1 files changed, 150 insertions, 0 deletions
diff --git a/src/error.rs b/src/error.rs
new file mode 100644
index 0000000..70fe436
--- /dev/null
+++ b/src/error.rs
@@ -0,0 +1,150 @@
+use std::error;
+use std::fmt;
+use std::result;
+
+use regex_syntax;
+
+pub type Result<T> = result::Result<T, Error>;
+
+/// An error that occurred during the construction of a DFA.
+#[derive(Clone, Debug)]
+pub struct Error {
+    kind: ErrorKind,
+}
+
+/// The kind of error that occurred.
+#[derive(Clone, Debug)]
+pub enum ErrorKind {
+    /// An error that occurred while parsing a regular expression. Note that
+    /// this error may be printed over multiple lines, and is generally
+    /// intended to be end user readable on its own.
+    Syntax(String),
+    /// An error that occurred because an unsupported regex feature was used.
+    /// The message string describes which unsupported feature was used.
+    ///
+    /// The primary regex features that are unsupported are those that require
+    /// look-around, such as the `^` and `$` anchors and the word boundary
+    /// assertion `\b`. These may be supported in the future.
+    Unsupported(String),
+    /// An error that occurred when attempting to serialize a DFA to bytes.
+    Serialize(String),
+    /// An error that occurs when constructing a DFA would require the use of
+    /// a state ID that overflows the chosen state ID representation. For
+    /// example, if one is using `u8` for state IDs and builds a DFA with
+    /// 257 states, then the last state's ID will be `256` which cannot be
+    /// represented with `u8`.
+    ///
+    /// Typically, this error occurs in the determinization process of building
+    /// a DFA (the conversion step from NFA to DFA). It can also occur when
+    /// trying to build a smaller DFA from an existing one.
+    StateIDOverflow {
+        /// The maximum possible state ID.
+        max: usize,
+    },
+    /// An error that occurs when premultiplication of state IDs is requested,
+    /// but doing so would overflow the chosen state ID representation.
+    ///
+    /// When `max == requested_max`, then the state ID would overflow `usize`.
+    PremultiplyOverflow {
+        /// The maximum possible state id.
+        max: usize,
+        /// The maximum ID required by premultiplication.
+        requested_max: usize,
+    },
+}
+
+impl Error {
+    /// Return the kind of this error.
+    pub fn kind(&self) -> &ErrorKind {
+        &self.kind
+    }
+
+    pub(crate) fn syntax(err: regex_syntax::Error) -> Error {
+        Error { kind: ErrorKind::Syntax(err.to_string()) }
+    }
+
+    pub(crate) fn unsupported_anchor() -> Error {
+        let msg = r"anchors such as ^, $, \A and \z are not supported";
+        Error { kind: ErrorKind::Unsupported(msg.to_string()) }
+    }
+
+    pub(crate) fn unsupported_word() -> Error {
+        let msg = r"word boundary assertions (\b and \B) are not supported";
+        Error { kind: ErrorKind::Unsupported(msg.to_string()) }
+    }
+
+    pub(crate) fn unsupported_longest_match() -> Error {
+        let msg = "unachored searches with longest match \
+                   semantics are not supported";
+        Error { kind: ErrorKind::Unsupported(msg.to_string()) }
+    }
+
+    pub(crate) fn serialize(message: &str) -> Error {
+        Error { kind: ErrorKind::Serialize(message.to_string()) }
+    }
+
+    pub(crate) fn state_id_overflow(max: usize) -> Error {
+        Error { kind: ErrorKind::StateIDOverflow { max } }
+    }
+
+    pub(crate) fn premultiply_overflow(
+        max: usize,
+        requested_max: usize,
+    ) -> Error {
+        Error { kind: ErrorKind::PremultiplyOverflow { max, requested_max } }
+    }
+}
+
+impl error::Error for Error {
+    fn description(&self) -> &str {
+        match self.kind {
+            ErrorKind::Syntax(_) => "syntax error",
+            ErrorKind::Unsupported(_) => "unsupported syntax",
+            ErrorKind::Serialize(_) => "serialization error",
+            ErrorKind::StateIDOverflow { .. } => {
+                "state id representation too small"
+            }
+            ErrorKind::PremultiplyOverflow { .. } => {
+                "state id representation too small for premultiplication"
+            }
+        }
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self.kind {
+            ErrorKind::Syntax(ref msg) => write!(f, "{}", msg),
+            ErrorKind::Unsupported(ref msg) => write!(f, "{}", msg),
+            ErrorKind::Serialize(ref msg) => {
+                write!(f, "DFA serialization error: {}", msg)
+            }
+            ErrorKind::StateIDOverflow { max } => write!(
+                f,
+                "building the DFA failed because it required building \
+                 more states that can be identified, where the maximum \
+                 ID for the chosen representation is {}",
+                max,
+            ),
+            ErrorKind::PremultiplyOverflow { max, requested_max } => {
+                if max == requested_max {
+                    write!(
+                        f,
+                        "premultiplication of states requires the ability to \
+                         represent a state ID greater than what can fit on \
+                         this platform's usize, which is {}",
+                        ::std::usize::MAX,
+                    )
+                } else {
+                    write!(
+                        f,
+                        "premultiplication of states requires the ability to \
+                         represent at least a state ID of {}, but the chosen \
+                         representation only permits a maximum state ID of {}",
+                        requested_max, max,
+                    )
+                }
+            }
+        }
+    }
+}