Configure devenv to build output

devenv.nix

@@ -6,6 +6,33 @@
   ...
 }:
 
+let
+  # devenv's `languages.rust.import` only builds single root-package crates
+  # (it hardcodes `cargoNix.rootCrate.build`). musicfs is a virtual workspace with
+  # no root package, so we drive crate2nix directly and select the `musicfs-client`
+  # member out of `workspaceMembers`. src = ./. gives crate2nix the whole workspace,
+  # so the member's path-dependencies (musicfs-core, musicfs-proto) resolve.
+  crate2nixTools = pkgs.callPackage "${inputs.crate2nix}/tools.nix" { };
+  cargoNix =
+    pkgs.callPackage
+      (crate2nixTools.generatedCargoNix {
+        name = "musicfs";
+        src = ./.;
+      })
+      {
+        # Build with the toolchain configured for this dev environment,
+        # matching what languages.rust.import does internally.
+        buildRustCrateForPkgs =
+          _:
+          pkgs.buildRustCrate.override {
+            rustc = config.languages.rust.toolchainPackage;
+            cargo = config.languages.rust.toolchainPackage;
+          };
+      };
+
+  # musicfs-client's binary is named `musicfs` (see [[bin]] in its Cargo.toml).
+  musicfs = cargoNix.workspaceMembers."musicfs-client".build;
+in
 {
   languages.rust.enable = true;
   git-hooks.hooks = {
@@ -42,7 +69,7 @@
   processes.musicfs = {
     after = [ "devenv:processes:postgres" ];
     exec = lib.mkDefault ''
-      cargo run -p musicfs-client -- \
+      ${musicfs}/bin/musicfs \
         --source /home/fujin/Music \
         --mountpoint /tmp/rust-fuse \
         --database "postgresql://fujin@localhost/musicfs?host=$PGHOST"
@@ -53,7 +80,7 @@
     processes.musicfs = {
       after = [ "devenv:processes:postgres" ];
       exec = ''
-        cargo run -p musicfs-client -- \
+        ${musicfs}/bin/musicfs \
           --source /home/fujin/Music \
           --mountpoint /tmp/rust-fuse \
           --database "postgresql://fujin@localhost/musicfs?host=$PGHOST"
@@ -65,7 +92,7 @@
     processes.musicfs = {
       after = [ "devenv:processes:postgres" ];
       exec = ''
-        cargo run -p musicfs-client -- \
+        ${musicfs}/bin/musicfs \
           --source http://10.185.226.145:50051 \
           --mountpoint /tmp/rust-fuse \
           --database "postgresql://fujin@localhost/musicfs?host=$PGHOST"
@@ -77,7 +104,7 @@
     processes.musicfs = {
       after = [ "devenv:processes:postgres" ];
       exec = ''
-        cargo run -p musicfs-client -- \
+        ${musicfs}/bin/musicfs \
           --source http://127.0.0.1:50061 \
           --mountpoint ./target/e2e/mnt \
           --database "postgresql://fujin@localhost/musicfs_e2e?host=$PGHOST" \
@@ -101,6 +128,6 @@
   };
 
   outputs = {
-    rust-app = config.languages.rust.import ./. { };
+    musicfs = musicfs;
   };
 }