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5e7ed085 FG |
1 | use std::collections::VecDeque; |
2 | ||
3 | use clippy_utils::diagnostics::span_lint_and_sugg; | |
4 | use clippy_utils::is_lint_allowed; | |
5 | use itertools::{izip, Itertools}; | |
6 | use rustc_ast::{walk_list, Label, Mutability}; | |
7 | use rustc_data_structures::fx::{FxHashMap, FxHashSet}; | |
8 | use rustc_errors::Applicability; | |
9 | use rustc_hir::def::{DefKind, Res}; | |
10 | use rustc_hir::def_id::DefId; | |
11 | use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData}; | |
12 | use rustc_hir::intravisit::{walk_expr, walk_stmt, FnKind, Visitor}; | |
13 | use rustc_hir::{ | |
14 | Arm, Block, Body, Expr, ExprKind, Guard, HirId, ImplicitSelfKind, Let, Local, Pat, PatKind, Path, PathSegment, | |
15 | QPath, Stmt, StmtKind, TyKind, UnOp, | |
16 | }; | |
17 | use rustc_lint::{LateContext, LateLintPass}; | |
18 | use rustc_middle::ty; | |
19 | use rustc_middle::ty::{Ty, TyCtxt, TypeckResults}; | |
20 | use rustc_session::{declare_lint_pass, declare_tool_lint}; | |
21 | use rustc_span::symbol::kw; | |
22 | use rustc_span::symbol::Ident; | |
23 | use rustc_span::Span; | |
24 | ||
25 | declare_clippy_lint! { | |
26 | /// ### What it does | |
27 | /// Checks for arguments that are only used in recursion with no side-effects. | |
28 | /// | |
29 | /// ### Why is this bad? | |
30 | /// It could contain a useless calculation and can make function simpler. | |
31 | /// | |
32 | /// The arguments can be involved in calculations and assignments but as long as | |
33 | /// the calculations have no side-effects (function calls or mutating dereference) | |
34 | /// and the assigned variables are also only in recursion, it is useless. | |
35 | /// | |
36 | /// ### Known problems | |
37 | /// Too many code paths in the linting code are currently untested and prone to produce false | |
38 | /// positives or are prone to have performance implications. | |
39 | /// | |
40 | /// In some cases, this would not catch all useless arguments. | |
41 | /// | |
42 | /// ```rust | |
43 | /// fn foo(a: usize, b: usize) -> usize { | |
44 | /// let f = |x| x + 1; | |
45 | /// | |
46 | /// if a == 0 { | |
47 | /// 1 | |
48 | /// } else { | |
49 | /// foo(a - 1, f(b)) | |
50 | /// } | |
51 | /// } | |
52 | /// ``` | |
53 | /// | |
54 | /// For example, the argument `b` is only used in recursion, but the lint would not catch it. | |
55 | /// | |
56 | /// List of some examples that can not be caught: | |
57 | /// - binary operation of non-primitive types | |
58 | /// - closure usage | |
59 | /// - some `break` relative operations | |
60 | /// - struct pattern binding | |
61 | /// | |
62 | /// Also, when you recurse the function name with path segments, it is not possible to detect. | |
63 | /// | |
64 | /// ### Example | |
65 | /// ```rust | |
66 | /// fn f(a: usize, b: usize) -> usize { | |
67 | /// if a == 0 { | |
68 | /// 1 | |
69 | /// } else { | |
70 | /// f(a - 1, b + 1) | |
71 | /// } | |
72 | /// } | |
73 | /// # fn main() { | |
