316 lines
11 KiB
Rust
316 lines
11 KiB
Rust
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use rustc_pattern_analysis::{
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constructor::{
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Constructor, ConstructorSet, IntRange, MaybeInfiniteInt, RangeEnd, VariantVisibility,
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},
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usefulness::{PlaceValidity, UsefulnessReport},
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Captures, MatchArm, PatCx, PrivateUninhabitedField,
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};
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/// Sets up `tracing` for easier debugging. Tries to look like the `rustc` setup.
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pub fn init_tracing() {
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use tracing_subscriber::layer::SubscriberExt;
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use tracing_subscriber::util::SubscriberInitExt;
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use tracing_subscriber::Layer;
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let _ = tracing_tree::HierarchicalLayer::default()
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.with_writer(std::io::stderr)
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.with_indent_lines(true)
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.with_ansi(true)
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.with_targets(true)
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.with_indent_amount(2)
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.with_subscriber(
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tracing_subscriber::Registry::default()
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.with(tracing_subscriber::EnvFilter::from_default_env()),
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)
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.try_init();
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}
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/// A simple set of types.
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#[allow(dead_code)]
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#[derive(Debug, Copy, Clone)]
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pub enum Ty {
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/// Booleans
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Bool,
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/// 8-bit unsigned integers
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U8,
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/// Tuples.
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Tuple(&'static [Ty]),
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/// A struct with `arity` fields of type `ty`.
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BigStruct { arity: usize, ty: &'static Ty },
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/// A enum with `arity` variants of type `ty`.
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BigEnum { arity: usize, ty: &'static Ty },
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}
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/// The important logic.
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impl Ty {
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pub fn sub_tys(&self, ctor: &Constructor<Cx>) -> Vec<Self> {
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use Constructor::*;
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match (ctor, *self) {
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(Struct, Ty::Tuple(tys)) => tys.iter().copied().collect(),
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(Struct, Ty::BigStruct { arity, ty }) => (0..arity).map(|_| *ty).collect(),
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(Variant(_), Ty::BigEnum { ty, .. }) => vec![*ty],
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(Bool(..) | IntRange(..) | NonExhaustive | Missing | Wildcard, _) => vec![],
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_ => panic!("Unexpected ctor {ctor:?} for type {self:?}"),
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}
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}
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pub fn ctor_set(&self) -> ConstructorSet<Cx> {
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match *self {
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Ty::Bool => ConstructorSet::Bool,
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Ty::U8 => ConstructorSet::Integers {
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range_1: IntRange::from_range(
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MaybeInfiniteInt::new_finite_uint(0),
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MaybeInfiniteInt::new_finite_uint(255),
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RangeEnd::Included,
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),
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range_2: None,
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},
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Ty::Tuple(..) | Ty::BigStruct { .. } => ConstructorSet::Struct { empty: false },
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Ty::BigEnum { arity, .. } => ConstructorSet::Variants {
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variants: (0..arity).map(|_| VariantVisibility::Visible).collect(),
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non_exhaustive: false,
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},
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}
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}
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pub fn write_variant_name(
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&self,
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f: &mut std::fmt::Formatter<'_>,
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ctor: &Constructor<Cx>,
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) -> std::fmt::Result {
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match (*self, ctor) {
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(Ty::Tuple(..), _) => Ok(()),
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(Ty::BigStruct { .. }, _) => write!(f, "BigStruct"),
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(Ty::BigEnum { .. }, Constructor::Variant(i)) => write!(f, "BigEnum::Variant{i}"),
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_ => write!(f, "{:?}::{:?}", self, ctor),
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}
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}
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}
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/// Compute usefulness in our simple context (and set up tracing for easier debugging).
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pub fn compute_match_usefulness<'p>(
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arms: &[MatchArm<'p, Cx>],
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ty: Ty,
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scrut_validity: PlaceValidity,
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complexity_limit: Option<usize>,
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) -> Result<UsefulnessReport<'p, Cx>, ()> {
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init_tracing();
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rustc_pattern_analysis::usefulness::compute_match_usefulness(
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&Cx,
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arms,
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ty,
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scrut_validity,
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complexity_limit,
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)
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}
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#[derive(Debug)]
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pub struct Cx;
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/// The context for pattern analysis. Forwards anything interesting to `Ty` methods.
