2 has_drop, in_macro, is_copy, match_def_path, match_type, paths, snippet_opt, span_lint_hir, span_lint_hir_and_then,
5 use if_chain::if_chain;
7 use rustc::hir::intravisit::FnKind;
8 use rustc::hir::{def_id, Body, FnDecl, HirId};
9 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
12 visit::{MutatingUseContext, PlaceContext, Visitor},
15 use rustc::ty::{self, Ty};
16 use rustc::{declare_tool_lint, lint_array};
17 use rustc_errors::Applicability;
18 use std::convert::TryFrom;
19 use syntax::source_map::{BytePos, Span};
21 macro_rules! unwrap_or_continue {
30 declare_clippy_lint! {
31 /// **What it does:** Checks for a redudant `clone()` (and its relatives) which clones an owned
32 /// value that is going to be dropped without further use.
34 /// **Why is this bad?** It is not always possible for the compiler to eliminate useless
35 /// allocations and deallocations generated by redundant `clone()`s.
37 /// **Known problems:**
39 /// * Suggestions made by this lint could require NLL to be enabled.
40 /// * False-positive if there is a borrow preventing the value from moving out.
43 /// let x = String::new();
47 /// foo(x.clone()); // This lint suggests to remove this `clone()`
53 /// let x = Foo::new();
55 /// call(x.clone()); // this can just pass `x`
58 /// ["lorem", "ipsum"].join(" ").to_string()
60 /// Path::new("/a/b").join("c").to_path_buf()
64 "`clone()` of an owned value that is going to be dropped immediately"
67 pub struct RedundantClone;
69 impl LintPass for RedundantClone {
70 fn get_lints(&self) -> LintArray {
71 lint_array!(REDUNDANT_CLONE)
74 fn name(&self) -> &'static str {
79 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantClone {
80 #[allow(clippy::too_many_lines)]
83 cx: &LateContext<'a, 'tcx>,
90 let def_id = cx.tcx.hir().body_owner_def_id(body.id());
91 let mir = cx.tcx.optimized_mir(def_id);
93 for (bb, bbdata) in mir.basic_blocks().iter_enumerated() {
94 let terminator = bbdata.terminator();
96 if in_macro(terminator.source_info.span) {
101 if terminator.successors().any(|s| *s == bb) {
105 let (fn_def_id, arg, arg_ty, _) = unwrap_or_continue!(is_call_with_ref_arg(cx, mir, &terminator.kind));
107 let from_borrow = match_def_path(cx.tcx, fn_def_id, &paths::CLONE_TRAIT_METHOD)
108 || match_def_path(cx.tcx, fn_def_id, &paths::TO_OWNED_METHOD)
109 || (match_def_path(cx.tcx, fn_def_id, &paths::TO_STRING_METHOD)
110 && match_type(cx, arg_ty, &paths::STRING));
112 let from_deref = !from_borrow
113 && (match_def_path(cx.tcx, fn_def_id, &paths::PATH_TO_PATH_BUF)
114 || match_def_path(cx.tcx, fn_def_id, &paths::OS_STR_TO_OS_STRING));
116 if !from_borrow && !from_deref {
120 // _1 in MIR `{ _2 = &_1; clone(move _2); }` or `{ _2 = _1; to_path_buf(_2); } (from_deref)
121 // In case of `from_deref`, `arg` is already a reference since it is `deref`ed in the previous
123 let (cloned, cannot_move_out) = unwrap_or_continue!(find_stmt_assigns_to(
128 bbdata.statements.iter()
131 if from_borrow && cannot_move_out {
135 // _1 in MIR `{ _2 = &_1; _3 = deref(move _2); } -> { _4 = _3; to_path_buf(move _4); }`
136 let referent = if from_deref {
137 let ps = mir.predecessors_for(bb);
141 let pred_terminator = mir[ps[0]].terminator();
143 let pred_arg = if_chain! {
144 if let Some((pred_fn_def_id, pred_arg, pred_arg_ty, Some(res))) =
145 is_call_with_ref_arg(cx, mir, &pred_terminator.kind);
146 if *res == mir::Place::Base(mir::PlaceBase::Local(cloned));
147 if match_def_path(cx.tcx, pred_fn_def_id, &paths::DEREF_TRAIT_METHOD);
148 if match_type(cx, pred_arg_ty, &paths::PATH_BUF)
149 || match_type(cx, pred_arg_ty, &paths::OS_STRING);
157 let (local, cannot_move_out) = unwrap_or_continue!(find_stmt_assigns_to(
162 mir[ps[0]].statements.iter()
172 let used_later = traversal::ReversePostorder::new(&mir, bb).skip(1).any(|(tbb, tdata)| {
174 if tdata.terminator().successors().any(|s| *s == bb) {
178 let mut vis = LocalUseVisitor {
180 used_other_than_drop: false,
182 vis.visit_basic_block_data(tbb, tdata);
183 vis.used_other_than_drop
187 let span = terminator.source_info.span;
188 let node = if let mir::ClearCrossCrate::Set(scope_local_data) = &mir.source_scope_local_data {
189 scope_local_data[terminator.source_info.scope].lint_root
195 if let Some(snip) = snippet_opt(cx, span);
196 if let Some(dot) = snip.rfind('.');
198 let sugg_span = span.with_lo(
199 span.lo() + BytePos(u32::try_from(dot).unwrap())
202 span_lint_hir_and_then(cx, REDUNDANT_CLONE, node, sugg_span, "redundant clone", |db| {
207 Applicability::MaybeIncorrect,
210 span.with_hi(span.lo() + BytePos(u32::try_from(dot).unwrap())),
211 "this value is dropped without further use",
215 span_lint_hir(cx, REDUNDANT_CLONE, node, span, "redundant clone");
223 /// If `kind` is `y = func(x: &T)` where `T: !Copy`, returns `(DefId of func, x, T, y)`.