74 | /// # print!("{}", f(1, 1)); | |
75 | /// # } | |
76 | /// ``` | |
77 | /// Use instead: | |
78 | /// ```rust | |
79 | /// fn f(a: usize) -> usize { | |
80 | /// if a == 0 { | |
81 | /// 1 | |
82 | /// } else { | |
83 | /// f(a - 1) | |
84 | /// } | |
85 | /// } | |
86 | /// # fn main() { | |
87 | /// # print!("{}", f(1)); | |
88 | /// # } | |
89 | /// ``` | |
90 | #[clippy::version = "1.60.0"] | |
91 | pub ONLY_USED_IN_RECURSION, | |
92 | nursery, | |
93 | "arguments that is only used in recursion can be removed" | |
94 | } | |
95 | declare_lint_pass!(OnlyUsedInRecursion => [ONLY_USED_IN_RECURSION]); | |
96 | ||
97 | impl<'tcx> LateLintPass<'tcx> for OnlyUsedInRecursion { | |
98 | fn check_fn( | |
99 | &mut self, | |
100 | cx: &LateContext<'tcx>, | |
101 | kind: FnKind<'tcx>, | |
102 | decl: &'tcx rustc_hir::FnDecl<'tcx>, | |
103 | body: &'tcx Body<'tcx>, | |
104 | _: Span, | |
105 | id: HirId, | |
106 | ) { | |
107 | if is_lint_allowed(cx, ONLY_USED_IN_RECURSION, id) { | |
108 | return; | |
109 | } | |
110 | if let FnKind::ItemFn(ident, ..) | FnKind::Method(ident, ..) = kind { | |
111 | let def_id = id.owner.to_def_id(); | |
112 | let data = cx.tcx.def_path(def_id).data; | |
113 | ||
114 | if data.len() > 1 { | |
115 | match data.get(data.len() - 2) { | |
116 | Some(DisambiguatedDefPathData { | |
117 | data: DefPathData::Impl, | |
118 | disambiguator, | |
119 | }) if *disambiguator != 0 => return, | |
120 | _ => {}, | |
121 | } | |
122 | } | |
123 | ||
124 | let has_self = !matches!(decl.implicit_self, ImplicitSelfKind::None); | |
125 | ||
126 | let ty_res = cx.typeck_results(); | |
127 | let param_span = body | |
128 | .params | |
129 | .iter() | |
130 | .flat_map(|param| { | |
131 | let mut v = Vec::new(); | |
132 | param.pat.each_binding(|_, hir_id, span, ident| { | |
133 | v.push((hir_id, span, ident)); | |
134 | }); | |
135 | v | |
136 | }) | |
137 | .skip(if has_self { 1 } else { 0 }) | |
138 | .filter(|(_, _, ident)| !ident.name.as_str().starts_with('_')) | |
139 | .collect_vec(); | |
140 | ||
141 | let params = body.params.iter().map(|param| param.pat).collect(); | |
142 | ||
143 | let mut visitor = SideEffectVisit { | |
144 | graph: FxHashMap::default(), | |
145 | has_side_effect: FxHashSet::default(), | |
146 | ret_vars: Vec::new(), | |
147 | contains_side_effect: false, | |
148 | break_vars: FxHashMap::default(), | |
149 | params, | |
150 | fn_ident: ident, | |
151 | fn_def_id: def_id, | |
152 | is_method: matches!(kind, FnKind::Method(..)), | |
153 | has_self, | |
154 | ty_res, | |
155 | tcx: cx.tcx, | |
156 | visited_exprs: FxHashSet::default(), | |
157 | }; | |
158 | ||
159 | visitor.visit_expr(&body.value); | |
160 | let vars = std::mem::take(&mut visitor.ret_vars); | |
161 | // this would set the return variables to side effect | |
162 | visitor.add_side_effect(vars); | |
163 | ||
164 | let mut queue = visitor.has_side_effect.iter().copied().collect::<VecDeque<_>>(); | |
165 | ||
166 | // a simple BFS to check all the variables that have side effect | |