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impl PatCx for Cx {
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type Ty = Ty;
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type Error = ();
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type VariantIdx = usize;
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type StrLit = ();
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type ArmData = ();
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type PatData = ();
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fn is_exhaustive_patterns_feature_on(&self) -> bool {
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false
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}
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fn is_min_exhaustive_patterns_feature_on(&self) -> bool {
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false
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}
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fn ctor_arity(&self, ctor: &Constructor<Self>, ty: &Self::Ty) -> usize {
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ty.sub_tys(ctor).len()
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}
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fn ctor_sub_tys<'a>(
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&'a self,
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ctor: &'a Constructor<Self>,
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ty: &'a Self::Ty,
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) -> impl Iterator<Item = (Self::Ty, PrivateUninhabitedField)> + ExactSizeIterator + Captures<'a>
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{
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ty.sub_tys(ctor).into_iter().map(|ty| (ty, PrivateUninhabitedField(false)))
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}
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fn ctors_for_ty(&self, ty: &Self::Ty) -> Result<ConstructorSet<Self>, Self::Error> {
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Ok(ty.ctor_set())
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}
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fn write_variant_name(
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f: &mut std::fmt::Formatter<'_>,
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ctor: &Constructor<Self>,
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ty: &Self::Ty,
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) -> std::fmt::Result {
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ty.write_variant_name(f, ctor)
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}
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fn bug(&self, fmt: std::fmt::Arguments<'_>) -> Self::Error {
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panic!("{}", fmt)
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}
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/// Abort when reaching the complexity limit. This is what we'll check in tests.
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fn complexity_exceeded(&self) -> Result<(), Self::Error> {
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Err(())
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}
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}
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/// Construct a single pattern; see `pats!()`.
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#[allow(unused_macros)]
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macro_rules! pat {
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($($rest:tt)*) => {{
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let mut vec = pats!($($rest)*);
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vec.pop().unwrap()
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}};
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}
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/// A macro to construct patterns. Called like `pats!(type_expr; pattern, pattern, ..)` and returns
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/// a `Vec<DeconstructedPat>`. A pattern can be nested and looks like `Constructor(pat, pat)` or
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/// `Constructor { .i: pat, .j: pat }`, where `Constructor` is `Struct`, `Variant.i` (with index
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/// `i`), as well as booleans and integer ranges.
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///
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/// The general structure of the macro is a tt-muncher with several stages identified with
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/// `@something(args)`. The args are a key-value list (the keys ensure we don't mix the arguments
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/// around) which is passed down and modified as needed. We then parse token-trees from
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/// left-to-right. Non-trivial recursion happens when we parse the arguments to a pattern: we
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/// recurse to parse the tokens inside `{..}`/`(..)`, and then we continue parsing anything that
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/// follows.
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macro_rules! pats {
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// Entrypoint
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// Parse `type; ..`
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($ty:expr; $($rest:tt)*) => {{
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#[allow(unused_imports)]
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use rustc_pattern_analysis::{
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constructor::{Constructor, IntRange, MaybeInfiniteInt, RangeEnd},
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pat::DeconstructedPat,
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};
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let ty = $ty;
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// The heart of the macro is designed to push `IndexedPat`s into a `Vec`, so we work around
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// that.
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let sub_tys = ::std::iter::repeat(&ty);
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let mut vec = Vec::new();
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pats!(@ctor(vec:vec, sub_tys:sub_tys, idx:0) $($rest)*);
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vec.into_iter().map(|ipat| ipat.pat).collect::<Vec<_>>()
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}};
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// Parse `constructor ..`
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(@ctor($($args:tt)*) true $($rest:tt)*) => {{
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let ctor = Constructor::Bool(true);
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pats!(@pat($($args)*, ctor:ctor) $($rest)*)
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}};
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(@ctor($($args:tt)*) false $($rest:tt)*) => {{
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let ctor = Constructor::Bool(false);
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pats!(@pat($($args)*, ctor:ctor) $($rest)*)
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}};
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(@ctor($($args:tt)*) Struct $($rest:tt)*) => {{
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let ctor = Constructor::Struct;
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pats!(@pat($($args)*, ctor:ctor) $($rest)*)
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}};
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(@ctor($($args:tt)*) ( $($fields:tt)* ) $($rest:tt)*) => {{
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let ctor = Constructor::Struct; // tuples
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pats!(@pat($($args)*, ctor:ctor) ( $($fields)* ) $($rest)*)
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}};
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(@ctor($($args:tt)*) Variant.$variant:ident $($rest:tt)*) => {{
