From 6a77ec7bbe6ddbf663dce9529d11d1bb56c5489a Mon Sep 17 00:00:00 2001 From: Aleksey Kladov Date: Thu, 13 Aug 2020 16:35:29 +0200 Subject: Rename ra_hir_ty -> hir_ty --- crates/hir_ty/src/diagnostics/match_check.rs | 1421 ++++++++++++++++++++++++++ 1 file changed, 1421 insertions(+) create mode 100644 crates/hir_ty/src/diagnostics/match_check.rs (limited to 'crates/hir_ty/src/diagnostics/match_check.rs') diff --git a/crates/hir_ty/src/diagnostics/match_check.rs b/crates/hir_ty/src/diagnostics/match_check.rs new file mode 100644 index 000000000..7f007f1d6 --- /dev/null +++ b/crates/hir_ty/src/diagnostics/match_check.rs @@ -0,0 +1,1421 @@ +//! This module implements match statement exhaustiveness checking and usefulness checking +//! for match arms. +//! +//! It is modeled on the rustc module `librustc_mir_build::hair::pattern::_match`, which +//! contains very detailed documentation about the algorithms used here. I've duplicated +//! most of that documentation below. +//! +//! This file includes the logic for exhaustiveness and usefulness checking for +//! pattern-matching. Specifically, given a list of patterns for a type, we can +//! tell whether: +//! - (a) the patterns cover every possible constructor for the type (exhaustiveness). +//! - (b) each pattern is necessary (usefulness). +//! +//! The algorithm implemented here is a modified version of the one described in +//! . +//! However, to save future implementors from reading the original paper, we +//! summarise the algorithm here to hopefully save time and be a little clearer +//! (without being so rigorous). +//! +//! The core of the algorithm revolves about a "usefulness" check. In particular, we +//! are trying to compute a predicate `U(P, p)` where `P` is a list of patterns (we refer to this as +//! a matrix). `U(P, p)` represents whether, given an existing list of patterns +//! `P_1 ..= P_m`, adding a new pattern `p` will be "useful" (that is, cover previously- +//! uncovered values of the type). +//! +//! If we have this predicate, then we can easily compute both exhaustiveness of an +//! entire set of patterns and the individual usefulness of each one. +//! (a) the set of patterns is exhaustive iff `U(P, _)` is false (i.e., adding a wildcard +//! match doesn't increase the number of values we're matching) +//! (b) a pattern `P_i` is not useful if `U(P[0..=(i-1), P_i)` is false (i.e., adding a +//! pattern to those that have come before it doesn't increase the number of values +//! we're matching). +//! +//! During the course of the algorithm, the rows of the matrix won't just be individual patterns, +//! but rather partially-deconstructed patterns in the form of a list of patterns. The paper +//! calls those pattern-vectors, and we will call them pattern-stacks. The same holds for the +//! new pattern `p`. +//! +//! For example, say we have the following: +//! +//! ```ignore +//! // x: (Option, Result<()>) +//! match x { +//! (Some(true), _) => (), +//! (None, Err(())) => (), +//! (None, Err(_)) => (), +//! } +//! ``` +//! +//! Here, the matrix `P` starts as: +//! +//! ```text +//! [ +//! [(Some(true), _)], +//! [(None, Err(()))], +//! [(None, Err(_))], +//! ] +//! ``` +//! +//! We can tell it's not exhaustive, because `U(P, _)` is true (we're not covering +//! `[(Some(false), _)]`, for instance). In addition, row 3 is not useful, because +//! all the values it covers are already covered by row 2. +//! +//! A list of patterns can be thought of as a stack, because we are mainly interested in the top of +//! the stack at any given point, and we can pop or apply constructors to get new pattern-stacks. +//! To match the paper, the top of the stack is at the beginning / on the left. +//! +//! There are two important operations on pattern-stacks necessary to understand the algorithm: +//! +//! 1. We can pop a given constructor off the top of a stack. This operation is called +//! `specialize`, and is denoted `S(c, p)` where `c` is a constructor (like `Some` or +//! `None`) and `p` a pattern-stack. +//! If the pattern on top of the stack can cover `c`, this removes the constructor and +//! pushes its arguments onto the stack. It also expands OR-patterns into distinct patterns. +//! Otherwise the pattern-stack is discarded. +//! This essentially filters those pattern-stacks whose top covers the constructor `c` and +//! discards the others. +//! +//! For example, the first pattern above initially gives a stack `[(Some(true), _)]`. If we +//! pop the tuple constructor, we are left with `[Some(true), _]`, and if we then pop the +//! `Some` constructor we get `[true, _]`. If we had popped `None` instead, we would get +//! nothing back. +//! +//! This returns zero or more new pattern-stacks, as follows. We look at the pattern `p_1` +//! on top of the stack, and we have four cases: +//! +//! * 1.1. `p_1 = c(r_1, .., r_a)`, i.e. the top of the stack has constructor `c`. We push onto +//! the stack the arguments of this constructor, and return the result: +//! +//! r_1, .., r_a, p_2, .., p_n +//! +//! * 1.2. `p_1 = c'(r_1, .., r_a')` where `c ≠ c'`. We discard the current stack and return +//! nothing. +//! * 1.3. `p_1 = _`. We push onto the stack as many wildcards as the constructor `c` has +//! arguments (its arity), and return the resulting stack: +//! +//! _, .., _, p_2, .., p_n +//! +//! * 1.4. `p_1 = r_1 | r_2`. We expand the OR-pattern and then recurse on each resulting stack: +//! +//! S(c, (r_1, p_2, .., p_n)) +//! S(c, (r_2, p_2, .., p_n)) +//! +//! 