event/error: add module Error, Result typedef

Plus some From impls for Reader, and Scanner error types.

src/event/error.rs

@@ -0,0 +1,93 @@
+/*
+ * 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 std::{
+    fmt::{self, Debug},
+    io,
+    str::Utf8Error,
+};
+
+use crate::{reader::ReaderError, scanner::error::ScanError};
+
+pub type ParseResult<T> = std::result::Result<T, ParseError>;
+
+#[derive(Debug)]
+pub enum ParseError
+{
+    CorruptStream,
+    DuplicateVersion,
+    DuplicateTagDirective,
+    UndefinedTag,
+    MissingDocumentStart,
+    MissingBlockEntry,
+    MissingNode,
+    MissingKey,
+    MissingFlowSequenceEntryOrEnd,
+    MissingFlowMappingEntryOrEnd,
+
+    Scanner(ScanError),
+    UTF8(Utf8Error),
+    IO(io::Error),
+
+    UnexpectedEOF,
+}
+
+impl From<ScanError> for ParseError
+{
+    fn from(e: ScanError) -> Self
+    {
+        Self::Scanner(e)
+    }
+}
+
+impl From<ReaderError> for ParseError
+{
+    fn from(e: ReaderError) -> Self
+    {
+        match e
+        {
+            ReaderError::UTF8(e) => Self::UTF8(e),
+            ReaderError::IO(e) => Self::IO(e),
+            ReaderError::Scanner(e) => Self::Scanner(e),
+        }
+    }
+}
+
+impl PartialEq for ParseError
+{
+    fn eq(&self, other: &Self) -> bool
+    {
+        match (self, other)
+        {
+            (Self::Scanner(s), Self::Scanner(o)) => s == o,
+            (Self::UTF8(s), Self::UTF8(o)) => s == o,
+            (Self::IO(s), Self::IO(o)) => s.kind() == o.kind(),
+            _ => core::mem::discriminant(self) == core::mem::discriminant(other),
+        }
+    }
+}
+
+impl fmt::Display for ParseError
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+    {
+        Debug::fmt(self, f)
+    }
+}
+
+impl std::error::Error for ParseError
+{
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)>
+    {
+        match self
+        {
+            Self::Scanner(e) => Some(e),
+            Self::UTF8(e) => Some(e),
+            Self::IO(e) => Some(e),
+            _ => None,
+        }
+    }
+}

src/event/mod.rs

@@ -5,3 +5,5 @@
  */
 
 mod state;
+
+pub mod error;