fetchgit: make sparseCheckout a list of strings

The `sparseCheckout` argument allows the user to specify directories or
patterns of files, which Git uses to filter files it should check-out.

Git expects a multi-line string on stdin ("newline-delimited list", see
`git-sparse-checkout(1)`), but within nixpkgs it is more consistent to
use a list of strings instead. The list elements are joined to a
multi-line string only before passing it to the builder script.

A deprecation warning is emitted if a (multi-line) string is passed to
`sparseCheckout`, but for the time being it is still accepted.

1 files changed, 11 insertions, 3 deletions

diff --git a/pkgs/build-support/fetchgit/default.nix b/pkgs/build-support/fetchgit/default.nix
index f516c3d5a03..1fec0c88747 100644
--- a/pkgs/build-support/fetchgit/default.nix
+++ b/pkgs/build-support/fetchgit/default.nix
@@ -15,7 +15,7 @@ in
 { url, rev ? "HEAD", md5 ? "", sha256 ? "", hash ? "", leaveDotGit ? deepClone
 , fetchSubmodules ? true, deepClone ? false
 , branchName ? null
-, sparseCheckout ? ""
+, sparseCheckout ? []
 , nonConeMode ? false
 , name ? urlToName url rev
 , # Shell code executed after the file has been fetched
@@ -55,13 +55,16 @@ in
 */
 
 assert deepClone -> leaveDotGit;
-assert nonConeMode -> (sparseCheckout != "");
+assert nonConeMode -> !(sparseCheckout == "" || sparseCheckout == []);
 
 if md5 != "" then
   throw "fetchgit does not support md5 anymore, please use sha256"
 else if hash != "" && sha256 != "" then
   throw "Only one of sha256 or hash can be set"
 else
+# Added 2022-11-12
+lib.warnIf (builtins.isString sparseCheckout)
+  "Please provide directories/patterns for sparse checkout as a list of strings. Support for passing a (multi-line) string is deprecated and will be removed in the next release."
 stdenvNoCC.mkDerivation {
   inherit name;
   builder = ./builder.sh;
@@ -79,7 +82,12 @@ stdenvNoCC.mkDerivation {
   else
     lib.fakeSha256;
 
-  inherit url rev leaveDotGit fetchLFS fetchSubmodules deepClone branchName sparseCheckout nonConeMode postFetch;
+  # git-sparse-checkout(1) says:
+  # > When the --stdin option is provided, the directories or patterns are read
+  # > from standard in as a newline-delimited list instead of from the arguments.
+  sparseCheckout = if builtins.isString sparseCheckout then sparseCheckout else builtins.concatStringsSep "\n" sparseCheckout;
+
+  inherit url rev leaveDotGit fetchLFS fetchSubmodules deepClone branchName nonConeMode postFetch;
 
   postHook = if netrcPhase == null then null else ''
     ${netrcPhase}