rust-clippy/clippy_lints/src/unnested_or_patterns.rs

426 lines
15 KiB
Rust

#![allow(clippy::wildcard_imports, clippy::enum_glob_use)]
use clippy_utils::ast_utils::{eq_field_pat, eq_id, eq_maybe_qself, eq_pat, eq_path};
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::msrvs::{self, Msrv};
use clippy_utils::over;
use rustc_ast::mut_visit::*;
use rustc_ast::ptr::P;
use rustc_ast::{self as ast, Mutability, Pat, PatKind, PatKind::*, DUMMY_NODE_ID};
use rustc_ast_pretty::pprust;
use rustc_errors::Applicability;
use rustc_lint::{EarlyContext, EarlyLintPass};
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::DUMMY_SP;
use std::cell::Cell;
use std::mem;
declare_clippy_lint! {
/// ### What it does
/// Checks for unnested or-patterns, e.g., `Some(0) | Some(2)` and
/// suggests replacing the pattern with a nested one, `Some(0 | 2)`.
///
/// Another way to think of this is that it rewrites patterns in
/// *disjunctive normal form (DNF)* into *conjunctive normal form (CNF)*.
///
/// ### Why is this bad?
/// In the example above, `Some` is repeated, which unnecessarily complicates the pattern.
///
/// ### Example
/// ```rust
/// fn main() {
/// if let Some(0) | Some(2) = Some(0) {}
/// }
/// ```
/// Use instead:
/// ```rust
/// fn main() {
/// if let Some(0 | 2) = Some(0) {}
/// }
/// ```
#[clippy::version = "1.46.0"]
pub UNNESTED_OR_PATTERNS,
pedantic,
"unnested or-patterns, e.g., `Foo(Bar) | Foo(Baz) instead of `Foo(Bar | Baz)`"
}
pub struct UnnestedOrPatterns {
msrv: Msrv,
}
impl UnnestedOrPatterns {
#[must_use]
pub fn new(msrv: Msrv) -> Self {
Self { msrv }
}
}
impl_lint_pass!(UnnestedOrPatterns => [UNNESTED_OR_PATTERNS]);
impl EarlyLintPass for UnnestedOrPatterns {
fn check_arm(&mut self, cx: &EarlyContext<'_>, a: &ast::Arm) {
if self.msrv.meets(msrvs::OR_PATTERNS) {
lint_unnested_or_patterns(cx, &a.pat);
}
}
fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
if self.msrv.meets(msrvs::OR_PATTERNS) {
if let ast::ExprKind::Let(pat, _, _) = &e.kind {
lint_unnested_or_patterns(cx, pat);
}
}
}
fn check_param(&mut self, cx: &EarlyContext<'_>, p: &ast::Param) {
if self.msrv.meets(msrvs::OR_PATTERNS) {
lint_unnested_or_patterns(cx, &p.pat);
}
}
fn check_local(&mut self, cx: &EarlyContext<'_>, l: &ast::Local) {
if self.msrv.meets(msrvs::OR_PATTERNS) {
lint_unnested_or_patterns(cx, &l.pat);
}
}
extract_msrv_attr!(EarlyContext);
}
fn lint_unnested_or_patterns(cx: &EarlyContext<'_>, pat: &Pat) {
if let Ident(.., None) | Lit(_) | Wild | Path(..) | Range(..) | Rest | MacCall(_) = pat.kind {
// This is a leaf pattern, so cloning is unprofitable.
return;
}
let mut pat = P(pat.clone());
// Nix all the paren patterns everywhere so that they aren't in our way.
remove_all_parens(&mut pat);
// Transform all unnested or-patterns into nested ones, and if there were none, quit.
if !unnest_or_patterns(&mut pat) {
return;
}
span_lint_and_then(cx, UNNESTED_OR_PATTERNS, pat.span, "unnested or-patterns", |db| {
insert_necessary_parens(&mut pat);
db.span_suggestion_verbose(
pat.span,
"nest the patterns",
pprust::pat_to_string(&pat),
Applicability::MachineApplicable,
);
});
}
/// Remove all `(p)` patterns in `pat`.
