2 has_drop, 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_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 /// # fn foo(x: String) {}
44 /// let x = String::new();
48 /// foo(x.clone()); // This lint suggests to remove this `clone()`
53 /// # use std::path::Path;
54 /// # #[derive(Clone)]
57 /// # fn new() -> Self { Foo {} }
59 /// # fn call(x: Foo) {}
61 /// let x = Foo::new();
63 /// call(x.clone()); // this can just pass `x`
66 /// ["lorem", "ipsum"].join(" ").to_string();
68 /// Path::new("/a/b").join("c").to_path_buf();
72 "`clone()` of an owned value that is going to be dropped immediately"
75 declare_lint_pass!(RedundantClone => [REDUNDANT_CLONE]);
77 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantClone {
78 #[allow(clippy::too_many_lines)]
81 cx: &LateContext<'a, 'tcx>,
88 let def_id = cx.tcx.hir().body_owner_def_id(body.id());
89 let mir = cx.tcx.optimized_mir(def_id);
91 for (bb, bbdata) in mir.basic_blocks().iter_enumerated() {
92 let terminator = bbdata.terminator();
94 if terminator.source_info.span.from_expansion() {
99 if terminator.successors().any(|s| *s == bb) {
103 let (fn_def_id, arg, arg_ty, _) = unwrap_or_continue!(is_call_with_ref_arg(cx, mir, &terminator.kind));
105 let from_borrow = match_def_path(cx, fn_def_id, &paths::CLONE_TRAIT_METHOD)
106 || match_def_path(cx, fn_def_id, &paths::TO_OWNED_METHOD)
107 || (match_def_path(cx, fn_def_id, &paths::TO_STRING_METHOD) && match_type(cx, arg_ty, &paths::STRING));
109 let from_deref = !from_borrow
110 && (match_def_path(cx, fn_def_id, &paths::PATH_TO_PATH_BUF)
111 || match_def_path(cx, fn_def_id, &paths::OS_STR_TO_OS_STRING));
113 if !from_borrow && !from_deref {
117 // _1 in MIR `{ _2 = &_1; clone(move _2); }` or `{ _2 = _1; to_path_buf(_2); } (from_deref)
118 // In case of `from_deref`, `arg` is already a reference since it is `deref`ed in the previous
120 let (cloned, cannot_move_out) = unwrap_or_continue!(find_stmt_assigns_to(
125 bbdata.statements.iter()
128 if from_borrow && cannot_move_out {
132 // _1 in MIR `{ _2 = &_1; _3 = deref(move _2); } -> { _4 = _3; to_path_buf(move _4); }`
133 let referent = if from_deref {
134 let ps = mir.predecessors_for(bb);
138 let pred_terminator = mir[ps[0]].terminator();
140 let pred_arg = if_chain! {
141 if let Some((pred_fn_def_id, pred_arg, pred_arg_ty, Some(res))) =
142 is_call_with_ref_arg(cx, mir, &pred_terminator.kind);
143 if res.base == mir::PlaceBase::Local(cloned);
144 if match_def_path(cx, pred_fn_def_id, &paths::DEREF_TRAIT_METHOD);
145 if match_type(cx, pred_arg_ty, &paths::PATH_BUF)
146 || match_type(cx, pred_arg_ty, &paths::OS_STRING);
154 let (local, cannot_move_out) = unwrap_or_continue!(find_stmt_assigns_to(
159 mir[ps[0]].statements.iter()
169 let used_later = traversal::ReversePostorder::new(&mir, bb).skip(1).any(|(tbb, tdata)| {
171 if tdata.terminator().successors().any(|s| *s == bb) {
175 let mut vis = LocalUseVisitor {
177 used_other_than_drop: false,
179 vis.visit_basic_block_data(tbb, tdata);
180 vis.used_other_than_drop
184 let span = terminator.source_info.span;
185 let node = if let mir::ClearCrossCrate::Set(scope_local_data) = &mir.source_scope_local_data {
186 scope_local_data[terminator.source_info.scope].lint_root
192 if let Some(snip) = snippet_opt(cx, span);
193 if let Some(dot) = snip.rfind('.');
195 let sugg_span = span.with_lo(
196 span.lo() + BytePos(u32::try_from(dot).unwrap())
199 span_lint_hir_and_then(cx, REDUNDANT_CLONE, node, sugg_span, "redundant clone", |db| {
204 Applicability::MaybeIncorrect,
207 span.with_hi(span.lo() + BytePos(u32::try_from(dot).unwrap())),
208 "this value is dropped without further use",
212 span_lint_hir(cx, REDUNDANT_CLONE, node, span, "redundant clone");
220 /// If `kind` is `y = func(x: &T)` where `T: !Copy`, returns `(DefId of func, x, T, y)`.
