Merge pull request #135549 from Prillan/emacs-elpa-fetcher

emacs: Add custom elpa fetcher (backport)

pkgs/applications/editors/emacs/elisp-packages/elpa-packages.nix

@@ -21,7 +21,7 @@ formats commits for you.
 
 */
 
-{ lib, stdenv, texinfo, writeText }:
+{ lib, stdenv, buildPackages, texinfo, writeText }:
 
 self: let
 
@@ -41,7 +41,10 @@ self: let
   }: let
 
     imported = import generated {
-      inherit (self) callPackage;
+      callPackage = pkgs: args: self.callPackage pkgs (args // {
+        # Use custom elpa url fetcher with fallback/uncompress
+        fetchurl = buildPackages.callPackage ./fetchelpa.nix { };
+      });
     };
 
     super = removeAttrs imported [ "dash" ];

pkgs/applications/editors/emacs/elisp-packages/fetchelpa.nix

@@ -0,0 +1,21 @@
+# Elpa only serves the latest version of a given package uncompressed.
+# Once that release is no longer the latest & greatest it gets archived and compressed
+# meaning that both the URL and the hash changes.
+#
+# To work around this issue we fall back to the URL with the .lz suffix and if that's the
+# one we downloaded we uncompress the file to ensure the hash matches regardless of compression.
+
+{ fetchurl, lzip }:
+
+{ url, ... }@args: fetchurl ((removeAttrs args [ "url" ]) // {
+  urls = [
+    url
+    (url + ".lz")
+  ];
+  postFetch = ''
+    if [[ $url == *.lz ]]; then
+      ${lzip}/bin/lzip -c -d $out > uncompressed
+      mv uncompressed $out
+    fi
+  '';
+})

pkgs/top-level/emacs-packages.nix

@@ -26,7 +26,7 @@
 let
 
   mkElpaPackages = { pkgs, lib }: import ../applications/editors/emacs/elisp-packages/elpa-packages.nix {
-    inherit (pkgs) stdenv texinfo writeText;
+    inherit (pkgs) stdenv texinfo writeText buildPackages;
     inherit lib;
   };