fetchurl: Introduce curlOptsList as an improvement over curlOpts

It's impossible to pass arguments with spaces with curlOpts.
curlOptsList supports that. Passing a list to curlOpts has been
deprecated. This commit is fully backwards compatible.

pkgs/build-support/fetchurl/builder.sh

@@ -22,6 +22,8 @@ if ! [ -f "$SSL_CERT_FILE" ]; then
     curl+=(--insecure)
 fi
 
+eval "curl+=($curlOptsList)"
+
 curl+=(
     $curlOpts
     $NIX_CURL_FLAGS

pkgs/build-support/fetchurl/default.nix

@@ -45,8 +45,13 @@ in
   urls ? []
 
 , # Additional curl options needed for the download to succeed.
+  # Warning: Each space (no matter the escaping) will start a new argument.
+  # If you wish to pass arguments with spaces, use `curlOptsList`
   curlOpts ? ""
 
+, # Additional curl options needed for the download to succeed.
+  curlOptsList ? []
+
 , # Name of the file.  If empty, use the basename of `url' (or of the
   # first element of `urls').
   name ? ""
@@ -148,7 +153,14 @@ stdenvNoCC.mkDerivation {
 
   outputHashMode = if (recursiveHash || executable) then "recursive" else "flat";
 
-  inherit curlOpts showURLs mirrorsFile postFetch downloadToTemp executable;
+  curlOpts = lib.warnIf (lib.isList curlOpts) ''
+    fetchurl for ${toString (builtins.head urls_)}: curlOpts is a list (${lib.generators.toPretty { multiline = false; } curlOpts}), which is not supported anymore.
+    - If you wish to get the same effect as before, for elements with spaces (even if escaped) to expand to multiple curl arguments, use a string argument instead:
+      curlOpts = ${lib.strings.escapeNixString (toString curlOpts)};
+    - If you wish for each list element to be passed as a separate curl argument, allowing arguments to contain spaces, use curlOptsList instead:
+      curlOptsList = [ ${lib.concatMapStringsSep " " lib.strings.escapeNixString curlOpts} ];'' curlOpts;
+  curlOptsList = lib.escapeShellArgs curlOptsList;
+  inherit showURLs mirrorsFile postFetch downloadToTemp executable;
 
   impureEnvVars = impureEnvVars ++ netrcImpureEnvVars;