lint-codes: add Hadrian targets

This commit adds new Hadrian targets:

  codes, codes:used - list all used diagnostic codes
  codes:outdated - list outdated diagnostic codes

This allows users to easily query GHC for used and outdated
diagnostic codes, e.g.

  hadrian/build -j --flavour=<..> codes

will list all used diagnostic codes in the command line by running
the lint-codes utility in the "list codes" mode of operation.

The diagnostic code consistency and coverage test is still run as usual,
through the testsuite:

  hadrian/build test --only="codes"

hadrian/hadrian.cabal

@@ -78,6 +78,7 @@ executable hadrian
                        , Rules.BinaryDist
                        , Rules.CabalReinstall
                        , Rules.Clean
+                       , Rules.Codes
                        , Rules.Compile
                        , Rules.Dependencies
                        , Rules.Docspec

hadrian/src/Main.hs

@@ -15,6 +15,7 @@ import qualified Base
 import qualified CommandLine
 import qualified Environment
 import qualified Rules
+import qualified Rules.Codes
 import qualified Rules.Clean
 import qualified Rules.Docspec
 import qualified Rules.Documentation
@@ -99,6 +100,7 @@ main = do
             Rules.Docspec.docspecRules
             Rules.Documentation.documentationRules
             Rules.Clean.cleanRules
+            Rules.Codes.codesRules
             Rules.Lint.lintRules
             Rules.Nofib.nofibRules
             Rules.oracleRules

hadrian/src/Rules/Codes.hs

+module Rules.Codes
+  ( codesRules
+  ) where
+
+import Base
+import Packages ( programPath, lintCodes )
+import Settings.Program ( programContext )
+
+data Usage
+  = Used
+  | Outdated
+
+describeUsage :: Usage -> String
+describeUsage Used     = "used"
+describeUsage Outdated = "outdated"
+
+usageArg :: Usage -> String
+usageArg Used     = "list"
+usageArg Outdated = "outdated"
+
+codesRules :: Rules ()
+codesRules = do
+  "codes:used"     ~> codes Used
+  "codes:outdated" ~> codes Outdated
+  "codes"          ~> codes Used
+
+codes :: Usage -> Action ()
+codes usage = do
+  let stage = Stage1 -- ?
+  codesProgram <- programPath =<< programContext stage lintCodes
+  need [ codesProgram ]
+  ghcLibDir <- stageLibPath stage
+  let args = [ usageArg usage, ghcLibDir ]
+      cmdLine = unwords ( codesProgram : args )
+  putBuild $ "| Computing " ++ describeUsage usage ++ " diagnostic codes."
+  putBuild $ "| " <> cmdLine
+  cmd_ cmdLine