fetchRadiclePatch: init

doc/build-helpers/fetchers.chapter.md

···
 }
 ```
 
+## `fetchRadiclePatch` {#fetchradiclepatch}
+
+`fetchRadiclePatch` works very similarly to `fetchFromRadicle` with almost the same arguments
+expected. However, instead of a `rev` or `tag` argument, a `revision` argument is expected, which
+contains the full revision id of the Radicle patch to fetch.
+
+```nix
+fetchRadiclePatch {
+  seed = "rosa.radicle.xyz";
+  repo = "z4V1sjrXqjvFdnCUbxPFqd5p4DtH5"; # radicle-explorer
+  revision = "d97d872386c70607beda2fb3fc2e60449e0f4ce4"; # patch: d77e064
+  hash = "sha256-ttnNqj0lhlSP6BGzEhhUOejKkkPruM9yMwA5p9Di4bk=";
+}
+```
+
 ## `requireFile` {#requirefile}
 
 `requireFile` allows requesting files that cannot be fetched automatically, but whose content is known.

doc/redirects.json

···
   "fetchfromradicle": [
     "index.html#fetchfromradicle"
   ],
+  "fetchradiclepatch": [
+    "index.html#fetchradiclepatch"
+  ],
   "requirefile": [
     "index.html#requirefile"
   ],

pkgs/build-support/fetchradiclepatch/default.nix

···
+{
+  fetchFromRadicle,
+  jq,
+  lib,
+}:
+
+lib.makeOverridable (
+  {
+    revision,
+    postFetch ? "",
+    nativeBuildInputs ? [ ],
+    ...
+  }@args:
+
+  assert lib.assertMsg (
+    !args ? rev && !args ? tag
+  ) "fetchRadiclePatch does not accept `rev` or `tag` arguments.";
+
+  fetchFromRadicle (
+    {
+      nativeBuildInputs = [ jq ] ++ nativeBuildInputs;
+      rev = revision;
+      leaveDotGit = true;
+      postFetch = ''
+        { read -r head; read -r base; } < <(jq -r '.oid, .base' $out/0)
+        git -C $out fetch --depth=1 "$url" "$base" "$head"
+        git -C $out diff "$base" "$head" > patch
+        rm -r $out
+        mv patch $out
+        ${postFetch}
+      '';
+    }
+    // removeAttrs args [
+      "revision"
+      "postFetch"
+      "nativeBuildInputs"
+      "leaveDotGit"
+    ]
+  )
+  // {
+    inherit revision;
+  }
+)

pkgs/top-level/all-packages.nix

···
   fetchFromRepoOrCz = callPackage ../build-support/fetchrepoorcz { };
 
   fetchFromRadicle = callPackage ../build-support/fetchradicle { };
+  fetchRadiclePatch = callPackage ../build-support/fetchradiclepatch { };
 
   fetchgx = callPackage ../build-support/fetchgx { };