167 | while let Some(id) = queue.pop_front() { | |
168 | if let Some(next) = visitor.graph.get(&id) { | |
169 | for i in next { | |
170 | if !visitor.has_side_effect.contains(i) { | |
171 | visitor.has_side_effect.insert(*i); | |
172 | queue.push_back(*i); | |
173 | } | |
174 | } | |
175 | } | |
176 | } | |
177 | ||
178 | for (id, span, ident) in param_span { | |
179 | // if the variable is not used in recursion, it would be marked as unused | |
180 | if !visitor.has_side_effect.contains(&id) { | |
181 | let mut queue = VecDeque::new(); | |
182 | let mut visited = FxHashSet::default(); | |
183 | ||
184 | queue.push_back(id); | |
185 | ||
186 | // a simple BFS to check the graph can reach to itself | |
187 | // if it can't, it means the variable is never used in recursion | |
188 | while let Some(id) = queue.pop_front() { | |
189 | if let Some(next) = visitor.graph.get(&id) { | |
190 | for i in next { | |
191 | if !visited.contains(i) { | |
192 | visited.insert(id); | |
193 | queue.push_back(*i); | |
194 | } | |
195 | } | |
196 | } | |
197 | } | |
198 | ||
199 | if visited.contains(&id) { | |
200 | span_lint_and_sugg( | |
201 | cx, | |
202 | ONLY_USED_IN_RECURSION, | |
203 | span, | |
204 | "parameter is only used in recursion", | |
205 | "if this is intentional, prefix with an underscore", | |
206 | format!("_{}", ident.name.as_str()), | |
207 | Applicability::MaybeIncorrect, | |
208 | ); | |
209 | } | |
210 | } | |
211 | } | |
212 | } | |
213 | } | |
214 | } | |
215 | ||
216 | pub fn is_primitive(ty: Ty<'_>) -> bool { | |
217 | let ty = ty.peel_refs(); | |
218 | ty.is_primitive() || ty.is_str() | |
219 | } | |
220 | ||
221 | pub fn is_array(ty: Ty<'_>) -> bool { | |
222 | let ty = ty.peel_refs(); | |
223 | ty.is_array() || ty.is_array_slice() | |
224 | } | |
225 | ||
226 | /// This builds the graph of side effect. | |
227 | /// The edge `a -> b` means if `a` has side effect, `b` will have side effect. | |
228 | /// | |
229 | /// There are some example in following code: | |
230 | /// ```rust, ignore | |
231 | /// let b = 1; | |
232 | /// let a = b; // a -> b | |
233 | /// let (c, d) = (a, b); // c -> b, d -> b | |
234 | /// | |
235 | /// let e = if a == 0 { // e -> a | |
236 | /// c // e -> c | |
237 | /// } else { | |
238 | /// d // e -> d | |
239 | /// }; | |
240 | /// ``` | |
241 | pub struct SideEffectVisit<'tcx> { | |
242 | graph: FxHashMap<HirId, FxHashSet<HirId>>, | |
243 | has_side_effect: FxHashSet<HirId>, | |
244 | // bool for if the variable was dereferenced from mutable reference | |
245 | ret_vars: Vec<(HirId, bool)>, | |
246 | contains_side_effect: bool, | |
247 | // break label | |
248 | break_vars: FxHashMap<Ident, Vec<(HirId, bool)>>, | |
249 | params: Vec<&'tcx Pat<'tcx>>, | |
250 | fn_ident: Ident, | |
251 | fn_def_id: DefId, | |
252 | is_method: bool, | |
253 | has_self: bool, | |
254 | ty_res: &'tcx TypeckResults<'tcx>, | |
255 | tcx: TyCtxt<'tcx>, | |
256 | visited_exprs: FxHashSet<HirId>, | |
257 | } | |
258 | ||
259 | impl<'tcx> Visitor<'tcx> for SideEffectVisit<'tcx> { | |