2. We can pop a wildcard off the top of the stack. This is called `D(p)`, where `p` is +//! a pattern-stack. +//! This is used when we know there are missing constructor cases, but there might be +//! existing wildcard patterns, so to check the usefulness of the matrix, we have to check +//! all its *other* components. +//! +//! It is computed as follows. We look at the pattern `p_1` on top of the stack, +//! and we have three cases: +//! * 1.1. `p_1 = c(r_1, .., r_a)`. We discard the current stack and return nothing. +//! * 1.2. `p_1 = _`. We return the rest of the stack: +//! +//! p_2, .., p_n +//! +//! * 1.3. `p_1 = r_1 | r_2`. We expand the OR-pattern and then recurse on each resulting stack: +//! +//! D((r_1, p_2, .., p_n)) +//! D((r_2, p_2, .., p_n)) +//! +//! Note that the OR-patterns are not always used directly in Rust, but are used to derive the +//! exhaustive integer matching rules, so they're written here for posterity. +//! +//! Both those operations extend straightforwardly to a list or pattern-stacks, i.e. a matrix, by +//! working row-by-row. Popping a constructor ends up keeping only the matrix rows that start with +//! the given constructor, and popping a wildcard keeps those rows that start with a wildcard. +//! +//! +//! The algorithm for computing `U` +//! ------------------------------- +//! The algorithm is inductive (on the number of columns: i.e., components of tuple patterns). +//! That means we're going to check the components from left-to-right, so the algorithm +//! operates principally on the first component of the matrix and new pattern-stack `p`. +//! This algorithm is realised in the `is_useful` function. +//! +//! Base case (`n = 0`, i.e., an empty tuple pattern): +//! - If `P` already contains an empty pattern (i.e., if the number of patterns `m > 0`), then +//! `U(P, p)` is false. +//! - Otherwise, `P` must be empty, so `U(P, p)` is true. +//! +//! Inductive step (`n > 0`, i.e., whether there's at least one column [which may then be expanded +//! into further columns later]). We're going to match on the top of the new pattern-stack, `p_1`: +//! +//! - If `p_1 == c(r_1, .., r_a)`, i.e. we have a constructor pattern. +//! Then, the usefulness of `p_1` can be reduced to whether it is useful when +//! we ignore all the patterns in the first column of `P` that involve other constructors. +//! This is where `S(c, P)` comes in: +//! +//! ```text +//! U(P, p) := U(S(c, P), S(c, p)) +//! ``` +//! +//! This special case is handled in `is_useful_specialized`. +//! +//! For example, if `P` is: +//! +//! ```text +//! [ +//! [Some(true), _], +//! [None, 0], +//! ] +//! ``` +//! +//! and `p` is `[Some(false), 0]`, then we don't care about row 2 since we know `p` only +//! matches values that row 2 doesn't. For row 1 however, we need to dig into the +//! arguments of `Some` to know whether some new value is covered. So we compute +//! `U([[true, _]], [false, 0])`. +//! +//! - If `p_1 == _`, then we look at the list of constructors that appear in the first component of +//! the rows of `P`: +//! - If there are some constructors that aren't present, then we might think that the +//! wildcard `_` is useful, since it covers those constructors that weren't covered +//! before. +//! That's almost correct, but only works if there were no wildcards in those first +//! components. So we need to check that `p` is useful with respect to the rows that +//! start with a wildcard, if there are any. This is where `D` comes in: +//! `U(P, p) := U(D(P), D(p))` +//! +//! For example, if `P` is: +//! ```text +//! [ +//! [_, true, _], +//! [None, false, 1], +//! ] +//! ``` +//! and `p` is `[_, false, _]`, the `Some` constructor doesn't appear in `P`. So if we +//! only had row 2, we'd know that `p` is useful. However row 1 starts with a +//! wildcard, so we need to check whether `U([[true, _]], [false, 1])`. +//! +//! - Otherwise, all possible constructors (for the relevant type) are present. In this +//! case we must check whether the wildcard pattern covers any unmatched value. For +//! that, we can think of the `_` pattern as a big OR-pattern that covers all +//! possible constructors. For `Option`, that would mean `_ = None | Some(_)` for +//! example. The wildcard pattern is useful in this case if it is useful when +//! specialized