buildRustPackage: add cargoDepsName attribute

The directory in the tarball of vendored dependencies contains `name`,
which is by default set to `${pname}-${version}`. This adds an
additional attribute to permit setting the name to something of the
user's choosing.

Since `cargoSha256`/`cargoHash` depend on the name of the directory of
vendored dependencies, `cargoDepsName` can be used to e.g. make the
hash invariant to the package version by setting `cargoDepsName =
pname`.

pkgs/build-support/rust/default.nix

@@ -23,6 +23,9 @@
   # Legacy hash
 , cargoSha256 ? ""
 
+  # Name for the vendored dependencies tarball
+, cargoDepsName ? name
+
 , src ? null
 , srcs ? null
 , unpackPhase ? null
@@ -60,7 +63,8 @@ let
 
   cargoDeps = if cargoVendorDir == null
     then fetchCargoTarball ({
-        inherit name src srcs sourceRoot unpackPhase cargoUpdateHook;
+        inherit src srcs sourceRoot unpackPhase cargoUpdateHook;
+        name = cargoDepsName;
         hash = cargoHash;
         patches = cargoPatches;
         sha256 = cargoSha256;