Handle licences starting with a digit

cabal has a devscript that parses a json file (containing SPDX licences)
and returns a number of of Haskell data constructors.

There have been problems when the SPDX short identifier starts with
a digit (e.g. “0BSD”), as that would generate an data constructor
starting with a digit, which is not valid Haskell.
The way to handle such occourrences was in an ad-hoc basis.

This patch prepends “N_” to the beginning of every SPDX licence starting
with a digit, future-proofing the script.

cabal-dev-scripts/src/GenUtils.hs

@@ -15,6 +15,7 @@ import Data.Text    (Text)
 import GHC.Generics (Generic)
 
 import qualified Data.Algorithm.Diff as Diff
+import qualified Data.Char           as C
 import qualified Data.Map            as Map
 import qualified Data.Set            as Set
 import qualified Data.Text           as T
@@ -160,9 +161,10 @@ toConstructorName t = t
     f c   = c
 
     special :: Text -> Text
-    special "0BSD"          = "NullBSD"
-    special "389_exception" = "DS389_exception"
-    special u               = u
+    special u
+      | Just (c, _) <- T.uncons u
+      , C.isDigit c = "N_" <> u
+    special u = u
 
 mkList :: [Text] -> Text
 mkList []     = "    []"

changelog.d/pr-10356

@@ -0,0 +1,11 @@
+synopsis: New licence constructors for SPDX licences starting with a digit
+packages: Cabal-syntax
+prs: #10356
+
+description: {
+
+- LicenseId constructor `NullBSD` is now `N_0BSD`.
+- LicenseId constructor `DS389_exception` is now and `N_389_exception`.
+- LicenseId constructor `X3D_Slicer_1_0` is now and `N_3D_Slicer_1_0`.
+
+}