feat(tools/emacs-pkgs): Add new builder for internal packages r/2503

Adds a new internal builder that makes it possible to override the
`emacsPackages` passed to our Emacs packages, which in turn makes it
possible to inject them into the emacsPackages fixpoint and use them
with features like Emacs native compilation.

Change-Id: I80dad57115c83cf5693ae6ba4e4cf3105d103d5e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3003
Tested-by: BuildkiteCI
Reviewed-by: adisbladis <adisbladis@gmail.com>
Reviewed-by: grfn <grfn@gws.fyi>

1 files changed, 34 insertions, 0 deletions

diff --git a/tools/emacs-pkgs/buildEmacsPackage.nix b/tools/emacs-pkgs/buildEmacsPackage.nix
new file mode 100644
index 0000000000..160c062613
--- /dev/null
+++ b/tools/emacs-pkgs/buildEmacsPackage.nix
@@ -0,0 +1,34 @@
+# Builder for depot-internal Emacs packages. Packages built using this
+# builder are added into the Emacs packages fixpoint under
+# `emacsPackages.tvlPackages`, which in turn makes it possible to use
+# them with special Emacs features like native compilation.
+#
+# Arguments passed to the builder are the same as
+# emacsPackages.trivialBuild, except:
+#
+# * packageRequires is not used
+#
+# * externalRequires takes a selection function for packages from
+#   emacsPackages
+#
+# * internalRequires takes other depot packages
+{ pkgs, ... }:
+
+buildArgs:
+
+pkgs.callPackage({ emacsPackages }:
+
+let
+  # Select external dependencies from the emacsPackages set
+  externalDeps = (buildArgs.externalRequires or (_: [])) emacsPackages;
+
+  # Override emacsPackages for depot-internal packages
+  internalDeps = map (p: p.override { inherit emacsPackages; })
+                     (buildArgs.internalRequires or []);
+
+  trivialBuildArgs = builtins.removeAttrs buildArgs [
+    "externalRequires" "internalRequires"
+  ] // {
+    packageRequires = externalDeps ++ internalDeps;
+  };
+in emacsPackages.trivialBuild trivialBuildArgs) {}