rust-clippy/clippy_lints/src/matches.rs

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2018-10-06 16:18:06 +00:00
// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
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use crate::consts::{constant, Constant};
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use crate::utils::paths;
use crate::utils::sugg::Sugg;
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use crate::utils::{
expr_block, in_macro, is_allowed, is_expn_of, match_qpath, match_type, multispan_sugg, remove_blocks, snippet,
snippet_with_applicability, span_lint_and_sugg, span_lint_and_then, span_note_and_lint, walk_ptrs_ty,
};
use if_chain::if_chain;
use rustc::hir::*;
use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
use rustc::ty::{self, Ty};
use rustc::{declare_tool_lint, lint_array};
use rustc_errors::Applicability;
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use std::cmp::Ordering;
use std::collections::Bound;
use syntax::ast::LitKind;
use syntax::source_map::Span;
/// **What it does:** Checks for matches with a single arm where an `if let`
/// will usually suffice.
///
/// **Why is this bad?** Just readability `if let` nests less than a `match`.
///
/// **Known problems:** None.
///
/// **Example:**
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/// ```rust
/// match x {
/// Some(ref foo) => bar(foo),
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/// _ => (),
/// }
/// ```
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declare_clippy_lint! {
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pub SINGLE_MATCH,
style,
"a match statement with a single nontrivial arm (i.e. where the other arm is `_ => {}`) instead of `if let`"
}
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/// **What it does:** Checks for matches with a two arms where an `if let else` will
/// usually suffice.
///
/// **Why is this bad?** Just readability `if let` nests less than a `match`.
///
/// **Known problems:** Personal style preferences may differ.
///
/// **Example:**
///
/// Using `match`:
///
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/// ```rust
/// match x {
/// Some(ref foo) => bar(foo),
/// _ => bar(other_ref),
/// }
/// ```
///
/// Using `if let` with `else`:
///
/// ```rust
/// if let Some(ref foo) = x {
/// bar(foo);
/// } else {
/// bar(other_ref);
/// }
/// ```
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declare_clippy_lint! {
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pub SINGLE_MATCH_ELSE,
pedantic,
"a match statement with a two arms where the second arm's pattern is a placeholder instead of a specific match pattern"
}
/// **What it does:** Checks for matches where all arms match a reference,
/// suggesting to remove the reference and deref the matched expression
/// instead. It also checks for `if let &foo = bar` blocks.
///
/// **Why is this bad?** It just makes the code less readable. That reference
/// destructuring adds nothing to the code.
///
/// **Known problems:** None.
///
/// **Example:**
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/// ```rust
/// match x {
/// &A(ref y) => foo(y),
/// &B => bar(),
/// _ => frob(&x),
/// }
/// ```
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declare_clippy_lint! {
pub MATCH_REF_PATS,
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style,
"a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression"
}
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/// **What it does:** Checks for matches where match expression is a `bool`. It
/// suggests to replace the expression with an `if...else` block.
///
/// **Why is this bad?** It makes the code less readable.
///
/// **Known problems:** None.
///
/// **Example:**
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/// ```rust
/// let condition: bool = true;
/// match condition {
/// true => foo(),
/// false => bar(),
/// }
/// ```
/// Use if/else instead:
/// ```rust
/// let condition: bool = true;
/// if condition {
/// foo();
/// } else {
/// bar();
/// }
/// ```
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declare_clippy_lint! {
pub MATCH_BOOL,
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style,
"a match on a boolean expression instead of an `if..else` block"
}
/// **What it does:** Checks for overlapping match arms.
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///
/// **Why is this bad?** It is likely to be an error and if not, makes the code
/// less obvious.
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///
/// **Known problems:** None.
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///
/// **Example:**
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/// ```rust
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/// let x = 5;
/// match x {
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/// 1...10 => println!("1 ... 10"),
/// 5...15 => println!("5 ... 15"),
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/// _ => (),
/// }
/// ```
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declare_clippy_lint! {
pub MATCH_OVERLAPPING_ARM,
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style,
"a match with overlapping arms"
}
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/// **What it does:** Checks for arm which matches all errors with `Err(_)`
/// and take drastic actions like `panic!`.
