fixup! Add --promised-dependency flag to Cabal ./Setup configure interface

Author: fgaz

cabal-install/src/Distribution/Client/Setup.hs

@@ -134,6 +134,8 @@ import Data.List
          ( deleteFirstsBy )
 import System.FilePath
          ( (</>) )
+import Control.Exception
+         ( assert )
 
 globalCommand :: [Command action] -> CommandUI GlobalFlags
 globalCommand commands = CommandUI {
@@ -497,16 +499,13 @@ filterConfigureFlags flags cabalLibVersion
       configConstraints = []
     }
 
-    flags_3_11_0 = if not . null $ configPromisedDependencies flags then error $
-        "--promised-dependencies was requested, likely through --enable-multi-repl,\n\
-        \but some package setup-depends on Cabal " ++ prettyShow cabalLibVersion ++ ",\n\
-        \which is too old to support --promised-dependencies. Use the flag\n\
-        \--constraint='setup.Cabal >= 3.11' to constrain Cabal to an appropriate\n\
-        \version or to see which package is requiring an older version.\n\
-        \TODO: automate the constraint, see https://github.com/haskell/cabal/issues/8954"
-        else flags_latest {
-          configPromisedDependencies = []
-        }
+    flags_3_11_0 = flags_latest {
+      -- It's too late to convert configPromisedDependencies to anything
+      -- meaningful, so we just assert that it's empty.
+      -- We add a Cabal>=3.11 constraint before solving when multi-repl is
+      -- enabled, so this should never trigger.
+      configPromisedDependencies = assert (null $ configPromisedDependencies flags) []
+    }
 
     flags_3_7_0 = flags_3_11_0 {
         -- Cabal < 3.7 does not know about --extra-lib-dirs-static