rust/clippy_lints/src/copies.rs

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use rustc::lint::*;
use rustc::ty::Ty;
use rustc::hir::*;
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use std::collections::HashMap;
use std::collections::hash_map::Entry;
use syntax::symbol::LocalInternedString;
use syntax::util::small_vector::SmallVector;
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use utils::{SpanlessEq, SpanlessHash};
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use utils::{get_parent_expr, in_macro, snippet, span_lint_and_then, span_note_and_lint};
/// **What it does:** Checks for consecutive `if`s with the same condition.
///
/// **Why is this bad?** This is probably a copy & paste error.
///
/// **Known problems:** Hopefully none.
///
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/// **Example:**
/// ```rust
/// if a == b {
/// …
/// } else if a == b {
/// …
/// }
/// ```
///
/// Note that this lint ignores all conditions with a function call as it could
/// have side effects:
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///
/// ```rust
/// if foo() {
/// …
/// } else if foo() { // not linted
/// …
/// }
/// ```
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declare_clippy_lint! {
pub IFS_SAME_COND,
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correctness,
"consecutive `ifs` with the same condition"
}
/// **What it does:** Checks for `if/else` with the same body as the *then* part
/// and the *else* part.
///
/// **Why is this bad?** This is probably a copy & paste error.
///
/// **Known problems:** Hopefully none.
///
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/// **Example:**
/// ```rust
/// let foo = if … {
/// 42
/// } else {
/// 42
/// };
/// ```
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declare_clippy_lint! {
pub IF_SAME_THEN_ELSE,
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correctness,
"if with the same *then* and *else* blocks"
}
/// **What it does:** Checks for `match` with identical arm bodies.
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///
/// **Why is this bad?** This is probably a copy & paste error. If arm bodies
/// are the same on purpose, you can factor them
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/// [using `|`](https://doc.rust-lang.org/book/patterns.html#multiple-patterns).
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///
/// **Known problems:** False positive possible with order dependent `match`
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/// (see issue
/// [#860](https://github.com/rust-lang-nursery/rust-clippy/issues/860)).
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///
/// **Example:**
/// ```rust,ignore
/// match foo {
/// Bar => bar(),
/// Quz => quz(),
/// Baz => bar(), // <= oops
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/// }
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/// ```
///
/// This should probably be
/// ```rust,ignore
/// match foo {
/// Bar => bar(),
/// Quz => quz(),
/// Baz => baz(), // <= fixed
/// }
/// ```
///
/// or if the original code was not a typo:
/// ```rust,ignore
/// match foo {
/// Bar | Baz => bar(), // <= shows the intent better
/// Quz => quz(),
/// }
/// ```
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declare_clippy_lint! {
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pub MATCH_SAME_ARMS,
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pedantic,
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"`match` with identical arm bodies"
}
#[derive(Copy, Clone, Debug)]
pub struct CopyAndPaste;
impl LintPass for CopyAndPaste {
fn get_lints(&self) -> LintArray {
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lint_array![IFS_SAME_COND, IF_SAME_THEN_ELSE, MATCH_SAME_ARMS]
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CopyAndPaste {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if !in_macro(expr.span) {
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// skip ifs directly in else, it will be checked in the parent if
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if let Some(&Expr {
node: ExprIf(_, _, Some(ref else_expr)),
..
}) = get_parent_expr(cx, expr)
{
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if else_expr.id == expr.id {
return;
}
}
let (conds, blocks) = if_sequence(expr);
lint_same_then_else(cx, &blocks);
lint_same_cond(cx, &conds);
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lint_match_arms(cx, expr);
}
}
}
/// Implementation of `IF_SAME_THEN_ELSE`.
fn lint_same_then_else(cx: &LateContext, blocks: &[&Block]) {
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let eq: &Fn(&&Block, &&Block) -> bool = &|&lhs, &rhs| -> bool { SpanlessEq::new(cx).eq_block(lhs, rhs) };
if let Some((i, j)) = search_same_sequenced(blocks, eq) {
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span_note_and_lint(
cx,
IF_SAME_THEN_ELSE,
j.span,
"this `if` has identical blocks",
i.span,
"same as this",
);
}
}
/// Implementation of `IFS_SAME_COND`.
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fn lint_same_cond(cx: &LateContext, conds: &[&Expr]) {
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let hash: &Fn(&&Expr) -> u64 = &|expr| -> u64 {
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let mut h = SpanlessHash::new(cx, cx.tables);
h.hash_expr(expr);
h.finish()
};
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let eq: &Fn(&&Expr, &&Expr) -> bool = &|&lhs, &rhs| -> bool { SpanlessEq::new(cx).ignore_fn().eq_expr(lhs, rhs) };
if let Some((i, j)) = search_same(conds, hash, eq) {
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span_note_and_lint(
cx,
IFS_SAME_COND,
j.span,
"this `if` has the same condition as a previous if",
i.span,
"same as this",
);
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}
}
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/// Implementation of `MATCH_SAME_ARMS`.