260 | fn visit_stmt(&mut self, s: &'tcx Stmt<'tcx>) { | |
261 | match s.kind { | |
262 | StmtKind::Local(Local { | |
263 | pat, init: Some(init), .. | |
264 | }) => { | |
265 | self.visit_pat_expr(pat, init, false); | |
266 | }, | |
267 | StmtKind::Item(_) | StmtKind::Expr(_) | StmtKind::Semi(_) => { | |
268 | walk_stmt(self, s); | |
269 | }, | |
270 | StmtKind::Local(_) => {}, | |
271 | } | |
272 | self.ret_vars.clear(); | |
273 | } | |
274 | ||
275 | fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) { | |
276 | if !self.visited_exprs.insert(ex.hir_id) { | |
277 | return; | |
278 | } | |
279 | match ex.kind { | |
280 | ExprKind::Array(exprs) | ExprKind::Tup(exprs) => { | |
281 | self.ret_vars = exprs | |
282 | .iter() | |
283 | .flat_map(|expr| { | |
284 | self.visit_expr(expr); | |
285 | std::mem::take(&mut self.ret_vars) | |
286 | }) | |
287 | .collect(); | |
288 | }, | |
289 | ExprKind::Call(callee, args) => self.visit_fn(callee, args), | |
290 | ExprKind::MethodCall(path, args, _) => self.visit_method_call(path, args), | |
291 | ExprKind::Binary(_, lhs, rhs) => { | |
292 | self.visit_bin_op(lhs, rhs); | |
293 | }, | |
294 | ExprKind::Unary(op, expr) => self.visit_un_op(op, expr), | |
295 | ExprKind::Let(Let { pat, init, .. }) => self.visit_pat_expr(pat, init, false), | |
296 | ExprKind::If(bind, then_expr, else_expr) => { | |
297 | self.visit_if(bind, then_expr, else_expr); | |
298 | }, | |
299 | ExprKind::Match(expr, arms, _) => self.visit_match(expr, arms), | |
300 | // since analysing the closure is not easy, just set all variables in it to side-effect | |
301 | ExprKind::Closure(_, _, body_id, _, _) => { | |
302 | let body = self.tcx.hir().body(body_id); | |
303 | self.visit_body(body); | |
304 | let vars = std::mem::take(&mut self.ret_vars); | |
305 | self.add_side_effect(vars); | |
306 | }, | |
307 | ExprKind::Loop(block, label, _, _) | ExprKind::Block(block, label) => { | |
308 | self.visit_block_label(block, label); | |
309 | }, | |
310 | ExprKind::Assign(bind, expr, _) => { | |
311 | self.visit_assign(bind, expr); | |
312 | }, | |
313 | ExprKind::AssignOp(_, bind, expr) => { | |
314 | self.visit_assign(bind, expr); | |
315 | self.visit_bin_op(bind, expr); | |
316 | }, | |
317 | ExprKind::Field(expr, _) => { | |
318 | self.visit_expr(expr); | |
319 | if matches!(self.ty_res.expr_ty(expr).kind(), ty::Ref(_, _, Mutability::Mut)) { | |
320 | self.ret_vars.iter_mut().for_each(|(_, b)| *b = true); | |
321 | } | |
322 | }, | |
323 | ExprKind::Index(expr, index) => { | |
324 | self.visit_expr(expr); | |
325 | let mut vars = std::mem::take(&mut self.ret_vars); | |
326 | self.visit_expr(index); | |
327 | self.ret_vars.append(&mut vars); | |
328 | ||
329 | if !is_array(self.ty_res.expr_ty(expr)) { | |
330 | self.add_side_effect(self.ret_vars.clone()); | |
331 | } else if matches!(self.ty_res.expr_ty(expr).kind(), ty::Ref(_, _, Mutability::Mut)) { | |
332 | self.ret_vars.iter_mut().for_each(|(_, b)| *b = true); | |
333 | } | |
334 | }, | |
335 | ExprKind::Break(dest, Some(expr)) => { | |
