file(GENERATE): Add policy CMP0070 to define relative path behavior

Previously `file(GENERATE)` did not define any behavior for relative
paths given to the `OUTPUT` or `INPUT` arguments.  Define behavior
consistent with CMake conventions and add a policy to provide
compatibility for projects that relied on the old accidental behavior.

Fixes: #16786

9 files changed, 78 insertions, 0 deletions

diff --git a/Tests/RunCMake/File_Generate/CMP0070-NEW-check.cmake b/Tests/RunCMake/File_Generate/CMP0070-NEW-check.cmake
new file mode 100644
index 0000000..05ec26e
--- /dev/null
+++ b/Tests/RunCMake/File_Generate/CMP0070-NEW-check.cmake
@@ -0,0 +1,13 @@
+foreach(f
+    "${RunCMake_TEST_SOURCE_DIR}/relative-input-NEW.txt"
+    "${RunCMake_TEST_BINARY_DIR}/relative-output-NEW.txt"
+    )
+  if(EXISTS "${f}")
+    file(READ "${f}" content)
+    if(NOT content MATCHES "^relative-input-NEW[\r\n]*$")
+      string(APPEND RunCMake_TEST_FAILED "File\n  ${f}\ndoes not have expected content.\n")
+    endif()
+  else()
+    string(APPEND RunCMake_TEST_FAILED "Missing\n  ${f}\n")
+  endif()
+endforeach()
diff --git a/Tests/RunCMake/File_Generate/CMP0070-NEW.cmake b/Tests/RunCMake/File_Generate/CMP0070-NEW.cmake
new file mode 100644
index 0000000..1a03822
--- /dev/null
+++ b/Tests/RunCMake/File_Generate/CMP0070-NEW.cmake
@@ -0,0 +1,2 @@
+cmake_policy(SET CMP0070 NEW)
+file(GENERATE OUTPUT relative-output-NEW.txt INPUT relative-input-NEW.txt)
diff --git a/Tests/RunCMake/File_Generate/CMP0070-OLD-check.cmake b/Tests/RunCMake/File_Generate/CMP0070-OLD-check.cmake
new file mode 100644
index 0000000..a71d822
--- /dev/null
+++ b/Tests/RunCMake/File_Generate/CMP0070-OLD-check.cmake
@@ -0,0 +1,13 @@
+foreach(f
+    "${RunCMake_TEST_BINARY_DIR}/relative-input-OLD.txt"
+    "${RunCMake_TEST_BINARY_DIR}/relative-output-OLD.txt"
+    )
+  if(EXISTS "${f}")
+    file(READ "${f}" content)
+    if(NOT content MATCHES "^relative-input-OLD[\r\n]*$")
+      string(APPEND RunCMake_TEST_FAILED "File\n  ${f}\ndoes not have expected content.\n")
+    endif()
+  else()
+    string(APPEND RunCMake_TEST_FAILED "Missing\n  ${f}\n")
+  endif()
+endforeach()
diff --git a/Tests/RunCMake/File_Generate/CMP0070-OLD.cmake b/Tests/RunCMake/File_Generate/CMP0070-OLD.cmake
new file mode 100644
index 0000000..0fb47cd
--- /dev/null
+++ b/Tests/RunCMake/File_Generate/CMP0070-OLD.cmake
@@ -0,0 +1,3 @@
+cmake_policy(SET CMP0070 OLD)
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/relative-input-OLD.txt "relative-input-OLD\n")
+file(GENERATE OUTPUT relative-output-OLD.txt INPUT relative-input-OLD.txt)
diff --git a/Tests/RunCMake/File_Generate/CMP0070-WARN-check.cmake b/Tests/RunCMake/File_Generate/CMP0070-WARN-check.cmake
new file mode 100644
index 0000000..1488df0
--- /dev/null
+++ b/Tests/RunCMake/File_Generate/CMP0070-WARN-check.cmake
@@ -0,0 +1,13 @@
+foreach(f
+    "${RunCMake_TEST_BINARY_DIR}/relative-input-WARN.txt"
