rustc_hir_typeck/
diverges.rs

Help
1use std::{cmp, ops};
2
3use rustc_span::{DUMMY_SP, Span};
4
5/// Tracks whether executing a node may exit normally (versus
6/// return/break/panic, which "diverge", leaving dead code in their
7/// wake). Tracked semi-automatically (through type variables marked
8/// as diverging), with some manual adjustments for control-flow
9/// primitives (approximating a CFG).
10#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
11pub(crate) enum Diverges {
12    /// Potentially unknown, some cases converge,
13    /// others require a CFG to determine them.
14    Maybe,
15
16    /// Definitely known to diverge and therefore
17    /// not reach the next sibling or its parent.
18    Always {
19        /// The `Span` points to the expression
20        /// that caused us to diverge
21        /// (e.g. `return`, `break`, etc).
22        span: Span,
23        /// In some cases (e.g. a `match` expression
24        /// where all arms diverge), we may be
25        /// able to provide a more informative
26        /// message to the user.
27        /// If this is `None`, a default message
28        /// will be generated, which is suitable
29        /// for most cases.
30        custom_note: Option<&'static str>,
31    },
32
33    /// Same as `Always` but with a reachability
34    /// warning already emitted.
35    WarnedAlways,
36}
37
38// Convenience impls for combining `Diverges`.
39
40impl ops::BitAnd for Diverges {
41    type Output = Self;
42    fn bitand(self, other: Self) -> Self {
43        cmp::min(self, other)
44    }
45}
46
47impl ops::BitOr for Diverges {
48    type Output = Self;
49    fn bitor(self, other: Self) -> Self {
50        cmp::max(self, other)
51    }
52}
53
54impl ops::BitAndAssign for Diverges {
55    fn bitand_assign(&mut self, other: Self) {
56        *self = *self & other;
57    }
58}
59
60impl ops::BitOrAssign for Diverges {
61    fn bitor_assign(&mut self, other: Self) {
62        *self = *self | other;
63    }
64}
65
66impl Diverges {
67    /// Creates a `Diverges::Always` with the provided `span` and the default note message.
68    pub(super) fn always(span: Span) -> Diverges {
69        Diverges::Always { span, custom_note: None }
70    }
71
72    pub(super) fn is_always(self) -> bool {
73        // Enum comparison ignores the
74        // contents of fields, so we just
75        // fill them in with garbage here.
76        self >= Diverges::Always { span: DUMMY_SP, custom_note: None }
77    }
78}
rustc_hir_typeck/diverges.rs

rustc_hir_typeck/
diverges.rs
