1 use rustc::hir::def::Def;
2 use rustc::hir::def_id::DefId;
5 use rustc::ty::adjustment;
6 use lint::{LateContext, EarlyContext, LintContext, LintArray};
7 use lint::{LintPass, EarlyLintPass, LateLintPass};
11 use syntax::errors::Applicability;
12 use syntax::feature_gate::{BUILTIN_ATTRIBUTES, AttributeType};
13 use syntax::print::pprust;
14 use syntax::symbol::keywords;
15 use syntax::util::parser;
25 "unused result of a type flagged as #[must_use]",
26 report_in_external_macro: true
32 "unused result of an expression in a statement"
35 #[derive(Copy, Clone)]
36 pub struct UnusedResults;
38 impl LintPass for UnusedResults {
39 fn name(&self) -> &'static str {
43 fn get_lints(&self) -> LintArray {
44 lint_array!(UNUSED_MUST_USE, UNUSED_RESULTS)
48 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
49 fn check_stmt(&mut self, cx: &LateContext<'_, '_>, s: &hir::Stmt) {
50 let expr = match s.node {
51 hir::StmtKind::Semi(ref expr) => &**expr,
55 if let hir::ExprKind::Ret(..) = expr.node {
59 let t = cx.tables.expr_ty(&expr);
60 let type_permits_lack_of_use = if t.is_unit()
61 || cx.tcx.is_ty_uninhabited_from(
62 cx.tcx.hir().get_module_parent_by_hir_id(expr.hir_id), t)
67 ty::Adt(def, _) => check_must_use(cx, def.did, s.span, "", ""),
68 ty::Opaque(def, _) => {
69 let mut must_use = false;
70 for (predicate, _) in &cx.tcx.predicates_of(def).predicates {
71 if let ty::Predicate::Trait(ref poly_trait_predicate) = predicate {
72 let trait_ref = poly_trait_predicate.skip_binder().trait_ref;
73 if check_must_use(cx, trait_ref.def_id, s.span, "implementer of ", "") {
81 ty::Dynamic(binder, _) => {
82 let mut must_use = false;
83 for predicate in binder.skip_binder().iter() {
84 if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate {
85 if check_must_use(cx, trait_ref.def_id, s.span, "", " trait object") {
97 let mut fn_warned = false;
98 let mut op_warned = false;
99 let maybe_def = match expr.node {
100 hir::ExprKind::Call(ref callee, _) => {
102 hir::ExprKind::Path(ref qpath) => {
103 let def = cx.tables.qpath_def(qpath, callee.hir_id);
105 Def::Fn(_) | Def::Method(_) => Some(def),
106 // `Def::Local` if it was a closure, for which we
107 // do not currently support must-use linting
114 hir::ExprKind::MethodCall(..) => {
115 cx.tables.type_dependent_defs().get(expr.hir_id).cloned()
119 if let Some(def) = maybe_def {
120 let def_id = def.def_id();
121 fn_warned = check_must_use(cx, def_id, s.span, "return value of ", "");
122 } else if type_permits_lack_of_use {
123 // We don't warn about unused unit or uninhabited types.
124 // (See https://github.com/rust-lang/rust/issues/43806 for details.)
