Derive some Semigroup/Monoid instances via Generics

This increases compile-time (until GHC becomes more clever) but the
generated code is expected to be at least as good (if not better) than
the manually generated code.

This addresses #3169

Cabal/Distribution/PackageDescription.hs

@@ -111,7 +111,7 @@ module Distribution.PackageDescription (
 
 import Distribution.Compat.Binary
 import qualified Distribution.Compat.Semigroup as Semi ((<>))
-import Distribution.Compat.Semigroup as Semi (Monoid(..), Semigroup)
+import Distribution.Compat.Semigroup as Semi (Monoid(..), Semigroup, gmempty, gmappend)
 import qualified Distribution.Compat.ReadP as Parse
 import Distribution.Compat.ReadP   ((<++))
 import Distribution.Package
@@ -314,15 +314,12 @@ data SetupBuildInfo = SetupBuildInfo {
 
 instance Binary SetupBuildInfo
 
-instance Monoid SetupBuildInfo where
-  mempty = SetupBuildInfo {
-    setupDepends = Semi.mempty
-  }
+instance Semi.Monoid SetupBuildInfo where
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup SetupBuildInfo where
-  a <> b = SetupBuildInfo { setupDepends = combine setupDepends }
-    where combine field = field a `mappend` field b
+  (<>) = gmappend
 
 -- ---------------------------------------------------------------------------
 -- Module renaming
@@ -498,11 +495,7 @@ data Executable = Executable {
 instance Binary Executable
 
 instance Monoid Executable where
-  mempty = Executable {
-    exeName    = mempty,
-    modulePath = mempty,
-    buildInfo  = mempty
-  }
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup Executable where

Cabal/Distribution/Simple/Haddock.hs

@@ -763,46 +763,11 @@ exeBuildDir lbi exe = buildDir lbi </> exeName exe </> exeName exe ++ "-tmp"
 -- ------------------------------------------------------------------------------
 -- Boilerplate Monoid instance.
 instance Monoid HaddockArgs where
-    mempty = HaddockArgs {
-                argInterfaceFile = mempty,
-                argPackageName = mempty,
-                argHideModules = mempty,
-                argIgnoreExports = mempty,
-                argLinkSource = mempty,
-                argCssFile = mempty,
-                argContents = mempty,
-                argVerbose = mempty,
-                argOutput = mempty,
-                argInterfaces = mempty,
-                argOutputDir = mempty,
-                argTitle = mempty,
-                argPrologue = mempty,
-                argGhcOptions = mempty,
-                argGhcLibDir = mempty,
-                argTargets = mempty
-             }
+    mempty = gmempty
     mappend = (Semi.<>)
 
 instance Semigroup HaddockArgs where
-    a <> b = HaddockArgs {
-                argInterfaceFile = mult argInterfaceFile,
-                argPackageName = mult argPackageName,
-                argHideModules = mult argHideModules,
-                argIgnoreExports = mult argIgnoreExports,
-                argLinkSource = mult argLinkSource,
-                argCssFile = mult argCssFile,
-                argContents = mult argContents,
-                argVerbose = mult argVerbose,
-                argOutput = mult argOutput,
-                argInterfaces = mult argInterfaces,
-                argOutputDir = mult argOutputDir,
-                argTitle = mult argTitle,
-                argPrologue = mult argPrologue,
-                argGhcOptions = mult argGhcOptions,
-                argGhcLibDir = mult argGhcLibDir,
-                argTargets = mult argTargets
-             }
-      where mult f = f a `mappend` f b
+    (<>) = gmappend
 
 instance Monoid Directory where
     mempty = Dir "."