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let ctor = Constructor::Variant($variant);
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pats!(@pat($($args)*, ctor:ctor) $($rest)*)
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}};
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(@ctor($($args:tt)*) Variant.$variant:literal $($rest:tt)*) => {{
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let ctor = Constructor::Variant($variant);
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pats!(@pat($($args)*, ctor:ctor) $($rest)*)
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}};
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(@ctor($($args:tt)*) _ $($rest:tt)*) => {{
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let ctor = Constructor::Wildcard;
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pats!(@pat($($args)*, ctor:ctor) $($rest)*)
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}};
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// Integers and int ranges
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(@ctor($($args:tt)*) $($start:literal)?..$end:literal $($rest:tt)*) => {{
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let ctor = Constructor::IntRange(IntRange::from_range(
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pats!(@rangeboundary- $($start)?),
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pats!(@rangeboundary+ $end),
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RangeEnd::Excluded,
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));
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pats!(@pat($($args)*, ctor:ctor) $($rest)*)
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}};
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(@ctor($($args:tt)*) $($start:literal)?.. $($rest:tt)*) => {{
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let ctor = Constructor::IntRange(IntRange::from_range(
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pats!(@rangeboundary- $($start)?),
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pats!(@rangeboundary+),
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RangeEnd::Excluded,
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));
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pats!(@pat($($args)*, ctor:ctor) $($rest)*)
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}};
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(@ctor($($args:tt)*) $($start:literal)?..=$end:literal $($rest:tt)*) => {{
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let ctor = Constructor::IntRange(IntRange::from_range(
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pats!(@rangeboundary- $($start)?),
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pats!(@rangeboundary+ $end),
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RangeEnd::Included,
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));
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pats!(@pat($($args)*, ctor:ctor) $($rest)*)
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}};
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(@ctor($($args:tt)*) $int:literal $($rest:tt)*) => {{
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let ctor = Constructor::IntRange(IntRange::from_range(
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pats!(@rangeboundary- $int),
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pats!(@rangeboundary+ $int),
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RangeEnd::Included,
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));
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pats!(@pat($($args)*, ctor:ctor) $($rest)*)
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}};
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// Utility to manage range boundaries.
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(@rangeboundary $sign:tt $int:literal) => { MaybeInfiniteInt::new_finite_uint($int) };
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(@rangeboundary -) => { MaybeInfiniteInt::NegInfinity };
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(@rangeboundary +) => { MaybeInfiniteInt::PosInfinity };
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// Parse subfields: `(..)` or `{..}`
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// Constructor with no fields, e.g. `bool` or `Variant.1`.
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(@pat($($args:tt)*) $(,)?) => {
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pats!(@pat($($args)*) {})
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};
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(@pat($($args:tt)*) , $($rest:tt)*) => {
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pats!(@pat($($args)*) {}, $($rest)*)
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};
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// `(..)` and `{..}` are treated the same.
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(@pat($($args:tt)*) ( $($subpat:tt)* ) $($rest:tt)*) => {{
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pats!(@pat($($args)*) { $($subpat)* } $($rest)*)
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}};
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(@pat(vec:$vec:expr, sub_tys:$sub_tys:expr, idx:$idx:expr, ctor:$ctor:expr) { $($fields:tt)* } $($rest:tt)*) => {{
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let sub_tys = $sub_tys;
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let index = $idx;
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// Silly dance to work with both a vec and `iter::repeat()`.
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let ty = *(&sub_tys).clone().into_iter().nth(index).unwrap();
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let ctor = $ctor;
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let ctor_sub_tys = &ty.sub_tys(&ctor);
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#[allow(unused_mut)]
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let mut fields = Vec::new();
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// Parse subpatterns (note the leading comma).
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pats!(@fields(idx:0, vec:fields, sub_tys:ctor_sub_tys) ,$($fields)*);
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let arity = ctor_sub_tys.len();
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let pat = DeconstructedPat::new(ctor, fields, arity, ty, ()).at_index(index);
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$vec.push(pat);
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// Continue parsing further patterns.
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pats!(@fields(idx:index+1, vec:$vec, sub_tys:sub_tys) $($rest)*);
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}};
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// Parse fields one by one.
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// No fields left.
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(@fields($($args:tt)*) $(,)?) => {};
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// `.i: pat` sets the current index to `i`.
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(@fields(idx:$_idx:expr, $($args:tt)*) , .$idx:literal : $($rest:tt)*) => {{
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pats!(@ctor($($args)*, idx:$idx) $($rest)*);
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}};
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(@fields(idx:$_idx:expr, $($args:tt)*) , .$idx:ident : $($rest:tt)*) => {{
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pats!(@ctor($($args)*, idx:$idx) $($rest)*);
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}};
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// Field without an explicit index; we use the current index which gets incremented above.
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(@fields(idx:$idx:expr, $($args:tt)*) , $($rest:tt)*) => {{
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pats!(@ctor($($args)*, idx:$idx) $($rest)*);
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}};
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}
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