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