to one of the possible constructors. So we compute: +//! `U(P, p) := ∃(k ϵ constructors) U(S(k, P), S(k, p))` +//! +//! For example, if `P` is: +//! ```text +//! [ +//! [Some(true), _], +//! [None, false], +//! ] +//! ``` +//! and `p` is `[_, false]`, both `None` and `Some` constructors appear in the first +//! components of `P`. We will therefore try popping both constructors in turn: we +//! compute `U([[true, _]], [_, false])` for the `Some` constructor, and `U([[false]], +//! [false])` for the `None` constructor. The first case returns true, so we know that +//! `p` is useful for `P`. Indeed, it matches `[Some(false), _]` that wasn't matched +//! before. +//! +//! - If `p_1 == r_1 | r_2`, then the usefulness depends on each `r_i` separately: +//! +//! ```text +//! U(P, p) := U(P, (r_1, p_2, .., p_n)) +//! || U(P, (r_2, p_2, .., p_n)) +//! ``` +use std::sync::Arc; + +use arena::Idx; +use hir_def::{ + adt::VariantData, + body::Body, + expr::{Expr, Literal, Pat, PatId}, + AdtId, EnumVariantId, VariantId, +}; +use smallvec::{smallvec, SmallVec}; + +use crate::{db::HirDatabase, ApplicationTy, InferenceResult, Ty, TypeCtor}; + +#[derive(Debug, Clone, Copy)] +/// Either a pattern from the source code being analyzed, represented as +/// as `PatId`, or a `Wild` pattern which is created as an intermediate +/// step in the match checking algorithm and thus is not backed by a +/// real `PatId`. +/// +/// Note that it is totally valid for the `PatId` variant to contain +/// a `PatId` which resolves to a `Wild` pattern, if that wild pattern +/// exists in the source code being analyzed. +enum PatIdOrWild { + PatId(PatId), + Wild, +} + +impl PatIdOrWild { + fn as_pat(self, cx: &MatchCheckCtx) -> Pat { + match self { + PatIdOrWild::PatId(id) => cx.body.pats[id].clone(), + PatIdOrWild::Wild => Pat::Wild, + } + } + + fn as_id(self) -> Option { + match self { + PatIdOrWild::PatId(id) => Some(id), + PatIdOrWild::Wild => None, + } + } +} + +impl From for PatIdOrWild { + fn from(pat_id: PatId) -> Self { + Self::PatId(pat_id) + } +} + +impl From<&PatId> for PatIdOrWild { + fn from(pat_id: &PatId) -> Self { + Self::PatId(*pat_id) + } +} + +#[derive(Debug, Clone, Copy, PartialEq)] +pub(super) enum MatchCheckErr { + NotImplemented, + MalformedMatchArm, + /// Used when type inference cannot resolve the type of + /// a pattern or expression. + Unknown, +} + +/// The return type of `is_useful` is either an indication of usefulness +/// of the match arm, or an error in the case the match statement +/// is made up of types for which exhaustiveness checking is currently +/// not completely implemented. +/// +/// The `std::result::Result` type is used here rather than a custom enum +/// to allow the use of `?`. +pub(super) type MatchCheckResult = Result; + +#[derive(Debug)] +/// A row in a Matrix. +/// +/// This type is modeled from the struct of the same name in `rustc`. +pub(super) struct PatStack(PatStackInner); +type PatStackInner = SmallVec<[PatIdOrWild; 2]>; + +impl PatStack { + pub(super) fn from_pattern(pat_id: PatId) -> PatStack { + Self(smallvec!(pat_id.into())) + } + + pub(super) fn from_wild() -> PatStack { + Self(smallvec!(PatIdOrWild::Wild)) + } + + fn from_slice(slice: &[PatIdOrWild]) -> PatStack { + Self(SmallVec::from_slice(slice)) + } + + fn from_vec(v: PatStackInner) -> PatStack { + Self(v) + } + + fn get_head(&self) -> Option { + self.0.first().copied() + } + + fn tail(&self) -> &[PatIdOrWild] { + self.0.get(1..).unwrap_or(&[]) + } + + fn to_tail(&self) -> PatStack { + Self::from_slice(self.tail()) + } + + fn replace_head_with(&self, pats: I) -> PatStack + where + I: Iterator, + T: Into, + { + let mut patterns: PatStackInner = smallvec![]; + for pat in pats { + patterns.push(pat.into()); + } + for pat in &self.0[1..] { + patterns.push(*pat); + } + PatStack::from_vec(patterns) + } + + /// Computes `D(self)`. + /// + /// See the module docs and the associated documentation in rustc for details. + fn specialize_wildcard(&self, cx: &MatchCheckCtx) -> Option { + if matches!(self.get_head()?.as_pat(cx), Pat::Wild) { + Some(self.to_tail()) + } else { + None + } + } + + /// Computes `S(constructor, self)`. + /// + /// See the module docs and the associated documentation in rustc for details. + fn specialize_constructor( + &self, + cx: &MatchCheckCtx, + constructor: &Constructor, + ) -> MatchCheckResult> { + let head = match self.get_head() { + Some(head) => head, + None => return Ok(None), + }; + + let head_pat = head.as_pat(cx); + let result = match (head_pat, constructor) { + (Pat::Tuple { args: ref pat_ids, ellipsis }, Constructor::Tuple { arity: _ }) => { + if ellipsis.is_some() { + // If there are ellipsis here, we should add the correct number of + // Pat::Wild patterns to `pat_ids`. We should be able to use the + // constructors arity for this, but at the time of writing we aren't + // correctly calculating this arity when