fn remove_all_parens(pat: &mut P<Pat>) {
struct Visitor;
impl MutVisitor for Visitor {
fn visit_pat(&mut self, pat: &mut P<Pat>) {
noop_visit_pat(pat, self);
let inner = match &mut pat.kind {
Paren(i) => mem::replace(&mut i.kind, Wild),
_ => return,
};
pat.kind = inner;
}
}
Visitor.visit_pat(pat);
}
/// Insert parens where necessary according to Rust's precedence rules for patterns.
fn insert_necessary_parens(pat: &mut P<Pat>) {
struct Visitor;
impl MutVisitor for Visitor {
fn visit_pat(&mut self, pat: &mut P<Pat>) {
use ast::BindingAnnotation;
noop_visit_pat(pat, self);
let target = match &mut pat.kind {
// `i @ a | b`, `box a | b`, and `& mut? a | b`.
Ident(.., Some(p)) | Box(p) | Ref(p, _) if matches!(&p.kind, Or(ps) if ps.len() > 1) => p,
Ref(p, Mutability::Not) if matches!(p.kind, Ident(BindingAnnotation::MUT, ..)) => p, // `&(mut x)`
_ => return,
};
target.kind = Paren(P(take_pat(target)));
}
}
Visitor.visit_pat(pat);
}
/// Unnest or-patterns `p0 | ... | p1` in the pattern `pat`.
/// For example, this would transform `Some(0) | FOO | Some(2)` into `Some(0 | 2) | FOO`.
fn unnest_or_patterns(pat: &mut P<Pat>) -> bool {
struct Visitor {
changed: bool,
}
impl MutVisitor for Visitor {
fn visit_pat(&mut self, p: &mut P<Pat>) {
// This is a bottom up transformation, so recurse first.
noop_visit_pat(p, self);
// Don't have an or-pattern? Just quit early on.
let Or(alternatives) = &mut p.kind else {
return
};
// Collapse or-patterns directly nested in or-patterns.
let mut idx = 0;
let mut this_level_changed = false;
while idx < alternatives.len() {
let inner = if let Or(ps) = &mut alternatives[idx].kind {
mem::take(ps)
} else {
idx += 1;
continue;
};
this_level_changed = true;
alternatives.splice(idx..=idx, inner);
}
// Focus on `p_n` and then try to transform all `p_i` where `i > n`.
let mut focus_idx = 0;
while focus_idx < alternatives.len() {
this_level_changed |= transform_with_focus_on_idx(alternatives, focus_idx);
focus_idx += 1;
}
self.changed |= this_level_changed;
// Deal with `Some(Some(0)) | Some(Some(1))`.
if this_level_changed {
noop_visit_pat(p, self);
}
}
}
let mut visitor = Visitor { changed: false };
visitor.visit_pat(pat);
visitor.changed
}
/// Match `$scrutinee` against `$pat` and extract `$then` from it.
/// Panics if there is no match.
macro_rules! always_pat {
($scrutinee:expr, $pat:pat => $then:expr) => {
match $scrutinee {
$pat => $then,
_ => unreachable!(),
}
};
}
/// Focus on `focus_idx` in `alternatives`,
/// attempting to extend it with elements of the same constructor `C`
/// in `alternatives[focus_idx + 1..]`.
fn transform_with_focus_on_idx(alternatives: &mut Vec<P<Pat>>, focus_idx: usize) -> bool {
// Extract the kind; we'll need to make some changes in it.
let mut focus_kind = mem::replace(&mut alternatives[focus_idx].kind, PatKind::Wild);
// We'll focus on `alternatives[focus_idx]`,
// so we're draining from `alternatives[focus_idx + 1..]`.
let start = focus_idx + 1;
// We're trying to find whatever kind (~"constructor") we found in `alternatives[start..]`.
let changed = match &mut focus_kind {
// These pattern forms are "leafs" and do not have sub-patterns.
// Therefore they are not some form of constructor `C`,
// with which a pattern `C(p_0)` may be formed,
// which we would want to join with other `C(p_j)`s.
Ident(.., None) | Lit(_) | Wild | Path(..) | Range(..) | Rest | MacCall(_)
// Skip immutable refs, as grouping them saves few characters,
// and almost always requires adding parens (increasing noisiness).
