fetchzip, fetchgit: cleanup handling of optional features and whitespace

No intended functional difference, just trying to polish to make this easier to
extend and more aligned with other nix conventions.

pkgs/build-support/fetchzip/default.nix

@@ -5,47 +5,46 @@
 # (e.g. due to minor changes in the compression algorithm, or changes
 # in timestamps).
 
-{ fetchurl, unzip }:
+{ lib, fetchurl, unzip }:
 
-{ # Optionally move the contents of the unpacked tree up one level.
-  stripRoot ? true
+{ name ? "source"
 , url
+  # Optionally move the contents of the unpacked tree up one level.
+, stripRoot ? true
 , extraPostFetch ? ""
-, name ? "source"
 , ... } @ args:
 
 (fetchurl ({
   inherit name;
 
   recursiveHash = true;
-
   downloadToTemp = true;
 
-  postFetch =
-    ''
-      unpackDir="$TMPDIR/unpack"
-      mkdir "$unpackDir"
-      cd "$unpackDir"
+  postFetch = ''
+    unpackDir="$TMPDIR/unpack"
+    mkdir "$unpackDir"
+    cd "$unpackDir"
+
+    renamed="$TMPDIR/${baseNameOf url}"
+    mv "$downloadedFile" "$renamed"
+    unpackFile "$renamed"
+    result=$unpackDir
+  ''
+  # Most src disted tarballs have a parent directory like foo-1.2.3/ to strip
+  + lib.optionalString stripRoot ''
+    if [ $(ls "$unpackDir" | wc -l) != 1 ]; then
+      echo "error: zip file must contain a single file or directory."
+      echo "hint: Pass stripRoot=false; to fetchzip to assume flat list of files."
+      exit 1
+    fi
+    fn=$(cd "$unpackDir" && echo *)
+    result="$unpackDir/$fn"
+  '' + ''
+    mkdir $out
+    mv "$result" "$out"
+  ''
+  + extraPostFetch;
 
-      renamed="$TMPDIR/${baseNameOf url}"
-      mv "$downloadedFile" "$renamed"
-      unpackFile "$renamed"
-    ''
-    + (if stripRoot then ''
-      if [ $(ls "$unpackDir" | wc -l) != 1 ]; then
-        echo "error: zip file must contain a single file or directory."
-        echo "hint: Pass stripRoot=false; to fetchzip to assume flat list of files."
-        exit 1
-      fi
-      fn=$(cd "$unpackDir" && echo *)
-      if [ -f "$unpackDir/$fn" ]; then
-        mkdir $out
-      fi
-      mv "$unpackDir/$fn" "$out"
-    '' else ''
-      mv "$unpackDir" "$out"
-    '') #*/
-    + extraPostFetch;
 } // removeAttrs args [ "stripRoot" "extraPostFetch" ])).overrideAttrs (x: {
   # Hackety-hack: we actually need unzip hooks, too
   nativeBuildInputs = x.nativeBuildInputs ++ [ unzip ];