Restore handling of build directory inside a symlinked path

In commit dd8365b3f1 (Merge branch 'upstream-KWSys' into update-kwsys,
2020-04-06, v3.18.0-rc1~397^2) we imported KWSys commit `019afb6ea`
(SystemTools: Drop GetCurrentWorkingDirectory 'collapse' argument,
2020-04-03).  That caused `GetCurrentWorkingDirectory` to no longer send
paths through the KWSys translation map and broke CMake's detection of
the absolute path to a build directory containing a symbolic link.
Add our own `cmSystemTools::GetCurrentWorkingDirectory` wrapper around
the KWSys method in order to restore that mapping.

Test-case-by: Ben Boeckel <ben.boeckel@kitware.com>
Issue: #16228
Fixes: #20900

6 files changed, 52 insertions, 0 deletions

diff --git a/Tests/RunCMake/CMakeLists.txt b/Tests/RunCMake/CMakeLists.txt
index 830566e..36409d8 100644
--- a/Tests/RunCMake/CMakeLists.txt
+++ b/Tests/RunCMake/CMakeLists.txt
@@ -436,6 +436,10 @@ else()
   message(STATUS "Could not find ctresalloc")
 endif()
 
+if(NOT WIN32)
+  add_RunCMake_test(SymlinkTrees)
+endif ()
+
 find_package(Qt4 QUIET)
 find_package(Qt5Core QUIET)
 if (QT4_FOUND AND Qt5Core_FOUND AND NOT Qt5Core_VERSION VERSION_LESS 5.1.0)
diff --git a/Tests/RunCMake/SymlinkTrees/CMakeLists.txt b/Tests/RunCMake/SymlinkTrees/CMakeLists.txt
new file mode 100644
index 0000000..d6fea2c
--- /dev/null
+++ b/Tests/RunCMake/SymlinkTrees/CMakeLists.txt
@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 2.8.12)
+project(${RunCMake_TEST} NONE)
+include("${include_dir}/${RunCMake_TEST}.cmake")
diff --git a/Tests/RunCMake/SymlinkTrees/PrintTrees.cmake b/Tests/RunCMake/SymlinkTrees/PrintTrees.cmake
new file mode 100644
index 0000000..aa99127
--- /dev/null
+++ b/Tests/RunCMake/SymlinkTrees/PrintTrees.cmake
@@ -0,0 +1,6 @@
+message(STATUS "source: '${CMAKE_SOURCE_DIR}'")
+message(STATUS "binary: '${CMAKE_BINARY_DIR}'")
+get_filename_component(real_source "${CMAKE_SOURCE_DIR}" REALPATH)
+get_filename_component(real_binary "${CMAKE_BINARY_DIR}" REALPATH)
+message(STATUS "real source: '${real_source}'")
+message(STATUS "real binary: '${real_binary}'")
diff --git a/Tests/RunCMake/SymlinkTrees/RunCMakeTest.cmake b/Tests/RunCMake/SymlinkTrees/RunCMakeTest.cmake
new file mode 100644
index 0000000..e5f1f7f
--- /dev/null
+++ b/Tests/RunCMake/SymlinkTrees/RunCMakeTest.cmake
@@ -0,0 +1,34 @@
+include(RunCMake)
+
+# This function assumes that ``${RunCMake_BINARY_DIR}/${name}/source`` and
+# ``${RunCMake_BINARY_DIR}/${name}/binary`` are set up properly prior to
+# calling it.
+function (run_symlink_test name)
+  set(RunCMake_TEST_NO_CLEAN TRUE)
+  configure_file(
+    "${CMAKE_CURRENT_LIST_DIR}/CMakeLists.txt"
+    "${RunCMake_BINARY_DIR}/${name}/source/CMakeLists.txt"
+    COPYONLY)
+  set(RunCMake_TEST_SOURCE_DIR "${RunCMake_BINARY_DIR}/${name}/source")
+  set(RunCMake_TEST_BINARY_DIR "${RunCMake_BINARY_DIR}/${name}/binary")
+  # Emulate a shell using this directory.
+  set(ENV{PWD} "${RunCMake_TEST_BINARY_DIR}")
+  set(RunCMake_TEST_OPTIONS
+    "-Dinclude_dir:PATH=${CMAKE_CURRENT_LIST_DIR}")
+  run_cmake("${name}_symlinks")
+endfunction ()
+
+# Create the following structure:
+#
+#   .../common_real/source
+#   .../common_real/binary
+#   .../common -> common_real
+#
+# In this case, CMake should act as if .../common *is* .../common_real for all
+# computations except ``REALPATH``.  This supports the case where a system has
+# a stable *symlink*, but not a stable target for that symlink.
+file(REMOVE_RECURSE "${RunCMake_BINARY_DIR}/common_real")
+file(REMOVE "${RunCMake_BINARY_DIR}/common")
+file(MAKE_DIRECTORY "${RunCMake_BINARY_DIR}/common_real/source")
+file(CREATE_LINK "common_real" "${RunCMake_BINARY_DIR}/common" SYMBOLIC)
+run_symlink_test(common)
diff --git a/Tests/RunCMake/SymlinkTrees/common_symlinks-stdout.txt b/Tests/RunCMake/SymlinkTrees/common_symlinks-stdout.txt
new file mode 100644
index 0000000..bb04450
--- /dev/null
+++ b/Tests/RunCMake/SymlinkTrees/common_symlinks-stdout.txt
@@ -0,0 +1,4 @@
+-- source: '[^']*/Tests/RunCMake/SymlinkTrees/common/source'
+-- binary: '[^']*/Tests/RunCMake/SymlinkTrees/common/binary'
+-- real source: '[^']*/Tests/RunCMake/SymlinkTrees/common_real/source'
+-- real binary: '[^']*/Tests/RunCMake/SymlinkTrees/common_real/binary'
diff --git a/Tests/RunCMake/SymlinkTrees/common_symlinks.cmake b/Tests/RunCMake/SymlinkTrees/common_symlinks.cmake
new file mode 100644
index 0000000..5eafe26
--- /dev/null
+++ b/Tests/RunCMake/SymlinkTrees/common_symlinks.cmake
@@ -0,0 +1 @@
+include("${CMAKE_CURRENT_LIST_DIR}/PrintTrees.cmake")