ellipsis are present. + return Err(MatchCheckErr::NotImplemented); + } + + Some(self.replace_head_with(pat_ids.iter())) + } + (Pat::Lit(lit_expr), Constructor::Bool(constructor_val)) => { + match cx.body.exprs[lit_expr] { + Expr::Literal(Literal::Bool(pat_val)) if *constructor_val == pat_val => { + Some(self.to_tail()) + } + // it was a bool but the value doesn't match + Expr::Literal(Literal::Bool(_)) => None, + // perhaps this is actually unreachable given we have + // already checked that these match arms have the appropriate type? + _ => return Err(MatchCheckErr::NotImplemented), + } + } + (Pat::Wild, constructor) => Some(self.expand_wildcard(cx, constructor)?), + (Pat::Path(_), Constructor::Enum(constructor)) => { + // unit enum variants become `Pat::Path` + let pat_id = head.as_id().expect("we know this isn't a wild"); + if !enum_variant_matches(cx, pat_id, *constructor) { + None + } else { + Some(self.to_tail()) + } + } + ( + Pat::TupleStruct { args: ref pat_ids, ellipsis, .. }, + Constructor::Enum(enum_constructor), + ) => { + let pat_id = head.as_id().expect("we know this isn't a wild"); + if !enum_variant_matches(cx, pat_id, *enum_constructor) { + None + } else { + let constructor_arity = constructor.arity(cx)?; + if let Some(ellipsis_position) = ellipsis { + // If there are ellipsis in the pattern, the ellipsis must take the place + // of at least one sub-pattern, so `pat_ids` should be smaller than the + // constructor arity. + if pat_ids.len() < constructor_arity { + let mut new_patterns: Vec = vec![]; + + for pat_id in &pat_ids[0..ellipsis_position] { + new_patterns.push((*pat_id).into()); + } + + for _ in 0..(constructor_arity - pat_ids.len()) { + new_patterns.push(PatIdOrWild::Wild); + } + + for pat_id in &pat_ids[ellipsis_position..pat_ids.len()] { + new_patterns.push((*pat_id).into()); + } + + Some(self.replace_head_with(new_patterns.into_iter())) + } else { + return Err(MatchCheckErr::MalformedMatchArm); + } + } else { + // If there is no ellipsis in the tuple pattern, the number + // of patterns must equal the constructor arity. + if pat_ids.len() == constructor_arity { + Some(self.replace_head_with(pat_ids.into_iter())) + } else { + return Err(MatchCheckErr::MalformedMatchArm); + } + } + } + } + (Pat::Record { args: ref arg_patterns, .. }, Constructor::Enum(e)) => { + let pat_id = head.as_id().expect("we know this isn't a wild"); + if !enum_variant_matches(cx, pat_id, *e) { + None + } else { + match cx.db.enum_data(e.parent).variants[e.local_id].variant_data.as_ref() { + VariantData::Record(struct_field_arena) => { + // Here we treat any missing fields in the record as the wild pattern, as + // if the record has ellipsis. We want to do this here even if the + // record does not contain ellipsis, because it allows us to continue + // enforcing exhaustiveness for the rest of the match statement. + // + // Creating the diagnostic for the missing field in the pattern + // should be done in a different diagnostic. + let patterns = struct_field_arena.iter().map(|(_, struct_field)| { + arg_patterns + .iter() + .find(|pat| pat.name == struct_field.name) + .map(|pat| PatIdOrWild::from(pat.pat)) + .unwrap_or(PatIdOrWild::Wild) + }); + + Some(self.replace_head_with(patterns)) + } + _ => return Err(MatchCheckErr::Unknown), + } + } + } + (Pat::Or(_), _) => return Err(MatchCheckErr::NotImplemented), + (_, _) => return Err(MatchCheckErr::NotImplemented), + }; + + Ok(result) + } + + /// A special case of `specialize_constructor` where the head of the pattern stack + /// is a Wild pattern. + /// + /// Replaces the Wild pattern at the head of the pattern stack with N Wild patterns + /// (N >= 0), where N is the arity of the given constructor. + fn expand_wildcard( + &self, + cx: &MatchCheckCtx, + constructor: &Constructor, + ) -> MatchCheckResult { + assert_eq!( + Pat::Wild, + self.get_head().expect("expand_wildcard called on empty PatStack").as_pat(cx), + "expand_wildcard must only be called on PatStack with wild at head", + ); + + let mut patterns: PatStackInner = smallvec![]; + + for _ in 0..constructor.arity(cx)? { + patterns.push(PatIdOrWild::Wild); + } + + for pat in &self.0[1..] { + patterns.push(*pat); + } + + Ok(PatStack::from_vec(patterns)) + } +} + +/// A collection of PatStack. +/// +/// This type is modeled from the struct of the same name in `rustc`. +pub(super) struct Matrix(Vec); + +impl Matrix { + pub(super) fn empty() -> Self { + Self(vec![]) + } + + pub(super) fn push(&mut self, cx: &MatchCheckCtx, row: PatStack) { + if let Some(Pat::Or(pat_ids)) = row.get_head().map(|pat_id| pat_id.as_pat(cx)) { + // Or patterns are expanded here + for pat_id in pat_ids { + self.0.push(PatStack::from_pattern(pat_id)); + } + } else { + self.0.push(row); + } + } + + fn is_empty(&self) -> bool { + self.0.is_empty() + } + + fn heads(&self) -> Vec { + self.0.iter().flat_map(|p| p.get_head()).collect() + } + + /// Computes `D(self)` for each contained PatStack. + /// + /// See the module docs and the associated documentation in rustc for details. + fn specialize_wildcard(&self, cx: &MatchCheckCtx) -> Self { + Self::collect(cx, self.0.iter().filter_map(|r| r.specialize_wildcard(cx))) + } + + /// Computes `S(constructor, self)` for each contained PatStack. + /// + /// See the module docs and the associated documentation in rustc for details. + fn specialize_constructor( + &self, + cx: &MatchCheckCtx, + constructor: &Constructor, + ) -> MatchCheckResult { + let mut new_matrix = Matrix::empty(); + for pat in &self.0 { + if let Some(pat) = pat.specialize_constructor(cx, constructor)? { + new_matrix.push(cx, pat); + } + } + + Ok(new_matrix) + } + + fn collect>(cx: &MatchCheckCtx, iter: T) -> Self { + let mut matrix = Matrix::empty(); + + for pat in iter { + // using push ensures we expand or-patterns + matrix.push(cx, pat); + } + + matrix + } +} + +#[derive(Clone, Debug, PartialEq)] +/// An indication of the usefulness of a given match arm, where +/// usefulness is defined as matching some patterns which were +/// not matched by an prior match arms. +/// +/// We may eventually need an `Unknown` variant here. +pub(super) enum Usefulness { + Useful, + NotUseful, +} + +pub(super) struct MatchCheckCtx<'a> { + pub(super) match_expr: Idx, + pub(super) body: Arc, + pub(super) infer: Arc, + pub(super) db: &'a dyn HirDatabase, +} + +/// Given a set of patterns `matrix`, and pattern to consider `v`, determines +/// whether `v` is useful. A pattern is useful if it covers cases which were +/// not previously covered. +/// +/// When calling this function externally (that is, not the recursive calls) it +/// expected that you have already type checked the match arms. All patterns in +/// matrix should be the same type as v, as well as they should all be the same +/// type as the match expression. +pub(super) fn is_useful( + cx: &MatchCheckCtx, + matrix: &Matrix, + v: &PatStack, +) -> MatchCheckResult { + // Handle two special cases: + // - enum with no variants + // - `!` type + // In those cases, no match arm is useful. + match cx.infer[cx.match_expr].strip_references() { + Ty::Apply(ApplicationTy { ctor: TypeCtor::Adt(AdtId::EnumId(enum_id)), .. }) => { + if cx.db.enum_data(*enum_id).variants.is_empty() { + return Ok(Usefulness::NotUseful); + } + } + Ty::Apply(ApplicationTy { ctor: TypeCtor::Never, .. }) => { + return Ok(Usefulness::NotUseful); + } + _ => (), + } + + let head = match v.get_head() { + Some(head) => head, + None => { + let result = if matrix.is_empty() { Usefulness::Useful } else { Usefulness::NotUseful }; + + return Ok(result); + } + }; + + if let Pat::Or(pat_ids) = head.as_pat(cx) { + let mut found_unimplemented = false; + let any_useful = pat_ids.iter().any(|&pat_id| { + let v = PatStack::from_pattern(pat_id); + + match is_useful(cx, matrix, &v) { + Ok(Usefulness::Useful) => true, + Ok(Usefulness::NotUseful) => false, + _ => { + found_unimplemented = true; + false + } + } + }); + + return if any_useful { + Ok(Usefulness::Useful) + } else if found_unimplemented { + Err(MatchCheckErr::NotImplemented) + } else { + Ok(Usefulness::NotUseful) + }; + } + + if let Some(constructor) = pat_constructor(cx, head)? { + let matrix = matrix.specialize_constructor(&cx, &constructor)?; + let v = v + .specialize_constructor(&cx, &constructor)? + .expect("we know this can't fail because we get the constructor from `v.head()` above"); + + is_useful(&cx, &matrix, &v) + } else { + // expanding wildcard + let mut used_constructors: Vec = vec![]; + for pat in matrix.heads() { + if let Some(constructor) = pat_constructor(cx, pat)? { + used_constructors.push(constructor); + } + } + + // We assume here that the first constructor is the "correct" type. Since we + // only care about the "type" of the constructor (i.e. if it is a bool we + // don't care about the value), this assumption should be valid as long as + // the match statement is well formed. We currently uphold this invariant by + // filtering match arms before calling `is_useful`, only passing in match arms + // whose type matches the type of the match expression. + match &used_constructors.first() { + Some(constructor) if all_constructors_covered(&cx, constructor, &used_constructors) => { + // If all constructors are covered, then we need to consider whether + // any values are covered by this wildcard. + // + // For example, with matrix '[[Some(true)], [None]]', all + // constructors are covered (`Some`/`None`), so we need + // to perform specialization to see that our wildcard will cover + // the `Some(false)` case. + // + // Here we create a constructor for each variant and then check + // usefulness after specializing for that constructor. + let mut found_unimplemented = false; + for constructor in constructor.all_constructors(cx) { + let matrix = matrix.specialize_constructor(&cx, &constructor)?; + let