Adds BORING_BSSL_CPLUS_INCLUDE_PATH env variable handling

Author: Isaiah Becker-Mayer

boring-sys/build/config.rs

@@ -24,6 +24,7 @@ pub(crate) struct Features {
 pub(crate) struct Env {
     pub(crate) path: Option<PathBuf>,
     pub(crate) include_path: Option<PathBuf>,
+    pub(crate) cplus_include_path: Option<PathBuf>,
     pub(crate) source_path: Option<PathBuf>,
     pub(crate) precompiled_bcm_o: Option<PathBuf>,
     pub(crate) assume_patched: bool,
@@ -146,6 +147,7 @@ impl Env {
         Self {
             path: boringssl_var("BORING_BSSL_PATH").map(PathBuf::from),
             include_path: boringssl_var("BORING_BSSL_INCLUDE_PATH").map(PathBuf::from),
+            cplus_include_path: boringssl_var("BORING_BSSL_CPLUS_INCLUDE_PATH").map(PathBuf::from),
             source_path: boringssl_var("BORING_BSSL_SOURCE_PATH").map(PathBuf::from),
             precompiled_bcm_o: boringssl_var("BORING_BSSL_PRECOMPILED_BCM_O").map(PathBuf::from),
             assume_patched: boringssl_var("BORING_BSSL_ASSUME_PATCHED")

boring-sys/build/main.rs

@@ -619,8 +619,23 @@ fn link_in_precompiled_bcm_o(config: &Config) {
     .unwrap();
 }
 
+// Note: this is the entrypoint into the boring-sys build process.
 fn main() {
     let config = Config::from_env();
+
+    if let Some(ref cplus_include_path) = config.env.cplus_include_path {
+        println!(
+            "Setting CPLUS_INCLUDE_PATH to {}",
+            cplus_include_path.display()
+        );
+        // Inject CPLUS_INCLUDE_PATH into the environment for the build.
+        // This must be done before we build the boring source path so that it can
+        // be used during that build process.
+        std::env::set_var("CPLUS_INCLUDE_PATH", cplus_include_path);
+    } else {
+        println!("Didn't set CPLUS_INCLUDE_PATH");
+    }
+
     let bssl_dir = built_boring_source_path(&config);
     let build_path = get_boringssl_platform_output_path(&config);