ExternalProject: Rerun download on SOURCE_DIR change

Fixes: #21748

4 files changed, 45 insertions, 5 deletions

diff --git a/Tests/RunCMake/ExternalProject/MultiCommand.cmake b/Tests/RunCMake/ExternalProject/MultiCommand.cmake
index 0849658..3e8bd94 100644
--- a/Tests/RunCMake/ExternalProject/MultiCommand.cmake
+++ b/Tests/RunCMake/ExternalProject/MultiCommand.cmake
@@ -1,5 +1,12 @@
 include(ExternalProject)
 
+# Force all steps to be re-run by removing timestamps from any previous run.
+# This has to happen before we call ExternalProject_Add() because that command
+# writes some files to the stamp directory for recording repository details.
+set(STAMP_DIR ${CMAKE_BINARY_DIR}/multiCommand-prefix/src/multiCommand-stamp)
+file(REMOVE_RECURSE "${STAMP_DIR}")
+file(MAKE_DIRECTORY "${STAMP_DIR}")
+
 # Verify COMMAND keyword is recognized after various *_COMMAND options
 ExternalProject_Add(multiCommand
   DOWNLOAD_COMMAND  "${CMAKE_COMMAND}" -E echo "download 1"
@@ -17,8 +24,3 @@ ExternalProject_Add(multiCommand
   INSTALL_COMMAND   "${CMAKE_COMMAND}" -E echo "install 1"
           COMMAND   "${CMAKE_COMMAND}" -E echo "install 2"
 )
-
-# Force all steps to be re-run by removing timestamps from any previous run
-ExternalProject_Get_Property(multiCommand STAMP_DIR)
-file(REMOVE_RECURSE "${STAMP_DIR}")
-file(MAKE_DIRECTORY "${STAMP_DIR}")
diff --git a/Tests/RunCMake/ExternalProject/RunCMakeTest.cmake b/Tests/RunCMake/ExternalProject/RunCMakeTest.cmake
index 48f8b23..fde384f 100644
--- a/Tests/RunCMake/ExternalProject/RunCMakeTest.cmake
+++ b/Tests/RunCMake/ExternalProject/RunCMakeTest.cmake
@@ -61,6 +61,23 @@ if(NOT XCODE_VERSION OR XCODE_VERSION VERSION_LESS 12)
 endif()
 run_steps_CMP0114(NEW)
 
+function(__ep_test_source_dir_change)
+  set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/SourceDirChange-build)
+  set(RunCMake_TEST_NO_CLEAN 1)
+  file(REMOVE_RECURSE "${RunCMake_TEST_BINARY_DIR}")
+  file(MAKE_DIRECTORY "${RunCMake_TEST_BINARY_DIR}")
+  run_cmake(SourceDirChange)
+  run_cmake_command(SourceDirChange-build1 ${CMAKE_COMMAND} --build .)
+  # Because some file systems have timestamps with only one second resolution,
+  # we have to ensure we don't re-run the configure stage too quickly after the
+  # first build. Otherwise, the modified RepositoryInfo.txt files the next
+  # configure writes might still have the same timestamp as the previous one.
+  execute_process(COMMAND ${CMAKE_COMMAND} -E sleep 1.125)
+  run_cmake_command(SourceDirChange-change ${CMAKE_COMMAND} -DSOURCE_DIR_CHANGE=YES .)
+  run_cmake_command(SourceDirChange-build2 ${CMAKE_COMMAND} --build .)
+endfunction()
+__ep_test_source_dir_change()
+
 # Run both cmake and build steps. We always do a clean before the
 # build to ensure that the download step re-runs each time.
 function(__ep_test_with_build testName)
diff --git a/Tests/RunCMake/ExternalProject/SourceDirChange-build2-stdout.txt b/Tests/RunCMake/ExternalProject/SourceDirChange-build2-stdout.txt
new file mode 100644
index 0000000..22dac9d
--- /dev/null
+++ b/Tests/RunCMake/ExternalProject/SourceDirChange-build2-stdout.txt
@@ -0,0 +1 @@
+Download command executed
diff --git a/Tests/RunCMake/ExternalProject/SourceDirChange.cmake b/Tests/RunCMake/ExternalProject/SourceDirChange.cmake
new file mode 100644
index 0000000..62213cd
--- /dev/null
+++ b/Tests/RunCMake/ExternalProject/SourceDirChange.cmake
@@ -0,0 +1,20 @@
+include(ExternalProject)
+
+file(MAKE_DIRECTORY "${CMAKE_BINARY_DIR}/first")
+file(MAKE_DIRECTORY "${CMAKE_BINARY_DIR}/second")
+
+if("${SOURCE_DIR_CHANGE}" STREQUAL "")
+  set(source_dir first)
+else()
+  set(source_dir second)
+endif()
+
+ExternalProject_Add(source_dir_change
+  SOURCE_DIR        "${CMAKE_BINARY_DIR}/${source_dir}"
+  DOWNLOAD_COMMAND  "${CMAKE_COMMAND}" -E echo "Download command executed"
+  UPDATE_COMMAND    ""
+  CONFIGURE_COMMAND ""
+  BUILD_COMMAND     ""
+  TEST_COMMAND      ""
+  INSTALL_COMMAND   ""
+)