pijul: Fix the build (broke due to a more recent Rust version)

This uses an upstream patch [0] to fix a compatibility error with a new
version of Rust. Fix #79150.

Unfortunately patching Rust dependencies in Nixpkgs turned out to be way
more hacky than I expected (maybe there is a nicer way?), but it should
be fine for now.

A new release might follow soonish [1] so that we can drop the patches.

References:
- https://nest.pijul.com/pijul_org/pijul/discussions/401
- https://nest.pijul.com/pijul_org/thrussh/discussions/31

[0]: https://nest.pijul.com/pijul_org/thrussh:master/patches/AsyuWkJg4jAwNaG3H1yv1kbECx5E3GQAtjzXWBDB8yEGMswyfKbxKvYmAGWCohTVaTipdvF8mHh63yU5PTr5F9py
[1]: https://discourse.pijul.org/t/is-this-project-still-active-yes-it-is/451

pkgs/applications/version-management/pijul/default.nix

@@ -20,6 +20,15 @@ in rustPlatform.buildRustPackage rec {
     sha256 = "1rm787kkh3ya8ix0rjvj7sbrg9armm0rnpkga6gjmsbg5bx20y4q";
   };
 
+  postPatch = ''
+    pushd ../${pname}-${version}-vendor/thrussh/
+    patch -p1 < ${./thrussh-build-fix.patch}
+    substituteInPlace .cargo-checksum.json --replace \
+      9696ed2422a483cd8de48ac241178a0441be6636909c76174c536b8b1cba9d45 \
+      a199f2bba520d56e11607b77be4dde0cfae576c90badb9fbd39af4784e8120d1
+    popd
+  '';
+
   nativeBuildInputs = [ pkgconfig clang ];
 
   postInstall = ''

pkgs/applications/version-management/pijul/thrussh-build-fix.patch

@@ -0,0 +1,12 @@
+--- a/src/client/connection.rs	2020-02-04 12:48:43.845299096 +0100
++++ b/src/client/connection.rs	2020-02-04 12:50:00.140329310 +0100
+@@ -546,8 +546,8 @@
+                 &[msg::NEWKEYS],
+                 &mut session.0.write_buffer,
+             );
+-            session.0.kex = Some(Kex::NewKeys(newkeys));
+             newkeys.sent = true;
++            session.0.kex = Some(Kex::NewKeys(newkeys));
+         }
+         Ok(())
+     }