Repository: rust-analyzer/rust-analyzer
Pull request #3878 (2020-04-07 14:40:51)

A more precise panic macro


bors r+
🤖


Patch:
diff --git a/Cargo.lock b/Cargo.lock
index eb9824218f..91a57bf796 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -995,7 +995,6 @@ dependencies = [
  "ra_prof",
  "ra_syntax",
  "rustc-hash",
- "smallvec",
  "stdx",
  "test_utils",
 ]
diff --git a/crates/ra_hir/src/diagnostics.rs b/crates/ra_hir/src/diagnostics.rs
index c82883d0c1..a9040ea3d5 100644
--- a/crates/ra_hir/src/diagnostics.rs
+++ b/crates/ra_hir/src/diagnostics.rs
@@ -1,4 +1,4 @@
 //! FIXME: write short doc here
 pub use hir_def::diagnostics::UnresolvedModule;
 pub use hir_expand::diagnostics::{AstDiagnostic, Diagnostic, DiagnosticSink};
-pub use hir_ty::diagnostics::{MissingFields, MissingMatchArms, MissingOkInTailExpr, NoSuchField};
+pub use hir_ty::diagnostics::{MissingFields, MissingOkInTailExpr, NoSuchField};
diff --git a/crates/ra_hir_ty/Cargo.toml b/crates/ra_hir_ty/Cargo.toml
index 9a4a7aa6f7..45be08430a 100644
--- a/crates/ra_hir_ty/Cargo.toml
+++ b/crates/ra_hir_ty/Cargo.toml
@@ -9,7 +9,6 @@ doctest = false
 
