Run cargo expand outside the normal target directory

vmx · emilio · commit 3e820849cb9c · 2019-08-06T12:59:25.000+02:00
When crates should get expanded, then cargo is run again from within cbindgen. When cbindgen is started from a build.rs file, this means that cargo is starting another cargo run. Cargo locks the directory it is running on. If two cargos spawn by each other run with the same target directory, then they both want to accquire a lock and hence deadlock. This commit fixes the problem with running the spawned cargo at a different directory. Please note that this will always be the same directory, hence any subsequent runs will be faster (as you would exepct it to be). This is part of mozilla#347.
diff --git a/src/bindgen/cargo/cargo_expand.rs b/src/bindgen/cargo/cargo_expand.rs
@@ -6,7 +6,7 @@ use std::env;
 use std::error;
 use std::fmt;
 use std::io;
-use std::path::Path;
+use std::path::{Path, PathBuf};
 use std::process::Command;
 use std::str::{from_utf8, Utf8Error};
 
@@ -75,6 +75,12 @@ pub fn expand(
         cmd.env("CARGO_TARGET_DIR", _temp_dir.unwrap().path());
     } else if let Ok(ref path) = env::var("CARGO_EXPAND_TARGET_DIR") {
         cmd.env("CARGO_TARGET_DIR", path);
+    } else if let Ok(ref path) = env::var("OUT_DIR") {
+        // When cbindgen was started programatically from a build.rs file, Cargo is running and
+        // locking the default target directory. In this case we need to use another directory,
+        // else we would end up in a deadlock. If Cargo is running `OUT_DIR` will be set, so we
+        // can use a directory relative to that.
+        cmd.env("CARGO_TARGET_DIR", PathBuf::from(path).join("expanded"));
     }
 
     cmd.arg("rustc");