v = v.expand_wildcard(&cx, &constructor)?; + + match is_useful(&cx, &matrix, &v) { + Ok(Usefulness::Useful) => return Ok(Usefulness::Useful), + Ok(Usefulness::NotUseful) => continue, + _ => found_unimplemented = true, + }; + } + + if found_unimplemented { + Err(MatchCheckErr::NotImplemented) + } else { + Ok(Usefulness::NotUseful) + } + } + _ => { + // Either not all constructors are covered, or the only other arms + // are wildcards. Either way, this pattern is useful if it is useful + // when compared to those arms with wildcards. + let matrix = matrix.specialize_wildcard(&cx); + let v = v.to_tail(); + + is_useful(&cx, &matrix, &v) + } + } + } +} + +#[derive(Debug, Clone, Copy)] +/// Similar to TypeCtor, but includes additional information about the specific +/// value being instantiated. For example, TypeCtor::Bool doesn't contain the +/// boolean value. +enum Constructor { + Bool(bool), + Tuple { arity: usize }, + Enum(EnumVariantId), +} + +impl Constructor { + fn arity(&self, cx: &MatchCheckCtx) -> MatchCheckResult { + let arity = match self { + Constructor::Bool(_) => 0, + Constructor::Tuple { arity } => *arity, + Constructor::Enum(e) => { + match cx.db.enum_data(e.parent).variants[e.local_id].variant_data.as_ref() { + VariantData::Tuple(struct_field_data) => struct_field_data.len(), + VariantData::Record(struct_field_data) => struct_field_data.len(), + VariantData::Unit => 0, + } + } + }; + + Ok(arity) + } + + fn all_constructors(&self, cx: &MatchCheckCtx) -> Vec { + match self { + Constructor::Bool(_) => vec![Constructor::Bool(true), Constructor::Bool(false)], + Constructor::Tuple { .. } => vec![*self], + Constructor::Enum(e) => cx + .db + .enum_data(e.parent) + .variants + .iter() + .map(|(local_id, _)| { + Constructor::Enum(EnumVariantId { parent: e.parent, local_id }) + }) + .collect(), + } + } +} + +/// Returns the constructor for the given pattern. Should only return None +/// in the case of a Wild pattern. +fn pat_constructor(cx: &MatchCheckCtx, pat: PatIdOrWild) -> MatchCheckResult> { + let res = match pat.as_pat(cx) { + Pat::Wild => None, + // FIXME somehow create the Tuple constructor with the proper arity. If there are + // ellipsis, the arity is not equal to the number of patterns. + Pat::Tuple { args: pats, ellipsis } if ellipsis.is_none() => { + Some(Constructor::Tuple { arity: pats.len() }) + } + Pat::Lit(lit_expr) => match cx.body.exprs[lit_expr] { + Expr::Literal(Literal::Bool(val)) => Some(Constructor::Bool(val)), + _ => return Err(MatchCheckErr::NotImplemented), + }, + Pat::TupleStruct { .. } | Pat::Path(_) | Pat::Record { .. } => { + let pat_id = pat.as_id().expect("we already know this pattern is not a wild"); + let variant_id = + cx.infer.variant_resolution_for_pat(pat_id).ok_or(MatchCheckErr::Unknown)?; + match variant_id { + VariantId::EnumVariantId(enum_variant_id) => { + Some(Constructor::Enum(enum_variant_id)) + } + _ => return Err(MatchCheckErr::NotImplemented), + } + } + _ => return Err(MatchCheckErr::NotImplemented), + }; + + Ok(res) +} + +fn all_constructors_covered( + cx: &MatchCheckCtx, + constructor: &Constructor, + used_constructors: &[Constructor], +) -> bool { + match constructor { + Constructor::Tuple { arity } => { + used_constructors.iter().any(|constructor| match constructor { + Constructor::Tuple { arity: used_arity } => arity == used_arity, + _ => false, + }) + } + Constructor::Bool(_) => { + if used_constructors.is_empty() { + return false; + } + + let covers_true = + used_constructors.iter().any(|c| matches!(c, Constructor::Bool(true))); + let covers_false = + used_constructors.iter().any(|c| matches!(c, Constructor::Bool(false))); + + covers_true && covers_false + } + Constructor::Enum(e) => cx.db.enum_data(e.parent).variants.iter().all(|(id, _)| { + for constructor in used_constructors { + if let Constructor::Enum(e) = constructor { + if id == e.local_id { + return true; + } + } + } + + false + }), + } +} + +fn enum_variant_matches(cx: &MatchCheckCtx, pat_id: PatId, enum_variant_id: EnumVariantId) -> bool { + Some(enum_variant_id.into()) == cx.infer.variant_resolution_for_pat(pat_id) +} + +#[cfg(test)] +mod tests { + use crate::diagnostics::tests::check_diagnostics; + + #[test] + fn empty_tuple() { + check_diagnostics( + r#" +fn main() { + match () { } + //^^ Missing match arm + match (()) { } + //^^^^ Missing match arm + + match () { _ => (), } + match () { () => (), } + match (()) { (()) => (), } +} +"#, + ); + } + + #[test] + fn tuple_of_two_empty_tuple() { + check_diagnostics( + r#" +fn main() { + match ((), ()) { } + //^^^^^^^^ Missing match arm + + match ((), ()) { ((), ()) => (), } +} +"#, + ); + } + + #[test] + fn boolean() { + check_diagnostics( + r#" +fn test_main() { + match false { } + //^^^^^ Missing match arm + match false { true => (), } + //^^^^^ Missing match arm + match (false, true) {} + //^^^^^^^^^^^^^ Missing match arm + match (false, true) { (true, true) => (), } + //^^^^^^^^^^^^^ Missing match arm + match (false, true) { + //^^^^^^^^^^^^^ Missing match arm + (false, true) => (), + (false, false) => (), + (true, false) => (), + } + match (false, true) { (true, _x) => (), } + //^^^^^^^^^^^^^ Missing match arm + + match false { true => (), false => (), } + match (false, true) { + (false, _) => (), + (true, false) => (), + (_, true) => (), + } + match (false, true) { + (true, true) => (), + (true, false) => (), + (false, true) => (), + (false, false) => (), + } + match (false, true) { + (true, _x) => (), + (false, true) => (), + (false, false) => (), + } + match (false, true, false) { + (false, ..) => (), + (true, ..) => (), + } + match (false, true, false) { + (.., false) => (), + (.., true) => (), + } + match (false, true, false) { (..) => (), } +} +"#, + ); + } + + #[test] + fn tuple_of_tuple_and_bools() { + check_diagnostics( + r#" +fn main() { + match (false, ((), false)) {} + //^^^^^^^^^^^^^^^^^^^^ Missing match arm + match (false, ((), false)) { (true, ((), true)) => (), } + //^^^^^^^^^^^^^^^^^^^^ Missing match arm + match (false, ((), false)) { (true, _) => (), } + //^^^^^^^^^^^^^^^^^^^^ Missing match arm + + match (false, ((), false)) { + (true, ((), true)) => (), + (true, ((), false)) => (), + (false, ((), true)) => (), + (false, ((), false)) => (), + } + match (false, ((), false)) { + (true, ((), true)) => (), + (true, ((), false)) => (), + (false, _) => (), + } +} +"#, + ); + } + + #[test] + fn enums() { + check_diagnostics( + r#" +enum Either { A, B, } + +fn main() { + match Either::A { } + //^^^^^^^^^ Missing match arm + match Either::B { Either::A => (), } + //^^^^^^^^^ Missing match arm + + match &Either::B { + //^^^^^^^^^^ Missing match arm + Either::A => (), + } + + match Either::B { + Either::A => (), Either::B => (), + } + match &Either::B { + Either::A => (), Either::B => (), + } +} +"#, + ); + } + + #[test] + fn enum_containing_bool() { + check_diagnostics( + r#" +enum Either { A(bool), B } + +fn main() { + match Either::B { } + //^^^^^^^^^ Missing match arm + match Either::B { + //^^^^^^^^^ Missing match arm + Either::A(true) => (), Either::B => () + } + + match Either::B { + Either::A(true) => (), + Either::A(false) => (), + Either::B => (), + } + match Either::B { + Either::B => (), + _ => (), + } + match Either::B { + Either::A(_) => (), + Either::B => (), + } + +} + "#, + ); + } + + #[test] + fn enum_different_sizes() { + check_diagnostics( + r#" +enum Either { A(bool), B(bool, bool) } + +fn main() { + match Either::A(false) { + //^^^^^^^^^^^^^^^^ Missing match arm + Either::A(_) => (), + Either::B(false, _) => (), + } + + match Either::A(false) { + Either::A(_) => (), + Either::B(true, _) => (), + Either::B(false, _) => (), + } + match Either::A(false) { + Either::A(true) | Either::A(false) => (), + Either::B(true, _) => (), + Either::B(false, _) => (), + } +} +"#, + ); + } + + #[test] + fn tuple_of_enum_no_diagnostic() { + check_diagnostics( + r#" +enum Either { A(bool), B(bool, bool) } +enum Either2 { C, D } + +fn main() { + match (Either::A(false), Either2::C) { + (Either::A(true), _) | (Either::A(false), _) => (), + (Either::B(true, _), Either2::C) => (), + (Either::B(false, _), Either2::C) => (), + (Either::B(_, _), Either2::D) => (), + } +} +"#, + ); + } + + #[test] + fn mismatched_types() { + // Match statements with arms that don't match the + // expression pattern do not fire this diagnostic. + check_diagnostics( + r#" +enum Either { A, B } +enum Either2 { C, D } + +fn main() { + match Either::A { + Either2::C => (), + Either2::D => (), + } + match (true, false) { + (true, false, true) => (), + (true) => (), + } + match (0) { () => () } + match Unresolved::Bar { Unresolved::Baz => () } +} + "#, + ); + } + + #[test] + fn malformed_match_arm_tuple_enum_missing_pattern() { + // We are testing to be sure we don't panic here when the match + // arm `Either::B` is missing its pattern. + check_diagnostics( + r#" +enum Either { A, B(u32) } + +fn main() { + match Either::A { + Either::A => (), + Either::B() => (), + } +} +"#, + ); + } + + #[test] + fn expr_diverges() { + check_diagnostics( + r#" +enum Either { A, B } + +fn main() { + match loop {} { + Either::A => (), + Either::B => (), + } + match loop {} { + Either::A => (), + } + match loop { break Foo::A } { + //^^^^^^^^^^^^^^^^^^^^^ Missing match arm + Either::A => (), + } + match loop { break Foo::A } { + Either::A => (), + Either::B => (), + } +} +"#, + ); + } + + #[test] + fn expr_partially_diverges() { + check_diagnostics( + r#" +enum Either { A(T), B } + +fn foo() -> Either { Either::B } +fn main() -> u32 { + match foo() { + Either::A(val) => val, + Either::B => 0, + } +} +"#, + ); + } + + #[test] + fn enum_record() { + check_diagnostics( + r#" +enum Either { A { foo: bool }, B } + +fn main() { + let a = Either::A { foo: true }; + match a { } + //^ Missing match arm + match a { Either::A { foo: true } => () } + //^ Missing match arm + match a { + Either::A { } => (), + //^^^^^^^^^ Missing structure fields: + // | - foo + Either::B => (), + } + match a { + //^ Missing match arm + Either::A { } => (), + } //^^^^^^^^^ Missing structure fields: + // | - foo + + match a { + Either::A { foo: true } => (), + Either::A { foo: false } => (), + Either::B => (), + } + match a { + Either::A { foo: _ } => (), + Either::B => (), + } +} +"#, + ); + } + + #[test] + fn enum_record_fields_out_of_order() { + check_diagnostics( + r#" +enum Either { + A { foo: bool, bar: () }, + B, +} + +fn main() { + let a = Either::A { foo: true, bar: () }; + match a { + //^ Missing match arm + Either::A { bar: (), foo: false } => (), + Either::A { foo: true, bar: () } => (), + } + + match a { + Either::A { bar: (), foo: false } => (), + Either::A { foo: true, bar: () } => (), + Either::B => (), + } +} +"#, + ); + } + + #[test] + fn enum_record_ellipsis() { + check_diagnostics( + r#" +enum Either { + A { foo: bool, bar: bool }, + B, +} + +fn main() { + let a = Either::B; + match a { + //^ Missing match arm + Either::A { foo: true, .. } => (), + Either::B => (), + } + match a { + //^ Missing match arm + Either::A { .. } => (), + } + + match a { + Either::A { foo: true, .. } => (), + Either::A { foo: false, .. } => (), + Either::B => (), + } + + match a { + Either::A { .. } => (), + Either::B => (), + } +} +"#, + ); + } + + #[test] + fn enum_tuple_partial_ellipsis() { + check_diagnostics( + r#" +enum Either { + A(bool, bool, bool, bool), + B, +} + +fn main() { + match Either::B { + //^^^^^^^^^ Missing match arm + Either::A(true, .., true) => (), + Either::A(true, .., false) => (), + Either::A(false, .., false) => (), + Either::B => (), + } + match Either::B { + //^^^^^^^^^ Missing match arm + Either::A(true, .., true) => (), + Either::A(true, .., false) => (), + Either::A(.., true) => (), + Either::B => (), + } + + match Either::B { + Either::A(true, .., true) => (), + Either::A(true, .., false) => (), + Either::A(false, .., true) => (), + Either::A(false, .., false) => (), + Either::B => (), + } + match Either::B { + Either::A(true, .., true) => (), + Either::A(true, .., false) => (), + Either::A(.., true) => (), + Either::A(.., false) => (), + Either::B => (), + } +} +"#, + ); + } + + #[test] + fn never() { + check_diagnostics( + r#" +enum Never {} + +fn enum_(never: Never) { + match never {} +} +fn enum_ref(never: &Never) { + match never {} +} +fn bang(never: !) { + match never {} +} +"#, + ); + } + + #[test] + fn or_pattern_panic() { + check_diagnostics( + r#" +pub enum Category { Infinity, Zero } + +fn panic(a: Category, b: Category) { + match (a, b) { + (Category::Zero | Category::Infinity, _) => (), + (_, Category::Zero | Category::Infinity) => (), + } + + // FIXME: This is a false positive, but the code used to cause a panic in the match checker, + // so this acts as a regression test for that. + match (a, b) { + //^^^^^^ Missing match arm + (Category::Infinity, Category::Infinity) | (Category::Zero, Category::Zero) => (), + (Category::Infinity | Category::Zero, _) => (), + } +} +"#, + ); + } + + mod false_negatives { + //! The implementation of match checking here is a work in progress. As we roll this out, we + //! prefer false negatives to false positives (ideally there would be no false positives). This + //! test module should document known false negatives. Eventually we will have a complete + //! implementation of match checking and this module will be empty. + //! + //! The reasons for documenting known false negatives: + //! + //! 1. It acts as a backlog of work that can be done to improve the behavior of the system. + //! 2. It ensures the code doesn't panic when handling these cases. + use super::*; + + #[test] + fn integers() { + // We don't currently check integer exhaustiveness. + check_diagnostics( + r#" +fn main() { + match 5 { + 10 => (), + 11..20 => (), + } +} +"#, + ); + } + + #[test] + fn internal_or() { + // We do not currently handle patterns with internal `or`s. + check_diagnostics( + r#" +fn main() { + enum Either { A(bool), B } + match Either::B { + Either::A(true | false) => (), + } +} +"#, + ); + } + + #[test] + fn tuple_of_bools_with_ellipsis_at_end_missing_arm() { + // We don't currently handle tuple patterns with ellipsis. + check_diagnostics( + r#" +fn main() { + match (false, true, false) { + (false, ..) => (), + } +} +"#, + ); + } + + #[test] + fn tuple_of_bools_with_ellipsis_at_beginning_missing_arm() { + // We don't currently handle tuple patterns with ellipsis. + check_diagnostics( + r#" +fn main() { + match (false, true, false) { + (.., false) => (), + } +} +"#, + ); + } + + #[test] + fn struct_missing_arm() { + // We don't currently handle structs. + check_diagnostics( + r#" +struct Foo { a: bool } +fn main(f: Foo) { + match f { Foo { a: true } => () } +} +"#, + ); + } + } +} -- cgit v1.2.3