Cabal/Distribution/Simple/InstallDirs.hs

@@ -113,26 +113,11 @@ instance Functor InstallDirs where
   }
 
 instance (Semigroup dir, Monoid dir) => Monoid (InstallDirs dir) where
-  mempty = InstallDirs {
-      prefix       = mempty,
-      bindir       = mempty,
-      libdir       = mempty,
-      libsubdir    = mempty,
-      dynlibdir    = mempty,
-      libexecdir   = mempty,
-      includedir   = mempty,
-      datadir      = mempty,
-      datasubdir   = mempty,
-      docdir       = mempty,
-      mandir       = mempty,
-      htmldir      = mempty,
-      haddockdir   = mempty,
-      sysconfdir   = mempty
-  }
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup dir => Semigroup (InstallDirs dir) where
-  (<>) = combineInstallDirs (<>)
+  (<>) = gmappend
 
 combineInstallDirs :: (a -> b -> c)
                    -> InstallDirs a

Cabal/Distribution/Simple/Program/GHC.hs

@@ -499,116 +499,8 @@ packageDbArgs implInfo
 -- Boilerplate Monoid instance for GhcOptions
 
 instance Monoid GhcOptions where
-  mempty = GhcOptions {
-    ghcOptMode               = mempty,
-    ghcOptExtra              = mempty,
-    ghcOptExtraDefault       = mempty,
-    ghcOptInputFiles         = mempty,
-    ghcOptInputModules       = mempty,
-    ghcOptOutputFile         = mempty,
-    ghcOptOutputDynFile      = mempty,
-    ghcOptSourcePathClear    = mempty,
-    ghcOptSourcePath         = mempty,
-    ghcOptThisUnitId         = mempty,
-    ghcOptPackageDBs         = mempty,
-    ghcOptPackages           = mempty,
-    ghcOptHideAllPackages    = mempty,
-    ghcOptNoAutoLinkPackages = mempty,
-    ghcOptLinkLibs           = mempty,
-    ghcOptLinkLibPath        = mempty,
-    ghcOptLinkOptions        = mempty,
-    ghcOptLinkFrameworks     = mempty,
-    ghcOptLinkFrameworkDirs  = mempty,
-    ghcOptNoLink             = mempty,
-    ghcOptLinkNoHsMain       = mempty,
-    ghcOptCcOptions          = mempty,
-    ghcOptCppOptions         = mempty,
-    ghcOptCppIncludePath     = mempty,
-    ghcOptCppIncludes        = mempty,
-    ghcOptFfiIncludes        = mempty,
-    ghcOptLanguage           = mempty,
-    ghcOptExtensions         = mempty,
-    ghcOptExtensionMap       = mempty,
-    ghcOptOptimisation       = mempty,
-    ghcOptDebugInfo          = mempty,
-    ghcOptProfilingMode      = mempty,
-    ghcOptProfilingAuto      = mempty,
-    ghcOptSplitObjs          = mempty,
-    ghcOptNumJobs            = mempty,
-    ghcOptHPCDir             = mempty,
-    ghcOptGHCiScripts        = mempty,
-    ghcOptHiSuffix           = mempty,
-    ghcOptObjSuffix          = mempty,
-    ghcOptDynHiSuffix        = mempty,
-    ghcOptDynObjSuffix       = mempty,
-    ghcOptHiDir              = mempty,
-    ghcOptObjDir             = mempty,
-    ghcOptOutputDir          = mempty,
-    ghcOptStubDir            = mempty,
-    ghcOptDynLinkMode        = mempty,
-    ghcOptShared             = mempty,
-    ghcOptFPic               = mempty,
-    ghcOptDylibName          = mempty,
-    ghcOptRPaths             = mempty,
-    ghcOptVerbosity          = mempty,
-    ghcOptCabal              = mempty
-  }
