Make running cbindgen with own create expansion from build.rs

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};
 
@@ -75,8 +75,18 @@ 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"));
     }
 
+    // Set this variable so that we don't call it recursively if we expand a crate that is using
+    // cbindgen
+    cmd.env("_CBINDGEN_IS_RUNNING", "1");
+
     cmd.arg("rustc");
     cmd.arg("--lib");
     cmd.arg("--manifest-path");

src/bindgen/parser.rs

@@ -179,6 +179,13 @@ impl<'a> Parser<'a> {
     fn parse_expand_crate(&mut self, pkg: &PackageRef) -> Result<(), Error> {
         assert!(self.lib.is_some());
 
+        // If you want to expand the crate you run cbindgen on you might end up in an endless
+        // recursion if the cbindgen generation is triggered from build.rs. Hence don't run the
+        // expansion if the build was already triggered by cbindgen.
+        if std::env::var("_CBINDGEN_IS_RUNNING").is_ok() {
+            return Ok(());
+        }
+
         let mod_parsed = {
             if !self.cache_expanded_crate.contains_key(&pkg.name) {
                 let s = self