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///
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/// **Why is this bad?** It is generally a bad practice, just like
/// catching all exceptions in java with `catch(Exception)`
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///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
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/// let x: Result(i32, &str) = Ok(3);
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/// match x {
/// Ok(_) => println!("ok"),
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/// Err(_) => panic!("err"),
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/// }
/// ```
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declare_clippy_lint! {
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pub MATCH_WILD_ERR_ARM,
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style,
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"a match with `Err(_)` arm and take drastic actions"
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}
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/// **What it does:** Checks for match which is used to add a reference to an
/// `Option` value.
///
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/// **Why is this bad?** Using `as_ref()` or `as_mut()` instead is shorter.
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///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// let x: Option<()> = None;
/// let r: Option<&()> = match x {
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/// None => None,
/// Some(ref v) => Some(v),
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/// };
/// ```
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declare_clippy_lint! {
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pub MATCH_AS_REF,
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complexity,
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"a match on an Option value instead of using `as_ref()` or `as_mut`"
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}
#[allow(missing_copy_implementations)]
pub struct MatchPass;
impl LintPass for MatchPass {
fn get_lints(&self) -> LintArray {
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lint_array!(
SINGLE_MATCH,
MATCH_REF_PATS,
MATCH_BOOL,
SINGLE_MATCH_ELSE,
MATCH_OVERLAPPING_ARM,
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MATCH_WILD_ERR_ARM,
MATCH_AS_REF
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)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchPass {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if in_external_macro(cx.sess(), expr.span) {
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return;
}
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if let ExprKind::Match(ref ex, ref arms, MatchSource::Normal) = expr.node {
check_single_match(cx, ex, arms, expr);
check_match_bool(cx, ex, arms, expr);
check_overlapping_arms(cx, ex, arms);
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check_wild_err_arm(cx, ex, arms);
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check_match_as_ref(cx, ex, arms, expr);
}
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if let ExprKind::Match(ref ex, ref arms, _) = expr.node {
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check_match_ref_pats(cx, ex, arms, expr);
}
}
}
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#[rustfmt::skip]
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fn check_single_match(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
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if arms.len() == 2 &&
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arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
arms[1].pats.len() == 1 && arms[1].guard.is_none() {
let els = remove_blocks(&arms[1].body);
let els = if is_unit_expr(els) {
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None
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} else if let ExprKind::Block(_, _) = els.node {
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// matches with blocks that contain statements are prettier as `if let + else`
Some(els)
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} else {
// allow match arms with just expressions
return;
};
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let ty = cx.tables.expr_ty(ex);
if ty.sty != ty::Bool || is_allowed(cx, MATCH_BOOL, ex.id) {
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check_single_match_single_pattern(cx, ex, arms, expr, els);
check_single_match_opt_like(cx, ex, arms, expr, ty, els);
}
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}
}
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fn check_single_match_single_pattern(
cx: &LateContext<'_, '_>,
ex: &Expr,
arms: &[Arm],
expr: &Expr,
els: Option<&Expr>,
) {
if is_wild(&arms[1].pats[0]) {
report_single_match_single_pattern(cx, ex, arms, expr, els);
}
}
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fn report_single_match_single_pattern(
cx: &LateContext<'_, '_>,
ex: &Expr,
arms: &[Arm],
expr: &Expr,
els: Option<&Expr>,
) {
let lint = if els.is_some() { SINGLE_MATCH_ELSE } else { SINGLE_MATCH };
let els_str = els.map_or(String::new(), |els| {
format!(" else {}", expr_block(cx, els, None, ".."))
