fetchipfs: simplify, error-out when given multiple hashes

Also dropped the `md5` attribute, as `stdenv.mkDerivation` rejects
MD5 since last year (87c22100a6)

pkgs/build-support/fetchipfs/default.nix

@@ -1,50 +1,36 @@
-{ stdenv
+{ lib
+, stdenv
 , curl
 }:
+lib.fetchers.withNormalizedHash { hashTypes = [ "sha1" "sha256" "sha512" ]; } (
+  { ipfs
+  , url            ? ""
+  , curlOpts       ? ""
+  , outputHash
+  , outputHashAlgo
+  , meta           ? {}
+  , port           ? "8080"
+  , postFetch      ? ""
+  , preferLocalBuild ? true
+  }:
+  stdenv.mkDerivation {
+    name = ipfs;
+    builder = ./builder.sh;
+    nativeBuildInputs = [ curl ];
 
-{ ipfs
+    # New-style output content requirements.
-, url            ? ""
+    inherit outputHash outputHashAlgo;
-, curlOpts       ? ""
+    outputHashMode = "recursive";
-, outputHash     ? ""
-, outputHashAlgo ? ""
-, md5            ? ""
-, sha1           ? ""
-, sha256         ? ""
-, sha512         ? ""
-, meta           ? {}
-, port           ? "8080"
-, postFetch      ? ""
-, preferLocalBuild ? true
-}:
 
-let
+    inherit curlOpts
+            postFetch
+            ipfs
+            url
+            port
+            meta;
 
-  hasHash = (outputHash != "" && outputHashAlgo != "")
+    # Doing the download on a remote machine just duplicates network
-    || md5 != "" || sha1 != "" || sha256 != "" || sha512 != "";
+    # traffic, so don't do that.
-
+    inherit preferLocalBuild;
-in
+  }
-
+)
-if (!hasHash) then throw "Specify sha for fetchipfs fixed-output derivation" else stdenv.mkDerivation {
-  name = ipfs;
-  builder = ./builder.sh;
-  nativeBuildInputs = [ curl ];
-
-  # New-style output content requirements.
-  outputHashAlgo = if outputHashAlgo != "" then outputHashAlgo else
-      if sha512 != "" then "sha512" else if sha256 != "" then "sha256" else if sha1 != "" then "sha1" else "md5";
-  outputHash = if outputHash != "" then outputHash else
-      if sha512 != "" then sha512 else if sha256 != "" then sha256 else if sha1 != "" then sha1 else md5;
-
-  outputHashMode = "recursive";
-
-  inherit curlOpts
-          postFetch
-          ipfs
-          url
-          port
-          meta;
-
-  # Doing the download on a remote machine just duplicates network
-  # traffic, so don't do that.
-  inherit preferLocalBuild;
-}

pkgs/top-level/all-packages.nix

@@ -1141,9 +1141,7 @@ with pkgs;
 
   fetchRepoProject = callPackage ../build-support/fetchrepoproject { };
 
-  fetchipfs = import ../build-support/fetchipfs {
+  fetchipfs = callPackage ../build-support/fetchipfs { };
-    inherit curl stdenv;
-  };
 
   fetchit = callPackage ../applications/networking/cluster/fetchit { };