336 | self.visit_expr(expr); | |
337 | if let Some(label) = dest.label { | |
338 | self.break_vars | |
339 | .entry(label.ident) | |
340 | .or_insert(Vec::new()) | |
341 | .append(&mut self.ret_vars); | |
342 | } | |
343 | self.contains_side_effect = true; | |
344 | }, | |
345 | ExprKind::Ret(Some(expr)) => { | |
346 | self.visit_expr(expr); | |
347 | let vars = std::mem::take(&mut self.ret_vars); | |
348 | self.add_side_effect(vars); | |
349 | self.contains_side_effect = true; | |
350 | }, | |
351 | ExprKind::Break(_, None) | ExprKind::Continue(_) | ExprKind::Ret(None) => { | |
352 | self.contains_side_effect = true; | |
353 | }, | |
354 | ExprKind::Struct(_, exprs, expr) => { | |
355 | let mut ret_vars = exprs | |
356 | .iter() | |
357 | .flat_map(|field| { | |
358 | self.visit_expr(field.expr); | |
359 | std::mem::take(&mut self.ret_vars) | |
360 | }) | |
361 | .collect(); | |
362 | ||
363 | walk_list!(self, visit_expr, expr); | |
364 | self.ret_vars.append(&mut ret_vars); | |
365 | }, | |
366 | _ => walk_expr(self, ex), | |
367 | } | |
368 | } | |
369 | ||
370 | fn visit_path(&mut self, path: &'tcx Path<'tcx>, _id: HirId) { | |
371 | if let Res::Local(id) = path.res { | |
372 | self.ret_vars.push((id, false)); | |
373 | } | |
374 | } | |
375 | } | |
376 | ||
377 | impl<'tcx> SideEffectVisit<'tcx> { | |
378 | fn visit_assign(&mut self, lhs: &'tcx Expr<'tcx>, rhs: &'tcx Expr<'tcx>) { | |
379 | // Just support array and tuple unwrapping for now. | |
380 | // | |
381 | // ex) `(a, b) = (c, d);` | |
382 | // The graph would look like this: | |
383 | // a -> c | |
384 | // b -> d | |
385 | // | |
386 | // This would minimize the connection of the side-effect graph. | |
387 | match (&lhs.kind, &rhs.kind) { | |
388 | (ExprKind::Array(lhs), ExprKind::Array(rhs)) | (ExprKind::Tup(lhs), ExprKind::Tup(rhs)) => { | |
389 | // if not, it is a compile error | |
390 | debug_assert!(lhs.len() == rhs.len()); | |
391 | izip!(*lhs, *rhs).for_each(|(lhs, rhs)| self.visit_assign(lhs, rhs)); | |
392 | }, | |
393 | // in other assigns, we have to connect all each other | |
394 | // because they can be connected somehow | |
395 | _ => { | |
396 | self.visit_expr(lhs); | |
397 | let lhs_vars = std::mem::take(&mut self.ret_vars); | |
398 | self.visit_expr(rhs); | |
399 | let rhs_vars = std::mem::take(&mut self.ret_vars); | |
400 | self.connect_assign(&lhs_vars, &rhs_vars, false); | |
401 | }, | |
402 | } | |
403 | } | |
404 | ||
405 | fn visit_block_label(&mut self, block: &'tcx Block<'tcx>, label: Option<Label>) { | |
406 | self.visit_block(block); | |
407 | let _ = label.and_then(|label| { | |
408 | self.break_vars | |
409 | .remove(&label.ident) | |
410 | .map(|mut break_vars| self.ret_vars.append(&mut break_vars)) | |
411 | }); | |
412 | } | |
413 | ||
414 | fn visit_bin_op(&mut self, lhs: &'tcx Expr<'tcx>, rhs: &'tcx Expr<'tcx>) { | |
415 | self.visit_expr(lhs); | |
416 | let mut ret_vars = std::mem::take(&mut self.ret_vars); | |
417 | self.visit_expr(rhs); | |
418 | self.ret_vars.append(&mut ret_vars); | |
419 | ||
