[llvm] 6e890ec - [CMake] Avoid __FakeVCSRevision.h with no git repository

[Jonas Hahnfeld via llvm-commits]

Author: Jonas Hahnfeld
Date: 2020-12-16T17:33:20+01:00
New Revision: 6e890ec7beb0874464a0af9f84e41a987f968b23

URL: https://github.com/llvm/llvm-project/commit/6e890ec7beb0874464a0af9f84e41a987f968b23
DIFF: https://github.com/llvm/llvm-project/commit/6e890ec7beb0874464a0af9f84e41a987f968b23.diff

LOG: [CMake] Avoid __FakeVCSRevision.h with no git repository

Set the return variable to "" in find_first_existing_vc_file to
say that there is a repository, but no file to depend on. This works
transparently for all other callers that handle undefinedness and
equality to an empty string the same way.

Use the knowledge to avoid depending on __FakeVCSRevision.h if there
is no git repository at all (for example when building a release) as
there is no point in regenerating an empty VCSRevision.h.

Differential Revision: https://reviews.llvm.org/D92718

Added: 
    

Modified: 
    llvm/cmake/modules/AddLLVM.cmake
    llvm/include/llvm/Support/CMakeLists.txt

Removed: 
    


################################################################################
diff  --git a/llvm/cmake/modules/AddLLVM.cmake b/llvm/cmake/modules/AddLLVM.cmake
index a3e9eaeeb262..b86fbdaaa6d8 100644
--- a/llvm/cmake/modules/AddLLVM.cmake
+++ b/llvm/cmake/modules/AddLLVM.cmake
@@ -2135,6 +2135,13 @@ function(setup_dependency_debugging name)
   set_target_properties(${name} PROPERTIES RULE_LAUNCH_COMPILE ${sandbox_command})
 endfunction()
 
+# If the sources at the given `path` are under version control, set `out_var`
+# to the the path of a file which will be modified when the VCS revision
+# changes, attempting to create that file if it does not exist; if no such
+# file exists and one cannot be created, instead set `out_var` to the
+# empty string.
+#
+# If the sources are not under version control, do not define `out_var`.
 function(find_first_existing_vc_file path out_var)
   if(NOT EXISTS "${path}")
     return()
@@ -2156,6 +2163,7 @@ function(find_first_existing_vc_file path out_var)
           RESULT_VARIABLE touch_head_result
           ERROR_QUIET)
         if (NOT touch_head_result EQUAL 0)
+          set(${out_var} "" PARENT_SCOPE)
           return()
         endif()
       endif()

diff  --git a/llvm/include/llvm/Support/CMakeLists.txt b/llvm/include/llvm/Support/CMakeLists.txt
index aa71b5572181..aeb5866ecbdd 100644
--- a/llvm/include/llvm/Support/CMakeLists.txt
+++ b/llvm/include/llvm/Support/CMakeLists.txt
@@ -11,7 +11,7 @@ if(LLVM_APPEND_VC_REV)
   # A fake version file and is not expected to exist. It is being used to
   # force regeneration of VCSRevision.h for source directory with no write
   # permission available.
-  if (NOT llvm_vc)
+  if (llvm_vc STREQUAL "")
     set(fake_version_inc "${CMAKE_CURRENT_BINARY_DIR}/__FakeVCSRevision.h")
   endif()
 endif()