pkgs/build-support/fetchgit: add fetchTags parameter

Added fetchTags feature to fetchgit, explicit and clear support for
fetching all tags after the source tree fetch completes. Doing this at
build-time in the fetcher is required for packages that invoke commands
like 'git describe' which require tags, and since the nix store is
read-only by design, it is not possible to git fetch --tags at
activation- or run-time. This feature may have been possible by
specifying a postFetch option including calling git fetch --tags,
however doing so obfuscates the solution to this very real problem.
Explicit support for fetching tags should be a first class citizen just
like fetching other refs.

.gitignore

@@ -8,6 +8,7 @@
 .nixos-test-history
 .vscode/
 .helix/
+*.vim
 outputs/
 result-*
 result

doc/build-helpers/fetchers.chapter.md

@@ -795,6 +795,10 @@ Additionally, the following optional arguments can be given:
 : Clone the entire repository as opposing to just creating a shallow clone.
   This implies `leaveDotGit`.
 
+*`fetchTags`* (Boolean)
+
+: Whether to fetch all tags from the remote repository. This is useful when the build process needs to run `git describe` or other commands that require tag information to be available. This parameter implies `leaveDotGit`, as tags are stored in the `.git` directory.
+
 *`sparseCheckout`* (List of String)
 
 : Prevent git from fetching unnecessary blobs from server.

pkgs/build-support/fetchgit/builder.sh

@@ -13,6 +13,7 @@ $SHELL $fetcher --builder --url "$url" --out "$out" --rev "$rev" --name "$name"
   ${fetchLFS:+--fetch-lfs} \
   ${deepClone:+--deepClone} \
   ${fetchSubmodules:+--fetch-submodules} \
+  ${fetchTags:+--fetch-tags} \
   ${sparseCheckout:+--sparse-checkout "$sparseCheckout"} \
   ${nonConeMode:+--non-cone-mode} \
   ${branchName:+--branch-name "$branchName"}

pkgs/build-support/fetchgit/default.nix

@@ -28,7 +28,7 @@ lib.makeOverridable (
       url,
       tag ? null,
       rev ? null,
-      leaveDotGit ? deepClone,
+      leaveDotGit ? deepClone || fetchTags,
       outputHash ? lib.fakeHash,
       outputHashAlgo ? null,
       fetchSubmodules ? true,
@@ -55,6 +55,8 @@ lib.makeOverridable (
       netrcImpureEnvVars ? [ ],
       meta ? { },
       allowedRequisites ? null,
+      # fetch all tags after tree (useful for git describe)
+      fetchTags ? false,
     }:
 
     /*
@@ -81,6 +83,7 @@ lib.makeOverridable (
     */
 
     assert nonConeMode -> (sparseCheckout != [ ]);
+    assert fetchTags -> leaveDotGit;
 
     let
       revWithTag =
@@ -136,6 +139,7 @@ lib.makeOverridable (
           nonConeMode
           preFetch
           postFetch
+          fetchTags
           ;
         rev = revWithTag;
 

pkgs/build-support/fetchgit/nix-prefetch-git

@@ -11,6 +11,7 @@ leaveDotGit=$NIX_PREFETCH_GIT_LEAVE_DOT_GIT
 fetchSubmodules=
 fetchLFS=
 builder=
+fetchTags=
 branchName=$NIX_PREFETCH_GIT_BRANCH_NAME
 
 # ENV params
@@ -56,6 +57,7 @@ Options:
       --leave-dotGit  Keep the .git directories.
       --fetch-lfs     Fetch git Large File Storage (LFS) files.
       --fetch-submodules Fetch submodules.
+      --fetch-tags    Fetch all tags (useful for git describe).
       --builder       Clone as fetchgit does, but url, rev, and out option are mandatory.
       --quiet         Only print the final json summary.
 "
@@ -86,6 +88,7 @@ for arg; do
             --leave-dotGit) leaveDotGit=true;;
             --fetch-lfs) fetchLFS=true;;
             --fetch-submodules) fetchSubmodules=true;;
+            --fetch-tags) fetchTags=true;;
             --builder) builder=true;;
             -h|--help) usage; exit;;
             *)
@@ -234,6 +237,12 @@ clone(){
         exit 1
     )
 
+    # Fetch all tags if requested
+    if test -n "$fetchTags"; then
+        echo "fetching all tags..." >&2
+        clean_git fetch origin 'refs/tags/*:refs/tags/*' || echo "warning: failed to fetch some tags" >&2
+    fi
+
     # Checkout linked sources.
     if test -n "$fetchSubmodules"; then
         init_submodules
@@ -403,6 +412,7 @@ print_results() {
   "fetchLFS": $([[ -n "$fetchLFS" ]] && echo true || echo false),
   "fetchSubmodules": $([[ -n "$fetchSubmodules" ]] && echo true || echo false),
   "deepClone": $([[ -n "$deepClone" ]] && echo true || echo false),
+  "fetchTags": $([[ -n "$fetchTags" ]] && echo true || echo false),
   "leaveDotGit": $([[ -n "$leaveDotGit" ]] && echo true || echo false)
 }
 EOF

pkgs/build-support/fetchgit/tests.nix

@@ -83,4 +83,16 @@
     rev = "v3.0.14";
     sha256 = "sha256-bd0Lx75Gd1pcBJtwz5WGki7XoYSpqhinCT3a77wpY2c=";
   };
+
+  fetchTags = testers.invalidateFetcherByDrvHash fetchgit {
+    name = "fetchgit-fetch-tags-test";
+    url = "https://github.com/NixOS/nix";
+    rev = "9d9dbe6ed05854e03811c361a3380e09183f4f4a";
+    fetchTags = true;
+    leaveDotGit = true;
+    sha256 = "sha256-2vfZnYjZlnC8ODz6B6aOqAqtb1Wbjojnn/5TmzwUrmo=";
+    postFetch = ''
+      cd $out && git describe --tags --always > describe-output.txt 2>&1 || echo "git describe failed" > describe-output.txt
+    '';
+  };
 }