128 let must_use_op = match expr.node {
129 // Hardcoding operators here seemed more expedient than the
130 // refactoring that would be needed to look up the `#[must_use]`
131 // attribute which does exist on the comparison trait methods
132 hir::ExprKind::Binary(bin_op, ..) => {
139 hir::BinOpKind::Gt => {
142 hir::BinOpKind::Add |
143 hir::BinOpKind::Sub |
144 hir::BinOpKind::Div |
145 hir::BinOpKind::Mul |
146 hir::BinOpKind::Rem => {
147 Some("arithmetic operation")
149 hir::BinOpKind::And | hir::BinOpKind::Or => {
150 Some("logical operation")
152 hir::BinOpKind::BitXor |
153 hir::BinOpKind::BitAnd |
154 hir::BinOpKind::BitOr |
155 hir::BinOpKind::Shl |
156 hir::BinOpKind::Shr => {
157 Some("bitwise operation")
161 hir::ExprKind::Unary(..) => Some("unary operation"),
165 if let Some(must_use_op) = must_use_op {
166 cx.span_lint(UNUSED_MUST_USE, expr.span,
167 &format!("unused {} that must be used", must_use_op));
171 if !(type_permits_lack_of_use || fn_warned || op_warned) {
172 cx.span_lint(UNUSED_RESULTS, s.span, "unused result");
176 cx: &LateContext<'_, '_>,
179 descr_pre_path: &str,
180 descr_post_path: &str,
182 for attr in cx.tcx.get_attrs(def_id).iter() {
183 if attr.check_name("must_use") {
184 let msg = format!("unused {}`{}`{} that must be used",
185 descr_pre_path, cx.tcx.def_path_str(def_id), descr_post_path);
186 let mut err = cx.struct_span_lint(UNUSED_MUST_USE, sp, &msg);
187 // check for #[must_use = "..."]
188 if let Some(note) = attr.value_str() {
189 err.note(¬e.as_str());
203 "path statements with no effect"
206 #[derive(Copy, Clone)]
207 pub struct PathStatements;
209 impl LintPass for PathStatements {
210 fn name(&self) -> &'static str {
214 fn get_lints(&self) -> LintArray {
215 lint_array!(PATH_STATEMENTS)
219 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PathStatements {
220 fn check_stmt(&mut self, cx: &LateContext<'_, '_>, s: &hir::Stmt) {
221 if let hir::StmtKind::Semi(ref expr) = s.node {
222 if let hir::ExprKind::Path(_) = expr.node {
223 cx.span_lint(PATH_STATEMENTS, s.span, "path statement with no effect");
230 pub UNUSED_ATTRIBUTES,
232 "detects attributes that were not used by the compiler"
235 #[derive(Copy, Clone)]
236 pub struct UnusedAttributes;
238 impl LintPass for UnusedAttributes {
239 fn name(&self) -> &'static str {
243 fn get_lints(&self) -> LintArray {
244 lint_array!(UNUSED_ATTRIBUTES)
248 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAttributes {
249 fn check_attribute(&mut self, cx: &LateContext<'_, '_>, attr: &ast::Attribute) {
250 debug!("checking attribute: {:?}", attr);
251 // Note that check_name() marks the attribute as used if it matches.
252 for &(name, ty, ..) in BUILTIN_ATTRIBUTES {
254 AttributeType::Whitelisted if attr.check_name(name) => {
255 debug!("{:?} is Whitelisted", name);
262 let plugin_attributes = cx.sess().plugin_attributes.borrow_mut();
263 for &(ref name, ty) in plugin_attributes.iter() {
264 if ty == AttributeType::Whitelisted && attr.check_name(&name) {
265 debug!("{:?} (plugin attr) is whitelisted with ty {:?}", name, ty);
270 let name = attr.name_or_empty();
271 if !attr::is_used(attr) {
272 debug!("Emitting warning for: {:?}", attr);
273 cx.span_lint(UNUSED_ATTRIBUTES, attr.span, "unused attribute");
274 // Is it a builtin attribute that must be used at the crate level?
