Tweak how 'allow-newer' looks like in the default config file.

Before:

    allow-newer: False

After:

    -- allow-newer: False

Cabal/Distribution/Simple/Configure.hs

@@ -315,7 +315,9 @@ configure (pkg_descr0', pbi) cfg = do
           -- Ignore '--allow-newer' when we're given '--exact-configuration'.
           if fromFlagOrDefault False (configExactConfiguration cfg)
           then pkg_descr0'
-          else relaxPackageDeps (configAllowNewer cfg) pkg_descr0'
+          else relaxPackageDeps
+               (fromMaybe AllowNewerNone $ configAllowNewer cfg)
+               pkg_descr0'
 
     setupMessage verbosity "Configuring" (packageId pkg_descr0)
 

Cabal/Distribution/Simple/Setup.hs

@@ -308,19 +308,19 @@ isAllowNewer AllowNewerNone     = False
 isAllowNewer (AllowNewerSome _) = True
 isAllowNewer AllowNewerAll      = True
 
-allowNewerParser :: ReadE AllowNewer
+allowNewerParser :: ReadE (Maybe AllowNewer)
 allowNewerParser = ReadE $ \s ->
   case readPToMaybe pkgsParser s of
-    Just pkgs -> Right . AllowNewerSome $ pkgs
+    Just pkgs -> Right . Just . AllowNewerSome $ pkgs
     Nothing   -> Left ("Cannot parse the list of packages: " ++ s)
   where
     pkgsParser = Parse.sepBy1 parse (Parse.char ',')
 
-allowNewerPrinter :: AllowNewer -> [Maybe String]
-allowNewerPrinter AllowNewerNone        = []
-allowNewerPrinter AllowNewerAll         = [Nothing]
-allowNewerPrinter (AllowNewerSome pkgs) =
-  [Just . intercalate "," . map display $ pkgs]
+allowNewerPrinter :: (Maybe AllowNewer) -> [Maybe String]
+allowNewerPrinter Nothing                      = []
+allowNewerPrinter (Just AllowNewerNone)        = []
+allowNewerPrinter (Just AllowNewerAll)         = [Nothing]
+allowNewerPrinter (Just (AllowNewerSome pkgs)) = map (Just . display) $ pkgs
 
 -- | Flags to @configure@ command.
 --
@@ -392,8 +392,9 @@ data ConfigFlags = ConfigFlags {
       -- ^Halt and show an error message indicating an error in flag assignment
     configRelocatable :: Flag Bool, -- ^ Enable relocatable package built
     configDebugInfo :: Flag DebugInfoLevel,  -- ^ Emit debug info.
-    configAllowNewer :: AllowNewer      -- ^ Ignore upper bounds on all or some
-                                        -- dependencies.
+    configAllowNewer :: Maybe AllowNewer
+    -- ^ Ignore upper bounds on all or some dependencies. Wrapped in 'Maybe' to
+    -- distinguish between "default" and "explicitly disabled".
   }
   deriving (Generic, Read, Show)
 
@@ -440,7 +441,7 @@ defaultConfigFlags progConf = emptyConfigFlags {
     configFlagError    = NoFlag,
     configRelocatable  = Flag False,
     configDebugInfo    = Flag NoDebugInfo,
-    configAllowNewer   = AllowNewerNone
+    configAllowNewer   = Nothing
   }
 
 configureCommand :: ProgramConfiguration -> CommandUI ConfigFlags
@@ -686,7 +687,7 @@ configureOptions showOrParseArgs =
       ,option [] ["allow-newer"]
        ("Ignore upper bounds in all dependencies or DEPS")
        configAllowNewer (\v flags -> flags { configAllowNewer = v})
-       (optArg "DEPS" allowNewerParser AllowNewerAll allowNewerPrinter)
+       (optArg "DEPS" allowNewerParser (Just AllowNewerAll) allowNewerPrinter)
 
       ,option "" ["exact-configuration"]
          "All direct dependencies and flags are provided on the command line."