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup GhcOptions where
-  a <> b = GhcOptions {
-    ghcOptMode               = combine ghcOptMode,
-    ghcOptExtra              = combine ghcOptExtra,
-    ghcOptExtraDefault       = combine ghcOptExtraDefault,
-    ghcOptInputFiles         = combine ghcOptInputFiles,
-    ghcOptInputModules       = combine ghcOptInputModules,
-    ghcOptOutputFile         = combine ghcOptOutputFile,
-    ghcOptOutputDynFile      = combine ghcOptOutputDynFile,
-    ghcOptSourcePathClear    = combine ghcOptSourcePathClear,
-    ghcOptSourcePath         = combine ghcOptSourcePath,
-    ghcOptThisUnitId         = combine ghcOptThisUnitId,
-    ghcOptPackageDBs         = combine ghcOptPackageDBs,
-    ghcOptPackages           = combine ghcOptPackages,
-    ghcOptHideAllPackages    = combine ghcOptHideAllPackages,
-    ghcOptNoAutoLinkPackages = combine ghcOptNoAutoLinkPackages,
-    ghcOptLinkLibs           = combine ghcOptLinkLibs,
-    ghcOptLinkLibPath        = combine ghcOptLinkLibPath,
-    ghcOptLinkOptions        = combine ghcOptLinkOptions,
-    ghcOptLinkFrameworks     = combine ghcOptLinkFrameworks,
-    ghcOptLinkFrameworkDirs  = combine ghcOptLinkFrameworkDirs,
-    ghcOptNoLink             = combine ghcOptNoLink,
-    ghcOptLinkNoHsMain       = combine ghcOptLinkNoHsMain,
-    ghcOptCcOptions          = combine ghcOptCcOptions,
-    ghcOptCppOptions         = combine ghcOptCppOptions,
-    ghcOptCppIncludePath     = combine ghcOptCppIncludePath,
-    ghcOptCppIncludes        = combine ghcOptCppIncludes,
-    ghcOptFfiIncludes        = combine ghcOptFfiIncludes,
-    ghcOptLanguage           = combine ghcOptLanguage,
-    ghcOptExtensions         = combine ghcOptExtensions,
-    ghcOptExtensionMap       = combine ghcOptExtensionMap,
-    ghcOptOptimisation       = combine ghcOptOptimisation,
-    ghcOptDebugInfo          = combine ghcOptDebugInfo,
-    ghcOptProfilingMode      = combine ghcOptProfilingMode,
-    ghcOptProfilingAuto      = combine ghcOptProfilingAuto,
-    ghcOptSplitObjs          = combine ghcOptSplitObjs,
-    ghcOptNumJobs            = combine ghcOptNumJobs,
-    ghcOptHPCDir             = combine ghcOptHPCDir,
-    ghcOptGHCiScripts        = combine ghcOptGHCiScripts,
-    ghcOptHiSuffix           = combine ghcOptHiSuffix,
-    ghcOptObjSuffix          = combine ghcOptObjSuffix,
-    ghcOptDynHiSuffix        = combine ghcOptDynHiSuffix,
-    ghcOptDynObjSuffix       = combine ghcOptDynObjSuffix,
-    ghcOptHiDir              = combine ghcOptHiDir,
-    ghcOptObjDir             = combine ghcOptObjDir,
-    ghcOptOutputDir          = combine ghcOptOutputDir,
-    ghcOptStubDir            = combine ghcOptStubDir,
-    ghcOptDynLinkMode        = combine ghcOptDynLinkMode,
-    ghcOptShared             = combine ghcOptShared,
-    ghcOptFPic               = combine ghcOptFPic,
-    ghcOptDylibName          = combine ghcOptDylibName,
-    ghcOptRPaths             = combine ghcOptRPaths,
-    ghcOptVerbosity          = combine ghcOptVerbosity,
-    ghcOptCabal              = combine ghcOptCabal
-  }
-    where
-      combine field = field a `mappend` field b
+  (<>) = gmappend

