lib.fileset: Refactor gitTracked and gitTrackedWith

Introduce an internal function for them to share more behavior.
This makes future changes easier.

lib/fileset/default.nix

@@ -107,7 +107,7 @@ let
     _printFileset
     _intersection
     _difference
-    _mirrorStorePath
+    _fromFetchGit
     _fetchGitSubmodulesMinver
     _emptyWithoutBase
     ;
@@ -148,7 +148,6 @@ let
   inherit (lib.trivial)
     isFunction
     pipe
-    inPureEvalMode
     ;
 
 in {
@@ -754,18 +753,11 @@ in {
       This directory must contain a `.git` file or subdirectory.
     */
     path:
-    # See the gitTrackedWith implementation for more explanatory comments
+    _fromFetchGit
-    let
+      "gitTracked"
-      fetchResult = builtins.fetchGit path;
+      "argument"
-    in
+      path
-    if inPureEvalMode then
+      {};
-      throw "lib.fileset.gitTracked: This function is currently not supported in pure evaluation mode, since it currently relies on `builtins.fetchGit`. See https://github.com/NixOS/nix/issues/9292."
-    else if ! isPath path then
-      throw "lib.fileset.gitTracked: Expected the argument to be a path, but it's a ${typeOf path} instead."
-    else if ! pathExists (path + "/.git") then
-      throw "lib.fileset.gitTracked: Expected the argument (${toString path}) to point to a local working tree of a Git repository, but it's not."
-    else
-      _mirrorStorePath path fetchResult.outPath;
 
   /*
     Create a file set containing all [Git-tracked files](https://git-scm.com/book/en/v2/Git-Basics-Recording-Changes-to-the-Repository) in a repository.
@@ -807,35 +799,19 @@ in {
       This directory must contain a `.git` file or subdirectory.
     */
     path:
-    let
+    if ! isBool recurseSubmodules then
-      # This imports the files unnecessarily, which currently can't be avoided
-      # because `builtins.fetchGit` is the only function exposing which files are tracked by Git.
-      # With the [lazy trees PR](https://github.com/NixOS/nix/pull/6530),
-      # the unnecessarily import could be avoided.
-      # However a simpler alternative still would be [a builtins.gitLsFiles](https://github.com/NixOS/nix/issues/2944).
-      fetchResult = builtins.fetchGit {
-        url = path;
-
-        # This is the only `fetchGit` parameter that makes sense in this context.
-        # We can't just pass `submodules = recurseSubmodules` here because
-        # this would fail for Nix versions that don't support `submodules`.
-        ${if recurseSubmodules then "submodules" else null} = true;
-      };
-    in
-    if inPureEvalMode then
-      throw "lib.fileset.gitTrackedWith: This function is currently not supported in pure evaluation mode, since it currently relies on `builtins.fetchGit`. See https://github.com/NixOS/nix/issues/9292."
-    else if ! isBool recurseSubmodules then
       throw "lib.fileset.gitTrackedWith: Expected the attribute `recurseSubmodules` of the first argument to be a boolean, but it's a ${typeOf recurseSubmodules} instead."
     else if recurseSubmodules && versionOlder nixVersion _fetchGitSubmodulesMinver then
       throw "lib.fileset.gitTrackedWith: Setting the attribute `recurseSubmodules` to `true` is only supported for Nix version ${_fetchGitSubmodulesMinver} and after, but Nix version ${nixVersion} is used."
-    else if ! isPath path then
-      throw "lib.fileset.gitTrackedWith: Expected the second argument to be a path, but it's a ${typeOf path} instead."
-    # We can identify local working directories by checking for .git,
-    # see https://git-scm.com/docs/gitrepository-layout#_description.
-    # Note that `builtins.fetchGit` _does_ work for bare repositories (where there's no `.git`),
-    # even though `git ls-files` wouldn't return any files in that case.
-    else if ! pathExists (path + "/.git") then
-      throw "lib.fileset.gitTrackedWith: Expected the second argument (${toString path}) to point to a local working tree of a Git repository, but it's not."
     else
-      _mirrorStorePath path fetchResult.outPath;
+      _fromFetchGit
+        "gitTrackedWith"
+        "second argument"
+        path
+        # This is the only `fetchGit` parameter that makes sense in this context.
+        # We can't just pass `submodules = recurseSubmodules` here because
+        # this would fail for Nix versions that don't support `submodules`.
+        (lib.optionalAttrs recurseSubmodules {
+          submodules = true;
+        });
 }

lib/fileset/internal.nix

@@ -10,6 +10,7 @@ let
     split
     trace
     typeOf
+    fetchGit
     ;
 
   inherit (lib.attrsets)
@@ -55,6 +56,9 @@ let
     hasSuffix
     ;
 
+  inherit (lib.trivial)
+    inPureEvalMode
+    ;
 in
 # Rare case of justified usage of rec:
 # - This file is internal, so the return value doesn't matter, no need to make things overridable
@@ -852,4 +856,31 @@ rec {
     in
     _create localPath
       (recurse storePath);
+
+  # Create a file set from the files included in the result of a fetchGit call
+  # Type: String -> String -> Path -> Attrs -> FileSet
+  _fromFetchGit = function: argument: path: extraFetchGitAttrs:
+    let
+      # This imports the files unnecessarily, which currently can't be avoided
+      # because `builtins.fetchGit` is the only function exposing which files are tracked by Git.
+      # With the [lazy trees PR](https://github.com/NixOS/nix/pull/6530),
+      # the unnecessarily import could be avoided.
+      # However a simpler alternative still would be [a builtins.gitLsFiles](https://github.com/NixOS/nix/issues/2944).
+      fetchResult = fetchGit ({
+        url = path;
+      } // extraFetchGitAttrs);
+    in
+    if inPureEvalMode then
+      throw "lib.fileset.${function}: This function is currently not supported in pure evaluation mode, since it currently relies on `builtins.fetchGit`. See https://github.com/NixOS/nix/issues/9292."
+    else if ! isPath path then
+      throw "lib.fileset.${function}: Expected the ${argument} to be a path, but it's a ${typeOf path} instead."
+    # We can identify local working directories by checking for .git,
+    # see https://git-scm.com/docs/gitrepository-layout#_description.
+    # Note that `builtins.fetchGit` _does_ work for bare repositories (where there's no `.git`),
+    # even though `git ls-files` wouldn't return any files in that case.
+    else if ! pathExists (path + "/.git") then
+      throw "lib.fileset.${function}: Expected the ${argument} (${toString path}) to point to a local working tree of a Git repository, but it's not."
+    else
+      _mirrorStorePath path fetchResult.outPath;
+
 }