallFlags {
     installPackageDB = NoFlag,
+    installDest      = Flag NoCopyDest,
     installDistPref  = NoFlag,
     installUseWrapper = Flag False,
     installInPlace    = Flag False,
@@ -1011,30 +1029,40 @@ installCommand = CommandUI
       "Usage: " ++ pname ++ " install [FLAGS]\n"
   , commandDefaultFlags = defaultInstallFlags
   , commandOptions      = \showOrParseArgs ->
-      [optionVerbosity installVerbosity (\v flags -> flags { installVerbosity = v })
-      ,optionDistPref
-         installDistPref (\d flags -> flags { installDistPref = d })
-         showOrParseArgs
-
-      ,option "" ["inplace"]
-         "install the package in the install subdirectory of the dist prefix, so it can be used without being installed"
-         installInPlace (\v flags -> flags { installInPlace = v })
-         trueArg
-
-      ,option "" ["shell-wrappers"]
-         "using shell script wrappers around executables"
-         installUseWrapper (\v flags -> flags { installUseWrapper = v })
-         (boolOpt [] [])
-
-      ,option "" ["package-db"] ""
-         installPackageDB (\v flags -> flags { installPackageDB = v })
-         (choiceOpt [ (Flag UserPackageDB, ([],["user"]),
-                      "upon configuration register this package in the user's local package database")
-                    , (Flag GlobalPackageDB, ([],["global"]),
-                      "(default) upon configuration register this package in the system-wide package database")])
-      ]
+      (filter ((`notElem` ["target-package-db"])
+        . optionName)) $ installOptions showOrParseArgs
   }
 
+installOptions ::  ShowOrParseArgs -> [OptionField InstallFlags]
+installOptions showOrParseArgs =
+  [optionVerbosity installVerbosity (\v flags -> flags { installVerbosity = v })
+  ,optionDistPref
+    installDistPref (\d flags -> flags { installDistPref = d })
+    showOrParseArgs
+
+  ,option "" ["inplace"]
+    "install the package in the install subdirectory of the dist prefix, so it can be used without being installed"
+    installInPlace (\v flags -> flags { installInPlace = v })
+    trueArg
+
+  ,option "" ["shell-wrappers"]
+    "using shell script wrappers around executables"
+    installUseWrapper (\v flags -> flags { installUseWrapper = v })
+    (boolOpt [] [])
+
+  ,option "" ["package-db"] ""
+    installPackageDB (\v flags -> flags { installPackageDB = v })
+    (choiceOpt [ (Flag UserPackageDB, ([],["user"]),
+                   "upon configuration register this package in the user's local package database")
+               , (Flag GlobalPackageDB, ([],["global"]),
+                   "(default) upon configuration register this package in the system-wide package database")])
+  ,option "" ["target-package-db"]
+    "package database to install into. Required when using ${pkgroot} prefix."
+    installDest (\v flags -> flags { installDest = v })
+    (reqArg "DATABASE" (succeedReadE (Flag . CopyToDb))
+      (\f -> case f of Flag (CopyToDb p) -> [p]; _ -> []))
+  ]
+
 emptyInstallFlags :: InstallFlags
 emptyInstallFlags = mempty
 

cabal-install/Distribution/Client/Config.hs

@@ -245,6 +245,7 @@ instance Semigroup SavedConfig where
         installDocumentation         = combine installDocumentation,
         installHaddockIndex          = combine installHaddockIndex,
         installDryRun                = combine installDryRun,
+        installDest                  = combine installDest,
         installMaxBackjumps          = combine installMaxBackjumps,
         installReorderGoals          = combine installReorderGoals,
         installCountConflicts        = combine installCountConflicts,

cabal-install/Distribution/Client/ProjectConfig/Legacy.hs

@@ -41,6 +41,7 @@ import Distribution.PackageDescription.Parse
          ( sourceRepoFieldDescrs )
 import Distribution.Simple.Compiler
          ( OptimisationLevel(..), DebugInfoLevel(..) )
+import Distribution.Simple.InstallDirs ( CopyDest (NoCopyDest) )
 import Distribution.Simple.Setup
          ( Flag(Flag), toFlag, fromFlagOrDefault
          , ConfigFlags(..), configureOptions
@@ -514,6 +515,7 @@ convertToLegacySharedConfig
     installFlags = InstallFlags {
       installDocumentation     = mempty,
       installHaddockIndex      = projectConfigHaddockIndex,
+      installDest              = Flag NoCopyDest,
       installDryRun            = projectConfigDryRun,
       installReinstall         = mempty, --projectConfigReinstall,
       installAvoidReinstalls   = mempty, --projectConfigAvoidReinstalls,

cabal-install/Distribution/Client/Setup.hs

@@ -1486,6 +1486,7 @@ instance Semigroup InfoFlags where
 data InstallFlags = InstallFlags {
     installDocumentation    :: Flag Bool,
     installHaddockIndex     :: Flag PathTemplate,
+    installDest             :: Flag Cabal.CopyDest,
     installDryRun           :: Flag Bool,
     installMaxBackjumps     :: Flag Int,
     installReorderGoals     :: Flag ReorderGoals,
@@ -1530,6 +1531,7 @@ defaultInstallFlags :: InstallFlags
 defaultInstallFlags = InstallFlags {
     installDocumentation   = Flag False,
     installHaddockIndex    = Flag docIndexFile,
+    installDest            = Flag Cabal.NoCopyDest,
     installDryRun          = Flag False,
     installMaxBackjumps    = Flag defaultMaxBackjumps,
     installReorderGoals    = Flag (ReorderGoals False),
@@ -1628,12 +1630,20 @@ installCommand = CommandUI {
   commandDefaultFlags = (mempty, mempty, mempty, mempty),
   commandOptions      = \showOrParseArgs ->
        liftOptions get1 set1
+       -- Note: [Hidden Flags]
+       -- hide "constraint", "dependency", and
+       -- "exact-configuration" from the configure options.
        (filter ((`notElem` ["constraint", "dependency"
                            , "exact-configuration"])
                 . optionName) $
                               configureOptions   showOrParseArgs)
     ++ liftOptions get2 set2 (configureExOptions showOrParseArgs ConstraintSourceCommandlineFlag)
-    ++ liftOptions get3 set3 (installOptions     showOrParseArgs)
+    ++ liftOptions get3 set3
+       -- hide "target-package-db" flag from the
+       -- install options.
+       (filter ((`notElem` ["target-package-db"])
+                . optionName) $
+                              installOptions     showOrParseArgs)
     ++ liftOptions get4 set4 (haddockOptions     showOrParseArgs)
   }
   where
@@ -1678,6 +1688,12 @@ installOptions showOrParseArgs =
           "Do not install anything, only print what would be installed."
           installDryRun (\v flags -> flags { installDryRun = v })
           trueArg
+
+      , option "" ["target-package-db"]
+         "package database to install into. Required when using ${pkgroot} prefix."
+         installDest (\v flags -> flags { installDest = v })
+         (reqArg "DATABASE" (succeedReadE (Flag . Cabal.CopyToDb))
+                            (\f -> case f of Flag (Cabal.CopyToDb p) -> [p]; _ -> []))
       ] ++
 
       optionSolverFlags showOrParseArgs