From 0a4fd6a0e460dd1cb5272898e5dcc37810965f1e Mon Sep 17 00:00:00 2001
From: Merijn Verstraaten <merijn@inconsistent.nl>
Date: Wed, 28 Mar 2018 15:31:12 +0200
Subject: [PATCH] Basic infrastructure for filtering the command-line arguments
 for programs from the new-build hash input to reduce redundant recompilation.

See #4247.
---
 Cabal/Distribution/Simple/Program/Types.hs           | 11 ++++++++---
 cabal-install/Distribution/Client/ProjectPlanning.hs | 10 +++++++++-
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/Cabal/Distribution/Simple/Program/Types.hs b/Cabal/Distribution/Simple/Program/Types.hs
index 6eb0695017b..5ba00de6d37 100644
--- a/Cabal/Distribution/Simple/Program/Types.hs
+++ b/Cabal/Distribution/Simple/Program/Types.hs
@@ -74,10 +74,14 @@ data Program = Program {
        -- | A function to do any additional configuration after we have
        -- located the program (and perhaps identified its version). For example
        -- it could add args, or environment vars.
-       programPostConf :: Verbosity -> ConfiguredProgram -> IO ConfiguredProgram
+       programPostConf :: Verbosity -> ConfiguredProgram -> IO ConfiguredProgram,
+       -- | A function that filters any arguments that don't impact the output
+       -- from a commandline. Used to limit the volatility of dependency hashes
+       -- when using new-build.
+       programFilterArgs :: Maybe Version -> [String] -> [String]
      }
 instance Show Program where
-  show (Program name _ _ _) = "Program: " ++ name
+  show (Program name _ _ _ _) = "Program: " ++ name
 
 type ProgArg = String
 
@@ -161,7 +165,8 @@ simpleProgram name = Program {
     programName         = name,
     programFindLocation = \v p -> findProgramOnSearchPath v p name,
     programFindVersion  = \_ _ -> return Nothing,
-    programPostConf     = \_ p -> return p
+    programPostConf     = \_ p -> return p,
+    programFilterArgs   = const id
   }
 
 -- | Make a simple 'ConfiguredProgram'.
diff --git a/cabal-install/Distribution/Client/ProjectPlanning.hs b/cabal-install/Distribution/Client/ProjectPlanning.hs
index 45b0a9efc6d..1495a9e0ff2 100644
--- a/cabal-install/Distribution/Client/ProjectPlanning.hs
+++ b/cabal-install/Distribution/Client/ProjectPlanning.hs
@@ -3522,13 +3522,21 @@ packageHashConfigInputs
       pkgHashStripLibs           = elabStripLibs,
       pkgHashStripExes           = elabStripExes,
       pkgHashDebugInfo           = elabDebugInfo,
-      pkgHashProgramArgs         = elabProgramArgs,
+      pkgHashProgramArgs         = Map.mapWithKey lookupFilter elabProgramArgs,
       pkgHashExtraLibDirs        = elabExtraLibDirs,
       pkgHashExtraFrameworkDirs  = elabExtraFrameworkDirs,
       pkgHashExtraIncludeDirs    = elabExtraIncludeDirs,
       pkgHashProgPrefix          = elabProgPrefix,
       pkgHashProgSuffix          = elabProgSuffix
     }
+  where
+    lookupFilter :: String -> [String] -> [String]
+    lookupFilter n = case lookupKnownProgram n pkgConfigCompilerProgs of
+        Just p -> programFilterArgs p (getVersion p)
+        Nothing -> id
+
+    getVersion :: Program -> Maybe Version
+    getVersion p = lookupProgram p pkgConfigCompilerProgs >>= programVersion
 
 
 -- | Given the 'InstalledPackageIndex' for a nix-style package store, and an