parser: force proc macro fallback

Incorporate dtolnay/proc-macro2#220 to fix
the case where a binary which is built with `panic = "abort"` aborts
when calling into cbindgen functionality.

mozilla#569

Signed-off-by: Grant Elbert <elbe0046@gmail.com>

src/bindgen/parser.rs

@@ -206,6 +206,7 @@ impl<'a> Parser<'a> {
                         self.config.parse.expand.profile,
                     )
                     .map_err(|x| Error::CargoExpand(pkg.name.clone(), x))?;
+                proc_macro2::fallback::force();
                 let i = syn::parse_file(&s).map_err(|x| Error::ParseSyntaxError {
                     crate_name: pkg.name.clone(),
                     src_path: "".to_owned(),
@@ -243,6 +244,7 @@ impl<'a> Parser<'a> {
                         src_path: mod_path.to_str().unwrap().to_owned(),
                     })?;
 
+                proc_macro2::fallback::force();
                 let i = syn::parse_file(&s).map_err(|x| Error::ParseSyntaxError {
                     crate_name: pkg.name.clone(),
                     src_path: mod_path.to_string_lossy().into(),

tests/basic_cbindgen_wrapper/.gitignore

@@ -0,0 +1 @@
+Cargo.lock

tests/basic_cbindgen_wrapper/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "panic_abort"
+version = "0.1.0"
+edition = "2018"
+
+[profile.dev]
+panic = "abort"
+
+[profile.release]
+panic = "abort"
+
+[dependencies]
+cbindgen = { path = "../.." }

tests/basic_cbindgen_wrapper/src/main.rs

@@ -0,0 +1,23 @@
+use std::{env, process};
+
+fn exit_with_usage(exe_name: impl AsRef<str>) -> ! {
+    eprintln!("Usage: {} MANIFEST_PATH PKG_NAME", exe_name.as_ref());
+    process::exit(1);
+}
+
+/// A cbindgen wrapper whose return status can be leveraged by tests. Of note is that it is built
+/// with `panic = "abort"` with respect to https://github.com/alexcrichton/proc-macro2/pull/220.
+pub fn main() {
+    let opts = env::args().collect::<Vec<String>>();
+    if opts.len() < 3 {
+        exit_with_usage(&opts[0]);
+    }
+    let crate_dir = &opts[1];
+    let pkg_name = &opts[2];
+
+    cbindgen::Builder::new()
+        .with_crate(crate_dir)
+        .with_parse_expand(&vec![pkg_name])
+        .generate()
+        .expect("Unable to generate bindings");
+}

tests/panic_abort_strategy.rs

@@ -0,0 +1,31 @@
+use std::{env, path::PathBuf, process::Command};
+
+#[test]
+fn test_panic_abort_strategy() {
+    // Validates cbindgen's incorporation of https://github.com/alexcrichton/proc-macro2/issues/218.
+    //
+    // Run a binary whose profile specifies `panic = "abort"` and where the binary proceeds to
+    // call into cbindgen's generation functionality. Prior to the incorporation of the above this
+    // would result in the binary aborting.
+    let cargo = env::var("CARGO").unwrap_or_else(|_| String::from("cargo"));
+    let mut cmd = Command::new(cargo);
+
+    let tests_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap()).join("tests");
+    let wrapper_manifest_path = tests_dir.join("basic_cbindgen_wrapper").join("Cargo.toml");
+    let arg_manifest_dir = tests_dir.join("rust").join("expand_dep");
+
+    cmd.arg("run");
+    cmd.arg("--manifest-path");
+    cmd.arg(wrapper_manifest_path.as_path().to_str().unwrap());
+    cmd.arg("--");
+    cmd.arg(arg_manifest_dir.as_path().to_str().unwrap());
+    cmd.arg("expand-dep");
+
+    let output = cmd.output().expect("Failed to run cargo command");
+
+    assert!(
+        output.status.success(),
+        "Cargo run failed: {}",
+        String::from_utf8_lossy(&output.stderr)
+    );
+}