Cabal/Distribution/Simple/Setup.hs

@@ -239,18 +239,11 @@ emptyGlobalFlags :: GlobalFlags
 emptyGlobalFlags = mempty
 
 instance Monoid GlobalFlags where
-  mempty = GlobalFlags {
-    globalVersion        = mempty,
-    globalNumericVersion = mempty
-  }
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup GlobalFlags where
-  a <> b = GlobalFlags {
-    globalVersion        = combine globalVersion,
-    globalNumericVersion = combine globalNumericVersion
-  }
-    where combine field = field a `mappend` field b
+  (<>) = gmappend
 
 -- ------------------------------------------------------------
 -- * Config flags
@@ -811,104 +804,11 @@ emptyConfigFlags :: ConfigFlags
 emptyConfigFlags = mempty
 
 instance Monoid ConfigFlags where
-  mempty = ConfigFlags {
-    configPrograms      = mempty,
-    configProgramPaths  = mempty,
-    configProgramArgs   = mempty,
-    configProgramPathExtra = mempty,
-    configHcFlavor      = mempty,
-    configHcPath        = mempty,
-    configHcPkg         = mempty,
-    configVanillaLib    = mempty,
-    configProfLib       = mempty,
-    configSharedLib     = mempty,
-    configDynExe        = mempty,
-    configProfExe       = mempty,
-    configProf          = mempty,
-    configProfDetail    = mempty,
-    configProfLibDetail = mempty,
-    configConfigureArgs = mempty,
-    configOptimization  = mempty,
-    configProgPrefix    = mempty,
-    configProgSuffix    = mempty,
-    configInstallDirs   = mempty,
-    configScratchDir    = mempty,
-    configDistPref      = mempty,
-    configVerbosity     = mempty,
-    configUserInstall   = mempty,
-    configPackageDBs    = mempty,
-    configGHCiLib       = mempty,
-    configSplitObjs     = mempty,
-    configStripExes     = mempty,
-    configStripLibs     = mempty,
-    configExtraLibDirs  = mempty,
-    configExtraFrameworkDirs = mempty,
-    configConstraints   = mempty,
-    configDependencies  = mempty,
-    configExtraIncludeDirs    = mempty,
-    configIPID          = mempty,
-    configConfigurationsFlags = mempty,
-    configTests               = mempty,
-    configCoverage         = mempty,
-    configLibCoverage   = mempty,
-    configExactConfiguration  = mempty,
-    configBenchmarks          = mempty,
-    configFlagError     = mempty,
-    configRelocatable   = mempty,
-    configDebugInfo     = mempty,
-    configAllowNewer    = mempty
-  }
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup ConfigFlags where
-  a <> b =  ConfigFlags {
-    configPrograms      = combine configPrograms,
-    configProgramPaths  = combine configProgramPaths,
-    configProgramArgs   = combine configProgramArgs,
-    configProgramPathExtra = combine configProgramPathExtra,
-    configHcFlavor      = combine configHcFlavor,
-    configHcPath        = combine configHcPath,
-    configHcPkg         = combine configHcPkg,
-    configVanillaLib    = combine configVanillaLib,
-    configProfLib       = combine configProfLib,
-    configSharedLib     = combine configSharedLib,
-    configDynExe        = combine configDynExe,
-    configProfExe       = combine configProfExe,
-    configProf          = combine configProf,
-    configProfDetail    = combine configProfDetail,
-    configProfLibDetail = combine configProfLibDetail,
-    configConfigureArgs = combine configConfigureArgs,
-    configOptimization  = combine configOptimization,
-    configProgPrefix    = combine configProgPrefix,
-    configProgSuffix    = combine configProgSuffix,
-    configInstallDirs   = combine configInstallDirs,
-    configScratchDir    = combine configScratchDir,
-    configDistPref      = combine configDistPref,
-    configVerbosity     = combine configVerbosity,
-    configUserInstall   = combine configUserInstall,
-    configPackageDBs    = combine configPackageDBs,
-    configGHCiLib       = combine configGHCiLib,
-    configSplitObjs     = combine configSplitObjs,
-    configStripExes     = combine configStripExes,
-    configStripLibs     = combine configStripLibs,
-    configExtraLibDirs  = combine configExtraLibDirs,
-    configExtraFrameworkDirs = combine configExtraFrameworkDirs,
-    configConstraints   = combine configConstraints,
-    configDependencies  = combine configDependencies,
-    configExtraIncludeDirs    = combine configExtraIncludeDirs,
-    configIPID          = combine configIPID,
-    configConfigurationsFlags = combine configConfigurationsFlags,
-    configTests               = combine configTests,
-    configCoverage         = combine configCoverage,
-    configLibCoverage         = combine configLibCoverage,
-    configExactConfiguration  = combine configExactConfiguration,
-    configBenchmarks          = combine configBenchmarks,
-    configFlagError     = combine configFlagError,
-    configRelocatable   = combine configRelocatable,
-    configDebugInfo     = combine configDebugInfo,
-    configAllowNewer    = combine configAllowNewer
-  }
-    where combine field = field a `mappend` field b
+  (<>) = gmappend
 
