2 files changed, 90 insertions, 0 deletions
diff --git a/xpcom/rust/nserror/Cargo.toml b/xpcom/rust/nserror/Cargo.toml
new file mode 100644
index 0000000000..4fca5a4c2c
--- /dev/null
+++ b/xpcom/rust/nserror/Cargo.toml
@@ -0,0 +1,11 @@
+[package]
+name = "nserror"
+version = "0.1.0"
+authors = ["Nika Layzell <nika@thelayzells.com>"]
+license = "MPL-2.0"
+description = "Rust bindings to xpcom nsresult and NS_ERROR_ values"
+edition = "2018"
+
+[dependencies]
+nsstring = { path = "../nsstring" }
+mozbuild = "0.1"
diff --git a/xpcom/rust/nserror/src/lib.rs b/xpcom/rust/nserror/src/lib.rs
new file mode 100644
index 0000000000..e4107d1b57
--- /dev/null
+++ b/xpcom/rust/nserror/src/lib.rs
@@ -0,0 +1,79 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use nsstring::{nsACString, nsCString};
+use std::error::Error;
+use std::fmt;
+
+/// The type of errors in gecko.  Uses a newtype to provide additional type
+/// safety in Rust and #[repr(transparent)] to ensure the same representation
+/// as the C++ equivalent.
+#[repr(transparent)]
+#[allow(non_camel_case_types)]
+#[derive(Clone, Copy, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub struct nsresult(pub u32);
+
+impl nsresult {
+    pub fn failed(self) -> bool {
+        (self.0 >> 31) != 0
+    }
+
+    pub fn succeeded(self) -> bool {
+        !self.failed()
+    }
+
+    pub fn to_result(self) -> Result<(), nsresult> {
+        if self.failed() {
+            Err(self)
+        } else {
+            Ok(())
+        }
+    }
+
+    /// Get a printable name for the nsresult error code. This function returns
+    /// a nsCString<'static>, which implements `Display`.
+    pub fn error_name(self) -> nsCString {
+        let mut cstr = nsCString::new();
+        unsafe {
+            Gecko_GetErrorName(self, &mut *cstr);
+        }
+        cstr
+    }
+}
+
+impl fmt::Display for nsresult {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.error_name())
+    }
+}
+
+impl fmt::Debug for nsresult {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.error_name())
+    }
+}
+
+impl<T, E> From<Result<T, E>> for nsresult
+where
+    E: Into<nsresult>,
+{
+    fn from(result: Result<T, E>) -> nsresult {
+        match result {
+            Ok(_) => NS_OK,
+            Err(e) => e.into(),
+        }
+    }
+}
+
+impl Error for nsresult {}
+
+extern "C" {
+    fn Gecko_GetErrorName(rv: nsresult, cstr: *mut nsACString);
+}
+
+mod error_list {
+    include!(mozbuild::objdir_path!("xpcom/base/error_list.rs"));
+}
+
+pub use error_list::*;