221 fn is_call_with_ref_arg<'tcx>(
222 cx: &LateContext<'_, 'tcx>,
223 mir: &'tcx mir::Body<'tcx>,
224 kind: &'tcx mir::TerminatorKind<'tcx>,
225 ) -> Option<(def_id::DefId, mir::Local, Ty<'tcx>, Option<&'tcx mir::Place<'tcx>>)> {
227 if let TerminatorKind::Call { func, args, destination, .. } = kind;
229 if let mir::Operand::Move(mir::Place { base: mir::PlaceBase::Local(local), .. }) = &args[0];
230 if let ty::FnDef(def_id, _) = func.ty(&*mir, cx.tcx).sty;
231 if let (inner_ty, 1) = walk_ptrs_ty_depth(args[0].ty(&*mir, cx.tcx));
232 if !is_copy(cx, inner_ty);
234 Some((def_id, *local, inner_ty, destination.as_ref().map(|(dest, _)| dest)))
241 type CannotMoveOut = bool;
243 /// Finds the first `to = (&)from`, and returns
244 /// ``Some((from, [`true` if `from` cannot be moved out]))``.
245 fn find_stmt_assigns_to<'a, 'tcx: 'a>(
246 cx: &LateContext<'_, 'tcx>,
247 mir: &mir::Body<'tcx>,
250 stmts: impl DoubleEndedIterator<Item = &'a mir::Statement<'tcx>>,
251 ) -> Option<(mir::Local, CannotMoveOut)> {
255 if let mir::StatementKind::Assign(box (
257 base: mir::PlaceBase::Local(local),
272 if let mir::Rvalue::Ref(_, _, ref place) = v {
273 return base_local_and_movability(cx, mir, place);
275 } else if let mir::Rvalue::Use(mir::Operand::Copy(ref place)) = v {
276 return base_local_and_movability(cx, mir, place);
282 /// Extracts and returns the undermost base `Local` of given `place`. Returns `place` itself
283 /// if it is already a `Local`.
285 /// Also reports whether given `place` cannot be moved out.
286 fn base_local_and_movability<'tcx>(
287 cx: &LateContext<'_, 'tcx>,
288 mir: &mir::Body<'tcx>,
289 place: &mir::Place<'tcx>,
290 ) -> Option<(mir::Local, CannotMoveOut)> {
291 use rustc::mir::Place;
292 use rustc::mir::PlaceBase;
293 use rustc::mir::PlaceRef;
295 // Dereference. You cannot move things out from a borrowed value.
296 let mut deref = false;
297 // Accessing a field of an ADT that has `Drop`. Moving the field out will cause E0509.
298 let mut field = false;
304 if let PlaceBase::Local(local) = place_base {
305 while let [base @ .., elem] = projection {
307 deref = matches!(elem, mir::ProjectionElem::Deref);
309 && matches!(elem, mir::ProjectionElem::Field(..))
310 && has_drop(cx, Place::ty_from(place_base, projection, &mir.local_decls, cx.tcx).ty);
313 Some((*local, deref || field))
319 struct LocalUseVisitor {
321 used_other_than_drop: bool,
324 impl<'tcx> mir::visit::Visitor<'tcx> for LocalUseVisitor {
325 fn visit_basic_block_data(&mut self, block: mir::BasicBlock, data: &mir::BasicBlockData<'tcx>) {
326 let statements = &data.statements;
327 for (statement_index, statement) in statements.iter().enumerate() {
328 self.visit_statement(statement, mir::Location { block, statement_index });
330 // Once flagged, skip remaining statements
331 if self.used_other_than_drop {
336 self.visit_terminator(
340 statement_index: statements.len(),
345 fn visit_local(&mut self, local: &mir::Local, ctx: PlaceContext, _: mir::Location) {
347 PlaceContext::MutatingUse(MutatingUseContext::Drop) | PlaceContext::NonUse(_) => return,
351 if *local == self.local {
352 self.used_other_than_drop = true;