Looks like you can't use fetchFromGitLab in the bootstrap process (like fetchpatch)? With this patch, it evals (I haven't built):

diff --git a/pkgs/development/libraries/libxml2/default.nix b/pkgs/development/libraries/libxml2/default.nix
index 41d2b1f953f0..43df6360ade5 100644
--- a/pkgs/development/libraries/libxml2/default.nix
+++ b/pkgs/development/libraries/libxml2/default.nix
@@ -2,6 +2,7 @@
   lib,
   callPackage,
   fetchFromGitLab,
+  fetchurl,
   fetchpatch,
 }:

@@ -49,14 +50,12 @@ let
         ];
       };
     };
-    libxml2 = callPackage ./common.nix {
+    libxml2 = callPackage ./common.nix rec {
       version = "2.15.1";
-      src = fetchFromGitLab {
-        domain = "gitlab.gnome.org";
-        owner = "GNOME";
-        repo = "libxml2";
-        tag = "v${packages.libxml2.version}";
-        hash = "sha256-FUfYMq5xT2i88JdIw9OtSofraUL3yjsyOVund+mfJKQ=";
+      src = fetchurl {
+        name = "libxml2-${version}-source.tar.gz";
+        url = "https://gitlab.gnome.org/api/v4/projects/GNOME%2Flibxml2/repository/archive.tar.gz?sha=refs/tags/v${packages.libxml2.version}";
+        hash = "sha256-2py4DlRIlD4h1x8379d+whzsNbh8ofHpNAad/QFsTuw=";
       };
       extraMeta = {
         maintainers = with lib.maintainers; [

Does anyone know where the fact that the Darwin stdenv builds CMake twice comes from? As far as I can tell, it's from stage 0, and then just gets used in the other stages from there. Am I missing something here, is it something with the overrides? It looks like it might be, but then the fact that those are only allowed in the final stage (per booter.nix) (when that doesn't seem true, since then they wouldn't be defined...?) comes up.

(Isn't this the same pattern (defining in one stage and referencing in the others) that makes Glibc only build a limited number of times in the Linux stdenv?)

You think cmake should be rebuild less? Or more?

glibc's is probably a bit different as it's a part of stdenv.cc.libc and mainly used by that I would guess. Also, if depends if the package is used or not by other packages in the derivation would affect rebuild count as well.

In reply to @trofi:matrix.org

You think cmake should be rebuild less? Or more?

glibc's is probably a bit different as it's a part of stdenv.cc.libc and mainly used by that I would guess. Also, if depends if the package is used or not by other packages in the derivation would affect rebuild count as well.

[The other day I found stdenv.__bootPackages as a way to refer to each stage's package set. Now I use it and nix-store --query --graph all the time to find out what gets built when and why.]

nod. Your description matches my understanding. Today we build glibc and gcc once during bootstrap (and 3 times binutils?). In this setup at least one of them will have to be built by bootstrapTools.