+    "${RunCMake_TEST_BINARY_DIR}/relative-output-WARN.txt"
+    )
+  if(EXISTS "${f}")
+    file(READ "${f}" content)
+    if(NOT content MATCHES "^relative-input-WARN[\r\n]*$")
+      string(APPEND RunCMake_TEST_FAILED "File\n  ${f}\ndoes not have expected content.\n")
+    endif()
+  else()
+    string(APPEND RunCMake_TEST_FAILED "Missing\n  ${f}\n")
+  endif()
+endforeach()
diff --git a/Tests/RunCMake/File_Generate/CMP0070-WARN-stderr.txt b/Tests/RunCMake/File_Generate/CMP0070-WARN-stderr.txt
new file mode 100644
index 0000000..dbabaa9
--- /dev/null
+++ b/Tests/RunCMake/File_Generate/CMP0070-WARN-stderr.txt
@@ -0,0 +1,27 @@
+^CMake Warning \(dev\) in CMakeLists.txt:
+  Policy CMP0070 is not set: Define file\(GENERATE\) behavior for relative
+  paths.  Run "cmake --help-policy CMP0070" for policy details.  Use the
+  cmake_policy command to set the policy and suppress this warning.
+
+  file\(GENERATE\) given relative INPUT path:
+
+    relative-input-WARN.txt
+
+  This is not defined behavior unless CMP0070 is set to NEW.  For
+  compatibility with older versions of CMake, the previous undefined behavior
+  will be used.
+This warning is for project developers.  Use -Wno-dev to suppress it.(
++
+CMake Warning \(dev\) in CMakeLists.txt:
+  Policy CMP0070 is not set: Define file\(GENERATE\) behavior for relative
+  paths.  Run "cmake --help-policy CMP0070" for policy details.  Use the
+  cmake_policy command to set the policy and suppress this warning.
+
+  file\(GENERATE\) given relative OUTPUT path:
+
+    relative-output-WARN.txt
+
+  This is not defined behavior unless CMP0070 is set to NEW.  For
+  compatibility with older versions of CMake, the previous undefined behavior
+  will be used.
+This warning is for project developers.  Use -Wno-dev to suppress it.)+$
diff --git a/Tests/RunCMake/File_Generate/CMP0070-WARN.cmake b/Tests/RunCMake/File_Generate/CMP0070-WARN.cmake
new file mode 100644
index 0000000..ccb0452
--- /dev/null
+++ b/Tests/RunCMake/File_Generate/CMP0070-WARN.cmake
@@ -0,0 +1,2 @@
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/relative-input-WARN.txt "relative-input-WARN\n")
+file(GENERATE OUTPUT relative-output-WARN.txt INPUT relative-input-WARN.txt)
diff --git a/Tests/RunCMake/File_Generate/RunCMakeTest.cmake b/Tests/RunCMake/File_Generate/RunCMakeTest.cmake
index 82e903d..b660463 100644
--- a/Tests/RunCMake/File_Generate/RunCMakeTest.cmake
+++ b/Tests/RunCMake/File_Generate/RunCMakeTest.cmake
@@ -1,5 +1,9 @@
 include(RunCMake)
 
+run_cmake(CMP0070-NEW)
+run_cmake(CMP0070-OLD)
+run_cmake(CMP0070-WARN)
+
 run_cmake(CommandConflict)
 if("${RunCMake_GENERATOR}" MATCHES "Visual Studio|Xcode")
   run_cmake(OutputConflict)
diff --git a/Tests/RunCMake/File_Generate/relative-input-NEW.txt b/Tests/RunCMake/File_Generate/relative-input-NEW.txt
new file mode 100644
index 0000000..7293e90
--- /dev/null
+++ b/Tests/RunCMake/File_Generate/relative-input-NEW.txt
@@ -0,0 +1 @@
+relative-input-NEW