patch-git: Do not use --filter with --unshallow on old git versions

Before git 2.28, --filter cannot be used if the clone did not use
it.

Related: RHEL-111490

patch-git.lua

@@ -283,6 +283,74 @@ do
    end
 end
 
+-- Sort the list lexicographically, in place, treating sequences of
+-- digits as a single positive decimal number.
+local function version_sort(list)
+   -- Sorting is only needed for two or more elements.
+   if #list <= 1 then
+      return
+   end
+
+   -- Maximum length of a sequence of consecutive digits in patch names.
+   local max_width = 1
+   for i=1,#list do
+      local s = list[i]
+      for number in string.gmatch(s, '%d+') do
+         if #number > max_width then
+            max_width = #number
+         end
+      end
+   end
+
+   -- Pad the number argument with leading '0' to max_width.
+   local function pad(s)
+      return string.rep('0', max_width - #s) .. s
+   end
+
+   local padded = {}
+   for i=1,#list do
+      local s = list[i]
+      padded[s] = string.gsub(s, '%d+', pad)
+   end
+
+   table.sort(list, function (a, b)
+                 return padded[a] < padded[b]
+   end)
+end
+-- Tests for version_sort.
+do
+   local test = {'b2-30b', 'b1', 'b10', 'b2', 'a', 'b2-30', 'b2-4'}
+   version_sort(test)
+   assert(#test == 7)
+   assert(test[1] == 'a')
+   assert(test[2] == 'b1')
+   assert(test[3] == 'b2')
+   assert(test[4] == 'b2-4')
+   assert(test[5] == 'b2-30')
+   assert(test[6] == 'b2-30b')
+   assert(test[7] == 'b10')
+end
+
+-- Returns true if the git command version is at least that of the
+-- argument string.
+local check_git_version
+do
+   -- Cached version of the git command.
+   local git_version
+
+   function check_git_version(reference)
+      if not git_version then
+	 local output = run_git('version')
+	 git_version = assert(
+	    string.match(output, '^git version (%d[^\n]*)\n'), output)
+      end
+      -- If the reference version sorts first, the version check succeeds.
+      local sorted = {git_version, reference}
+      version_sort(sorted)
+      return sorted[1] == reference
+   end
+end
+
 -- Called to generate the files (if HEAD or the script version has changed).
 local function generate_files()
    -- True if %_sourcedir refers to a Git repository and git is installed.
@@ -311,7 +379,13 @@ local function generate_files()
    do
       local shallow = run_git('rev-parse --is-shallow-repository')
       if shallow == 'true\n' then
-         check_git('fetch --unshallow --filter=blob:none')
+	 if check_git_version('2.28') then
+	    check_git('fetch --unshallow --filter=blob:none')
+	 else
+	    -- 2.27 and earlier error out if the original clone did not
+	    -- use --filter.
+	    check_git('fetch --unshallow')
+	 end
       else
          assert(shallow == 'false\n', shallow)
       end
@@ -499,54 +573,6 @@ local function parse_commits()
    patchgit.commits = commits
 end
 
--- Sort the list lexicographically, in place, treating sequences of
--- digits as a single positive decimal number.
-local function version_sort(list)
-   -- Sorting is only needed for two or more elements.
-   if #list <= 1 then
-      return
-   end
-
-   -- Maximum length of a sequence of consecutive digits in patch names.
-   local max_width = 1
-   for i=1,#list do
-      local s = list[i]
-      for number in string.gmatch(s, '%d+') do
-         if #number > max_width then
-            max_width = #number
-         end
-      end
-   end
-
-   -- Pad the number argument with leading '0' to max_width.
-   local function pad(s)
-      return string.rep('0', max_width - #s) .. s
-   end
-
-   local padded = {}
-   for i=1,#list do
-      local s = list[i]
-      padded[s] = string.gsub(s, '%d+', pad)
-   end
-
-   table.sort(list, function (a, b)
-                 return padded[a] < padded[b]
-   end)
-end
--- Tests for version_sort.
-do
-   local test = {'b2-30b', 'b1', 'b10', 'b2', 'a', 'b2-30', 'b2-4'}
-   version_sort(test)
-   assert(#test == 7)
-   assert(test[1] == 'a')
-   assert(test[2] == 'b1')
-   assert(test[3] == 'b2')
-   assert(test[4] == 'b2-4')
-   assert(test[5] == 'b2-30')
-   assert(test[6] == 'b2-30b')
-   assert(test[7] == 'b10')
-end
-
 -- Inject the Patch: lines into the spec file, in the appropriate
 -- (commit) order.  Unapplied patches found in the source directory
 -- and that are not present in the Git history are applied last.