});
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span_lint_and_sugg(
cx,
lint,
expr.span,
"you seem to be trying to use match for destructuring a single pattern. Consider using `if \
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let`",
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"try this",
format!(
"if let {} = {} {}{}",
snippet(cx, arms[0].pats[0].span, ".."),
snippet(cx, ex.span, ".."),
expr_block(cx, &arms[0].body, None, ".."),
els_str,
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),
Applicability::HasPlaceholders,
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);
}
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fn check_single_match_opt_like(
cx: &LateContext<'_, '_>,
ex: &Expr,
arms: &[Arm],
expr: &Expr,
ty: Ty<'_>,
els: Option<&Expr>,
) {
// list of candidate Enums we know will never get any more members
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let candidates = &[
(&paths::COW, "Borrowed"),
(&paths::COW, "Cow::Borrowed"),
(&paths::COW, "Cow::Owned"),
(&paths::COW, "Owned"),
(&paths::OPTION, "None"),
(&paths::RESULT, "Err"),
(&paths::RESULT, "Ok"),
];
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let path = match arms[1].pats[0].node {
PatKind::TupleStruct(ref path, ref inner, _) => {
// contains any non wildcard patterns? e.g. Err(err)
if !inner.iter().all(is_wild) {
return;
}
print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
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},
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PatKind::Binding(BindingAnnotation::Unannotated, _, ident, None) => ident.to_string(),
PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
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_ => return,
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};
for &(ty_path, pat_path) in candidates {
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if path == *pat_path && match_type(cx, ty, ty_path) {
report_single_match_single_pattern(cx, ex, arms, expr, els);
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}
}
}
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fn check_match_bool(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
// type of expression == bool
if cx.tables.expr_ty(ex).sty == ty::Bool {
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span_lint_and_then(
cx,
MATCH_BOOL,
expr.span,
"you seem to be trying to match on a boolean expression",
move |db| {
if arms.len() == 2 && arms[0].pats.len() == 1 {
// no guards
let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node {
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if let ExprKind::Lit(ref lit) = arm_bool.node {
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match lit.node {
LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
_ => None,
}
} else {
None
}
} else {
None
};
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if let Some((true_expr, false_expr)) = exprs {
let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
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(false, false) => Some(format!(
"if {} {} else {}",
snippet(cx, ex.span, "b"),
expr_block(cx, true_expr, None, ".."),
expr_block(cx, false_expr, None, "..")
)),
(false, true) => Some(format!(
"if {} {}",
snippet(cx, ex.span, "b"),
expr_block(cx, true_expr, None, "..")
)),
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(true, false) => {
let test = Sugg::hir(cx, ex, "..");
Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
},
(true, true) => None,
};
if let Some(sugg) = sugg {
db.span_suggestion_with_applicability(
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expr.span,
"consider using an if/else expression",
sugg,
Applicability::HasPlaceholders,
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);
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}
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}
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}
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},
);
}
}
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fn check_overlapping_arms<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ex: &'tcx Expr, arms: &'tcx [Arm]) {
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if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
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let ranges = all_ranges(cx, arms);
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let type_ranges = type_ranges(&ranges);
if !type_ranges.is_empty() {
if let Some((start, end)) = overlapping(&type_ranges) {
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span_note_and_lint(
cx,
MATCH_OVERLAPPING_ARM,
start.span,
"some ranges overlap",
end.span,
"overlaps with this",
);
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}
}
}
}
fn is_wild(pat: &impl std::ops::Deref<Target = Pat>) -> bool {
match pat.node {
PatKind::Wild => true,
_ => false,
}
}
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fn check_wild_err_arm(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm]) {
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let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
if match_type(cx, ex_ty, &paths::RESULT) {
for arm in arms {
if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pats[0].node {
let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false));
if_chain! {
if path_str == "Err";
if inner.iter().any(is_wild);
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if let ExprKind::Block(ref block, _) = arm.body.node;
if is_panic_block(block);
then {
// `Err(_)` arm with `panic!` found
span_note_and_lint(cx,
MATCH_WILD_ERR_ARM,
arm.pats[0].span,
"Err(_) will match all errors, maybe not a good idea",
arm.pats[0].span,
"to remove this warning, match each error separately \
or use unreachable macro");
}
}
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}