 [dependencies]
 arrayvec = "0.5.1"
-smallvec = "1.2.0"
 ena = "0.13.1"
 log = "0.4.8"
 rustc-hash = "1.1.0"
diff --git a/crates/ra_hir_ty/src/_match.rs b/crates/ra_hir_ty/src/_match.rs
deleted file mode 100644
index f29a25505b..0000000000
--- a/crates/ra_hir_ty/src/_match.rs
+++ /dev/null
@@ -1,1411 +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:
-//! http://moscova.inria.fr/~maranget/papers/warn/index.html
-//! 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:
-//! ```
-//!     // x: (Option<bool>, Result<()>)
-//!     match x {
-//!         (Some(true), _) => {}
-//!         (None, Err(())) => {}
-//!         (None, Err(_)) => {}
-//!     }
-//! ```
-//! Here, the matrix `P` starts as:
-//! [
-//!     [(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:
-//!           `U(P, p) := U(S(c, P), S(c, p))`
-//!           This special case is handled in `is_useful_specialized`.
-//!
-//!           For example, if `P` is:
-//!           [
-//!               [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:
-//!               [
-//!                   [_, 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:
-//!               [
-//!                   [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:
-//!           `U(P, p) := U(P, (r_1, p_2, .., p_n))
-//!                    || U(P, (r_2, p_2, .., p_n))`
-use std::sync::Arc;
-
-use smallvec::{smallvec, SmallVec};
-
-use crate::{
-    db::HirDatabase,
-    expr::{Body, Expr, Literal, Pat, PatId},
-    InferenceResult,
-};
-use hir_def::{adt::VariantData, EnumVariantId, VariantId};
-
-#[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<PatId> {
-        match self {
-            PatIdOrWild::PatId(id) => Some(id),
-            PatIdOrWild::Wild => None,
-        }
-    }
-}
-
-impl From<PatId> for PatIdOrWild {
-    fn from(pat_id: PatId) -> Self {
-        Self::PatId(pat_id)
-    }
-}
-
-#[derive(Debug, Clone, Copy, PartialEq)]
-pub struct MatchCheckNotImplemented;
-
-/// 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 type MatchCheckResult<T> = Result<T, MatchCheckNotImplemented>;
-
-#[derive(Debug)]
-/// A row in a Matrix.
-///
-/// This type is modeled from the struct of the same name in `rustc`.
-pub(crate) struct PatStack(PatStackInner);
-type PatStackInner = SmallVec<[PatIdOrWild; 2]>;
-
-impl PatStack {
-    pub(crate) fn from_pattern(pat_id: PatId) -> PatStack {
-        Self(smallvec!(pat_id.into()))
-    }
-
-    pub(crate) 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 is_empty(&self) -> bool {
-        self.0.is_empty()
-    }
-
-    fn head(&self) -> PatIdOrWild {
-        self.0[0]
-    }
-
-    fn get_head(&self) -> Option<PatIdOrWild> {
-        self.0.first().copied()
-    }
-
-    fn to_tail(&self) -> PatStack {
-        Self::from_slice(&self.0[1..])
-    }
-
-    fn replace_head_with(&self, pat_ids: &[PatId]) -> PatStack {
-        let mut patterns: PatStackInner = smallvec![];
-        for pat in pat_ids {
-            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<PatStack> {
-        if matches!(self.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<Option<PatStack>> {
-        let result = match (self.head().as_pat(cx), constructor) {
-            (Pat::Tuple(ref pat_ids), Constructor::Tuple { arity }) => {
-                debug_assert_eq!(
-                    pat_ids.len(),
-                    *arity,
-                    "we type check before calling this code, so we should never hit this case",
-                );
-
-                Some(self.replace_head_with(pat_ids))
-            }
-            (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(MatchCheckNotImplemented),
-                }
-            }
-            (Pat::Wild, constructor) => Some(self.expand_wildcard(cx, constructor)?),
-            (Pat::Path(_), Constructor::Enum(constructor)) => {
-                // enums with no associated data become `Pat::Path`
-                let pat_id = self.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, .. }, Constructor::Enum(constructor)) => {
-                let pat_id = self.head().as_id().expect("we know this isn't a wild");
-                if !enum_variant_matches(cx, pat_id, *constructor) {
-                    None
-                } else {
-                    Some(self.replace_head_with(pat_ids))
-                }
-            }
-            (Pat::Or(_), _) => return Err(MatchCheckNotImplemented),
-            (_, _) => return Err(MatchCheckNotImplemented),
-        };
-
-        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<PatStack> {
-        assert_eq!(
-            Pat::Wild,
-            self.head().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))
-    }
-}
-
-#[derive(Debug)]
-/// A collection of PatStack.
-///
-/// This type is modeled from the struct of the same name in `rustc`.
-pub(crate) struct Matrix(Vec<PatStack>);
-
-impl Matrix {
-    pub(crate) fn empty() -> Self {
-        Self(vec![])
-    }
-
-    pub(crate) 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<PatIdOrWild> {
-        self.0.iter().map(|p| p.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<Self> {
-        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<T: IntoIterator<Item = PatStack>>(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 enum Usefulness {
-    Useful,
-    NotUseful,
-}
-
-pub struct MatchCheckCtx<'a> {
-    pub body: Arc<Body>,
-    pub infer: Arc<InferenceResult>,
-    pub 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(crate) fn is_useful(
-    cx: &MatchCheckCtx,
-    matrix: &Matrix,
-    v: &PatStack,
-) -> MatchCheckResult<Usefulness> {
-    if v.is_empty() {
-        let result = if matrix.is_empty() { Usefulness::Useful } else { Usefulness::NotUseful };
-
-        return Ok(result);
-    }
-
-    if let Pat::Or(pat_ids) = v.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(MatchCheckNotImplemented)
-        } else {
-            Ok(Usefulness::NotUseful)
-        };
-    }
-
-    if let Some(constructor) = pat_constructor(cx, v.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<Constructor> = 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(MatchCheckNotImplemented)
-                } 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<usize> {
-        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::Unit => 0,
-                    _ => return Err(MatchCheckNotImplemented),
-                }
-            }
-        };
-
-        Ok(arity)
-    }
-
-    fn all_constructors(&self, cx: &MatchCheckCtx) -> Vec<Constructor> {
-        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<Option<Constructor>> {
-    let res = match pat.as_pat(cx) {
-        Pat::Wild => None,
-        Pat::Tuple(pats) => 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(MatchCheckNotImplemented),
-        },
-        Pat::TupleStruct { .. } | Pat::Path(_) => {
-            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(MatchCheckNotImplemented)?;
-            match variant_id {
-                VariantId::EnumVariantId(enum_variant_id) => {
-                    Some(Constructor::Enum(enum_variant_id))
