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use crate::{hybrid::id::LazyStateIDError, nfa};
/// An error that occurs when initial construction of a lazy DFA fails.
///
/// A build error can occur when insufficient cache capacity is configured or
/// if something about the NFA is unsupported. (For example, if one attempts
/// to build a lazy DFA without heuristic Unicode support but with an NFA that
/// contains a Unicode word boundary.)
///
/// This error does not provide many introspection capabilities. There are
/// generally only two things you can do with it:
///
/// * Obtain a human readable message via its `std::fmt::Display` impl.
/// * Access an underlying
/// [`nfa::thompson::BuildError`](crate::nfa::thompson::BuildError)
/// type from its `source` method via the `std::error::Error` trait. This error
/// only occurs when using convenience routines for building a lazy DFA
/// directly from a pattern string.
///
/// When the `std` feature is enabled, this implements the `std::error::Error`
/// trait.
#[derive(Clone, Debug)]
pub struct BuildError {
kind: BuildErrorKind,
}
#[derive(Clone, Debug)]
enum BuildErrorKind {
NFA(nfa::thompson::BuildError),
InsufficientCacheCapacity { minimum: usize, given: usize },
InsufficientStateIDCapacity { err: LazyStateIDError },
Unsupported(&'static str),
}
impl BuildError {
pub(crate) fn nfa(err: nfa::thompson::BuildError) -> BuildError {
BuildError { kind: BuildErrorKind::NFA(err) }
}
pub(crate) fn insufficient_cache_capacity(
minimum: usize,
given: usize,
) -> BuildError {
BuildError {
kind: BuildErrorKind::InsufficientCacheCapacity { minimum, given },
}
}
pub(crate) fn insufficient_state_id_capacity(
err: LazyStateIDError,
) -> BuildError {
BuildError {
kind: BuildErrorKind::InsufficientStateIDCapacity { err },
}
}
pub(crate) fn unsupported_dfa_word_boundary_unicode() -> BuildError {
let msg = "cannot build lazy DFAs for regexes with Unicode word \
boundaries; switch to ASCII word boundaries, or \
heuristically enable Unicode word boundaries or use a \
different regex engine";
BuildError { kind: BuildErrorKind::Unsupported(msg) }
}
}
#[cfg(feature = "std")]
impl std::error::Error for BuildError {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
match self.kind {
BuildErrorKind::NFA(ref err) => Some(err),
_ => None,
}
}
}
impl core::fmt::Display for BuildError {
fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
match self.kind {
BuildErrorKind::NFA(_) => write!(f, "error building NFA"),
BuildErrorKind::InsufficientCacheCapacity { minimum, given } => {
write!(
f,
"given cache capacity ({}) is smaller than \
minimum required ({})",
given, minimum,
)
}
BuildErrorKind::InsufficientStateIDCapacity { ref err } => {
err.fmt(f)
}
BuildErrorKind::Unsupported(ref msg) => {
write!(f, "unsupported regex feature for DFAs: {}", msg)
}
}
}
}
/// An error that occurs when cache usage has become inefficient.
///
/// One of the weaknesses of a lazy DFA is that it may need to clear its
/// cache repeatedly if it's not big enough. If this happens too much, then it
/// can slow searching down significantly. A mitigation to this is to use
/// heuristics to detect whether the cache is being used efficiently or not.
/// If not, then a lazy DFA can return a `CacheError`.
///
/// The default configuration of a lazy DFA in this crate is
/// set such that a `CacheError` will never occur. Instead,
/// callers must opt into this behavior with settings like
/// [`dfa::Config::minimum_cache_clear_count`](crate::hybrid::dfa::Config::minimum_cache_clear_count)
/// and
/// [`dfa::Config::minimum_bytes_per_state`](crate::hybrid::dfa::Config::minimum_bytes_per_state).
///
/// When the `std` feature is enabled, this implements the `std::error::Error`
/// trait.
#[derive(Clone, Debug)]
pub struct CacheError(());
impl CacheError {
pub(crate) fn too_many_cache_clears() -> CacheError {
CacheError(())
}
pub(crate) fn bad_efficiency() -> CacheError {
CacheError(())
}
}
#[cfg(feature = "std")]
impl std::error::Error for CacheError {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
None
}
}
impl core::fmt::Display for CacheError {
fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
write!(f, "lazy DFA cache has been cleared too many times")
}
}