2 has_drop, in_macro_or_desugar, is_copy, match_def_path, match_type, paths, snippet_opt, span_lint_hir,
3 span_lint_hir_and_then, walk_ptrs_ty_depth,
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_lint_pass, declare_tool_lint};
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 declare_lint_pass!(RedundantClone => [REDUNDANT_CLONE]);
69 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantClone {
70 #[allow(clippy::too_many_lines)]
73 cx: &LateContext<'a, 'tcx>,
80 let def_id = cx.tcx.hir().body_owner_def_id(body.id());
81 let mir = cx.tcx.optimized_mir(def_id);
83 for (bb, bbdata) in mir.basic_blocks().iter_enumerated() {
84 let terminator = bbdata.terminator();
86 if in_macro_or_desugar(terminator.source_info.span) {
91 if terminator.successors().any(|s| *s == bb) {
95 let (fn_def_id, arg, arg_ty, _) = unwrap_or_continue!(is_call_with_ref_arg(cx, mir, &terminator.kind));
97 let from_borrow = match_def_path(cx, fn_def_id, &paths::CLONE_TRAIT_METHOD)
98 || match_def_path(cx, fn_def_id, &paths::TO_OWNED_METHOD)
99 || (match_def_path(cx, fn_def_id, &paths::TO_STRING_METHOD)
100 && match_type(cx, arg_ty, &paths::STRING));
102 let from_deref = !from_borrow
103 && (match_def_path(cx, fn_def_id, &paths::PATH_TO_PATH_BUF)
104 || match_def_path(cx, fn_def_id, &paths::OS_STR_TO_OS_STRING));
106 if !from_borrow && !from_deref {
110 // _1 in MIR `{ _2 = &_1; clone(move _2); }` or `{ _2 = _1; to_path_buf(_2); } (from_deref)
111 // In case of `from_deref`, `arg` is already a reference since it is `deref`ed in the previous
113 let (cloned, cannot_move_out) = unwrap_or_continue!(find_stmt_assigns_to(
118 bbdata.statements.iter()
121 if from_borrow && cannot_move_out {
125 // _1 in MIR `{ _2 = &_1; _3 = deref(move _2); } -> { _4 = _3; to_path_buf(move _4); }`
126 let referent = if from_deref {
127 let ps = mir.predecessors_for(bb);
131 let pred_terminator = mir[ps[0]].terminator();
133 let pred_arg = if_chain! {
134 if let Some((pred_fn_def_id, pred_arg, pred_arg_ty, Some(res))) =
135 is_call_with_ref_arg(cx, mir, &pred_terminator.kind);
136 if *res == mir::Place::Base(mir::PlaceBase::Local(cloned));
137 if match_def_path(cx, pred_fn_def_id, &paths::DEREF_TRAIT_METHOD);
138 if match_type(cx, pred_arg_ty, &paths::PATH_BUF)
139 || match_type(cx, pred_arg_ty, &paths::OS_STRING);
147 let (local, cannot_move_out) = unwrap_or_continue!(find_stmt_assigns_to(
152 mir[ps[0]].statements.iter()
162 let used_later = traversal::ReversePostorder::new(&mir, bb).skip(1).any(|(tbb, tdata)| {
164 if tdata.terminator().successors().any(|s| *s == bb) {
168 let mut vis = LocalUseVisitor {
170 used_other_than_drop: false,
172 vis.visit_basic_block_data(tbb, tdata);
173 vis.used_other_than_drop
177 let span = terminator.source_info.span;
178 let node = if let mir::ClearCrossCrate::Set(scope_local_data) = &mir.source_scope_local_data {
179 scope_local_data[terminator.source_info.scope].lint_root
185 if let Some(snip) = snippet_opt(cx, span);
186 if let Some(dot) = snip.rfind('.');
188 let sugg_span = span.with_lo(
189 span.lo() + BytePos(u32::try_from(dot).unwrap())
192 span_lint_hir_and_then(cx, REDUNDANT_CLONE, node, sugg_span, "redundant clone", |db| {
197 Applicability::MaybeIncorrect,
200 span.with_hi(span.lo() + BytePos(u32::try_from(dot).unwrap())),
201 "this value is dropped without further use",
205 span_lint_hir(cx, REDUNDANT_CLONE, node, span, "redundant clone");
213 /// If `kind` is `y = func(x: &T)` where `T: !Copy`, returns `(DefId of func, x, T, y)`.
