Merge topic 'symlinks-rebase-master'

58d10cf6f1 Alternative symlink-creating mode for file(INSTALL ...)

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Ben Boeckel <ben.boeckel@kitware.com>
Merge-request: !6396

5 files changed, 63 insertions, 0 deletions

diff --git a/Help/command/file.rst b/Help/command/file.rst
index f038871..96a55ee 100644
--- a/Help/command/file.rst
+++ b/Help/command/file.rst
@@ -843,6 +843,11 @@ and ``NO_SOURCE_PERMISSIONS`` is default.
 Installation scripts generated by the :command:`install` command
 use this signature (with some undocumented options for internal use).
 
+.. versionchanged:: 3.22
+
+  The environment variable :envvar:`CMAKE_INSTALL_MODE` can override the
+  default copying behavior of :command:`file(INSTALL)`.
+
 .. _SIZE:
 
 .. code-block:: cmake
diff --git a/Help/command/install.rst b/Help/command/install.rst
index c6af489..1236f1d 100644
--- a/Help/command/install.rst
+++ b/Help/command/install.rst
@@ -30,6 +30,10 @@ are executed in order during installation.
   with those in the parent directory to run in the order declared (see
   policy :policy:`CMP0082`).
 
+.. versionchanged:: 3.22
+  The environment variable :envvar:`CMAKE_INSTALL_MODE` can override the
+  default copying behavior of :command:`install()`.
+
 There are multiple signatures for this command.  Some of them define
 installation options for files and targets.  Options common to
 multiple signatures are covered here but they are valid only for
diff --git a/Help/envvar/CMAKE_INSTALL_MODE.rst b/Help/envvar/CMAKE_INSTALL_MODE.rst
new file mode 100644
index 0000000..37db0d7
--- /dev/null
+++ b/Help/envvar/CMAKE_INSTALL_MODE.rst
@@ -0,0 +1,37 @@
+CMAKE_INSTALL_MODE
+------------------
+
+.. versionadded:: 3.22
+
+.. include:: ENV_VAR.txt
+
+The ``CMAKE_INSTALL_MODE`` environment variable allows users to operate
+CMake in an alternate mode of :command:`file(INSTALL)` and :command:`install()`.
+
+The default behavior for an installation is to copy a source file from a
+source directory into a destination directory. This environment variable
+however allows the user to override this behavior, causing CMake to create
+symbolic links instead.
+
+.. note::
+  A symbolic link consists of a reference file path rather than contents of its own,
+  hence there are two ways to express the relation, either by a relative or an absolute path.
+
+The following values are allowed for ``CMAKE_INSTALL_MODE``:
+
+* empty, unset or ``COPY``: default behavior, duplicate the file at its destination
+* ``ABS_SYMLINK``: create an *absolute* symbolic link to the source file at the destination *or fail*
+* ``ABS_SYMLINK_OR_COPY``: like ``ABS_SYMLINK`` but silently copy on error
+* ``REL_SYMLINK``: create an *relative* symbolic link to the source file at the destination *or fail*
+* ``REL_SYMLINK_OR_COPY``: like ``REL_SYMLINK`` but silently copy on error
+* ``SYMLINK``: try as if through ``REL_SYMLINK`` and fall back to ``ABS_SYMLINK`` if the referenced
+  file cannot be expressed using a relative path. Fail on error.
+* ``SYMLINK_OR_COPY``: like ``SYMLINK`` but silently copy on error
+
+Installing symbolic links rather than copying files can help conserve storage space because files do
+not have to be duplicated on disk. However, modifications applied to the source immediately affects
+the symbolic link and vice versa. *Use with caution*.
+
+.. note:: ``CMAKE_INSTALL_MODE`` only affects files, *not* directories.
+
+.. note:: Symbolic links are not available on all platforms.
diff --git a/Help/manual/cmake-env-variables.7.rst b/Help/manual/cmake-env-variables.7.rst
index 3db189e..0799fdd 100644
--- a/Help/manual/cmake-env-variables.7.rst
+++ b/Help/manual/cmake-env-variables.7.rst
@@ -38,6 +38,7 @@ Environment Variables that Control the Build
    /envvar/CMAKE_GENERATOR_INSTANCE
    /envvar/CMAKE_GENERATOR_PLATFORM
    /envvar/CMAKE_GENERATOR_TOOLSET
+   /envvar/CMAKE_INSTALL_MODE
    /envvar/CMAKE_LANG_COMPILER_LAUNCHER
    /envvar/CMAKE_LANG_LINKER_LAUNCHER
    /envvar/CMAKE_MSVCIDE_RUN_PATH
diff --git a/Help/release/dev/cmake-install-mode-symlink.rst b/Help/release/dev/cmake-install-mode-symlink.rst
new file mode 100644
index 0000000..a5f75ca
--- /dev/null
+++ b/Help/release/dev/cmake-install-mode-symlink.rst
@@ -0,0 +1,16 @@
+cmake-install-mode-symlink
+--------------------------
+
+* The :envvar:`CMAKE_INSTALL_MODE` environment variable was added to
+  allow users to override the default file-copying behavior of
+  :command:`install` and :command:`file(INSTALL)` into creating
+  symbolic links. This can aid in lowering storage space requirements
+  and avoiding redundancy.
+
+* The :command:`file(INSTALL)` can now be affected / modified by the
+  :envvar:`CMAKE_INSTALL_MODE` environment variable causing installation
+  of symbolic links instead of copying of files.
+
+* The :command:`install` can now be affected / modified by the
+  :envvar:`CMAKE_INSTALL_MODE` environment variable causing installation
+  of symbolic links instead of copying of files.