emacs: Add basic tree-sitter support (#219559)

This commit adds basic support for tree-sitter in the emacs build,
such that (if the user opts into tree-sitter support), tree-sitter
will be enabled and binary library files for tree-sitter can be
included in the `lib` directory of packages passed to
`emacsWithPackages`. The libraries will be aggregated and included in
treesit-extra-load-path.

The previous pattern for this in the community was to add tree-sitter
libaries by patching emacs's `RUNPATH` with `patchelf` in a post-fixup
phase. However, this has the substantial drawback that two different
emacs installations with different lists of available tree-sitter
libraries must be entirely separate builds. By supplying the
tree-sitter libraries in the wrapping layer of `emacsWithpackages`, it
becomes possible to share a single, more-cacheable "core emacs".

This support defaults to "on" only in emacs 29 and up, since previous
versions do not support tree-sitter out of the box.

pkgs/applications/editors/emacs/generic.nix

@@ -45,6 +45,7 @@
   else if withAthena then "athena"
   else "lucid")
 , withSystemd ? lib.meta.availableOn stdenv.hostPlatform systemd, systemd
+, withTreeSitter ? lib.versionAtLeast version "29", tree-sitter ? null
 }:
 
 assert (libXft != null) -> libpng != null;      # probably a bug
@@ -58,6 +59,7 @@ assert withGTK2 -> !withGTK3 && gtk2-x11 != null && !withPgtk;
 assert withGTK3 -> !withGTK2 && ((gtk3-x11 != null) || withPgtk);
 assert withPgtk -> withGTK3 && !withX && gtk3 != null;
 assert withXwidgets -> withGTK3 && webkitgtk != null;
+assert withTreeSitter -> tree-sitter != null;
 
 
 (if withMacport then llvmPackages_6.stdenv else stdenv).mkDerivation (finalAttrs: (lib.optionalAttrs nativeComp {
@@ -164,7 +166,8 @@ assert withXwidgets -> withGTK3 && webkitgtk != null;
       ImageCaptureCore GSS ImageIO
     ]
     ++ lib.optionals stdenv.isDarwin [ sigtool ]
-    ++ lib.optionals nativeComp [ libgccjit ];
+    ++ lib.optionals nativeComp [ libgccjit ]
+    ++ lib.optionals withTreeSitter [ tree-sitter ];
 
   hardeningDisable = [ "format" ];
 
@@ -193,6 +196,7 @@ assert withXwidgets -> withGTK3 && webkitgtk != null;
     ++ lib.optional withImageMagick "--with-imagemagick"
     ++ lib.optional withXinput2 "--with-xinput2"
     ++ lib.optional (!withToolkitScrollBars) "--without-toolkit-scroll-bars"
+    ++ lib.optional withTreeSitter "--with-tree-sitter"
   ;
 
   installTargets = [ "tags" "install" ];
@@ -241,6 +245,7 @@ assert withXwidgets -> withGTK3 && webkitgtk != null;
 
   passthru = {
     inherit nativeComp;
+    treeSitter = withTreeSitter;
     pkgs = recurseIntoAttrs (emacsPackagesFor finalAttrs.finalPackage);
     tests = { inherit (nixosTests) emacs-daemon; };
   };

pkgs/build-support/emacs/wrapper.nix

@@ -42,6 +42,8 @@ let
 
   nativeComp = emacs.nativeComp or false;
 
+  treeSitter = emacs.treeSitter or false;
+
 in
 
 packagesFun: # packages explicitly requested by the user
@@ -109,6 +111,9 @@ runCommand
         ${optionalString nativeComp ''
           mkdir -p $out/share/emacs/native-lisp
         ''}
+        ${optionalString treeSitter ''
+          mkdir -p $out/lib
+        ''}
 
         local requires
         for pkg in $explicitRequires; do
@@ -133,6 +138,9 @@ runCommand
           ${optionalString nativeComp ''
             linkPath "$1" "share/emacs/native-lisp" "share/emacs/native-lisp"
           ''}
+          ${optionalString treeSitter ''
+            linkPath "$1" "lib" "lib"
+          ''}
         }
 
         # Iterate over the array of inputs (avoiding nix's own interpolation)
@@ -164,6 +172,9 @@ runCommand
         ${optionalString nativeComp ''
           (add-to-list 'native-comp-eln-load-path "$out/share/emacs/native-lisp/")
         ''}
+        ${optionalString treeSitter ''
+          (add-to-list 'treesit-extra-load-path "$out/lib/")
+        ''}
         EOF
 
         # Generate a subdirs.el that statically adds all subdirectories to load-path.