 -- ------------------------------------------------------------
 -- * Copy flags
@@ -959,20 +859,11 @@ emptyCopyFlags :: CopyFlags
 emptyCopyFlags = mempty
 
 instance Monoid CopyFlags where
-  mempty = CopyFlags {
-    copyDest      = mempty,
-    copyDistPref  = mempty,
-    copyVerbosity = mempty
-  }
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup CopyFlags where
-  a <> b = CopyFlags {
-    copyDest      = combine copyDest,
-    copyDistPref  = combine copyDistPref,
-    copyVerbosity = combine copyVerbosity
-  }
-    where combine field = field a `mappend` field b
+  (<>) = gmappend
 
 -- ------------------------------------------------------------
 -- * Install flags
@@ -1039,24 +930,11 @@ emptyInstallFlags :: InstallFlags
 emptyInstallFlags = mempty
 
 instance Monoid InstallFlags where
-  mempty = InstallFlags{
-    installPackageDB = mempty,
-    installDistPref  = mempty,
-    installUseWrapper = mempty,
-    installInPlace    = mempty,
-    installVerbosity = mempty
-  }
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup InstallFlags where
-  a <> b = InstallFlags{
-    installPackageDB = combine installPackageDB,
-    installDistPref  = combine installDistPref,
-    installUseWrapper = combine installUseWrapper,
-    installInPlace    = combine installInPlace,
-    installVerbosity = combine installVerbosity
-  }
-    where combine field = field a `mappend` field b
+  (<>) = gmappend
 
 -- ------------------------------------------------------------
 -- * SDist flags
@@ -1119,24 +997,11 @@ emptySDistFlags :: SDistFlags
 emptySDistFlags = mempty
 
 instance Monoid SDistFlags where
-  mempty = SDistFlags {
-    sDistSnapshot    = mempty,
-    sDistDirectory   = mempty,
-    sDistDistPref    = mempty,
-    sDistListSources = mempty,
-    sDistVerbosity   = mempty
-  }
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup SDistFlags where
-  a <> b = SDistFlags {
-    sDistSnapshot    = combine sDistSnapshot,
-    sDistDirectory   = combine sDistDirectory,
-    sDistDistPref    = combine sDistDistPref,
-    sDistListSources = combine sDistListSources,
-    sDistVerbosity   = combine sDistVerbosity
-  }
-    where combine field = field a `mappend` field b
+  (<>) = gmappend
 
 -- ------------------------------------------------------------
 -- * Register flags
@@ -1245,28 +1110,11 @@ emptyRegisterFlags :: RegisterFlags
 emptyRegisterFlags = mempty
 
 instance Monoid RegisterFlags where
-  mempty = RegisterFlags {
-    regPackageDB   = mempty,
-    regGenScript   = mempty,
-    regGenPkgConf  = mempty,
-    regInPlace     = mempty,
-    regPrintId     = mempty,
-    regDistPref    = mempty,
-    regVerbosity   = mempty
-  }
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup RegisterFlags where
-  a <> b = RegisterFlags {
-    regPackageDB   = combine regPackageDB,
-    regGenScript   = combine regGenScript,
-    regGenPkgConf  = combine regGenPkgConf,
-    regInPlace     = combine regInPlace,
-    regPrintId     = combine regPrintId,
-    regDistPref    = combine regDistPref,
-    regVerbosity   = combine regVerbosity
-  }
-    where combine field = field a `mappend` field b
+  (<>) = gmappend
 
 -- ------------------------------------------------------------
 -- * HsColour flags
@@ -1296,26 +1144,11 @@ defaultHscolourFlags = HscolourFlags {
   }
 
 instance Monoid HscolourFlags where
-  mempty = HscolourFlags {
-    hscolourCSS         = mempty,
-    hscolourExecutables = mempty,
-    hscolourTestSuites  = mempty,
-    hscolourBenchmarks  = mempty,
-    hscolourDistPref    = mempty,
-    hscolourVerbosity   = mempty
-  }
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup HscolourFlags where
-  a <> b = HscolourFlags {
-    hscolourCSS         = combine hscolourCSS,
-    hscolourExecutables = combine hscolourExecutables,
-    hscolourTestSuites  = combine hscolourTestSuites,
-    hscolourBenchmarks  = combine hscolourBenchmarks,
-    hscolourDistPref    = combine hscolourDistPref,
-    hscolourVerbosity   = combine hscolourVerbosity
-  }
-    where combine field = field a `mappend` field b
+  (<>) = gmappend
 