-                }
-                _ => return Err(MatchCheckNotImplemented),
-            }
-        }
-        _ => return Err(MatchCheckNotImplemented),
-    };
-
-    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 {
-    pub(super) use insta::assert_snapshot;
-    pub(super) use ra_db::fixture::WithFixture;
-
-    pub(super) use crate::test_db::TestDB;
-
-    pub(super) fn check_diagnostic_message(content: &str) -> String {
-        TestDB::with_single_file(content).0.diagnostics().0
-    }
-
-    pub(super) fn check_diagnostic(content: &str) {
-        let diagnostic_count = TestDB::with_single_file(content).0.diagnostics().1;
-
-        assert_eq!(1, diagnostic_count, "no diagnostic reported");
-    }
-
-    pub(super) fn check_no_diagnostic(content: &str) {
-        let diagnostic_count = TestDB::with_single_file(content).0.diagnostics().1;
-
-        assert_eq!(0, diagnostic_count, "expected no diagnostic, found one");
-    }
-
-    #[test]
-    fn empty_tuple_no_arms_diagnostic_message() {
-        let content = r"
-            fn test_fn() {
-                match () {
-                }
-            }
-        ";
-
-        assert_snapshot!(
-            check_diagnostic_message(content),
-            @"\"()\": Missing match arm\n"
-        );
-    }
-
-    #[test]
-    fn empty_tuple_no_arms() {
-        let content = r"
-            fn test_fn() {
-                match () {
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn empty_tuple_wild() {
-        let content = r"
-            fn test_fn() {
-                match () {
-                    _ => {}
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn empty_tuple_no_diagnostic() {
-        let content = r"
-            fn test_fn() {
-                match () {
-                    () => {}
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_empty_tuple_no_arms() {
-        let content = r"
-            fn test_fn() {
-                match (()) {
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_empty_tuple_no_diagnostic() {
-        let content = r"
-            fn test_fn() {
-                match (()) {
-                    (()) => {}
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_two_empty_tuple_no_arms() {
-        let content = r"
-            fn test_fn() {
-                match ((), ()) {
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_two_empty_tuple_no_diagnostic() {
-        let content = r"
-            fn test_fn() {
-                match ((), ()) {
-                    ((), ()) => {}
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn bool_no_arms() {
-        let content = r"
-            fn test_fn() {
-                match false {
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn bool_missing_arm() {
-        let content = r"
-            fn test_fn() {
-                match false {
-                    true => {}
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn bool_no_diagnostic() {
-        let content = r"
-            fn test_fn() {
-                match false {
-                    true => {}
-                    false => {}
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_bools_no_arms() {
-        let content = r"
-            fn test_fn() {
-                match (false, true) {
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_bools_missing_arms() {
-        let content = r"
-            fn test_fn() {
-                match (false, true) {
-                    (true, true) => {},
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_bools_missing_arm() {
-        let content = r"
-            fn test_fn() {
-                match (false, true) {
-                    (false, true) => {},
-                    (false, false) => {},
-                    (true, false) => {},
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_bools_with_wilds() {
-        let content = r"
-            fn test_fn() {
-                match (false, true) {
-                    (false, _) => {},
-                    (true, false) => {},
-                    (_, true) => {},
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_bools_no_diagnostic() {
-        let content = r"
-            fn test_fn() {
-                match (false, true) {
-                    (true, true) => {},
-                    (true, false) => {},
-                    (false, true) => {},
-                    (false, false) => {},
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_bools_binding_missing_arms() {
-        let content = r"
-            fn test_fn() {
-                match (false, true) {
-                    (true, _x) => {},
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_bools_binding_no_diagnostic() {
-        let content = r"
-            fn test_fn() {
-                match (false, true) {
-                    (true, _x) => {},
-                    (false, true) => {},
-                    (false, false) => {},
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_tuple_and_bools_no_arms() {
-        let content = r"
-            fn test_fn() {
-                match (false, ((), false)) {
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_tuple_and_bools_missing_arms() {
-        let content = r"
-            fn test_fn() {
-                match (false, ((), false)) {
-                    (true, ((), true)) => {},
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_tuple_and_bools_no_diagnostic() {
-        let content = r"
-            fn test_fn() {
-                match (false, ((), false)) {
-                    (true, ((), true)) => {},
-                    (true, ((), false)) => {},
-                    (false, ((), true)) => {},
-                    (false, ((), false)) => {},
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_tuple_and_bools_wildcard_missing_arms() {
-        let content = r"
-            fn test_fn() {
-                match (false, ((), false)) {
-                    (true, _) => {},
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_tuple_and_bools_wildcard_no_diagnostic() {
-        let content = r"
-            fn test_fn() {
-                match (false, ((), false)) {
-                    (true, ((), true)) => {},
-                    (true, ((), false)) => {},
-                    (false, _) => {},
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_no_arms() {
-        let content = r"
-            enum Either {
-                A,
-                B,
-            }
-            fn test_fn() {
-                match Either::A {
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_missing_arms() {
-        let content = r"
-            enum Either {
-                A,
-                B,
-            }
-            fn test_fn() {
-                match Either::B {
-                    Either::A => {},
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_no_diagnostic() {
-        let content = r"
-            enum Either {
-                A,
-                B,
-            }
-            fn test_fn() {
-                match Either::B {
-                    Either::A => {},
-                    Either::B => {},
