[PATCH] D34955: [Basic] Detect Git submodule version in CMake

[Brian Gesiak via Phabricator via cfe-commits]

modocache created this revision.
Herald added a subscriber: mgorny.

When searching for Git version control information, libBasic's CMake
checks for the path '.git/logs/HEAD'. However, when LLVM is included as
a Git submodule, this path does not exist. Instead, it contains a '.git'
file with the following:

  gitdir: ../../.git/modules/external/llvm

Where '../..' is the relative path to the root repository that contains
the LLVM Git submodule.

Because of this discrepancy, `clang --version` does not output source
control information if built from a Git submodule.

The full '.git/logs/HEAD' path is only used to gate the invocation of LLVM
CMake's GetSVN.cmake script, which is invoked using the `LLVM_MAIN_SRC_DIR`
and `CLANG_SOURCE_DIR` paths, which point to the right places even when
Clang is built as a submodule. Once invoked with these paths, GetSVN.cmake
works just fine, and correct version control information is retrieved, even
when Clang is built as a submodule.

To work around the problem, truncate the path being checked for: just
'.git' instead of '.git/logs/HEAD'.

Test Plan:

1. Before applying this change, build Clang as a Git submodule in a repository that places it in external/clang, and confirm no revision information is output when `clang --version` is invoked (just "clang 5.0.0" is output, no Git hashes).
2. Apply these changes and build Clang as a Git repository nested under llvm/tools/clang, and confirm that `clang --version` displays correct version information.
3. Apply these changes and build Clang as a Git submodule using the structure described in (1), and confirm version control information is output as in (2).


https://reviews.llvm.org/D34955

Files:
  lib/Basic/CMakeLists.txt


Index: lib/Basic/CMakeLists.txt
===================================================================
--- lib/Basic/CMakeLists.txt
+++ lib/Basic/CMakeLists.txt
@@ -16,7 +16,7 @@
 
 macro(find_first_existing_vc_file out_var path)
   find_first_existing_file(${out_var}
-    "${path}/.git/logs/HEAD" # Git
+    "${path}/.git"           # Git
     "${path}/.svn/wc.db"     # SVN 1.7
     "${path}/.svn/entries"   # SVN 1.6
     )


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