From 2df4c33974769c39f618bd25a352588b51143959 Mon Sep 17 00:00:00 2001
From: Michael-F-Bryan <michaelfbryan@gmail.com>
Date: Sat, 16 Jul 2022 03:26:36 +0800
Subject: [PATCH] Try to use the "cargo metadata" command when automatically
 discovering the target dir

---
 Cargo.lock                |  1 +
 crates/fj-host/Cargo.toml |  1 +
 crates/fj-host/src/lib.rs | 18 ++++++++++++++++--
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index e33938e92..4cb7bf150 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -870,6 +870,7 @@ dependencies = [
 name = "fj-host"
 version = "0.8.0"
 dependencies = [
+ "cargo_metadata",
  "fj",
  "libloading",
  "notify",
diff --git a/crates/fj-host/Cargo.toml b/crates/fj-host/Cargo.toml
index 395486a0b..4fcd24d4b 100644
--- a/crates/fj-host/Cargo.toml
+++ b/crates/fj-host/Cargo.toml
@@ -16,6 +16,7 @@ categories = ["encoding", "mathematics", "rendering"]
 libloading = "0.7.2"
 notify = "5.0.0-pre.15"
 thiserror = "1.0.31"
+cargo_metadata = "0.15.0"
 
 [dependencies.fj]
 version = "0.8.0"
diff --git a/crates/fj-host/src/lib.rs b/crates/fj-host/src/lib.rs
index c8ddc6463..f71ad9d42 100644
--- a/crates/fj-host/src/lib.rs
+++ b/crates/fj-host/src/lib.rs
@@ -21,12 +21,13 @@ use std::{
     collections::{HashMap, HashSet},
     ffi::OsStr,
     io,
-    path::PathBuf,
+    path::{Path, PathBuf},
     process::Command,
     sync::mpsc,
     thread,
 };
 
+use cargo_metadata::Metadata;
 use notify::Watcher as _;
 use thiserror::Error;
 
@@ -64,7 +65,9 @@ impl Model {
 
         let lib_path = {
             let file = HostPlatform::lib_file_name(&name);
-            let target_dir = target_dir.unwrap_or_else(|| path.join("target"));
+            let target_dir = target_dir
+                .or_else(|| cargo_metadata_target_dir(&path))
+                .unwrap_or_else(|| path.join("target"));
             target_dir.join("debug").join(file)
         };
 
@@ -285,3 +288,14 @@ pub enum Error {
 }
 
 type ModelFn = unsafe extern "C" fn(args: &Parameters) -> fj::Shape;
+
+fn cargo_metadata_target_dir(model: &Path) -> Option<PathBuf> {
+    let Metadata {
+        target_directory, ..
+    } = cargo_metadata::MetadataCommand::new()
+        .current_dir(model)
+        .exec()
+        .ok()?;
+
+    Some(target_directory.into())
+}