[nix] use a single vendor dir for all deps

This fixes some annoying edge cases where the guest .cargo/config.toml
vendor file were not picked up.

Signed-off-by: Lucy Menon <168595099+syntactically@users.noreply.github.com>

Author: syntactically

flake.nix

@@ -109,6 +109,16 @@
             rustc = toolchains.stable.rust;
           };
 
+          manifests = [
+            "Cargo.toml"
+            "src/tests/rust_guests/dummyguest/Cargo.toml"
+            "src/tests/rust_guests/simpleguest/Cargo.toml"
+            "src/tests/rust_guests/witguest/Cargo.toml"
+          ];
+          manifestDeps = builtins.map (manifest:
+            let lockPath = builtins.replaceStrings [ "toml" ] [ "lock" ] manifest; in
+            let lockFile = ./${lockPath}; in
+            rust-platform.importCargoLock { inherit lockFile; }) manifests;
           # when building a guest with cargo-hyperlight, or when
           # building a miri sysroot for the main workspace, we need to
           # include any crates.io dependencies of the standard library
@@ -118,20 +128,9 @@
           ) toolchains;
           stdlibDeps = builtins.map (lockFile:
             rust-platform.importCargoLock { inherit lockFile; }) stdlibLocks;
-          withStdlibLock = lockFile:
-            pkgs.symlinkJoin {
-              name = "cargo-deps";
-              paths = stdlibDeps ++ [
-                (rust-platform.importCargoLock {
-                  inherit lockFile;
-                })
-              ];
-            };
-          deps = {
-            "Cargo.toml" = withStdlibLock ./Cargo.lock;
-            "src/tests/rust_guests/dummyguest/Cargo.toml" = withStdlibLock ./src/tests/rust_guests/dummyguest/Cargo.lock;
-            "src/tests/rust_guests/simpleguest/Cargo.toml" = withStdlibLock ./src/tests/rust_guests/simpleguest/Cargo.lock;
-            "src/tests/rust_guests/witguest/Cargo.toml" = withStdlibLock ./src/tests/rust_guests/witguest/Cargo.lock;
+          deps = pkgs.symlinkJoin {
+            name = "cargo-deps";
+            paths = stdlibDeps ++ manifestDeps;
           };
 
           # Script snippet, used in the cargo/rustc wrappers below,
@@ -144,26 +143,10 @@
           # like `cargo clippy` and `cargo hyperlight` (see
           # https://github.com/rust-lang/cargo/issues/11031).
           materialiseDeps = let
-            sortedNames =  lib.lists.reverseList (builtins.attrNames deps);
+            sortedManifests = lib.lists.sort (p: q: p > q) manifests;
             matchClause = path: ''  */${path}) root="''${manifest%${path}}" ;;'';
             matchClauses = lib.strings.concatStringsSep "\n"
-              (builtins.map matchClause sortedNames);
-            makeClause = manifest: vendor: let
-              dir = builtins.dirOf manifest;
-              gitExclude = builtins.toString (/. + "${dir}/.cargo");
-            in ''
-              mkdir -p $root/${dir}/.cargo
-              cat >$root/${dir}/.cargo/config.toml <<EOF
-              [source.crates-io]
-              replace-with = "vendored-sources"
-
-              [source.vendored-sources]
-              directory = "${vendor}"
-              EOF
-              printf "# vendor dependency configuration generated by nix\n%s\n" "${gitExclude}" >> $root/.git/info/exclude
-            '';
-            makeClauses = lib.strings.concatStringsSep "\n"
-              (lib.mapAttrsToList makeClause deps);
+              (builtins.map matchClause sortedManifests);
           in ''
             base_cargo() {
               PATH="$base/bin:$PATH" "$base/bin/cargo" "$@"
@@ -174,8 +157,18 @@
               ${matchClauses}
             esac
             if [ -f ''${root}/flake.nix ]; then
+
+              mkdir -p $root/$.cargo
+              cat >$root/.cargo/config.toml <<EOF
+              [source.crates-io]
+              replace-with = "vendored-sources"
+
+              [source.vendored-sources]
+              directory = "${deps}"
+            EOF
+
               sed -i '/# vendor dependency configuration generated by nix/{N;d;}' $root/.git/info/exclude
-              ${makeClauses}
+              printf "# vendor dependency configuration generated by nix\n%s\n" "/.cargo" >> $root/.git/info/exclude
             fi
 
             # libgit2-sys copies a vendored git2 into the target/
@@ -238,7 +231,7 @@
           pname = "hyperlight";
           version = "0.0.0";
           src = lib.cleanSource ./.;
-          cargoDeps = deps."Cargo.toml";
+          cargoDeps = deps;
 
           nativeBuildInputs = [
             azure-cli