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_ref_missing_arms() {
-        let content = r"
-            enum Either {
-                A,
-                B,
-            }
-            fn test_fn() {
-                match &Either::B {
-                    Either::A => {},
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_ref_no_diagnostic() {
-        let content = r"
-            enum Either {
-                A,
-                B,
-            }
-            fn test_fn() {
-                match &Either::B {
-                    Either::A => {},
-                    Either::B => {},
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_containing_bool_no_arms() {
-        let content = r"
-            enum Either {
-                A(bool),
-                B,
-            }
-            fn test_fn() {
-                match Either::B {
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_containing_bool_missing_arms() {
-        let content = r"
-            enum Either {
-                A(bool),
-                B,
-            }
-            fn test_fn() {
-                match Either::B {
-                    Either::A(true) => (),
-                    Either::B => (),
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_containing_bool_no_diagnostic() {
-        let content = r"
-            enum Either {
-                A(bool),
-                B,
-            }
-            fn test_fn() {
-                match Either::B {
-                    Either::A(true) => (),
-                    Either::A(false) => (),
-                    Either::B => (),
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_containing_bool_with_wild_no_diagnostic() {
-        let content = r"
-            enum Either {
-                A(bool),
-                B,
-            }
-            fn test_fn() {
-                match Either::B {
-                    Either::B => (),
-                    _ => (),
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_containing_bool_with_wild_2_no_diagnostic() {
-        let content = r"
-            enum Either {
-                A(bool),
-                B,
-            }
-            fn test_fn() {
-                match Either::B {
-                    Either::A(_) => (),
-                    Either::B => (),
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_different_sizes_missing_arms() {
-        let content = r"
-            enum Either {
-                A(bool),
-                B(bool, bool),
-            }
-            fn test_fn() {
-                match Either::A(false) {
-                    Either::A(_) => (),
-                    Either::B(false, _) => (),
-                }
-            }
-        ";
-
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_different_sizes_no_diagnostic() {
-        let content = r"
-            enum Either {
-                A(bool),
-                B(bool, bool),
-            }
-            fn test_fn() {
-                match Either::A(false) {
-                    Either::A(_) => (),
-                    Either::B(true, _) => (),
-                    Either::B(false, _) => (),
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn or_no_diagnostic() {
-        let content = r"
-            enum Either {
-                A(bool),
-                B(bool, bool),
-            }
-            fn test_fn() {
-                match Either::A(false) {
-                    Either::A(true) | Either::A(false) => (),
-                    Either::B(true, _) => (),
-                    Either::B(false, _) => (),
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn tuple_of_enum_no_diagnostic() {
-        let content = r"
-            enum Either {
-                A(bool),
-                B(bool, bool),
-            }
-            enum Either2 {
-                C,
-                D,
-            }
-            fn test_fn() {
-                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) => (),
-                }
-            }
-        ";
-
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn mismatched_types() {
-        let content = r"
-            enum Either {
-                A,
-                B,
-            }
-            enum Either2 {
-                C,
-                D,
-            }
-            fn test_fn() {
-                match Either::A {
-                    Either2::C => (),
-                    Either2::D => (),
-                }
-            }
-        ";
-
-        // Match arms with the incorrect type are filtered out.
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn mismatched_types_with_different_arity() {
-        let content = r"
-            fn test_fn() {
-                match (true, false) {
-                    (true, false, true) => (),
-                    (true) => (),
-                }
-            }
-        ";
-
-        // Match arms with the incorrect type are filtered out.
-        check_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_not_in_scope() {
-        let content = r"
-            fn test_fn() {
-                match Foo::Bar {
-                    Foo::Baz => (),
-                }
-            }
-        ";
-
-        // The enum is not in scope so we don't perform exhaustiveness
-        // checking, but we want to be sure we don't panic here (and
-        // we don't create a diagnostic).
-        check_no_diagnostic(content);
-    }
-}
-
-#[cfg(test)]
-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::tests::*;
-
-    #[test]
-    fn integers() {
-        let content = r"
-            fn test_fn() {
-                match 5 {
-                    10 => (),
-                    11..20 => (),
-                }
-            }
-        ";
-
-        // This is a false negative.
-        // We don't currently check integer exhaustiveness.
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_record() {
-        let content = r"
-            enum Either {
-                A { foo: u32 },
-                B,
-            }
-            fn test_fn() {
-                match Either::B {
-                    Either::A { foo: 5 } => (),
-                }
-            }
-        ";
-
-        // This is a false negative.
-        // We don't currently handle enum record types.
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn internal_or() {
-        let content = r"
-            fn test_fn() {
-                enum Either {
-                    A(bool),
-                    B,
-                }
-                match Either::B {
-                    Either::A(true | false) => (),
-                }
-            }
-        ";
-
-        // This is a false negative.
-        // We do not currently handle patterns with internal `or`s.
-        check_no_diagnostic(content);
-    }
-}
diff --git a/crates/ra_hir_ty/src/diagnostics.rs b/crates/ra_hir_ty/src/diagnostics.rs
index 8cbce11686..0f8522021e 100644
--- a/crates/ra_hir_ty/src/diagnostics.rs
+++ b/crates/ra_hir_ty/src/diagnostics.rs
@@ -6,7 +6,7 @@ use hir_expand::{db::AstDatabase, name::Name, HirFileId, InFile};
 use ra_syntax::{ast, AstNode, AstPtr, SyntaxNodePtr};
 use stdx::format_to;
 