 hscolourCommand :: CommandUI HscolourFlags
 hscolourCommand = CommandUI
@@ -1526,48 +1359,11 @@ emptyHaddockFlags :: HaddockFlags
 emptyHaddockFlags = mempty
 
 instance Monoid HaddockFlags where
-  mempty = HaddockFlags {
-    haddockProgramPaths = mempty,
-    haddockProgramArgs  = mempty,
-    haddockHoogle       = mempty,
-    haddockHtml         = mempty,
-    haddockHtmlLocation = mempty,
-    haddockForHackage   = mempty,
-    haddockExecutables  = mempty,
-    haddockTestSuites   = mempty,
-    haddockBenchmarks   = mempty,
-    haddockInternal     = mempty,
-    haddockCss          = mempty,
-    haddockHscolour     = mempty,
-    haddockHscolourCss  = mempty,
-    haddockContents     = mempty,
-    haddockDistPref     = mempty,
-    haddockKeepTempFiles= mempty,
-    haddockVerbosity    = mempty
-  }
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup HaddockFlags where
-  a <> b = HaddockFlags {
-    haddockProgramPaths = combine haddockProgramPaths,
-    haddockProgramArgs  = combine haddockProgramArgs,
-    haddockHoogle       = combine haddockHoogle,
-    haddockHtml         = combine haddockHtml,
-    haddockHtmlLocation = combine haddockHtmlLocation,
-    haddockForHackage   = combine haddockForHackage,
-    haddockExecutables  = combine haddockExecutables,
-    haddockTestSuites   = combine haddockTestSuites,
-    haddockBenchmarks   = combine haddockBenchmarks,
-    haddockInternal     = combine haddockInternal,
-    haddockCss          = combine haddockCss,
-    haddockHscolour     = combine haddockHscolour,
-    haddockHscolourCss  = combine haddockHscolourCss,
-    haddockContents     = combine haddockContents,
-    haddockDistPref     = combine haddockDistPref,
-    haddockKeepTempFiles= combine haddockKeepTempFiles,
-    haddockVerbosity    = combine haddockVerbosity
-  }
-    where combine field = field a `mappend` field b
+  (<>) = gmappend
 
 -- ------------------------------------------------------------
 -- * Clean flags
@@ -1614,20 +1410,11 @@ emptyCleanFlags :: CleanFlags
 emptyCleanFlags = mempty
 
 instance Monoid CleanFlags where
-  mempty = CleanFlags {
-    cleanSaveConf  = mempty,
-    cleanDistPref  = mempty,
-    cleanVerbosity = mempty
-  }
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup CleanFlags where
-  a <> b = CleanFlags {
-    cleanSaveConf  = combine cleanSaveConf,
-    cleanDistPref  = combine cleanDistPref,
-    cleanVerbosity = combine cleanVerbosity
-  }
-    where combine field = field a `mappend` field b
+  (<>) = gmappend
 
 -- ------------------------------------------------------------
 -- * Build flags
@@ -1718,26 +1505,11 @@ emptyBuildFlags :: BuildFlags
 emptyBuildFlags = mempty
 
 instance Monoid BuildFlags where
-  mempty = BuildFlags {
-    buildProgramPaths = mempty,
-    buildProgramArgs = mempty,
-    buildVerbosity   = mempty,
-    buildDistPref    = mempty,
-    buildNumJobs     = mempty,
-    buildArgs        = mempty
-  }
+  mempty = gmempty
   mappend = (Semi.<>)
 
 instance Semigroup BuildFlags where
-  a <> b = BuildFlags {
-    buildProgramPaths = combine buildProgramPaths,
-    buildProgramArgs = combine buildProgramArgs,
-    buildVerbosity   = combine buildVerbosity,
-    buildDistPref    = combine buildDistPref,
-    buildNumJobs     = combine buildNumJobs,
-    buildArgs        = combine buildArgs
-  }
-    where combine field = field a `mappend` field b
+  (<>) = gmappend
 
 -- ------------------------------------------------------------
 -- * REPL Flags
@@ -1762,24 +1534,11 @@ defaultReplFlags  = ReplFlags {
   }
 
 instance Monoid ReplFlags where
-  mempty = ReplFlags {
-    replProgramPaths = mempty,