Improve cbindgen detection in tests

Since our MSRV is now Rust 1.54, we can rely on cargo setting `CARGO_BIN_EXE_cbindgen`
to the cbindgen path in integration tests.
This is more reliable than guessing the path, since cargo knows where it placed the bin.

build.rs

@@ -16,19 +16,6 @@ fn generate_tests() {
 
     println!("cargo:rerun-if-changed={}", tests_dir.display());
 
-    // Try to make a decent guess at where our binary will end up in.
-    //
-    // TODO(emilio): Ideally running tests will just use the library-version of
-    // cbindgen instead of the built binary.
-    let cbindgen_path = out_dir
-        .parent()
-        .unwrap()
-        .parent()
-        .unwrap()
-        .parent()
-        .unwrap()
-        .join("cbindgen");
-
     for entry in entries {
         let path_segment = if entry.file_type().unwrap().is_file() {
             match entry.path().extension().and_then(OsStr::to_str) {
@@ -53,8 +40,7 @@ fn generate_tests() {
 
         writeln!(
             dst,
-            "test_file!({:?}, test_{}, {:?}, {:?});",
-            cbindgen_path,
+            "test_file!(test_{}, {:?}, {:?});",
             identifier,
             path_segment,
             entry.path(),

tests/profile.rs

@@ -40,26 +40,14 @@ fn build_using_bin(extra_args: &[&str]) -> tempfile::TempDir {
         .tempdir()
         .expect("Creating tmp dir failed");
 
-    let cbindgen_path = match option_env!("CARGO_BIN_EXE_cbindgen") {
-        Some(path) => path.into(),
-        None => {
-            // We must be on an older version of Rust.
-            // Guess where cbindgen would be relative to OUT_DIR.
-            let mut path = PathBuf::from(env!("OUT_DIR"));
-            path.pop();
-            path.pop();
-            path.pop();
-            path.push("cbindgen");
-            path.into_os_string()
-        }
-    };
+    let cbindgen_path = env!("CARGO_BIN_EXE_cbindgen");
 
     Command::new(cbindgen_path)
         .current_dir(expand_dep_test_dir)
         .env("CARGO_EXPAND_TARGET_DIR", tmp_dir.path())
         .args(extra_args)
         .output()
-        .expect("build should succed");
+        .expect("build should succeed");
 
     tmp_dir
 }

tests/tests.rs

@@ -6,6 +6,9 @@ use std::path::Path;
 use std::process::Command;
 use std::{env, fs, str};
 
+// Set automatically by cargo for integration tests
+static CBINDGEN_PATH: &str = env!("CARGO_BIN_EXE_cbindgen");
+
 fn style_str(style: Style) -> &'static str {
     match style {
         Style::Both => "both",
@@ -15,14 +18,13 @@ fn style_str(style: Style) -> &'static str {
 }
 
 fn run_cbindgen(
-    cbindgen_path: &'static str,
     path: &Path,
     output: &Path,
     language: Language,
     cpp_compat: bool,
     style: Option<Style>,
 ) -> Vec<u8> {
-    let program = Path::new(cbindgen_path);
+    let program = Path::new(CBINDGEN_PATH);
     let mut command = Command::new(program);
     match language {
         Language::Cxx => {}
@@ -144,7 +146,6 @@ const SKIP_WARNING_AS_ERROR_SUFFIX: &str = ".skip_warning_as_error";
 
 #[allow(clippy::too_many_arguments)]
 fn run_compile_test(
-    cbindgen_path: &'static str,
     name: &'static str,
     path: &Path,
     tmp_dir: &Path,
@@ -183,7 +184,6 @@ fn run_compile_test(
     generated_file.push(source_file);
 
     let cbindgen_output = run_cbindgen(
-        cbindgen_path,
         path,
         &generated_file,
         language,
@@ -234,7 +234,7 @@ fn run_compile_test(
     }
 }
 
-fn test_file(cbindgen_path: &'static str, name: &'static str, filename: &'static str) {
+fn test_file(name: &'static str, filename: &'static str) {
     let test = Path::new(filename);
     let tmp_dir = tempfile::Builder::new()
         .prefix("cbindgen-test-output")
@@ -247,7 +247,6 @@ fn test_file(cbindgen_path: &'static str, name: &'static str, filename: &'static
     for cpp_compat in &[true, false] {
         for style in &[Style::Type, Style::Tag, Style::Both] {
             run_compile_test(
-                cbindgen_path,
                 name,
                 test,
                 tmp_dir,
@@ -260,7 +259,6 @@ fn test_file(cbindgen_path: &'static str, name: &'static str, filename: &'static
     }
 
     run_compile_test(
-        cbindgen_path,
         name,
         test,
         tmp_dir,
@@ -274,7 +272,6 @@ fn test_file(cbindgen_path: &'static str, name: &'static str, filename: &'static
     let mut cbindgen_outputs = HashSet::new();
     for style in &[Style::Type, Style::Tag] {
         run_compile_test(
-            cbindgen_path,
             name,
             test,
             tmp_dir,
@@ -287,10 +284,10 @@ fn test_file(cbindgen_path: &'static str, name: &'static str, filename: &'static
 }
 
 macro_rules! test_file {
-    ($cbindgen_path:expr, $test_function_name:ident, $name:expr, $file:tt) => {
+    ($test_function_name:ident, $name:expr, $file:tt) => {
         #[test]
         fn $test_function_name() {
-            test_file($cbindgen_path, $name, $file);
+            test_file($name, $file);
         }
     };
 }