-pub use hir_def::{diagnostics::UnresolvedModule, expr::MatchArm};
+pub use hir_def::diagnostics::UnresolvedModule;
 pub use hir_expand::diagnostics::{AstDiagnostic, Diagnostic, DiagnosticSink};
 
 #[derive(Debug)]
@@ -62,25 +62,6 @@ impl AstDiagnostic for MissingFields {
     }
 }
 
-#[derive(Debug)]
-pub struct MissingMatchArms {
-    pub file: HirFileId,
-    pub match_expr: AstPtr<ast::Expr>,
-    pub arms: AstPtr<ast::MatchArmList>,
-}
-
-impl Diagnostic for MissingMatchArms {
-    fn message(&self) -> String {
-        String::from("Missing match arm")
-    }
-    fn source(&self) -> InFile<SyntaxNodePtr> {
-        InFile { file_id: self.file, value: self.match_expr.into() }
-    }
-    fn as_any(&self) -> &(dyn Any + Send + 'static) {
-        self
-    }
-}
-
 #[derive(Debug)]
 pub struct MissingOkInTailExpr {
     pub file: HirFileId,
diff --git a/crates/ra_hir_ty/src/expr.rs b/crates/ra_hir_ty/src/expr.rs
index 1e7395b164..b7b476b4c1 100644
--- a/crates/ra_hir_ty/src/expr.rs
+++ b/crates/ra_hir_ty/src/expr.rs
@@ -14,10 +14,9 @@ use rustc_hash::FxHashSet;
 
 use crate::{
     db::HirDatabase,
-    diagnostics::{MissingFields, MissingMatchArms, MissingOkInTailExpr},
+    diagnostics::{MissingFields, MissingOkInTailExpr},
     utils::variant_data,
     ApplicationTy, InferenceResult, Ty, TypeCtor,
-    _match::{is_useful, MatchCheckCtx, Matrix, PatStack, Usefulness},
 };
 
 pub use hir_def::{
@@ -53,99 +52,15 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
         for e in body.exprs.iter() {
             if let (id, Expr::RecordLit { path, fields, spread }) = e {
                 self.validate_record_literal(id, path, fields, *spread, db);
-            } else if let (id, Expr::Match { expr, arms }) = e {
-                self.validate_match(id, *expr, arms, db, self.infer.clone());
             }
         }
 
         let body_expr = &body[body.body_expr];
-        if let Expr::Block { tail: Some(t), .. } = body_expr {
+        if let Expr::Block { statements: _, tail: Some(t) } = body_expr {
             self.validate_results_in_tail_expr(body.body_expr, *t, db);
         }
     }
 