}
}
}
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// If the block contains only a `panic!` macro (as expression or statement)
fn is_panic_block(block: &Block) -> bool {
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match (&block.expr, block.stmts.len(), block.stmts.first()) {
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(&Some(ref exp), 0, _) => {
is_expn_of(exp.span, "panic").is_some() && is_expn_of(exp.span, "unreachable").is_none()
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},
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(&None, 1, Some(stmt)) => {
is_expn_of(stmt.span, "panic").is_some() && is_expn_of(stmt.span, "unreachable").is_none()
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},
_ => false,
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}
}
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fn check_match_ref_pats(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
if has_only_ref_pats(arms) {
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let mut suggs = Vec::new();
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let (title, msg) = if let ExprKind::AddrOf(Mutability::MutImmutable, ref inner) = ex.node {
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suggs.push((ex.span, Sugg::hir(cx, inner, "..").to_string()));
(
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"you don't need to add `&` to both the expression and the patterns",
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"try",
)
} else {
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suggs.push((ex.span, Sugg::hir(cx, ex, "..").deref().to_string()));
(
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"you don't need to add `&` to all patterns",
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"instead of prefixing all patterns with `&`, you can dereference the expression",
)
};
suggs.extend(arms.iter().flat_map(|a| &a.pats).filter_map(|p| {
if let PatKind::Ref(ref refp, _) = p.node {
Some((p.span, snippet(cx, refp.span, "..").to_string()))
} else {
None
}
}));
span_lint_and_then(cx, MATCH_REF_PATS, expr.span, title, |db| {
if !in_macro(expr.span) {
multispan_sugg(db, msg.to_owned(), suggs);
}
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});
}
}
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fn check_match_as_ref(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
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if arms.len() == 2
&& arms[0].pats.len() == 1
&& arms[0].guard.is_none()
&& arms[1].pats.len() == 1
&& arms[1].guard.is_none()
{
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let arm_ref: Option<BindingAnnotation> = if is_none_arm(&arms[0]) {
is_ref_some_arm(&arms[1])
} else if is_none_arm(&arms[1]) {
is_ref_some_arm(&arms[0])
} else {
None
};
if let Some(rb) = arm_ref {
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let suggestion = if rb == BindingAnnotation::Ref {
"as_ref"
} else {
"as_mut"
};
let mut applicability = Applicability::MachineApplicable;
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span_lint_and_sugg(
cx,
MATCH_AS_REF,
expr.span,
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&format!("use {}() instead", suggestion),
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"try this",
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format!(
"{}.{}()",
snippet_with_applicability(cx, ex.span, "_", &mut applicability),
suggestion
),
applicability,
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)
}
}
}
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/// Get all arms that are unbounded `PatRange`s.
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fn all_ranges<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arms: &'tcx [Arm]) -> Vec<SpannedRange<Constant>> {
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arms.iter()
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.flat_map(|arm| {
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if let Arm {
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ref pats, guard: None, ..
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} = *arm
{
pats.iter()
} else {
[].iter()
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}
.filter_map(|pat| {
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if let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node {
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let lhs = constant(cx, cx.tables, lhs)?.0;
let rhs = constant(cx, cx.tables, rhs)?.0;
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let rhs = match *range_end {
RangeEnd::Included => Bound::Included(rhs),
RangeEnd::Excluded => Bound::Excluded(rhs),
};
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return Some(SpannedRange {
span: pat.span,
node: (lhs, rhs),
});
}
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if let PatKind::Lit(ref value) = pat.node {
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let value = constant(cx, cx.tables, value)?.0;
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return Some(SpannedRange {
span: pat.span,
node: (value.clone(), Bound::Included(value)),
});
}
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None
})
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})
.collect()
}
#[derive(Debug, Eq, PartialEq)]
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pub struct SpannedRange<T> {
pub span: Span,
pub node: (T, Bound<T>),
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}
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type TypedRanges = Vec<SpannedRange<u128>>;
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/// Get all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway
/// and other types than
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/// `Uint` and `Int` probably don't make sense.
