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`.

doc/languages-frameworks/rust.section.md

@@ -80,6 +80,33 @@ The fetcher will verify that the `Cargo.lock` file is in sync with the `src`
 attribute, and fail the build if not. It will also will compress the vendor
 directory into a tar.gz archive.
 
+The tarball with vendored dependencies contains a directory with the
+package's `name`, which is normally composed of `pname` and
+`version`. This means that the vendored dependencies hash
+(`cargoSha256`/`cargoHash`) is dependent on the package name and
+version. The `cargoDepsName` attribute can be used to use another name
+for the directory of vendored dependencies. For example, the hash can
+be made invariant to the version by setting `cargoDepsName` to
+`pname`:
+
+```nix
+rustPlatform.buildRustPackage rec {
+  pname = "broot";
+  version = "1.2.0";
+
+  src = fetchCrate {
+    inherit pname version;
+    sha256 = "1mqaynrqaas82f5957lx31x80v74zwmwmjxxlbywajb61vh00d38";
+  };
+
+  cargoHash = "sha256-JmBZcDVYJaK1cK05cxx5BrnGWp4t8ca6FLUbvIot67s=";
+  cargoDepsName = pname;
+
+  # ...
+}
+```
+
+
 ### Cross compilation
 
 By default, Rust packages are compiled for the host platform, just like any

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;