diff options
Diffstat (limited to 'compiler/rustc_typeck/src/check/diverges.rs')
-rw-r--r-- | compiler/rustc_typeck/src/check/diverges.rs | 78 |
1 files changed, 78 insertions, 0 deletions
diff --git a/compiler/rustc_typeck/src/check/diverges.rs b/compiler/rustc_typeck/src/check/diverges.rs new file mode 100644 index 000000000..963a93a95 --- /dev/null +++ b/compiler/rustc_typeck/src/check/diverges.rs @@ -0,0 +1,78 @@ +use rustc_span::source_map::DUMMY_SP; +use rustc_span::{self, Span}; +use std::{cmp, ops}; + +/// Tracks whether executing a node may exit normally (versus +/// return/break/panic, which "diverge", leaving dead code in their +/// wake). Tracked semi-automatically (through type variables marked +/// as diverging), with some manual adjustments for control-flow +/// primitives (approximating a CFG). +#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)] +pub enum Diverges { + /// Potentially unknown, some cases converge, + /// others require a CFG to determine them. + Maybe, + + /// Definitely known to diverge and therefore + /// not reach the next sibling or its parent. + Always { + /// The `Span` points to the expression + /// that caused us to diverge + /// (e.g. `return`, `break`, etc). + span: Span, + /// In some cases (e.g. a `match` expression + /// where all arms diverge), we may be + /// able to provide a more informative + /// message to the user. + /// If this is `None`, a default message + /// will be generated, which is suitable + /// for most cases. + custom_note: Option<&'static str>, + }, + + /// Same as `Always` but with a reachability + /// warning already emitted. + WarnedAlways, +} + +// Convenience impls for combining `Diverges`. + +impl ops::BitAnd for Diverges { + type Output = Self; + fn bitand(self, other: Self) -> Self { + cmp::min(self, other) + } +} + +impl ops::BitOr for Diverges { + type Output = Self; + fn bitor(self, other: Self) -> Self { + cmp::max(self, other) + } +} + +impl ops::BitAndAssign for Diverges { + fn bitand_assign(&mut self, other: Self) { + *self = *self & other; + } +} + +impl ops::BitOrAssign for Diverges { + fn bitor_assign(&mut self, other: Self) { + *self = *self | other; + } +} + +impl Diverges { + /// Creates a `Diverges::Always` with the provided `span` and the default note message. + pub(super) fn always(span: Span) -> Diverges { + Diverges::Always { span, custom_note: None } + } + + pub(super) fn is_always(self) -> bool { + // Enum comparison ignores the + // contents of fields, so we just + // fill them in with garbage here. + self >= Diverges::Always { span: DUMMY_SP, custom_note: None } + } +} |