224 fn is_call_with_ref_arg<'tcx>(
225 cx: &LateContext<'_, 'tcx>,
226 mir: &'tcx mir::Mir<'tcx>,
227 kind: &'tcx mir::TerminatorKind<'tcx>,
228 ) -> Option<(def_id::DefId, mir::Local, Ty<'tcx>, Option<&'tcx mir::Place<'tcx>>)> {
230 if let TerminatorKind::Call { func, args, destination, .. } = kind;
232 if let mir::Operand::Move(mir::Place::Base(mir::PlaceBase::Local(local))) = &args[0];
233 if let ty::FnDef(def_id, _) = func.ty(&*mir, cx.tcx).sty;
234 if let (inner_ty, 1) = walk_ptrs_ty_depth(args[0].ty(&*mir, cx.tcx));
235 if !is_copy(cx, inner_ty);
237 Some((def_id, *local, inner_ty, destination.as_ref().map(|(dest, _)| dest)))
244 type CannotMoveOut = bool;
246 /// Finds the first `to = (&)from`, and returns
247 /// ``Some((from, [`true` if `from` cannot be moved out]))``.
248 fn find_stmt_assigns_to<'a, 'tcx: 'a>(
249 cx: &LateContext<'_, 'tcx>,
250 mir: &mir::Mir<'tcx>,
253 stmts: impl DoubleEndedIterator<Item = &'a mir::Statement<'tcx>>,
254 ) -> Option<(mir::Local, CannotMoveOut)> {
258 if let mir::StatementKind::Assign(mir::Place::Base(mir::PlaceBase::Local(local)), v) = &stmt.kind {
268 if let mir::Rvalue::Ref(_, _, ref place) = **v {
269 return base_local_and_movability(cx, mir, place);
271 } else if let mir::Rvalue::Use(mir::Operand::Copy(ref place)) = **v {
272 return base_local_and_movability(cx, mir, place);
278 /// Extracts and returns the undermost base `Local` of given `place`. Returns `place` itself
279 /// if it is already a `Local`.
281 /// Also reports whether given `place` cannot be moved out.
282 fn base_local_and_movability<'tcx>(
283 cx: &LateContext<'_, 'tcx>,
284 mir: &mir::Mir<'tcx>,
285 mut place: &mir::Place<'tcx>,
286 ) -> Option<(mir::Local, CannotMoveOut)> {
287 use rustc::mir::Place::*;
288 use rustc::mir::PlaceBase;
290 // Dereference. You cannot move things out from a borrowed value.
291 let mut deref = false;
292 // Accessing a field of an ADT that has `Drop`. Moving the field out will cause E0509.
293 let mut field = false;
297 Base(PlaceBase::Local(local)) => return Some((*local, deref || field)),
298 Projection(proj) => {
300 deref = deref || matches!(proj.elem, mir::ProjectionElem::Deref);
301 if !field && matches!(proj.elem, mir::ProjectionElem::Field(..)) {
302 field = has_drop(cx, place.ty(&mir.local_decls, cx.tcx).ty);
310 struct LocalUseVisitor {
312 used_other_than_drop: bool,
315 impl<'tcx> mir::visit::Visitor<'tcx> for LocalUseVisitor {
316 fn visit_basic_block_data(&mut self, block: mir::BasicBlock, data: &mir::BasicBlockData<'tcx>) {
317 let statements = &data.statements;
318 for (statement_index, statement) in statements.iter().enumerate() {
319 self.visit_statement(block, statement, mir::Location { block, statement_index });
321 // Once flagged, skip remaining statements
322 if self.used_other_than_drop {
327 self.visit_terminator(
332 statement_index: statements.len(),
337 fn visit_local(&mut self, local: &mir::Local, ctx: PlaceContext<'tcx>, _: mir::Location) {
339 PlaceContext::MutatingUse(MutatingUseContext::Drop) | PlaceContext::NonUse(_) => return,
343 if *local == self.local {
344 self.used_other_than_drop = true;