-    fn validate_match(
-        &mut self,
-        id: ExprId,
-        match_expr: ExprId,
-        arms: &[MatchArm],
-        db: &dyn HirDatabase,
-        infer: Arc<InferenceResult>,
-    ) {
-        let (body, source_map): (Arc<Body>, Arc<BodySourceMap>) =
-            db.body_with_source_map(self.func.into());
-
-        let match_expr_ty = match infer.type_of_expr.get(match_expr) {
-            Some(ty) => ty,
-            // If we can't resolve the type of the match expression
-            // we cannot perform exhaustiveness checks.
-            None => return,
-        };
-
-        let cx = MatchCheckCtx { body, infer: infer.clone(), db };
-        let pats = arms.iter().map(|arm| arm.pat);
-
-        let mut seen = Matrix::empty();
-        for pat in pats {
-            // We skip any patterns whose type we cannot resolve.
-            //
-            // This could lead to false positives in this diagnostic, so
-            // it might be better to skip the entire diagnostic if we either
-            // cannot resolve a match arm or determine that the match arm has
-            // the wrong type.
-            if let Some(pat_ty) = infer.type_of_pat.get(pat) {
-                // We only include patterns whose type matches the type
-                // of the match expression. If we had a InvalidMatchArmPattern
-                // diagnostic or similar we could raise that in an else
-                // block here.
-                //
-                // When comparing the types, we also have to consider that rustc
-                // will automatically de-reference the match expression type if
-                // necessary.
-                //
-                // FIXME we should use the type checker for this.
-                if pat_ty == match_expr_ty
-                    || match_expr_ty
-                        .as_reference()
-                        .map(|(match_expr_ty, _)| match_expr_ty == pat_ty)
-                        .unwrap_or(false)
-                {
-                    // If we had a NotUsefulMatchArm diagnostic, we could
-                    // check the usefulness of each pattern as we added it
-                    // to the matrix here.
-                    let v = PatStack::from_pattern(pat);
-                    seen.push(&cx, v);
-                }
-            }
-        }
-
-        match is_useful(&cx, &seen, &PatStack::from_wild()) {
-            Ok(Usefulness::Useful) => (),
-            // if a wildcard pattern is not useful, then all patterns are covered
-            Ok(Usefulness::NotUseful) => return,
-            // this path is for unimplemented checks, so we err on the side of not
-            // reporting any errors
-            _ => return,
-        }
-
-        if let Ok(source_ptr) = source_map.expr_syntax(id) {
-            if let Some(expr) = source_ptr.value.left() {
-                let root = source_ptr.file_syntax(db.upcast());
-                if let ast::Expr::MatchExpr(match_expr) = expr.to_node(&root) {
-                    if let (Some(match_expr), Some(arms)) =
-                        (match_expr.expr(), match_expr.match_arm_list())
-                    {
-                        self.sink.push(MissingMatchArms {
-                            file: source_ptr.file_id,
-                            match_expr: AstPtr::new(&match_expr),
-                            arms: AstPtr::new(&arms),
-                        })
-                    }
-                }
-            }
-        }
-    }
-
     fn validate_record_literal(
         &mut self,
         id: ExprId,
diff --git a/crates/ra_hir_ty/src/infer/pat.rs b/crates/ra_hir_ty/src/infer/pat.rs
index 69bbb4307f..86acd27f8d 100644
--- a/crates/ra_hir_ty/src/infer/pat.rs
+++ b/crates/ra_hir_ty/src/infer/pat.rs
@@ -21,13 +21,9 @@ impl<'a> InferenceContext<'a> {
         subpats: &[PatId],
         expected: &Ty,
         default_bm: BindingMode,
-        id: PatId,
     ) -> Ty {
         let (ty, def) = self.resolve_variant(path);
         let var_data = def.map(|it| variant_data(self.db.upcast(), it));
-        if let Some(variant) = def {
-            self.write_variant_resolution(id.into(), variant);
-        }
         self.unify(&ty, expected);
 
         let substs = ty.substs().unwrap_or_else(Substs::empty);
@@ -156,7 +152,7 @@ impl<'a> InferenceContext<'a> {
                 Ty::apply_one(TypeCtor::Ref(*mutability), subty)
             }
             Pat::TupleStruct { path: p, args: subpats } => {
-                self.infer_tuple_struct_pat(p.as_ref(), subpats, expected, default_bm, pat)
+                self.infer_tuple_struct_pat(p.as_ref(), subpats, expected, default_bm)
             }
             Pat::Record { path: p, args: fields } => {
                 self.infer_record_pat(p.as_ref(), fields, expected, default_bm, pat)
diff --git a/crates/ra_hir_ty/src/infer/path.rs b/crates/ra_hir_ty/src/infer/path.rs
index 2b6bc0f798..318652c611 100644
--- a/crates/ra_hir_ty/src/infer/path.rs
+++ b/crates/ra_hir_ty/src/infer/path.rs
@@ -67,16 +67,8 @@ impl<'a> InferenceContext<'a> {
             ValueNs::FunctionId(it) => it.into(),
             ValueNs::ConstId(it) => it.into(),
             ValueNs::StaticId(it) => it.into(),
-            ValueNs::StructId(it) => {
-                self.write_variant_resolution(id, it.into());
-
-                it.into()
-            }
-            ValueNs::EnumVariantId(it) => {
-                self.write_variant_resolution(id, it.into());
-
-                it.into()
-            }
+            ValueNs::StructId(it) => it.into(),
+            ValueNs::EnumVariantId(it) => it.into(),
         };
 
         let ty = self.db.value_ty(typable);
diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index 18f74d3b12..717399b6de 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -43,7 +43,6 @@ mod tests;
 #[cfg(test)]
 mod test_db;
 mod marks;
-mod _match;
 
 use std::ops::Deref;
 use std::sync::Arc;
diff --git a/crates/ra_ide/src/completion/complete_record.rs b/crates/ra_ide/src/completion/complete_record.rs
index 01dd8c6db7..79f5c8c8f9 100644
--- a/crates/ra_ide/src/completion/complete_record.rs
+++ b/crates/ra_ide/src/completion/complete_record.rs
@@ -1,12 +1,13 @@
 //! Complete fields in record literals and patterns.
-use crate::completion::{CompletionContext, Completions};
 use ra_syntax::{ast, ast::NameOwner, SmolStr};
 