// In the case of only two patterns, replacement adds net characters.
| Ref(_, Mutability::Not)
// Dealt with elsewhere.
| Or(_) | Paren(_) => false,
// Transform `box x | ... | box y` into `box (x | y)`.
//
// The cases below until `Slice(...)` deal with *singleton* products.
// These patterns have the shape `C(p)`, and not e.g., `C(p0, ..., pn)`.
Box(target) => extend_with_matching(
target, start, alternatives,
|k| matches!(k, Box(_)),
|k| always_pat!(k, Box(p) => p),
),
// Transform `&mut x | ... | &mut y` into `&mut (x | y)`.
Ref(target, Mutability::Mut) => extend_with_matching(
target, start, alternatives,
|k| matches!(k, Ref(_, Mutability::Mut)),
|k| always_pat!(k, Ref(p, _) => p),
),
// Transform `b @ p0 | ... b @ p1` into `b @ (p0 | p1)`.
Ident(b1, i1, Some(target)) => extend_with_matching(
target, start, alternatives,
// Binding names must match.
|k| matches!(k, Ident(b2, i2, Some(_)) if b1 == b2 && eq_id(*i1, *i2)),
|k| always_pat!(k, Ident(_, _, Some(p)) => p),
),
// Transform `[pre, x, post] | ... | [pre, y, post]` into `[pre, x | y, post]`.
Slice(ps1) => extend_with_matching_product(
ps1, start, alternatives,
|k, ps1, idx| matches!(k, Slice(ps2) if eq_pre_post(ps1, ps2, idx)),
|k| always_pat!(k, Slice(ps) => ps),
),
// Transform `(pre, x, post) | ... | (pre, y, post)` into `(pre, x | y, post)`.
Tuple(ps1) => extend_with_matching_product(
ps1, start, alternatives,
|k, ps1, idx| matches!(k, Tuple(ps2) if eq_pre_post(ps1, ps2, idx)),
|k| always_pat!(k, Tuple(ps) => ps),
),
// Transform `S(pre, x, post) | ... | S(pre, y, post)` into `S(pre, x | y, post)`.
TupleStruct(qself1, path1, ps1) => extend_with_matching_product(
ps1, start, alternatives,
|k, ps1, idx| matches!(
k,
TupleStruct(qself2, path2, ps2)
if eq_maybe_qself(qself1, qself2) && eq_path(path1, path2) && eq_pre_post(ps1, ps2, idx)
),
|k| always_pat!(k, TupleStruct(_, _, ps) => ps),
),
// Transform a record pattern `S { fp_0, ..., fp_n }`.
Struct(qself1, path1, fps1, rest1) => extend_with_struct_pat(qself1, path1, fps1, *rest1, start, alternatives),
};
alternatives[focus_idx].kind = focus_kind;
changed
}
/// Here we focusing on a record pattern `S { fp_0, ..., fp_n }`.
/// In particular, for a record pattern, the order in which the field patterns is irrelevant.
/// So when we fixate on some `ident_k: pat_k`, we try to find `ident_k` in the other pattern
/// and check that all `fp_i` where `i ∈ ((0...n) \ k)` between two patterns are equal.
fn extend_with_struct_pat(
qself1: &Option<P<ast::QSelf>>,
path1: &ast::Path,
fps1: &mut [ast::PatField],
rest1: bool,
start: usize,
alternatives: &mut Vec<P<Pat>>,
) -> bool {
(0..fps1.len()).any(|idx| {
let pos_in_2 = Cell::new(None); // The element `k`.
let tail_or = drain_matching(
start,
alternatives,
|k| {
matches!(k, Struct(qself2, path2, fps2, rest2)
if rest1 == *rest2 // If one struct pattern has `..` so must the other.
