Move call-flake.nix to nix-flake

As suggested by Ericson2314 in review
https://github.com/NixOS/nix/pull/12759#issuecomment-2755352343

src/libexpr/call-flake.nix

@@ -1,96 +0,0 @@
-# This is a helper to callFlake() to lazily fetch flake inputs.
-
-# The contents of the lock file, in JSON format.
-lockFileStr:
-
-# A mapping of lock file node IDs to { sourceInfo, subdir } attrsets,
-# with sourceInfo.outPath providing an SourceAccessor to a previously
-# fetched tree. This is necessary for possibly unlocked inputs, in
-# particular the root input, but also --override-inputs pointing to
-# unlocked trees.
-overrides:
-
-# This is `prim_fetchFinalTree`.
-fetchTreeFinal:
-
-let
-
-  lockFile = builtins.fromJSON lockFileStr;
-
-  # Resolve a input spec into a node name. An input spec is
-  # either a node name, or a 'follows' path from the root
-  # node.
-  resolveInput =
-    inputSpec: if builtins.isList inputSpec then getInputByPath lockFile.root inputSpec else inputSpec;
-
-  # Follow an input attrpath (e.g. ["dwarffs" "nixpkgs"]) from the
-  # root node, returning the final node.
-  getInputByPath =
-    nodeName: path:
-    if path == [ ] then
-      nodeName
-    else
-      getInputByPath
-        # Since this could be a 'follows' input, call resolveInput.
-        (resolveInput lockFile.nodes.${nodeName}.inputs.${builtins.head path})
-        (builtins.tail path);
-
-  allNodes = builtins.mapAttrs (
-    key: node:
-    let
-
-      parentNode = allNodes.${getInputByPath lockFile.root node.parent};
-
-      sourceInfo =
-        if overrides ? ${key} then
-          overrides.${key}.sourceInfo
-        else if node.locked.type == "path" && builtins.substring 0 1 node.locked.path != "/" then
-          parentNode.sourceInfo
-          // {
-            outPath = parentNode.outPath + ("/" + node.locked.path);
-          }
-        else
-          # FIXME: remove obsolete node.info.
-          # Note: lock file entries are always final.
-          fetchTreeFinal (node.info or { } // removeAttrs node.locked [ "dir" ]);
-
-      subdir = overrides.${key}.dir or node.locked.dir or "";
-
-      outPath = sourceInfo + ((if subdir == "" then "" else "/") + subdir);
-
-      flake = import (outPath + "/flake.nix");
-
-      inputs = builtins.mapAttrs (inputName: inputSpec: allNodes.${resolveInput inputSpec}) (
-        node.inputs or { }
-      );
-
-      outputs = flake.outputs (inputs // { self = result; });
-
-      result =
-        outputs
-        # We add the sourceInfo attribute for its metadata, as they are
-        # relevant metadata for the flake. However, the outPath of the
-        # sourceInfo does not necessarily match the outPath of the flake,
-        # as the flake may be in a subdirectory of a source.
-        # This is shadowed in the next //
-        // sourceInfo
-        // {
-          # This shadows the sourceInfo.outPath
-          inherit outPath;
-
-          inherit inputs;
-          inherit outputs;
-          inherit sourceInfo;
-          _type = "flake";
-        };
-
-    in
-    if node.flake or true then
-      assert builtins.isFunction flake.outputs;
-      result
-    else
-      sourceInfo
-  ) lockFile.nodes;
-
-in
-allNodes.${lockFile.root}

src/libexpr/eval.cc

@@ -288,10 +288,6 @@ EvalState::EvalState(
         CanonPath("derivation-internal.nix"),
         #include "primops/derivation.nix.gen.hh"
     )}
-    , callFlakeInternal{internalFS->addFile(
-        CanonPath("call-flake.nix"),
-        #include "call-flake.nix.gen.hh"
-    )}
     , store(store)
     , buildStore(buildStore ? buildStore : store)
     , debugRepl(nullptr)

src/libexpr/eval.hh

@@ -274,14 +274,12 @@ public:
 
     /**
      * In-memory filesystem for internal, non-user-callable Nix
-     * expressions like call-flake.nix.
+     * expressions like `derivation.nix`.
      */
     const ref<MemorySourceAccessor> internalFS;
 
     const SourcePath derivationInternal;
 
-    const SourcePath callFlakeInternal;
-
     /**
      * Store used to materialise .drv files.
      */

src/libexpr/meson.build

@@ -126,7 +126,6 @@ generated_headers = []
 foreach header : [
   'imported-drv-to-derivation.nix',
   'fetchurl.nix',
-  'call-flake.nix',
 ]
   generated_headers += gen_header.process(header)
 endforeach