2017-06-26 12:42:24 +00:00
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//! Checks for useless borrowed references.
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2017-06-24 10:04:56 +00:00
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//!
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//! This lint is **warn** by default
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use rustc::lint::*;
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2017-07-01 10:01:39 +00:00
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<<<<<<< HEAD
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2017-08-01 07:11:05 +00:00
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use rustc::hir::{MutImmutable, Pat, PatKind, BindingAnnotation};
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2017-07-01 10:01:39 +00:00
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=======
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use rustc::hir::{MutImmutable, Pat, PatKind};
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2017-07-01 14:56:19 +00:00
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<<<<<<< HEAD
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2017-07-01 10:01:39 +00:00
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>>>>>>> e30bf721... Improve needless_borrowed_ref and add suggestion to it.
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2017-06-24 10:04:56 +00:00
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use rustc::ty;
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2017-07-01 14:56:19 +00:00
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=======
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>>>>>>> 4ae45c87... Improve needless_borrowed_ref lint: remove the hand rolled span part.
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2017-07-01 10:01:39 +00:00
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use utils::{span_lint_and_then, in_macro, snippet};
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2017-07-01 14:56:19 +00:00
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use rustc::hir::BindingMode::BindByRef;
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2017-06-24 10:04:56 +00:00
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2017-06-26 12:42:24 +00:00
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/// **What it does:** Checks for useless borrowed references.
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2017-06-24 10:04:56 +00:00
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///
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2017-08-09 07:30:56 +00:00
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/// **Why is this bad?** It is completely useless and make the code look more
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/// complex than it
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2017-06-29 14:07:43 +00:00
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/// actually is.
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2017-06-24 10:04:56 +00:00
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// let mut v = Vec::<String>::new();
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/// let _ = v.iter_mut().filter(|&ref a| a.is_empty());
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/// ```
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2017-08-09 07:30:56 +00:00
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/// This clojure takes a reference on something that has been matched as a
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/// reference and
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2017-06-29 14:07:43 +00:00
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/// de-referenced.
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2017-06-26 12:42:24 +00:00
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/// As such, it could just be |a| a.is_empty()
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2017-06-24 10:04:56 +00:00
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declare_lint! {
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pub NEEDLESS_BORROWED_REFERENCE,
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Warn,
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"taking a needless borrowed reference"
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}
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#[derive(Copy, Clone)]
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pub struct NeedlessBorrowedRef;
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impl LintPass for NeedlessBorrowedRef {
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fn get_lints(&self) -> LintArray {
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lint_array!(NEEDLESS_BORROWED_REFERENCE)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBorrowedRef {
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fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
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if in_macro(pat.span) {
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// OK, simple enough, lints doesn't check in macro.
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return;
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}
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if_let_chain! {[
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// Pat is a pattern whose node
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2017-06-29 11:45:54 +00:00
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// is a binding which "involves" an immutable reference...
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2017-08-01 07:11:05 +00:00
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let PatKind::Binding(BindingAnnotation::Ref, ..) = pat.node,
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2017-06-24 10:04:56 +00:00
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// Pattern's type is a reference. Get the type and mutability of referenced value (tam: TypeAndMut).
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let ty::TyRef(_, ref tam) = cx.tables.pat_ty(pat).sty,
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2017-06-29 11:45:54 +00:00
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// Only lint immutable refs, because `&mut ref T` may be useful.
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2017-07-01 10:01:39 +00:00
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let PatKind::Ref(ref sub_pat, MutImmutable) = pat.node,
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2017-07-01 14:56:19 +00:00
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// Check sub_pat got a `ref` keyword (excluding `ref mut`).
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let PatKind::Binding(BindByRef(MutImmutable), _, spanned_name, ..) = sub_pat.node,
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2017-06-24 10:04:56 +00:00
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], {
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2017-07-01 10:01:39 +00:00
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span_lint_and_then(cx, NEEDLESS_BORROWED_REFERENCE, pat.span,
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"this pattern takes a reference on something that is being de-referenced",
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|db| {
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2017-07-01 14:56:19 +00:00
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let hint = snippet(cx, spanned_name.span, "..").into_owned();
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2017-07-01 10:01:39 +00:00
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db.span_suggestion(pat.span, "try removing the `&ref` part and just keep", hint);
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});
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2017-06-24 10:04:56 +00:00
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}}
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}
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}
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