Handle some more edge cases.

src/MicroCabal/Backend/GHC.hs

@@ -110,8 +110,10 @@ findMainIs env (d:ds) fn = do
    else
     findMainIs env ds fn
 
+-- It can happen that there are no exposed modules.
+-- E.g., for a package only needed for certain versions.
 getExposedModules :: [Field] -> [String]
-getExposedModules flds = getFieldStrings flds (error "no exposed-modules") "exposed-modules"
+getExposedModules flds = getFieldStrings flds [] "exposed-modules"
 
 getOtherModules :: [Field] -> [String]
 getOtherModules flds = getFieldStrings flds [] "other-modules"
@@ -120,17 +122,21 @@ ghcBuildLib :: Env -> Section -> Section -> IO ()
 ghcBuildLib env (Section _ _ glob) (Section _ name flds) = do
   initDB env
   stdArgs <- setupStdArgs env flds
-  let mdls = getExposedModules flds
+  let emdls = getExposedModules flds
       omdls = getOtherModules flds
+      mdls = emdls ++ omdls
       ver  = getVersion glob "version"
       args = unwords $ ["-O"] ++ stdArgs ++
                        ["--make", "-no-link", "-this-unit-id", key ] ++
                        ["-fbuilding-cabal-package", "-static" ] ++
-                       (omdls ++ mdls) ++
+                       mdls ++
                        [ ">/dev/null" | verbose env <= 0 ]
       key = name ++ "-" ++ showVersion ver ++ "-mcabal"
-  message env 0 $ "Building library " ++ name ++ " with ghc"
-  cmd env $ "ghc " ++ args
+  if null mdls then
+    message env 0 $ "Building library " ++ name ++ " with ghc skipped, no modules"
+   else do
+    message env 0 $ "Building library " ++ name ++ " with ghc"
+    cmd env $ "ghc " ++ args
 
 ghcInstallExe :: Env -> Section -> Section -> IO ()
 ghcInstallExe env (Section _ _ _glob) (Section _ name _) = do
@@ -159,19 +165,21 @@ ghcInstallLib env (Section _ _ glob) (Section _ name flds) = do
       archOut = destDir </> "libHS" ++ namever ++ "-mcabal.a"
   mkdir env destDir
   rmrf env archOut
-  cmd env $ "ar -c -r -s " ++ archOut ++ " `find " ++ buildDir ++ " -name '*.o'`"
 
   let files = map mdlToHi (omdls ++ mdls)
       mdls = getExposedModules flds
       omdls = getOtherModules flds
       mdlToHi = (++ ".hi") . map (\ c -> if c == '.' then '/' else c)
-  copyFiles env buildDir files destDir
+
+  when (not (null files)) $ do
+    cmd env $ "ar -c -r -s " ++ archOut ++ " `find " ++ buildDir ++ " -name '*.o'`"
+    copyFiles env buildDir files destDir
 
   db <- getGhcDir env
   let extraLibs = getFieldStrings flds [] "extra-libraries"
       deps = getBuildDependsPkg flds
   depends <- nub <$> mapM (getPackageId env) deps
-  let desc = unlines
+  let desc = unlines $
         [ "name: " ++ name
         , "version: " ++ showVersion vers
         , "visibility: public"
@@ -182,10 +190,10 @@ ghcInstallLib env (Section _ _ glob) (Section _ name flds) = do
         , "import-dirs: " ++ destDir
         , "library-dirs: " ++ destDir
         , "library-dirs-static: " ++ destDir
-        , "hs-libraries: HS" ++ key
         , "extra-libraries: " ++ unwords extraLibs
         , "depends: " ++ unwords depends
-        ]
+        ] ++
+        [ "hs-libraries: HS" ++ key | not (null files) ]
       key = namever ++ "-mcabal"
       pkgFn = db </> key ++ ".conf"
       quiet = if verbose env > 0 then "" else " >/dev/null"

src/MicroCabal/Env.hs

@@ -1,5 +1,6 @@
 module MicroCabal.Env(
   Env(..),
+  Target(..),
   Backend(..),
   PackageName,
   message,
@@ -13,9 +14,13 @@ data Env = Env {
   verbose  :: Int,                -- how chatty, default is 0, -1=say nothing, 0=minimal messages, 1=debug info
   depth    :: Int,                -- nesting depth for recursive builds, default is 0
   recursive:: Bool,               -- do recursive builds, default is False
-  backend  :: Backend             -- which compiler to use, default is MHS
+  backend  :: Backend,            -- which compiler to use, default is MHS
+  targets  :: [Target]            -- only build/install these
   }
 
