This makes the scripts easier to work on, since the separate files
don't require the extra level of escaping that the inlined code did.
This also means the scripts can be rendered with appropriate
syntax highlighting in IDEs, etc.
Refactoring of the ExternalProject and FetchContent modules moved
the commands into CMake scripts. This broke custom commands that
used shell redirection or special build tool variables of the form
$(MakeVar). Undo the sequence of commits that performed this
refactoring and follow-up fixes associated with it.
The following commits are reverted by this change:
4f3d1abbb4 (ExternalProject: Refactor pre-configure steps to support
no-target uses, 2021-02-05)
17e5516e60 (FetchContent: Invoke steps directly and avoid a separate
sub-build, 2021-01-29)
bd876f3849 (FetchContent: Restore patch command support,
2021-02-18)
404cddb7bb (ExternalProject: Fix misuse of IS_NEWER_THAN in
timestamp checks, 2021-02-21)
b0da671243 (FetchContent: Don't update timestamps if files don't
change, 2021-02-18)
Fixes: #21892
When using a file system which only has second resolution timestamps,
there is a reasonably high likelihood of timestamps being the same.
The IS_NEWER_THAN test returns true when timestamps are the same,
so don't redo downloads when they match exactly.
The cost of setting up and executing a separate sub-build to do the
download, update and patch steps required for FetchContent population
can be significant with some platforms and CMake generators. Avoid the
sub-build altogether by invoking the step scripts directly.
Previously, if no generator was set (e.g. population was being done in
script mode), a generator needed to be available on the default PATH.
Since we no longer use a sub-build, this restriction is also now gone.
Fixes: #21703
The mkdir, download, update and patch steps are used by
FetchContent during the configure phase of the main build. Because
these steps need a target, this has so far required a sub-build to be
set up. The changes here factor out the preparation of the scripts
from the creation of the targets, allowing future work to leverage these
steps without a sub-build (see #21703).
As part of the refactoring, some rationalisation of the stamp files,
repository info files and script names was done to make things more
consistent between download methods and step implementations.
Every download method now records its own specific repository info
in a file and that file is a dependency of the download step. The source
directory is also written to that file, so if the SOURCE_DIR changes, the
download will be retriggered (the existing implementation fails in this
scenario). Each download method now also has just one driver script
that implements the whole step (it may pull in other scripts to do its
task though). The patch step gained support for USES_TERMINAL as
a result of generalising the implementation for custom commands.
Fixes: #21748
