Replace projectile with project.el

[hlissner]

Important

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To replace projectile with project.el (built in since 26, but became mature enough to use by 27).

Motivations

• Relevant to our goal to prioritize native functionality, where equivalent or superior,
• project.el is tied to more native functionality (e.g. vc.el, grep.el, capf, etc),
• project.el has reached sufficient (but not total) feature parity with projectile,
• project.el is a simpler, lighter, and more stable codebase, and so is easier to build upon.

Challenges

• project.el file list collectors lack a caching mechanism (but maybe we don't need them?)
• project.el cannot simply be reconfigured to use fd/ripgrep (fast) instead of find/grep (slow, and potentially buggy on BSD systems).
• project.el is built into Emacs. I plan to install a newer version anyway, but care must be taken to avoid the built-in version shadowing the new one.

Tasks

• find-sibling-file replaces projectile-find-other-file, but only searches the current directory (whereas the latter searches the whole project for matches). An advice (or another command altogether) is needed to replicate projectile's behavior. (wrong-numbe-of-arguments error from backported find-sibling-file command doomemacs#7795, 198fe82b6d49)
• Modify project--files-in-directory to use fd or ripgrep (falling back to find+xref otherwise).
• Replace references to projectile variables with project.el analogues:
  • projectile-project-root-files -> project-vc-extra-root-markers
  • projectile-globally-ignored-directories -> one or more of of project-vc-ignores, vc-directory-exclusion-list, grep-find-ignored-files
• Invalidate project-vc property if project-vc-merge-submodules/project-vc-extra-root-markers changes.
• Add interactive version of project-remember-project (see project-forget-project for reference).
• Adapt projectile references in lisp/lib/{buffers,projects,scratch,files}.el to project.el.
• Adapt projectile references in modules (not an exhaustive list, just the more important ones):
  • ui/workspaces
  • ui/modeline
  • config/default (autoloads, keybindings)
  • completion/*