From 2af26fcfa1795543d20ffddd18d6a6b84ea38fe4 Mon Sep 17 00:00:00 2001
From: Marien Zwart <marien.zwart@gmail.com>
Date: Sun, 26 May 2024 22:42:51 +1000
Subject: [PATCH] Use fetchTree / github fetcher for CI

This seems to be much more space-efficient: ~/.cache/nix/tarball-cache
is about 700MiB uncompressed, under 300MiB as tzst (using tar's
defaults, CI uses zstdmt but I assume will be in the same ballpark). The
gitv3 cache is multiple GiB.

CI will still build doom-example using fetchGit. I intend to shrink the
number of modules enabled in the example to keep gitv3 cache size under
control.
---
 checks.nix  |  1 +
 default.nix | 55 ++++++++++++++++++++++++++++++++++-------------------
 flake.nix   |  1 +
 3 files changed, 37 insertions(+), 20 deletions(-)

diff --git a/checks.nix b/checks.nix
index b0cc7a8..f2695af 100644
--- a/checks.nix
+++ b/checks.nix
@@ -31,6 +31,7 @@ let
     # TODO: drop after NixOS 24.05 release.
     emacs = emacs29;
     doomLocalDir = "~/.local/share/nix-doom-unstraightened";
+    experimentalFetchTree = true;
   };
   mkDoom = args: (makeDoomPackages (common // args)).doomEmacs;
   mkDoomDir = args: writeTextDir "init.el" (toInit args);
diff --git a/default.nix b/default.nix
index 24f4558..506d4ff 100644
--- a/default.nix
+++ b/default.nix
@@ -39,6 +39,8 @@
   profileName ? "nix",
   /* Disable profile early in startup, so "normal" cache/state dirs are used. */
   noProfileHack ? false,
+  /* Use fetchTree instead of fetchGit for package fetches. */
+  experimentalFetchTree ? false,
 
   callPackages,
   git,
@@ -233,27 +235,40 @@ let
                   else (throw "${name}: cannot derive url from recipe ${p.recipe or "<missing>"}"));
             # Use builtins.fetchGit instead of nixpkgs's fetchFromGitHub because
             # fetchGit allows fetching a specific git commit without a hash.
-            # TODO: port to fetchTree once (mostly) stable
-            # (in particular the github fetcher may be noticably more efficient)
-            src = builtins.fetchGit (
-              {
-                inherit url;
-                rev = pin;
-                allRefs = true;
-                # Skip submodules by default because they seem to be hitting
-                # https://github.com/NixOS/nix/issues/10773 (or a similar caching issue) and for
-                # parity between fetchTree's github fetcher and fetchGit (Github's exports don't
-                # seem to contain submodules).
-                submodules = !(p.recipe.nonrecursive or true);
-                # TODO: pull ref from derivation.src when not pulling it from p.recipe?
-                # Note Doom does have packages with pin + branch (or nonrecursive) set,
-                # expecting to inherit the rest of the recipe from Straight.
+            fetchGitArgs = {
+              inherit url;
+              rev = pin;
+              allRefs = true;
+              # Skip submodules by default because they seem to be hitting
+              # https://github.com/NixOS/nix/issues/10773 (or a similar caching issue) and for
+              # parity between fetchTree's github fetcher and fetchGit (Github's exports don't
+              # seem to contain submodules).
+              submodules = !(p.recipe.nonrecursive or true);
+              # TODO: pull ref from derivation.src when not pulling it from p.recipe?
+              # Note Doom does have packages with pin + branch (or nonrecursive) set,
+              # expecting to inherit the rest of the recipe from Straight.
 
-                # Always specify a ref to work around https://github.com/NixOS/nix/issues/10773
-                ref = p.recipe.branch or "HEAD";
-              }
-              // optionalAttrs (p ? recipe.depth) { shallow = p.recipe.depth == 1; }
-            );
+              # Always specify a ref to work around https://github.com/NixOS/nix/issues/10773
+              ref = p.recipe.branch or "HEAD";
+            }
+            // optionalAttrs (p ? recipe.depth) { shallow = p.recipe.depth == 1; };
+            src =
+              if experimentalFetchTree
+              then builtins.fetchTree (
+                if lib.hasPrefix "https://github.com/" url
+                then let
+                  tail = lib.removePrefix "https://github.com/" url;
+                  split = lib.splitString "/" tail;
+                  owner = lib.head split;
+                  repo = lib.removeSuffix ".git" (lib.elemAt split 1);
+                in {
+                  type = "github";
+                  inherit owner repo;
+                  rev = pin;
+                } else ({
+                  type = "git";
+                } // fetchGitArgs))
+              else builtins.fetchGit fetchGitArgs;
             # Run locally to avoid a network roundtrip.
             reqfile = runCommandLocal "${name}-deps" { } ''
               ${lib.getExe emacs} -Q --batch --script \
diff --git a/flake.nix b/flake.nix
index c015a1f..712c321 100644
--- a/flake.nix
+++ b/flake.nix
@@ -101,6 +101,7 @@
             doomDir = ./doomdirs/minimal;
             doomLocalDir = "~/.local/share/nix-doom-unstraightened";
             full = true;
+            experimentalFetchTree = true;
           }).doomEmacs.emacsWithPackages.deps;
         };
       });