275 let known_crate = BUILTIN_ATTRIBUTES.iter()
276 .find(|&&(builtin, ty, ..)| {
277 name == builtin && ty == AttributeType::CrateLevel
281 // Has a plugin registered this attribute as one that must be used at
283 let plugin_crate = plugin_attributes.iter()
284 .find(|&&(ref x, t)| name == x.as_str() && AttributeType::CrateLevel == t)
286 if known_crate || plugin_crate {
287 let msg = match attr.style {
288 ast::AttrStyle::Outer => {
289 "crate-level attribute should be an inner attribute: add an exclamation \
292 ast::AttrStyle::Inner => "crate-level attribute should be in the root module",
294 cx.span_lint(UNUSED_ATTRIBUTES, attr.span, msg);
297 debug!("Attr was used: {:?}", attr);
303 pub(super) UNUSED_PARENS,
305 "`if`, `match`, `while` and `return` do not need parentheses"
308 #[derive(Copy, Clone)]
309 pub struct UnusedParens;
312 fn check_unused_parens_expr(&self,
313 cx: &EarlyContext<'_>,
316 followed_by_block: bool) {
317 if let ast::ExprKind::Paren(ref inner) = value.node {
318 let necessary = followed_by_block && match inner.node {
319 ast::ExprKind::Ret(_) | ast::ExprKind::Break(..) => true,
320 _ => parser::contains_exterior_struct_lit(&inner),
323 let expr_text = if let Ok(snippet) = cx.sess().source_map()
324 .span_to_snippet(value.span) {
327 pprust::expr_to_string(value)
329 Self::remove_outer_parens(cx, value.span, &expr_text, msg);
334 fn check_unused_parens_pat(&self,
335 cx: &EarlyContext<'_>,
338 if let ast::PatKind::Paren(_) = value.node {
339 let pattern_text = if let Ok(snippet) = cx.sess().source_map()
340 .span_to_snippet(value.span) {
343 pprust::pat_to_string(value)
345 Self::remove_outer_parens(cx, value.span, &pattern_text, msg);
349 fn remove_outer_parens(cx: &EarlyContext<'_>, span: Span, pattern: &str, msg: &str) {
350 let span_msg = format!("unnecessary parentheses around {}", msg);
351 let mut err = cx.struct_span_lint(UNUSED_PARENS, span, &span_msg);
352 let mut ate_left_paren = false;
353 let mut ate_right_paren = false;
354 let parens_removed = pattern
361 ate_left_paren = true;
369 ate_right_paren = true;
376 err.span_suggestion_short(
378 "remove these parentheses",
380 Applicability::MachineApplicable,
386 impl LintPass for UnusedParens {
387 fn name(&self) -> &'static str {
391 fn get_lints(&self) -> LintArray {
392 lint_array!(UNUSED_PARENS)
396 impl EarlyLintPass for UnusedParens {
397 fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
398 use syntax::ast::ExprKind::*;
399 let (value, msg, followed_by_block) = match e.node {
400 If(ref cond, ..) => (cond, "`if` condition", true),
401 While(ref cond, ..) => (cond, "`while` condition", true),
402 IfLet(_, ref cond, ..) => (cond, "`if let` head expression", true),
403 WhileLet(_, ref cond, ..) => (cond, "`while let` head expression", true),
404 ForLoop(_, ref cond, ..) => (cond, "`for` head expression", true),
405 Match(ref head, _) => (head, "`match` head expression", true),
406 Ret(Some(ref value)) => (value, "`return` value", false),
407 Assign(_, ref value) => (value, "assigned value", false),
408 AssignOp(.., ref value) => (value, "assigned value", false),
409 // either function/method call, or something this lint doesn't care about
410 ref call_or_other => {
411 let (args_to_check, call_kind) = match *call_or_other {
412 Call(_, ref args) => (&args[..], "function"),
413 // first "argument" is self (which sometimes needs parens)
414 MethodCall(_, ref args) => (&args[1..], "method"),
415 // actual catch-all arm
420 // Don't lint if this is a nested macro expansion: otherwise, the lint could
421 // trigger in situations that macro authors shouldn't have to care about, e.g.,
422 // when a parenthesized token tree matched in one macro expansion is matched as
423 // an expression in another and used as a fn/method argument (Issue #47775)
424 if e.span.ctxt().outer().expn_info()
425 .map_or(false, |info| info.call_site.ctxt().outer()
426 .expn_info().is_some()) {
429 let msg = format!("{} argument", call_kind);
430 for arg in args_to_check {
431 self.check_unused_parens_expr(cx, arg, &msg, false);
436 self.check_unused_parens_expr(cx, &value, msg, followed_by_block);
439 fn check_pat(&mut self, cx: &EarlyContext<'_>, p: &ast::Pat, _: &mut bool) {
440 use ast::PatKind::{Paren, Range};
441 // The lint visitor will visit each subpattern of `p`. We do not want to lint any range
442 // pattern no matter where it occurs in the pattern. For something like `&(a..=b)`, there
443 // is a recursive `check_pat` on `a` and `b`, but we will assume that if there are
444 // unnecessary parens they serve a purpose of readability.
