Update `ld.lld --version` string for monorepo.

[ruiu]

Summary

This patch basically does the same thing as
https://reviews.llvm.org/rL352729 did to clang.

With this patch, lld now prints out a correct version string including
a git commit id like this:

$ bin/ld.lld --version
LLD 9.0.0 (https://github.com/llvm/llvm-project.git c027658504fa9e68173f53dedaf223695a65e910) (compatible with GNU linkers)

Fixes https://bugs.llvm.org/show_bug.cgi?id=40780

[ruiu]

• fix typo

[ruiu]

• Simplify

[phosek]

lld/Common/CMakeLists.txt

5

I don't think this is used?

[mgorny]

lld/Common/Version.cpp

36–37

Are you actually using it?

[ruiu]

• address review comments

lld/Common/CMakeLists.txt

5

Removed.

lld/Common/Version.cpp

36–37

Removed.

[mgorny]

LGTM

[xbolva00]

Common/CMakeLists.txt

39 ↗

(On Diff #187822)

Maybe this should be ${version_inc}?

lld/Common/CMakeLists.txt

 if(NOT LLD_BUILT_STANDALONE)
   set(tablegen_deps intrinsics_gen)
 endif()
 
+find_first_existing_vc_file("${LLVM_MAIN_SRC_DIR}" llvm_vc)
+find_first_existing_vc_file("${LLD_SOURCE_DIR}" lld_vc)
+
+set(version_inc "${CMAKE_CURRENT_BINARY_DIR}/VCSVersion.inc")
+set(generate_vcs_version_script "${LLVM_CMAKE_PATH}/GenerateVersionFromVCS.cmake")
+
+if(lld_vc)
+  set(lld_source_dir ${LLD_SOURCE_DIR})
+endif()
+
+add_custom_command(OUTPUT "${version_inc}"
+  DEPENDS "${lld_vc}" "${generate_vcs_version_script}"
+  COMMAND ${CMAKE_COMMAND} "-DNAMES=LLD"
+  "-DLLD_SOURCE_DIR=${LLD_SOURCE_DIR}"
+  "-DHEADER_FILE=${version_inc}"
+  -P "${generate_vcs_version_script}")
+
+# Mark the generated header as being generated.
+set_source_files_properties("${version_inc}"
+  PROPERTIES GENERATED TRUE
+  HEADER_FILE_ONLY TRUE)
+
+set_property(SOURCE Version.cpp APPEND PROPERTY
+  COMPILE_DEFINITIONS "HAVE_VCS_VERSION_INC")
+
 add_lld_library(lldCommon
   Args.cpp
   ErrorHandler.cpp
   Memory.cpp
   Reproduce.cpp
   Strings.cpp
   TargetOptionsCommandFlags.cpp
   Threads.cpp
   Timer.cpp
   Version.cpp
+  VCSVersion.inc
 
   ADDITIONAL_HEADER_DIRS
   ${LLD_INCLUDE_DIR}/lld/Common
 
   LINK_COMPONENTS
   Codegen
   Core
   Demangle

lld/Common/Version.cpp

 //===- lib/Common/Version.cpp - LLD Version Number ---------------*- C++-=====//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines several version-related utility functions for LLD.
 //
 //===----------------------------------------------------------------------===//
 
 #include "lld/Common/Version.h"
+#include "llvm/ADT/StringExtras.h"
 
-using namespace llvm;
+#ifdef HAVE_VCS_VERSION_INC
+#include "VCSVersion.inc"
+#endif
 
-// Returns an SVN repository path, which is usually "trunk".
-static std::string getRepositoryPath() {
-  StringRef S = LLD_REPOSITORY_STRING;
-  size_t Pos = S.find("lld/");
-  if (Pos != StringRef::npos)
-    return S.substr(Pos + 4);
-  return S;
-}
+using namespace llvm;
 
-// Returns an SVN repository name, e.g., " (trunk 284614)"
-// or an empty string if no repository info is available.
-static std::string getRepository() {
-  std::string Repo = getRepositoryPath();
-  std::string Rev = LLD_REVISION_STRING;
+// Returns a version string, e.g.:
+// lld 9.00 (https://github.com/llvm/llvm-project.git 9efdd7ac5e914d3c9fa1ef)
+std::string lld::getLLDVersion() {
+  std::string Repo;
+#ifdef LLD_REPOSITORY
+  Repo = LLD_REPOSITORY;
+#endif
+
+  std::string Rev;
+#ifdef LLD_REVISION
+  Rev = LLD_REVISION;
+#endif
 
+  std::string Version = std::string("LLD ") + LLD_VERSION_STRING;
   if (Repo.empty() && Rev.empty())
-    return "";
-  if (!Repo.empty() && !Rev.empty())
-    return " (" + Repo + " " + Rev + ")";
-  return " (" + Repo + Rev + ")";
-}
-
-// Returns a version string, e.g., "LLD 4.0 (lld/trunk 284614)".
-std::string lld::getLLDVersion() {
-  return "LLD " + std::string(LLD_VERSION_STRING) + getRepository();
+    return Version;
+  return Version + " (" + Repo + " " + Rev + ")";
 }