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fn lint_match_arms(cx: &LateContext, expr: &Expr) {
if let ExprMatch(_, ref arms, MatchSource::Normal) = expr.node {
let hash = |&(_, arm): &(usize, &Arm)| -> u64 {
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let mut h = SpanlessHash::new(cx, cx.tables);
h.hash_expr(&arm.body);
h.finish()
};
let eq = |&(lindex, lhs): &(usize, &Arm), &(rindex, rhs): &(usize, &Arm)| -> bool {
let min_index = usize::min(lindex, rindex);
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let max_index = usize::max(lindex, rindex);
// Arms with a guard are ignored, those cant always be merged together
// This is also the case for arms in-between each there is an arm with a guard
(min_index..=max_index).all(|index| arms[index].guard.is_none()) &&
SpanlessEq::new(cx).eq_expr(&lhs.body, &rhs.body) &&
// all patterns should have the same bindings
bindings(cx, &lhs.pats[0]) == bindings(cx, &rhs.pats[0])
};
let indexed_arms: Vec<(usize, &Arm)> = arms.iter().enumerate().collect();
if let Some((&(_, i), &(_, j))) = search_same(&indexed_arms, hash, eq) {
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span_lint_and_then(
cx,
MATCH_SAME_ARMS,
j.body.span,
"this `match` has identical arm bodies",
|db| {
db.span_note(i.body.span, "same as this");
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// Note: this does not use `span_suggestion` on purpose: there is no clean way
// to remove the other arm. Building a span and suggest to replace it to ""
// makes an even more confusing error message. Also in order not to make up a
// span for the whole pattern, the suggestion is only shown when there is only
// one pattern. The user should know about `|` if they are already using it…
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if i.pats.len() == 1 && j.pats.len() == 1 {
let lhs = snippet(cx, i.pats[0].span, "<pat1>");
let rhs = snippet(cx, j.pats[0].span, "<pat2>");
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if let PatKind::Wild = j.pats[0].node {
// if the last arm is _, then i could be integrated into _
// note that i.pats[0] cannot be _, because that would mean that we're
// hiding all the subsequent arms, and rust won't compile
db.span_note(
i.body.span,
&format!("`{}` has the same arm body as the `_` wildcard, consider removing it`", lhs),
);
} else {
db.span_note(i.body.span, &format!("consider refactoring into `{} | {}`", lhs, rhs));
}
}
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},
);
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}
}
}
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/// Return the list of condition expressions and the list of blocks in a
/// sequence of `if/else`.
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/// Eg. would return `([a, b], [c, d, e])` for the expression
/// `if a { c } else if b { d } else { e }`.
fn if_sequence(mut expr: &Expr) -> (SmallVector<&Expr>, SmallVector<&Block>) {
let mut conds = SmallVector::new();
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let mut blocks: SmallVector<&Block> = SmallVector::new();
while let ExprIf(ref cond, ref then_expr, ref else_expr) = expr.node {
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conds.push(&**cond);
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if let ExprBlock(ref block, _) = then_expr.node {
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blocks.push(block);
} else {
panic!("ExprIf node is not an ExprBlock");
}
if let Some(ref else_expr) = *else_expr {
expr = else_expr;
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} else {
break;
}
}
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// final `else {..}`
if !blocks.is_empty() {
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if let ExprBlock(ref block, _) = expr.node {
blocks.push(&**block);
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}
}
(conds, blocks)
}
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/// Return the list of bindings in a pattern.
fn bindings<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, pat: &Pat) -> HashMap<LocalInternedString, Ty<'tcx>> {
fn bindings_impl<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, pat: &Pat, map: &mut HashMap<LocalInternedString, Ty<'tcx>>) {
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match pat.node {
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PatKind::Box(ref pat) | PatKind::Ref(ref pat, _) => bindings_impl(cx, pat, map),
PatKind::TupleStruct(_, ref pats, _) => for pat in pats {
bindings_impl(cx, pat, map);
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},
PatKind::Binding(_, _, ref ident, ref as_pat) => {
if let Entry::Vacant(v) = map.entry(ident.node.as_str()) {
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v.insert(cx.tables.pat_ty(pat));
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}
if let Some(ref as_pat) = *as_pat {
bindings_impl(cx, as_pat, map);
}
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},
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PatKind::Struct(_, ref fields, _) => for pat in fields {
bindings_impl(cx, &pat.node.pat, map);
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},
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PatKind::Tuple(ref fields, _) => for pat in fields {
bindings_impl(cx, pat, map);
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},
PatKind::Slice(ref lhs, ref mid, ref rhs) => {
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for pat in lhs {
bindings_impl(cx, pat, map);
}
if let Some(ref mid) = *mid {
bindings_impl(cx, mid, map);
}
for pat in rhs {
bindings_impl(cx, pat, map);
}
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},
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PatKind::Lit(..) | PatKind::Range(..) | PatKind::Wild | PatKind::Path(..) => (),
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}
}
let mut result = HashMap::new();
bindings_impl(cx, pat, &mut result);
result
}
fn search_same_sequenced<T, Eq>(exprs: &[T], eq: Eq) -> Option<(&T, &T)>
where
Eq: Fn(&T, &T) -> bool,
{
for win in exprs.windows(2) {
if eq(&win[0], &win[1]) {
return Some((&win[0], &win[1]));
}
}
None
}
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fn search_same<T, Hash, Eq>(exprs: &[T], hash: Hash, eq: Eq) -> Option<(&T, &T)>
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where
Hash: Fn(&T) -> u64,
Eq: Fn(&T, &T) -> bool,
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{
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// common cases
if exprs.len() < 2 {
return None;
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} else if exprs.len() == 2 {
return if eq(&exprs[0], &exprs[1]) {
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Some((&exprs[0], &exprs[1]))
} else {
None
};
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}
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let mut map: HashMap<_, Vec<&_>> = HashMap::with_capacity(exprs.len());
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for expr in exprs {
match map.entry(hash(expr)) {
Entry::Occupied(mut o) => {
for o in o.get() {
if eq(o, expr) {
return Some((o, expr));
}
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}
o.get_mut().push(expr);
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},
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Entry::Vacant(v) => {
v.insert(vec![expr]);
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},
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}
}
None
}