rust/clippy_lints/src/copies.rs

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use rustc::lint::*;
use rustc::ty;
use rustc::hir::*;
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use std::collections::HashMap;
use std::collections::hash_map::Entry;
use syntax::symbol::InternedString;
use syntax::util::small_vector::SmallVector;
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use utils::{SpanlessEq, SpanlessHash};
use utils::{get_parent_expr, in_macro, span_lint_and_then, span_note_and_lint, snippet};
/// **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
/// …
/// }
/// ```
declare_lint! {
pub IFS_SAME_COND,
Warn,
"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
/// };
/// ```
declare_lint! {
pub IF_SAME_THEN_ELSE,
Warn,
"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`
/// (see issue [#860](https://github.com/Manishearth/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_lint! {
pub MATCH_SAME_ARMS,
Warn,
"`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(cx, 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 hash: &Fn(&&Block) -> u64 = &|block| -> u64 {
let mut h = SpanlessHash::new(cx);
h.hash_block(block);
h.finish()
};
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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(blocks, hash, 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 {
let mut h = SpanlessHash::new(cx);
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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}
}
/// Implementation if `MATCH_SAME_ARMS`.
fn lint_match_arms(cx: &LateContext, expr: &Expr) {
let hash = |arm: &Arm| -> u64 {
let mut h = SpanlessHash::new(cx);
h.hash_expr(&arm.body);
h.finish()
};
let eq = |lhs: &Arm, rhs: &Arm| -> bool {
// Arms with a guard are ignored, those cant always be merged together
lhs.guard.is_none() && rhs.guard.is_none() &&
SpanlessEq::new(cx).eq_expr(&lhs.body, &rhs.body) &&
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// all patterns should have the same bindings
bindings(cx, &lhs.pats[0]) == bindings(cx, &rhs.pats[0])
};
if let ExprMatch(_, ref arms, MatchSource::Normal) = expr.node {
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if let Some((i, j)) = search_same(arms, hash, eq) {
span_lint_and_then(cx,
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MATCH_SAME_ARMS,
j.body.span,
"this `match` has identical arm bodies",
|db| {
db.span_note(i.body.span, "same as this");
// 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…
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>");
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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/// Return the list of condition expressions and the list of blocks in a sequence of `if/else`.
/// 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();
let mut blocks = SmallVector::new();
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while let ExprIf(ref cond, ref then_block, ref else_expr) = expr.node {
conds.push(&**cond);
blocks.push(&**then_block);
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() {
if let ExprBlock(ref block) = expr.node {
blocks.push(&**block);
}
}
(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<InternedString, ty::Ty<'tcx>> {
fn bindings_impl<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, pat: &Pat, map: &mut HashMap<InternedString, ty::Ty<'tcx>>) {
match pat.node {
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PatKind::Box(ref pat) |
PatKind::Ref(ref pat, _) => bindings_impl(cx, pat, map),
PatKind::TupleStruct(_, ref pats, _) => {
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for pat in pats {
bindings_impl(cx, pat, map);
}
}
PatKind::Binding(_, _, ref ident, ref as_pat) => {
if let Entry::Vacant(v) = map.entry(ident.node.as_str()) {
v.insert(cx.tcx.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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}
PatKind::Struct(_, ref fields, _) => {
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for pat in fields {
bindings_impl(cx, &pat.node.pat, map);
}
}
PatKind::Tuple(ref fields, _) => {
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for pat in fields {
bindings_impl(cx, pat, map);
}
}
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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PatKind::Lit(..) |
PatKind::Range(..) |
PatKind::Wild |
PatKind::Path(..) => (),
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}
}
let mut result = HashMap::new();
bindings_impl(cx, pat, &mut result);
result
}
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fn search_same<T, Hash, Eq>(exprs: &[T], hash: Hash, eq: Eq) -> Option<(&T, &T)>
where Hash: Fn(&T) -> u64,
Eq: Fn(&T, &T) -> bool
{
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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]))
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} else {
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None
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};
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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)) {
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Entry::Occupied(o) => {
for o in o.get() {
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if eq(o, expr) {
return Some((o, expr));
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}
}
}
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Entry::Vacant(v) => {
v.insert(vec![expr]);
}
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}
}
None
}