420 | // the binary operation between non primitive values are overloaded operators | |
421 | // so they can have side-effects | |
422 | if !is_primitive(self.ty_res.expr_ty(lhs)) || !is_primitive(self.ty_res.expr_ty(rhs)) { | |
423 | self.ret_vars.iter().for_each(|id| { | |
424 | self.has_side_effect.insert(id.0); | |
425 | }); | |
426 | self.contains_side_effect = true; | |
427 | } | |
428 | } | |
429 | ||
430 | fn visit_un_op(&mut self, op: UnOp, expr: &'tcx Expr<'tcx>) { | |
431 | self.visit_expr(expr); | |
432 | let ty = self.ty_res.expr_ty(expr); | |
433 | // dereferencing a reference has no side-effect | |
434 | if !is_primitive(ty) && !matches!((op, ty.kind()), (UnOp::Deref, ty::Ref(..))) { | |
435 | self.add_side_effect(self.ret_vars.clone()); | |
436 | } | |
437 | ||
438 | if matches!((op, ty.kind()), (UnOp::Deref, ty::Ref(_, _, Mutability::Mut))) { | |
439 | self.ret_vars.iter_mut().for_each(|(_, b)| *b = true); | |
440 | } | |
441 | } | |
442 | ||
443 | fn visit_pat_expr(&mut self, pat: &'tcx Pat<'tcx>, expr: &'tcx Expr<'tcx>, connect_self: bool) { | |
444 | match (&pat.kind, &expr.kind) { | |
445 | (PatKind::Tuple(pats, _), ExprKind::Tup(exprs)) => { | |
446 | self.ret_vars = izip!(*pats, *exprs) | |
447 | .flat_map(|(pat, expr)| { | |
448 | self.visit_pat_expr(pat, expr, connect_self); | |
449 | std::mem::take(&mut self.ret_vars) | |
450 | }) | |
451 | .collect(); | |
452 | }, | |
453 | (PatKind::Slice(front_exprs, _, back_exprs), ExprKind::Array(exprs)) => { | |
454 | let mut vars = izip!(*front_exprs, *exprs) | |
455 | .flat_map(|(pat, expr)| { | |
456 | self.visit_pat_expr(pat, expr, connect_self); | |
457 | std::mem::take(&mut self.ret_vars) | |
458 | }) | |
459 | .collect(); | |
460 | self.ret_vars = izip!(back_exprs.iter().rev(), exprs.iter().rev()) | |
461 | .flat_map(|(pat, expr)| { | |
462 | self.visit_pat_expr(pat, expr, connect_self); | |
463 | std::mem::take(&mut self.ret_vars) | |
464 | }) | |
465 | .collect(); | |
466 | self.ret_vars.append(&mut vars); | |
467 | }, | |
468 | _ => { | |
469 | let mut lhs_vars = Vec::new(); | |
470 | pat.each_binding(|_, id, _, _| lhs_vars.push((id, false))); | |
471 | self.visit_expr(expr); | |
472 | let rhs_vars = std::mem::take(&mut self.ret_vars); | |
473 | self.connect_assign(&lhs_vars, &rhs_vars, connect_self); | |
474 | self.ret_vars = rhs_vars; | |
475 | }, | |
476 | } | |
477 | } | |
478 | ||
479 | fn visit_fn(&mut self, callee: &'tcx Expr<'tcx>, args: &'tcx [Expr<'tcx>]) { | |
480 | self.visit_expr(callee); | |
481 | let mut ret_vars = std::mem::take(&mut self.ret_vars); | |
482 | self.add_side_effect(ret_vars.clone()); | |
483 | ||
484 | let mut is_recursive = false; | |
485 | ||
486 | if_chain! { | |
487 | if !self.has_self; | |
488 | if let ExprKind::Path(QPath::Resolved(_, path)) = callee.kind; | |
489 | if let Res::Def(DefKind::Fn, def_id) = path.res; | |
490 | if self.fn_def_id == def_id; | |
491 | then { | |
492 | is_recursive = true; | |
493 | } | |
494 | } | |
495 | ||
496 | if_chain! { | |