+use crate::completion::{CompletionContext, Completions};
+
 pub(super) fn complete_record(acc: &mut Completions, ctx: &CompletionContext) -> Option<()> {
     let (ty, variant, already_present_fields) =
         match (ctx.record_lit_pat.as_ref(), ctx.record_lit_syntax.as_ref()) {
             (None, None) => return None,
-            (Some(_), Some(_)) => panic!("A record cannot be both a literal and a pattern"),
+            (Some(_), Some(_)) => unreachable!("A record cannot be both a literal and a pattern"),
             (Some(record_pat), _) => (
                 ctx.sema.type_of_pat(&record_pat.clone().into())?,
                 ctx.sema.resolve_record_pattern(record_pat)?,
@@ -59,9 +60,10 @@ fn pattern_ascribed_fields(record_pat: &ast::RecordPat) -> Vec<SmolStr> {
 #[cfg(test)]
 mod tests {
     mod record_lit_tests {
-        use crate::completion::{test_utils::do_completion, CompletionItem, CompletionKind};
         use insta::assert_debug_snapshot;
 
+        use crate::completion::{test_utils::do_completion, CompletionItem, CompletionKind};
+
         fn complete(code: &str) -> Vec<CompletionItem> {
             do_completion(code, CompletionKind::Reference)
         }
@@ -204,9 +206,10 @@ mod tests {
     }
 
     mod record_pat_tests {
-        use crate::completion::{test_utils::do_completion, CompletionItem, CompletionKind};
         use insta::assert_debug_snapshot;
 
+        use crate::completion::{test_utils::do_completion, CompletionItem, CompletionKind};
+
         fn complete(code: &str) -> Vec<CompletionItem> {
             do_completion(code, CompletionKind::Reference)
         }
diff --git a/crates/ra_ide/src/completion/completion_context.rs b/crates/ra_ide/src/completion/completion_context.rs
index b8213d62f5..f833d2a9ad 100644
--- a/crates/ra_ide/src/completion/completion_context.rs
+++ b/crates/ra_ide/src/completion/completion_context.rs
@@ -50,6 +50,8 @@ pub(crate) struct CompletionContext<'a> {
     pub(super) dot_receiver_is_ambiguous_float_literal: bool,
     /// If this is a call (method or function) in particular, i.e. the () are already there.
     pub(super) is_call: bool,
+    /// If this is a macro call, i.e. the () are already there.
+    pub(super) is_macro_call: bool,
     pub(super) is_path_type: bool,
     pub(super) has_type_args: bool,
 }
@@ -102,6 +104,7 @@ impl<'a> CompletionContext<'a> {
             is_new_item: false,
             dot_receiver: None,
             is_call: false,
+            is_macro_call: false,
             is_path_type: false,
             has_type_args: false,
             dot_receiver_is_ambiguous_float_literal: false,
@@ -269,6 +272,7 @@ impl<'a> CompletionContext<'a> {
                 .and_then(ast::PathExpr::cast)
                 .and_then(|it| it.syntax().parent().and_then(ast::CallExpr::cast))
                 .is_some();
+            self.is_macro_call = path.syntax().parent().and_then(ast::MacroCall::cast).is_some();
 
             self.is_path_type = path.syntax().parent().and_then(ast::PathType::cast).is_some();
             self.has_type_args = segment.type_arg_list().is_some();
diff --git a/crates/ra_ide/src/completion/presentation.rs b/crates/ra_ide/src/completion/presentation.rs
index cdfd7bc324..55f75b15aa 100644
--- a/crates/ra_ide/src/completion/presentation.rs
+++ b/crates/ra_ide/src/completion/presentation.rs
@@ -174,7 +174,8 @@ impl Completions {
                 .set_deprecated(is_deprecated(macro_, ctx.db))
                 .detail(detail);
 
-        builder = if ctx.use_item_syntax.is_some() {
+        builder = if ctx.use_item_syntax.is_some() || ctx.is_macro_call {
+            tested_by!(dont_insert_macro_call_parens_unncessary);
             builder.insert_text(name)
         } else {
             let macro_braces_to_insert =
@@ -960,7 +961,8 @@ mod tests {
     }
 