214 fn is_call_with_ref_arg<'tcx>(
215 cx: &LateContext<'_, 'tcx>,
216 mir: &'tcx mir::Mir<'tcx>,
217 kind: &'tcx mir::TerminatorKind<'tcx>,
218 ) -> Option<(def_id::DefId, mir::Local, Ty<'tcx>, Option<&'tcx mir::Place<'tcx>>)> {
220 if let TerminatorKind::Call { func, args, destination, .. } = kind;
222 if let mir::Operand::Move(mir::Place::Base(mir::PlaceBase::Local(local))) = &args[0];
223 if let ty::FnDef(def_id, _) = func.ty(&*mir, cx.tcx).sty;
224 if let (inner_ty, 1) = walk_ptrs_ty_depth(args[0].ty(&*mir, cx.tcx));
225 if !is_copy(cx, inner_ty);
227 Some((def_id, *local, inner_ty, destination.as_ref().map(|(dest, _)| dest)))
234 type CannotMoveOut = bool;
236 /// Finds the first `to = (&)from`, and returns
237 /// ``Some((from, [`true` if `from` cannot be moved out]))``.
238 fn find_stmt_assigns_to<'a, 'tcx: 'a>(
239 cx: &LateContext<'_, 'tcx>,
240 mir: &mir::Mir<'tcx>,
243 stmts: impl DoubleEndedIterator<Item = &'a mir::Statement<'tcx>>,
244 ) -> Option<(mir::Local, CannotMoveOut)> {
248 if let mir::StatementKind::Assign(mir::Place::Base(mir::PlaceBase::Local(local)), v) = &stmt.kind {
258 if let mir::Rvalue::Ref(_, _, ref place) = **v {
259 return base_local_and_movability(cx, mir, place);
261 } else if let mir::Rvalue::Use(mir::Operand::Copy(ref place)) = **v {
262 return base_local_and_movability(cx, mir, place);
268 /// Extracts and returns the undermost base `Local` of given `place`. Returns `place` itself
269 /// if it is already a `Local`.
271 /// Also reports whether given `place` cannot be moved out.
272 fn base_local_and_movability<'tcx>(
273 cx: &LateContext<'_, 'tcx>,
274 mir: &mir::Mir<'tcx>,
275 mut place: &mir::Place<'tcx>,
276 ) -> Option<(mir::Local, CannotMoveOut)> {
277 use rustc::mir::Place::*;
278 use rustc::mir::PlaceBase;
280 // Dereference. You cannot move things out from a borrowed value.
281 let mut deref = false;
282 // Accessing a field of an ADT that has `Drop`. Moving the field out will cause E0509.
283 let mut field = false;
287 Base(PlaceBase::Local(local)) => return Some((*local, deref || field)),
288 Projection(proj) => {
290 deref = deref || matches!(proj.elem, mir::ProjectionElem::Deref);
291 if !field && matches!(proj.elem, mir::ProjectionElem::Field(..)) {
292 field = has_drop(cx, place.ty(&mir.local_decls, cx.tcx).ty);
300 struct LocalUseVisitor {
302 used_other_than_drop: bool,
305 impl<'tcx> mir::visit::Visitor<'tcx> for LocalUseVisitor {
306 fn visit_basic_block_data(&mut self, block: mir::BasicBlock, data: &mir::BasicBlockData<'tcx>) {
307 let statements = &data.statements;
308 for (statement_index, statement) in statements.iter().enumerate() {
309 self.visit_statement(statement, mir::Location { block, statement_index });
311 // Once flagged, skip remaining statements
312 if self.used_other_than_drop {
317 self.visit_terminator(
321 statement_index: statements.len(),
326 fn visit_local(&mut self, local: &mir::Local, ctx: PlaceContext, _: mir::Location) {
328 PlaceContext::MutatingUse(MutatingUseContext::Drop) | PlaceContext::NonUse(_) => return,
332 if *local == self.local {
333 self.used_other_than_drop = true;