commit 8dbefc3ca6ab7043efb85bcfb6b53aa22c31b1df
author Nate Avers <nathan.avers@alumni.case.edu> Thu Jul 23 22:25:22 2020 -0400
committer Brad King <brad.king@kitware.com> Fri Jul 24 09:39:06 2020 -0400
tree ca4a44de7dff99492415d222b1e1c0f783342d6c
parent d421274e3e11a0e6480358faa8a8e5cf48d7b3c2

ExternalProject: omit --no-checkout from git clone when using git 2.20.x.

The optimization from commit 627fc5b44f (ExternalProject: Avoid
unnecessary checkout on clone, 2019-07-29, v3.16.0-rc1~325^2) triggers a
bug in the Git 2.20.x series that is not in older or newer versions.
Drop the optimization for that specific range of Git versions.

Fixes: #21009

Modules/ExternalProject.cmake

diff --git a/Modules/ExternalProject.cmake b/Modules/ExternalProject.cmake
index 3a47090..aecc00b 100644
--- a/Modules/ExternalProject.cmake
+++ b/Modules/ExternalProject.cmake
@@ -1124,7 +1124,11 @@
     message(FATAL_ERROR "Tag for git checkout should not be empty.")
   endif()
 
-  set(git_clone_options "--no-checkout")
+  if(GIT_VERSION_STRING VERSION_LESS 2.20 OR 2.21 VERSION_LESS_EQUAL GIT_VERSION_STRING)
+    set(git_clone_options "--no-checkout")
+  else()
+    set(git_clone_options)
+  endif()
   if(git_shallow)
     if(NOT GIT_VERSION_STRING VERSION_LESS 1.7.10)
       list(APPEND git_clone_options "--depth 1 --no-single-branch")