     #[test]
-    fn dont_insert_macro_call_braces_in_use() {
+    fn dont_insert_macro_call_parens_unncessary() {
+        covers!(dont_insert_macro_call_parens_unncessary);
         assert_debug_snapshot!(
             do_reference_completion(
                 r"
@@ -986,6 +988,41 @@ mod tests {
             },
         ]
         "###
-        )
+        );
+
+        assert_debug_snapshot!(
+            do_reference_completion(
+                r"
+                //- /main.rs
+                macro_rules frobnicate {
+                    () => ()
+                }
+                fn main() {
+                    frob<|>!();
+                }
+                "
+            ),
+            @r###"
+        [
+            CompletionItem {
+                label: "frobnicate!",
+                source_range: [56; 60),
+                delete: [56; 60),
+                insert: "frobnicate",
+                kind: Macro,
+                detail: "macro_rules! frobnicate",
+            },
+            CompletionItem {
+                label: "main()",
+                source_range: [56; 60),
+                delete: [56; 60),
+                insert: "main()$0",
+                kind: Function,
+                lookup: "main",
+                detail: "fn main()",
+            },
+        ]
+        "###
+        );
     }
 }
diff --git a/crates/ra_ide/src/diagnostics.rs b/crates/ra_ide/src/diagnostics.rs
index 901ad104c1..c1d7ddaf23 100644
--- a/crates/ra_ide/src/diagnostics.rs
+++ b/crates/ra_ide/src/diagnostics.rs
@@ -101,14 +101,6 @@ pub(crate) fn diagnostics(db: &RootDatabase, file_id: FileId) -> Vec<Diagnostic>
             fix,
         })
     })
-    .on::<hir::diagnostics::MissingMatchArms, _>(|d| {
-        res.borrow_mut().push(Diagnostic {
-            range: d.highlight_range(),
-            message: d.message(),
-            severity: Severity::Error,
-            fix: None,
-        })
-    })
     .on::<hir::diagnostics::MissingOkInTailExpr, _>(|d| {
         let node = d.ast(db);
         let replacement = format!("Ok({})", node.syntax());
@@ -299,7 +291,7 @@ mod tests {
     fn check_no_diagnostic(content: &str) {
         let (analysis, file_id) = single_file(content);
         let diagnostics = analysis.diagnostics(file_id).unwrap();
-        assert_eq!(diagnostics.len(), 0, "expected no diagnostic, found one");
+        assert_eq!(diagnostics.len(), 0);
     }
 
     #[test]
diff --git a/crates/ra_ide/src/marks.rs b/crates/ra_ide/src/marks.rs
index 1236cb773c..5e1f135c56 100644
--- a/crates/ra_ide/src/marks.rs
+++ b/crates/ra_ide/src/marks.rs
@@ -7,4 +7,5 @@ test_utils::marks!(
     dont_complete_current_use
     test_resolve_parent_module_on_module_decl
     search_filters_by_range
+    dont_insert_macro_call_parens_unncessary
 );


Test patch:
diff --git a/crates/ra_hir_ty/src/test_db.rs b/crates/ra_hir_ty/src/test_db.rs
index 3a4d58bf9c..208096aab6 100644
--- a/crates/ra_hir_ty/src/test_db.rs
+++ b/crates/ra_hir_ty/src/test_db.rs
@@ -105,9 +105,8 @@ impl TestDB {
     }
 
     // FIXME: don't duplicate this
-    pub fn diagnostics(&self) -> (String, u32) {
+    pub fn diagnostics(&self) -> String {
         let mut buf = String::new();
-        let mut count = 0;
         let crate_graph = self.crate_graph();
         for krate in crate_graph.iter() {
             let crate_def_map = self.crate_def_map(krate);
@@ -134,14 +133,13 @@ impl TestDB {
                 let infer = self.infer(f.into());
                 let mut sink = DiagnosticSink::new(|d| {
                     format_to!(buf, "{:?}: {}\n", d.syntax_node(self).text(), d.message());
-                    count += 1;
                 });
                 infer.add_diagnostics(self, f, &mut sink);
                 let mut validator = ExprValidator::new(f, infer, &mut sink);
                 validator.validate_body(self);
             }
         }
-        (buf, count)
+        buf
     }
 }
 
diff --git a/crates/ra_hir_ty/src/tests.rs b/crates/ra_hir_ty/src/tests.rs
index e4a103d1be..027e5a8f88 100644
--- a/crates/ra_hir_ty/src/tests.rs
+++ b/crates/ra_hir_ty/src/tests.rs
@@ -309,8 +309,7 @@ fn no_such_field_diagnostics() {
         }
         ",
     )
-    .diagnostics()
-    .0;
+    .diagnostics();
 
     assert_snapshot!(diagnostics, @r###"
     "baz: 62": no such field