497 | if !self.has_self && self.is_method; | |
498 | if let ExprKind::Path(QPath::TypeRelative(ty, segment)) = callee.kind; | |
499 | if segment.ident == self.fn_ident; | |
500 | if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind; | |
501 | if let Res::SelfTy{ .. } = path.res; | |
502 | then { | |
503 | is_recursive = true; | |
504 | } | |
505 | } | |
506 | ||
507 | if is_recursive { | |
508 | izip!(self.params.clone(), args).for_each(|(pat, expr)| { | |
509 | self.visit_pat_expr(pat, expr, true); | |
510 | self.ret_vars.clear(); | |
511 | }); | |
512 | } else { | |
513 | // This would set arguments used in closure that does not have side-effect. | |
514 | // Closure itself can be detected whether there is a side-effect, but the | |
515 | // value of variable that is holding closure can change. | |
516 | // So, we just check the variables. | |
517 | self.ret_vars = args | |
518 | .iter() | |
519 | .flat_map(|expr| { | |
520 | self.visit_expr(expr); | |
521 | std::mem::take(&mut self.ret_vars) | |
522 | }) | |
523 | .collect_vec() | |
524 | .into_iter() | |
525 | .map(|id| { | |
526 | self.has_side_effect.insert(id.0); | |
527 | id | |
528 | }) | |
529 | .collect(); | |
530 | self.contains_side_effect = true; | |
531 | } | |
532 | ||
533 | self.ret_vars.append(&mut ret_vars); | |
534 | } | |
535 | ||
536 | fn visit_method_call(&mut self, path: &'tcx PathSegment<'tcx>, args: &'tcx [Expr<'tcx>]) { | |
537 | if_chain! { | |
538 | if self.is_method; | |
539 | if path.ident == self.fn_ident; | |
540 | if let ExprKind::Path(QPath::Resolved(_, path)) = args.first().unwrap().kind; | |
541 | if let Res::Local(..) = path.res; | |
542 | let ident = path.segments.last().unwrap().ident; | |
543 | if ident.name == kw::SelfLower; | |
544 | then { | |
545 | izip!(self.params.clone(), args.iter()) | |
546 | .for_each(|(pat, expr)| { | |
547 | self.visit_pat_expr(pat, expr, true); | |
548 | self.ret_vars.clear(); | |
549 | }); | |
550 | } else { | |
551 | self.ret_vars = args | |
552 | .iter() | |
553 | .flat_map(|expr| { | |
554 | self.visit_expr(expr); | |
555 | std::mem::take(&mut self.ret_vars) | |
556 | }) | |
557 | .collect_vec() | |
558 | .into_iter() | |
559 | .map(|a| { | |
560 | self.has_side_effect.insert(a.0); | |
561 | a | |
562 | }) | |
563 | .collect(); | |
564 | self.contains_side_effect = true; | |
565 | } | |
566 | } | |
567 | } | |
568 | ||
569 | fn visit_if(&mut self, bind: &'tcx Expr<'tcx>, then_expr: &'tcx Expr<'tcx>, else_expr: Option<&'tcx Expr<'tcx>>) { | |
570 | let contains_side_effect = self.contains_side_effect; | |
571 | self.contains_side_effect = false; | |
572 | self.visit_expr(bind); | |
573 | let mut vars = std::mem::take(&mut self.ret_vars); | |
574 | self.visit_expr(then_expr); | |
575 | let mut then_vars = std::mem::take(&mut self.ret_vars); | |
576 | walk_list!(self, visit_expr, else_expr); | |
577 | if self.contains_side_effect { | |
578 | self.add_side_effect(vars.clone()); | |
579 | } | |
580 | self.contains_side_effect |= contains_side_effect; | |
581 | self.ret_vars.append(&mut vars); | |