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fn type_ranges(ranges: &[SpannedRange<Constant>]) -> TypedRanges {
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ranges
.iter()
.filter_map(|range| match range.node {
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(Constant::Int(start), Bound::Included(Constant::Int(end))) => Some(SpannedRange {
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span: range.span,
node: (start, Bound::Included(end)),
}),
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(Constant::Int(start), Bound::Excluded(Constant::Int(end))) => Some(SpannedRange {
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span: range.span,
node: (start, Bound::Excluded(end)),
}),
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(Constant::Int(start), Bound::Unbounded) => Some(SpannedRange {
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span: range.span,
node: (start, Bound::Unbounded),
}),
_ => None,
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})
.collect()
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}
fn is_unit_expr(expr: &Expr) -> bool {
match expr.node {
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ExprKind::Tup(ref v) if v.is_empty() => true,
ExprKind::Block(ref b, _) if b.stmts.is_empty() && b.expr.is_none() => true,
_ => false,
}
}
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// Checks if arm has the form `None => None`
fn is_none_arm(arm: &Arm) -> bool {
match arm.pats[0].node {
PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => true,
_ => false,
}
}
// Checks if arm has the form `Some(ref v) => Some(v)` (checks for `ref` and `ref mut`)
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fn is_ref_some_arm(arm: &Arm) -> Option<BindingAnnotation> {
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if_chain! {
if let PatKind::TupleStruct(ref path, ref pats, _) = arm.pats[0].node;
if pats.len() == 1 && match_qpath(path, &paths::OPTION_SOME);
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if let PatKind::Binding(rb, _, ident, _) = pats[0].node;
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if rb == BindingAnnotation::Ref || rb == BindingAnnotation::RefMut;
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if let ExprKind::Call(ref e, ref args) = remove_blocks(&arm.body).node;
if let ExprKind::Path(ref some_path) = e.node;
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if match_qpath(some_path, &paths::OPTION_SOME) && args.len() == 1;
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if let ExprKind::Path(ref qpath) = args[0].node;
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if let &QPath::Resolved(_, ref path2) = qpath;
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if path2.segments.len() == 1 && ident.name == path2.segments[0].ident.name;
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then {
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return Some(rb)
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}
}
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None
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}
fn has_only_ref_pats(arms: &[Arm]) -> bool {
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let mapped = arms
.iter()
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.flat_map(|a| &a.pats)
.map(|p| {
match p.node {
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PatKind::Ref(..) => Some(true), // &-patterns
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PatKind::Wild => Some(false), // an "anything" wildcard is also fine
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_ => None, // any other pattern is not fine
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}
})
.collect::<Option<Vec<bool>>>();
// look for Some(v) where there's at least one true element
mapped.map_or(false, |v| v.iter().any(|el| *el))
}
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pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
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where
T: Copy + Ord,
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{
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#[derive(Copy, Clone, Debug, Eq, PartialEq)]
enum Kind<'a, T: 'a> {
Start(T, &'a SpannedRange<T>),
End(Bound<T>, &'a SpannedRange<T>),
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}
impl<'a, T: Copy> Kind<'a, T> {
fn range(&self) -> &'a SpannedRange<T> {
match *self {
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Kind::Start(_, r) | Kind::End(_, r) => r,
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}
}
fn value(self) -> Bound<T> {
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match self {
Kind::Start(t, _) => Bound::Included(t),
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Kind::End(t, _) => t,
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}
}
}
impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
Some(self.cmp(other))
}
}
impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
fn cmp(&self, other: &Self) -> Ordering {
match (self.value(), other.value()) {
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(Bound::Included(a), Bound::Included(b)) | (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
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// Range patterns cannot be unbounded (yet)
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(Bound::Unbounded, _) | (_, Bound::Unbounded) => unimplemented!(),
(Bound::Included(a), Bound::Excluded(b)) => match a.cmp(&b) {
Ordering::Equal => Ordering::Greater,
other => other,
},
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(Bound::Excluded(a), Bound::Included(b)) => match a.cmp(&b) {
Ordering::Equal => Ordering::Less,
other => other,
},
}
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}
}
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let mut values = Vec::with_capacity(2 * ranges.len());
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for r in ranges {
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values.push(Kind::Start(r.node.0, r));
values.push(Kind::End(r.node.1, r));
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}
values.sort();
for (a, b) in values.iter().zip(values.iter().skip(1)) {
match (a, b) {
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(&Kind::Start(_, ra), &Kind::End(_, rb)) => {
if ra.node != rb.node {
return Some((ra, rb));
}
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},
(&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
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_ => return Some((a.range(), b.range())),
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}
}
None
}