cabal-install/Distribution/Client/Config.hs

@@ -62,7 +62,7 @@ import Distribution.Simple.Compiler
          ( DebugInfoLevel(..), OptimisationLevel(..) )
 import Distribution.Simple.Setup
          ( ConfigFlags(..), configureOptions, defaultConfigFlags
-         , AllowNewer(..), isAllowNewer
+         , AllowNewer(..)
          , HaddockFlags(..), haddockOptions, defaultHaddockFlags
          , installDirsOptions, optionDistPref
          , programConfigurationPaths', programConfigurationOptions
@@ -75,7 +75,7 @@ import Distribution.ParseUtils
          , ParseResult(..), PError(..), PWarning(..)
          , locatedErrorMsg, showPWarning
          , readFields, warning, lineNo
-         , simpleField, boolField, listField, spaceListField
+         , simpleField, listField, spaceListField
          , parseFilePathQ, parseTokenQ )
 import Distribution.Client.ParseUtils
          ( parseFields, ppFields, ppSection )
@@ -640,7 +640,8 @@ commentSavedConfig = do
     savedInstallFlags      = defaultInstallFlags,
     savedConfigureExFlags  = defaultConfigExFlags,
     savedConfigureFlags    = (defaultConfigFlags defaultProgramConfiguration) {
-      configUserInstall    = toFlag defaultUserInstall
+      configUserInstall    = toFlag defaultUserInstall,
+      configAllowNewer     = Just AllowNewerNone
     },
     savedUserInstallDirs   = fmap toFlag userInstallDirs,
     savedGlobalInstallDirs = fmap toFlag globalInstallDirs,
@@ -669,10 +670,17 @@ configFieldDescriptions src =
        [simpleField "compiler"
           (fromFlagOrDefault Disp.empty . fmap Text.disp) (optional Text.parse)
           configHcFlavor (\v flags -> flags { configHcFlavor = v })
-       ,let toAllowNewer True  = AllowNewerAll
-            toAllowNewer False = AllowNewerNone in
-        boolField "allow-newer" (isAllowNewer . configAllowNewer)
-        (\v flags -> flags { configAllowNewer = toAllowNewer v })
+       ,let showAllowNewer Nothing               = mempty
+            showAllowNewer (Just AllowNewerNone) = Disp.text "False"
+            showAllowNewer (Just _)              = Disp.text "True"
+
+            toAllowNewer True  = Just AllowNewerAll
+            toAllowNewer False = Just AllowNewerNone
+
+            parseAllowNewer = toAllowNewer `fmap` Text.parse in
+        simpleField "allow-newer"
+        showAllowNewer parseAllowNewer
+        configAllowNewer (\v flags -> flags { configAllowNewer = v })
         -- TODO: The following is a temporary fix. The "optimization"
         -- and "debug-info" fields are OptArg, and viewAsFieldDescr
         -- fails on that. Instead of a hand-written hackaged parser

cabal-install/Distribution/Client/Configure.hs

@@ -43,7 +43,8 @@ import Distribution.Simple.Compiler
          ( Compiler, CompilerInfo, compilerInfo, PackageDB(..), PackageDBStack )
 import Distribution.Simple.Program (ProgramConfiguration )
 import Distribution.Simple.Setup
-         ( ConfigFlags(..), fromFlag, toFlag, flagToMaybe, fromFlagOrDefault )
+         ( ConfigFlags(..), AllowNewer(..)
+         , fromFlag, toFlag, flagToMaybe, fromFlagOrDefault )
 import Distribution.Simple.PackageIndex
          ( InstalledPackageIndex, lookupPackageName )
 import Distribution.Simple.Utils
@@ -86,7 +87,8 @@ chooseCabalVersion configFlags maybeVersion =
   where
     -- Cabal < 1.19.2 doesn't support '--exact-configuration' which is needed
     -- for '--allow-newer' to work.
-    allowNewer = isAllowNewer (configAllowNewer configFlags)
+    allowNewer = isAllowNewer
+                 (fromMaybe AllowNewerNone $ configAllowNewer configFlags)
 
     defaultVersionRange = if allowNewer
                           then orLaterVersion (Version [1,19,2] [])
@@ -288,7 +290,8 @@ planLocalPackage verbosity comp platform configFlags configExFlags
         fromFlagOrDefault False $ configBenchmarks configFlags
 
       resolverParams =
-          removeUpperBounds (configAllowNewer configFlags)
+          removeUpperBounds
+          (fromMaybe AllowNewerNone $ configAllowNewer configFlags)
 
         . addPreferences
             -- preferences from the config file or command line

cabal-install/Distribution/Client/Install.hs

@@ -124,6 +124,7 @@ import qualified Distribution.Simple.Configure as Configure
 import Distribution.Simple.Setup
          ( haddockCommand, HaddockFlags(..)
          , buildCommand, BuildFlags(..), emptyBuildFlags
+         , AllowNewer(..)
          , toFlag, fromFlag, fromFlagOrDefault, flagToMaybe, defaultDistPref )
 import qualified Distribution.Simple.Setup as Cabal
          ( Flag(..)
@@ -417,7 +418,7 @@ planPackages comp platform mSandboxPkgInfo solver
     maxBackjumps     = fromFlag (installMaxBackjumps      installFlags)
     upgradeDeps      = fromFlag (installUpgradeDeps       installFlags)
     onlyDeps         = fromFlag (installOnlyDeps          installFlags)
-    allowNewer       = (configAllowNewer         configFlags)
+    allowNewer       = fromMaybe AllowNewerNone (configAllowNewer configFlags)
 
 -- | Remove the provided targets from the install plan.
 pruneInstallPlan :: Package targetpkg

cabal-install/Distribution/Client/Setup.hs

@@ -370,7 +370,7 @@ filterConfigureFlags flags cabalLibVersion
       configConstraints = [],
       -- Passing '--allow-newer' to Setup.hs is unnecessary, we use
       -- '--exact-configuration' instead.
-      configAllowNewer  = Cabal.AllowNewerNone
+      configAllowNewer  = Just Cabal.AllowNewerNone
       }
 
     -- Cabal < 1.23 doesn't know about '--profiling-detail'.