More reliable target dir discovery

crates/bindings/src/main.rs

@@ -25,7 +25,7 @@ fn main() -> std::io::Result<()> {
         },
     };
 
-    let mut path = windows_gen::workspace_dir();
+    let mut path: std::path::PathBuf = windows_gen::workspace_dir().into();
     path.push("src");
     path.push("bindings.rs");
 

crates/fmt/src/main.rs

@@ -74,7 +74,7 @@ fn walk_path(path: &Path) -> Result<()> {
 }
 
 fn main() -> Result<()> {
-    let dir = windows_gen::workspace_dir();
+    let dir: std::path::PathBuf = windows_gen::workspace_dir().into();
     walk_path(&dir)?;
 
     format_file(

crates/gen/src/workspace.rs

@@ -14,12 +14,10 @@ pub fn crate_winmds() -> &'static [File] {
     unsafe { &*VALUE.as_ptr() }
 }
 
-pub fn workspace_dir() -> std::path::PathBuf {
+fn cargo_metadata() -> &'static str {
     use std::{mem::MaybeUninit, sync::Once};
     static ONCE: Once = Once::new();
-    static mut VALUE: MaybeUninit<std::path::PathBuf> = MaybeUninit::uninit();
-
-    // TODO: calling `cargo metadata` just to get the workspace dir takes about 40ms.
+    static mut VALUE: MaybeUninit<String> = MaybeUninit::uninit();
 
     ONCE.call_once(|| {
         let output = std::process::Command::new(env!("CARGO"))
@@ -30,27 +28,49 @@ pub fn workspace_dir() -> std::path::PathBuf {
             .output()
             .expect("Failed to run `cargo metadata`");
 
-        const JSON_KEY: &str = r#""workspace_root":"#;
-        let json = String::from_utf8(output.stdout).expect("Cargo metadata is not utf-8");
-        let beginning_index = json
-            .rfind(JSON_KEY)
-            .expect("Cargo metadata did not contain `workspace_root` key.")
-            + JSON_KEY.len()
-            + 1;
+        unsafe {
+            VALUE = MaybeUninit::new(
+                String::from_utf8(output.stdout).expect("Cargo metadata is not utf-8"),
+            )
+        }
+    });
+
+    // This is safe because `call_once` has already been called.
+    unsafe { &*VALUE.as_ptr() }
+}
 
-        let ending_index = json[beginning_index..]
-            .find('"')
-            .expect("Cargo metadata ended before closing '\"' in `workspace_root` value");
+pub fn workspace_dir() -> String {
+    const JSON_KEY: &str = r#""workspace_root":"#;
+    let json = cargo_metadata();
 
-        let workspace_root =
-            json[beginning_index..beginning_index + ending_index].replace("\\\\", "\\");
+    let beginning_index = json
+        .rfind(JSON_KEY)
+        .expect("Cargo metadata did not contain `workspace_root` key.")
+        + JSON_KEY.len()
+        + 1;
 
-        // This is safe because `Once` provides thread-safe one-time initialization
-        unsafe { VALUE = MaybeUninit::new(workspace_root.into()) }
-    });
+    let ending_index = json[beginning_index..]
+        .find('"')
+        .expect("Cargo metadata ended before closing '\"' in `workspace_root` value");
 
-    // This is safe because `call_once` has already been called.
-    unsafe { (*VALUE.as_ptr()).clone() }
+    json[beginning_index..beginning_index + ending_index].replace("\\\\", "\\")
+}
+
+pub fn target_dir() -> String {
+    const JSON_KEY: &str = r#""target_directory":"#;
+    let json = cargo_metadata();
+
+    let beginning_index = json
+        .rfind(JSON_KEY)
+        .expect("Cargo metadata did not contain `target_directory` key.")
+        + JSON_KEY.len()
+        + 1;
+
+    let ending_index = json[beginning_index..]
+        .find('"')
+        .expect("Cargo metadata ended before closing '\"' in `target_directory` value");
+
+    json[beginning_index..beginning_index + ending_index].replace("\\\\", "\\")
 }
 
 fn get_crate_winmds() -> Vec<File> {
@@ -81,17 +101,7 @@ fn get_crate_winmds() -> Vec<File> {
     dir.push("winmd");
     push_dir(&mut result, &dir);
 
-    let dir = std::env::var("PATH").expect("No `PATH` env variable set");
-    let end = dir.find(';').expect("Path not ending in `;`");
-    let mut dir: std::path::PathBuf = dir[..end].into();
-    dir.pop();
-    dir.pop();
-    dir.push(".windows");
-    dir.push("winmd");
-    push_dir(&mut result, &dir);
-
-    let mut dir = workspace_dir();
-    dir.push("target");
+    let mut dir: std::path::PathBuf = target_dir().into();
     dir.push(".windows");
     dir.push("winmd");
     push_dir(&mut result, &dir);

crates/macros/src/lib.rs

@@ -44,6 +44,7 @@ impl ToTokens for RawString {
 pub fn build(stream: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let build = parse_macro_input!(stream as BuildMacro);
     let tokens = RawString(build.into_tokens_string());
+    let target_dir = RawString(gen::target_dir());
 
     let tokens = quote! {
         {
@@ -118,22 +119,8 @@ pub fn build(stream: proc_macro::TokenStream) -> proc_macro::TokenStream {
             });
 
             println!("cargo:rustc-link-search=native={}", source.to_str().expect("`CARGO_MANIFEST_DIR` not a valid path"));
-            let mut destination : ::std::path::PathBuf = ::std::env::var("OUT_DIR").expect("No `OUT_DIR` env variable set").into();
-
-            loop {
-                destination.pop();
-                destination.push("Cargo.toml");
-
-                if destination.exists() {
-                    break;
-                }
-
-                destination.pop();
-            }
-
-            destination.pop();
-            destination.push("target");
 
+            let mut destination : ::std::path::PathBuf = #target_dir.into();
             let profile = ::std::env::var("PROFILE").expect("No `PROFILE` env variable set");
             copy_to_profile(&source, &destination, &profile);