Implement Xgit.Core.FilePath.starts_with?/2.

lib/xgit/core/file_path.ex

@@ -534,6 +534,18 @@ defmodule Xgit.Core.FilePath do
   defp to_lower(b) when b >= ?A and b <= ?Z, do: cover(b + 32)
   defp to_lower(b), do: cover(b)
 
+  @doc ~S"""
+  Returns `true` if `path` starts with `prefix`.
+
+  Unlike `String.starts_with?/2`, only accepts a single prefix path.
+  """
+  @spec starts_with?(path :: t, prefix :: t) :: boolean
+  def starts_with?(path, prefix)
+
+  def starts_with?(_path, []), do: cover(true)
+  def starts_with?([c | path], [c | prefix]), do: starts_with?(path, prefix)
+  def starts_with?(_path, _prefix), do: cover(false)
+
   @doc ~S"""
   Ensure that a trailing `/` is present.
 

test/xgit/core/file_path_test.exs

@@ -491,6 +491,17 @@ defmodule Xgit.Core.FilePathTest do
     end
   end
 
+  test "starts_with?/2" do
+    assert starts_with?('', '')
+    assert starts_with?('abc', '')
+    assert starts_with?('abc', 'a')
+    assert starts_with?('abc', 'abc')
+    refute starts_with?('xabc', 'abc')
+    refute starts_with?('abc', 'abd')
+    refute starts_with?('ab', 'abc')
+    refute starts_with?('', 'a')
+  end
+
   describe "ensure_trailing_separator/1" do
     test "empty list" do
       assert ensure_trailing_separator([]) == []