cmake: Convert no source/build dir error to warning

Temporarily restore previous behavior that allowed specifying
no source or build directory to work, even though it was
neither documented nor supported. This commit is expected
to eventually be reverted to restore the fatal error for such
cases.

Relates: #18817

4 files changed, 20 insertions, 5 deletions

diff --git a/Source/cmake.cxx b/Source/cmake.cxx
index 74542df..d0863b0 100644
--- a/Source/cmake.cxx
+++ b/Source/cmake.cxx
@@ -808,8 +808,11 @@ void cmake::SetArgs(const std::vector<std::string>& args)
 
   if (this->CurrentWorkingMode == cmake::NORMAL_MODE && !haveSourceDir &&
       !haveBinaryDir) {
-    cmSystemTools::Error("No source or binary directory provided");
-    return;
+    this->IssueMessage(
+      cmake::WARNING,
+      "No source or binary directory provided. Both will be assumed to be "
+      "the same as the current working directory, but note that this "
+      "warning will become a fatal error in future CMake releases.");
   }
 
   if (!haveSourceDir) {
diff --git a/Tests/RunCMake/CommandLine/RunCMakeTest.cmake b/Tests/RunCMake/CommandLine/RunCMakeTest.cmake
index 32e20ac..3e56c25 100644
--- a/Tests/RunCMake/CommandLine/RunCMakeTest.cmake
+++ b/Tests/RunCMake/CommandLine/RunCMakeTest.cmake
@@ -54,12 +54,22 @@ run_cmake_command(cache-empty-entry
   ${CMAKE_COMMAND} --build ${RunCMake_SOURCE_DIR}/cache-empty-entry/)
 
 function(run_ExplicitDirs)
+  set(source_dir ${RunCMake_BINARY_DIR}/ExplicitDirsMissing)
+
+  file(REMOVE_RECURSE "${source_dir}")
+  file(MAKE_DIRECTORY "${source_dir}")
+  file(WRITE ${source_dir}/CMakeLists.txt [=[
+cmake_minimum_required(VERSION 3.13)
+project(ExplicitDirsMissing LANGUAGES NONE)
+]=])
+  run_cmake_command(no-S-B ${CMAKE_COMMAND} -E chdir ${source_dir}
+    ${CMAKE_COMMAND} -DFOO=BAR)
+
   set(source_dir ${RunCMake_SOURCE_DIR}/ExplicitDirs)
   set(binary_dir ${RunCMake_BINARY_DIR}/ExplicitDirs-build)
 
   file(REMOVE_RECURSE "${binary_dir}")
   file(MAKE_DIRECTORY "${binary_dir}")
-  run_cmake_command(no-S-B ${CMAKE_COMMAND} -DFOO=BAR)
   run_cmake_command(S-arg ${CMAKE_COMMAND} -S ${source_dir} ${binary_dir})
   run_cmake_command(S-arg-reverse-order ${CMAKE_COMMAND} ${binary_dir} -S${source_dir} )
   run_cmake_command(S-no-arg ${CMAKE_COMMAND} -S )
diff --git a/Tests/RunCMake/CommandLine/no-S-B-result.txt b/Tests/RunCMake/CommandLine/no-S-B-result.txt
deleted file mode 100644
index d00491f..0000000
--- a/Tests/RunCMake/CommandLine/no-S-B-result.txt
+++ /dev/null
@@ -1 +0,0 @@
-1
diff --git a/Tests/RunCMake/CommandLine/no-S-B-stderr.txt b/Tests/RunCMake/CommandLine/no-S-B-stderr.txt
index 7a94307..c166dcf 100644
--- a/Tests/RunCMake/CommandLine/no-S-B-stderr.txt
+++ b/Tests/RunCMake/CommandLine/no-S-B-stderr.txt
@@ -1 +1,4 @@
-CMake Error: No source or binary directory provided
+CMake Warning:
+  No source or binary directory provided.  Both will be assumed to be the
+  same as the current working directory, but note that this warning will
+  become a fatal error in future CMake releases.