582 | self.ret_vars.append(&mut then_vars); | |
583 | } | |
584 | ||
585 | fn visit_match(&mut self, expr: &'tcx Expr<'tcx>, arms: &'tcx [Arm<'tcx>]) { | |
586 | self.visit_expr(expr); | |
587 | let mut expr_vars = std::mem::take(&mut self.ret_vars); | |
588 | self.ret_vars = arms | |
589 | .iter() | |
590 | .flat_map(|arm| { | |
591 | let contains_side_effect = self.contains_side_effect; | |
592 | self.contains_side_effect = false; | |
593 | // this would visit `expr` multiple times | |
594 | // but couldn't think of a better way | |
595 | self.visit_pat_expr(arm.pat, expr, false); | |
596 | let mut vars = std::mem::take(&mut self.ret_vars); | |
597 | let _ = arm.guard.as_ref().map(|guard| { | |
598 | self.visit_expr(match guard { | |
599 | Guard::If(expr) | Guard::IfLet(_, expr) => expr, | |
600 | }); | |
601 | vars.append(&mut self.ret_vars); | |
602 | }); | |
603 | self.visit_expr(arm.body); | |
604 | if self.contains_side_effect { | |
605 | self.add_side_effect(vars.clone()); | |
606 | self.add_side_effect(expr_vars.clone()); | |
607 | } | |
608 | self.contains_side_effect |= contains_side_effect; | |
609 | vars.append(&mut self.ret_vars); | |
610 | vars | |
611 | }) | |
612 | .collect(); | |
613 | self.ret_vars.append(&mut expr_vars); | |
614 | } | |
615 | ||
616 | fn connect_assign(&mut self, lhs: &[(HirId, bool)], rhs: &[(HirId, bool)], connect_self: bool) { | |
617 | // if mutable dereference is on assignment it can have side-effect | |
618 | // (this can lead to parameter mutable dereference and change the original value) | |
619 | // too hard to detect whether this value is from parameter, so this would all | |
620 | // check mutable dereference assignment to side effect | |
621 | lhs.iter().filter(|(_, b)| *b).for_each(|(id, _)| { | |
622 | self.has_side_effect.insert(*id); | |
623 | self.contains_side_effect = true; | |
624 | }); | |
625 | ||
626 | // there is no connection | |
627 | if lhs.is_empty() || rhs.is_empty() { | |
628 | return; | |
629 | } | |
630 | ||
631 | // by connected rhs in cycle, the connections would decrease | |
632 | // from `n * m` to `n + m` | |
633 | // where `n` and `m` are length of `lhs` and `rhs`. | |
634 | ||
635 | // unwrap is possible since rhs is not empty | |
636 | let rhs_first = rhs.first().unwrap(); | |
637 | for (id, _) in lhs.iter() { | |
638 | if connect_self || *id != rhs_first.0 { | |
639 | self.graph | |
640 | .entry(*id) | |
641 | .or_insert_with(FxHashSet::default) | |
642 | .insert(rhs_first.0); | |
643 | } | |
644 | } | |
645 | ||
646 | let rhs = rhs.iter(); | |
647 | izip!(rhs.clone().cycle().skip(1), rhs).for_each(|(from, to)| { | |
648 | if connect_self || from.0 != to.0 { | |
649 | self.graph.entry(from.0).or_insert_with(FxHashSet::default).insert(to.0); | |
650 | } | |
651 | }); | |
652 | } | |
653 | ||
654 | fn add_side_effect(&mut self, v: Vec<(HirId, bool)>) { | |
655 | for (id, _) in v { | |
656 | self.has_side_effect.insert(id); | |
657 | self.contains_side_effect = true; | |
658 | } | |
659 | } | |
660 | } |