&& eq_maybe_qself(qself1, qself2)
&& eq_path(path1, path2)
&& fps1.len() == fps2.len()
&& fps1.iter().enumerate().all(|(idx_1, fp1)| {
if idx_1 == idx {
// In the case of `k`, we merely require identical field names
// so that we will transform into `ident_k: p1_k | p2_k`.
let pos = fps2.iter().position(|fp2| eq_id(fp1.ident, fp2.ident));
pos_in_2.set(pos);
pos.is_some()
} else {
fps2.iter().any(|fp2| eq_field_pat(fp1, fp2))
}
}))
},
// Extract `p2_k`.
|k| always_pat!(k, Struct(_, _, mut fps, _) => fps.swap_remove(pos_in_2.take().unwrap()).pat),
);
extend_with_tail_or(&mut fps1[idx].pat, tail_or)
})
}
/// Like `extend_with_matching` but for products with > 1 factor, e.g., `C(p_0, ..., p_n)`.
/// Here, the idea is that we fixate on some `p_k` in `C`,
/// allowing it to vary between two `targets` and `ps2` (returned by `extract`),
/// while also requiring `ps1[..n] ~ ps2[..n]` (pre) and `ps1[n + 1..] ~ ps2[n + 1..]` (post),
/// where `~` denotes semantic equality.
fn extend_with_matching_product(
targets: &mut [P<Pat>],
start: usize,
alternatives: &mut Vec<P<Pat>>,
predicate: impl Fn(&PatKind, &[P<Pat>], usize) -> bool,
extract: impl Fn(PatKind) -> Vec<P<Pat>>,
) -> bool {
(0..targets.len()).any(|idx| {
let tail_or = drain_matching(
start,
alternatives,
|k| predicate(k, targets, idx),
|k| extract(k).swap_remove(idx),
);
extend_with_tail_or(&mut targets[idx], tail_or)
})
}
/// Extract the pattern from the given one and replace it with `Wild`.
/// This is meant for temporarily swapping out the pattern for manipulation.
fn take_pat(from: &mut Pat) -> Pat {
let dummy = Pat {
id: DUMMY_NODE_ID,
kind: Wild,
span: DUMMY_SP,
tokens: None,
};
mem::replace(from, dummy)
}
/// Extend `target` as an or-pattern with the alternatives
/// in `tail_or` if there are any and return if there were.
fn extend_with_tail_or(target: &mut Pat, tail_or: Vec<P<Pat>>) -> bool {
fn extend(target: &mut Pat, mut tail_or: Vec<P<Pat>>) {
match target {
// On an existing or-pattern in the target, append to it.
Pat { kind: Or(ps), .. } => ps.append(&mut tail_or),
// Otherwise convert the target to an or-pattern.
target => {
let mut init_or = vec![P(take_pat(target))];
init_or.append(&mut tail_or);
target.kind = Or(init_or);
},
}
}
let changed = !tail_or.is_empty();
if changed {
// Extend the target.
extend(target, tail_or);
}
changed
}
// Extract all inner patterns in `alternatives` matching our `predicate`.
// Only elements beginning with `start` are considered for extraction.
fn drain_matching(
start: usize,
alternatives: &mut Vec<P<Pat>>,
predicate: impl Fn(&PatKind) -> bool,
extract: impl Fn(PatKind) -> P<Pat>,
) -> Vec<P<Pat>> {
let mut tail_or = vec![];
let mut idx = 0;
for pat in alternatives.drain_filter(|p| {
// Check if we should extract, but only if `idx >= start`.
idx += 1;
idx > start && predicate(&p.kind)
}) {
tail_or.push(extract(pat.into_inner().kind));
}
tail_or
}
fn extend_with_matching(
target: &mut Pat,
start: usize,
alternatives: &mut Vec<P<Pat>>,
predicate: impl Fn(&PatKind) -> bool,
extract: impl Fn(PatKind) -> P<Pat>,
) -> bool {
extend_with_tail_or(target, drain_matching(start, alternatives, predicate, extract))
}
/// Are the patterns in `ps1` and `ps2` equal save for `ps1[idx]` compared to `ps2[idx]`?
fn eq_pre_post(ps1: &[P<Pat>], ps2: &[P<Pat>], idx: usize) -> bool {
ps1.len() == ps2.len()
&& ps1[idx].is_rest() == ps2[idx].is_rest() // Avoid `[x, ..] | [x, 0]` => `[x, .. | 0]`.
&& over(&ps1[..idx], &ps2[..idx], |l, r| eq_pat(l, r))
&& over(&ps1[idx + 1..], &ps2[idx + 1..], |l, r| eq_pat(l, r))
}