docs: mention fetchCargoVendor

doc/languages-frameworks/rust.section.md

@@ -64,10 +64,18 @@ hash using `nix-hash --to-sri --type sha256 "<original sha256>"`.
 ```
 
 Exception: If the application has cargo `git` dependencies, the `cargoHash`
-approach will not work, and you will need to copy the `Cargo.lock` file of the application
-to nixpkgs and continue with the next section for specifying the options of the `cargoLock`
-section.
+approach will not work by default. In this case, you can set `useFetchCargoVendor = true`
+to use an improved fetcher that supports handling `git` dependencies.
 
+```nix
+{
+  useFetchCargoVendor = true;
+  cargoHash = "sha256-RqPVFovDaD2rW31HyETJfQ0qVwFxoGEvqkIgag3H6KU=";
+}
+```
+
+If this method still does not work, you can resort to copying the `Cargo.lock` file into nixpkgs
+and importing it as described in the [next section](#importing-a-cargo.lock-file).
 
 Both types of hashes are permitted when contributing to nixpkgs. The
 Cargo hash is obtained by inserting a fake checksum into the
@@ -462,6 +470,17 @@ also be used:
   the `Cargo.lock`/`Cargo.toml` files need to be patched before
   vendoring.
 
+In case the lockfile contains cargo `git` dependencies, you can use
+`fetchCargoVendor` instead.
+```nix
+{
+  cargoDeps = rustPlatform.fetchCargoVendor {
+    inherit src;
+    hash = "sha256-RqPVFovDaD2rW31HyETJfQ0qVwFxoGEvqkIgag3H6KU=";
+  };
+}
+```
+
 If a `Cargo.lock` file is available, you can alternatively use the
 `importCargoLock` function. In contrast to `fetchCargoTarball`, this
 function does not require a hash (unless git dependencies are used)

pkgs/build-support/rust/fetch-cargo-tarball/default.nix

@@ -120,8 +120,9 @@ stdenv.mkDerivation (
           echo
           echo "ERROR: The Cargo.lock contains git dependencies"
           echo
-          echo "This is currently not supported in the fixed-output derivation fetcher."
-          echo "Use cargoLock.lockFile / importCargoLock instead."
+          echo "This is not supported in the default fixed-output derivation fetcher."
+          echo "Set \`useFetchCargoVendor = true\` / use fetchCargoVendor"
+          echo "or use cargoLock.lockFile / importCargoLock instead."
           echo
 
           exit 1