Add file location information when failing to parse WebIDL files. (#562)

crates/webidl/src/error.rs

@@ -0,0 +1,65 @@
+use failure::{Backtrace, Context, Fail};
+use std::fmt;
+
+/// Either `Ok(t)` or `Err(Error)`.
+pub type Result<T> = ::std::result::Result<T, Error>;
+
+/// The different contexts an error can occur in in this crate.
+#[derive(Debug, Fail, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub enum ErrorKind {
+    /// Failed to open a WebIDL file.
+    #[fail(display="opening WebIDL file")]
+    OpeningWebIDLFile,
+    /// Failed to read a WebIDL file.
+    #[fail(display="reading WebIDL file")]
+    ReadingWebIDLFile,
+    /// Failed to parse a WebIDL file.
+    #[fail(display="parsing WebIDL source text at {}", _0)]
+    ParsingWebIDLSourcePos(usize),
+    /// Failed to parse a WebIDL file.
+    #[fail(display="parsing WebIDL source text")]
+    ParsingWebIDLSource,
+}
+
+/// The error type for this crate.
+#[derive(Debug)]
+pub struct Error {
+    inner: Context<ErrorKind>,
+}
+
+impl Fail for Error {
+    fn cause(&self) -> Option<&Fail> {
+        self.inner.cause()
+    }
+
+    fn backtrace(&self) -> Option<&Backtrace> {
+        self.inner.backtrace()
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(&self.inner, f)
+    }
+}
+
+impl Error {
+    /// The context for this error.
+    pub fn kind(&self) -> ErrorKind {
+        *self.inner.get_context()
+    }
+}
+
+impl From<ErrorKind> for Error {
+    fn from(kind: ErrorKind) -> Error {
+        Error { inner: Context::new(kind) }
+    }
+}
+
+impl From<Context<ErrorKind>> for Error {
+    fn from(inner: Context<ErrorKind>) -> Error {
+        Error { inner: inner }
+    }
+}
+
+