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/ra_hir_ty/src/diagnostics/match_check.rs | 1421 ----------------------- 1 file changed, 1421 deletions(-) delete mode 100644 crates/ra_hir_ty/src/diagnostics/match_check.rs (limited to 'crates/ra_hir_ty/src/diagnostics/match_check.rs') diff --git a/crates/ra_hir_ty/src/diagnostics/match_check.rs b/crates/ra_hir_ty/src/diagnostics/match_check.rs deleted file mode 100644 index 7f007f1d6..000000000 --- a/crates/ra_hir_ty/src/diagnostics/match_check.rs +++ /dev/null @@ -1,1421 +0,0 @@ -//! 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