Implement new build rule: buildPackageLibrary.

src/Package/Library.hs

+{-# LANGUAGE NoImplicitPrelude #-}
+module Package.Library (buildPackageLibrary) where
+
+import Package.Base
+
+{- "/usr/bin/ar" q  
+libraries/deepseq/dist-install/build/libHSdeeps_FT5iVCELxOr62eHY0nbvnU.a
+@libraries/deepseq/dist-install/build/libHSdeeps_FT5iVCELxOr62eHY0nbvnU.a.contents
+-}
+
+--  "$$(XARGS)" $$(XARGS_OPTS) "$$($1_$2_AR)" $$($1_$2_AR_OPTS) $$($1_$2_EXTRA_AR_ARGS) $$@ < $$@.contents
+-- AR_OPTS            = $(SRC_AR_OPTS) $(WAY$(_way)_AR_OPTS) $(EXTRA_AR_OPTS)
+
+buildPackageLibrary :: Package -> TodoItem -> Rules ()
+buildPackageLibrary (Package _ path _) (stage, dist, _) =
+    let buildDir = path </> dist </> "build"
+        pkgData  = path </> dist </> "package-data.mk"
+    in
+    (buildDir <//> "*a") %> \out -> do
+        let way = detectWay $ tail $ takeExtension out
+        need ["shake/src/Package/Library.hs"]
+        depObjs <- pkgDepObjects path dist way
+        need depObjs
+        libObjs <- pkgLibObjects path dist stage way
+        terseRun Ar $ arArgs <+> out <+> libObjs