fix: Patch commands fail trying to re-apply the same patch twice

[BohdanBuinich]

Fix repeated patch application

Problem

PATCHES used to build a shell-style PATCH_COMMAND that applied patch files with input redirection.

That made patching fragile:

• repeated configure runs could try to apply the same patch again;
• patch paths with spaces were harder to handle safely;
• CPM had no explicit record that a patch set had already been applied;
• changing a patch file at the same path could still look like the same patch command.

What changed

Patch handling now generates a small CMake script and uses it as the PATCH_COMMAND.

The script applies patches from the dependency source directory without shell redirection. For each patch, it first checks whether the patch can apply normally. If not, it checks whether the patch is already present by running a reverse dry-run.

This makes repeated configure runs safe:

• apply the patch if it is not applied yet;
• skip it if the same patch set was already completed;
• accept it if the source tree already contains the patch changes;
• fail clearly if the patch is neither applicable nor already applied.

Main idea

Patch state is now stored next to the dependency source tree:

.cpm_patches/<patch_set_hash>.stamp

The patch-set hash includes the patch executable, patch arguments, working-directory behavior, patch file paths, and patch file contents.

That means changing a patch file creates a new patch set, even if the file path stays the same.

Fixes #618

[BohdanBuinich]

@TheLartians, Could you please review this change and let me know if you agree with it?

[aaeberharter]

I pulled CPM.cmake from the PR and it works for me.
cmake version 3.31.6-msvc6 (bundled with Visual Studio 2022)

Thank you

[aaeberharter]

PATCH_OPTIONS are mentioned in README.md but are not used in CPM.cmake. After this PR is merged we should discuss how to add meaningful patch options.

[edunad]

Any updates? I'm using the temp fix of SET after the first time cmake runs, but that doesn't work 100% of the time, would be awesome to get this merged soon 💖

[BohdanBuinich]

@TheLartians, what do you think about this fix? Or do you think it’s too messy and have a better idea for handling it?