+data Target = TgtLib | TgtExe
+  deriving (Eq)
+
 data Backend = Backend {
   backendNameVers:: Env ->                       IO (String, Version), -- name and version
   doesPkgExist   :: Env -> PackageName        -> IO Bool,   -- is the package available in the database?

src/MicroCabal/Main.hs

@@ -41,7 +41,8 @@ setupEnv :: IO Env
 setupEnv = do
   home <- getEnv "HOME"
   let cdir = home </> ".mcabal"
-  return Env{ cabalDir = cdir, distDir = "dist-mcabal", verbose = 0, depth = 0, backend = mhsBackend, recursive = False }
+  return Env{ cabalDir = cdir, distDir = "dist-mcabal", verbose = 0, depth = 0,
+              backend = mhsBackend, recursive = False, targets = [TgtLib, TgtExe] }
 
 decodeCommonArgs :: Env -> IO (Env, [String])
 decodeCommonArgs env = do
@@ -236,10 +237,10 @@ build env = do
       info = FlagInfo { os = I.os, arch = I.arch, flags = [], impl = comp }
       ncbl@(Cabal sects) = normalize info cbl
       glob = getGlobal ncbl
-      sect s@(Section "executable" _ _) = buildExe env glob s
-      sect s@(Section "library"    _ _) = buildLib env glob s
+      sect s@(Section "executable" _ _) | TgtExe `elem` targets env = buildExe env glob s
+      sect s@(Section "library"    _ _) | TgtLib `elem` targets env = buildLib env glob s
       sect _ = return ()
-  mapM_ sect sects
+  mapM_ sect $ addMissing sects
 
 buildExe :: Env -> Section -> Section -> IO ()
 buildExe env glob sect@(Section _ name flds) = do
@@ -266,10 +267,16 @@ checkDep env pkg = do
     if recursive env then do
       let env' = env { depth = depth env + 1 }
       preserveCurrentDirectory $
-        cmdInstall env' [pkg]
+        cmdInstallLib env' [pkg]
     else
       error $ "dependency not installed: " ++ pkg
 
+-- If there is no section, except the global one, then just make a
+-- library section.
+addMissing :: [Section] -> [Section]
+addMissing [glb@(Section "global" _ flds)] = [glb, Section "library" (getFieldString flds "name") flds]
+addMissing sects = sects
+
 -----------------------------------------
 
 cmdInstall :: Env -> [String] -> IO ()
@@ -278,6 +285,9 @@ cmdInstall env args = do
   cmdBuild env args
   install env
 
+cmdInstallLib :: Env -> [String] -> IO ()
+cmdInstallLib env args = cmdInstall env{ targets = [TgtLib] } args
+
 install :: Env -> IO ()
 install env = do
   fn <- findCabalFile env
@@ -287,10 +297,10 @@ install env = do
       info = FlagInfo { os = I.os, arch = I.arch, flags = [], impl = comp }
       ncbl@(Cabal sects) = normalize info cbl
       glob = getGlobal ncbl
-      sect s@(Section "executable" _ _) = installExe env glob s
-      sect s@(Section "library"    _ _) = installLib env glob s
+      sect s@(Section "executable" _ _) | TgtExe `elem` targets env = installExe env glob s
+      sect s@(Section "library"    _ _) | TgtLib `elem` targets env = installLib env glob s
       sect _ = return ()
-  mapM_ sect sects
+  mapM_ sect $ addMissing sects
 
 installExe :: Env -> Section -> Section -> IO ()
 installExe env glob sect@(Section _ name _) = do

src/MicroCabal/Normalize.hs

@@ -45,7 +45,7 @@ libName (Cabal []) = undefined
 libName (Cabal (g@(Section _ _ gs):ss)) = Cabal $ g : map set ss
   where set (Section "library" "" fs) = Section "library" name fs
         set s = s
-        name = head $ [ n | Field "name" (VItem n) <- gs ] ++ [error "no name field"]  
+        name = getFieldString gs "name"
 
 reduce :: FlagInfo -> Cabal -> Cabal
 reduce info c = reduce' (addFlags c) c

src/MicroCabal/Parse.hs

@@ -421,7 +421,7 @@ parsers =
   , "package-url"                    # pFreeText
   , "stability"                      # pFreeText
   , "subdir"                         # pFreeText
-  , "synopsis"                       # pFreeText
+  , "synopsis"                       # pFreeTextX
   , "tested-with"                    # pFreeText
   , "version"                        # (VVersion <$> pVersion)
   -- test suite fields