445 if let Paren(ref pat) = p.node {
448 _ => self.check_unused_parens_pat(cx, &p, "pattern")
453 fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) {
454 if let ast::StmtKind::Local(ref local) = s.node {
455 if let Some(ref value) = local.init {
456 self.check_unused_parens_expr(cx, &value, "assigned value", false);
463 UNUSED_IMPORT_BRACES,
465 "unnecessary braces around an imported item"
468 #[derive(Copy, Clone)]
469 pub struct UnusedImportBraces;
471 impl UnusedImportBraces {
472 fn check_use_tree(&self, cx: &EarlyContext<'_>, use_tree: &ast::UseTree, item: &ast::Item) {
473 if let ast::UseTreeKind::Nested(ref items) = use_tree.kind {
474 // Recursively check nested UseTrees
475 for &(ref tree, _) in items {
476 self.check_use_tree(cx, tree, item);
479 // Trigger the lint only if there is one nested item
480 if items.len() != 1 {
484 // Trigger the lint if the nested item is a non-self single item
486 match items[0].0.kind {
487 ast::UseTreeKind::Simple(rename, ..) => {
488 let orig_ident = items[0].0.prefix.segments.last().unwrap().ident;
489 if orig_ident.name == keywords::SelfLower.name() {
492 node_ident = rename.unwrap_or(orig_ident);
494 ast::UseTreeKind::Glob => {
495 node_ident = ast::Ident::from_str("*");
497 ast::UseTreeKind::Nested(_) => {
502 let msg = format!("braces around {} is unnecessary", node_ident.name);
503 cx.span_lint(UNUSED_IMPORT_BRACES, item.span, &msg);
508 impl LintPass for UnusedImportBraces {
509 fn name(&self) -> &'static str {
513 fn get_lints(&self) -> LintArray {
514 lint_array!(UNUSED_IMPORT_BRACES)
518 impl EarlyLintPass for UnusedImportBraces {
519 fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
520 if let ast::ItemKind::Use(ref use_tree) = item.node {
521 self.check_use_tree(cx, use_tree, item);
527 pub(super) UNUSED_ALLOCATION,
529 "detects unnecessary allocations that can be eliminated"
532 #[derive(Copy, Clone)]
533 pub struct UnusedAllocation;
535 impl LintPass for UnusedAllocation {
536 fn name(&self) -> &'static str {
540 fn get_lints(&self) -> LintArray {
541 lint_array!(UNUSED_ALLOCATION)
545 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAllocation {
546 fn check_expr(&mut self, cx: &LateContext<'_, '_>, e: &hir::Expr) {
548 hir::ExprKind::Box(_) => {}
552 for adj in cx.tables.expr_adjustments(e) {
553 if let adjustment::Adjust::Borrow(adjustment::AutoBorrow::Ref(_, m)) = adj.kind {
555 adjustment::AutoBorrowMutability::Immutable =>
556 "unnecessary allocation, use & instead",
557 adjustment::AutoBorrowMutability::Mutable { .. }=>
558 "unnecessary allocation, use &mut instead"
560 cx.span_lint(UNUSED_ALLOCATION, e.span, msg);