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.item_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();
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, ..)| name == builtin && ty == AttributeType::CrateLevel)
279 // Has a plugin registered this attribute as one that must be used at
281 let plugin_crate = plugin_attributes.iter()
282 .find(|&&(ref x, t)| name == &**x && AttributeType::CrateLevel == t)
284 if known_crate || plugin_crate {
285 let msg = match attr.style {
286 ast::AttrStyle::Outer => {
287 "crate-level attribute should be an inner attribute: add an exclamation \
290 ast::AttrStyle::Inner => "crate-level attribute should be in the root module",
292 cx.span_lint(UNUSED_ATTRIBUTES, attr.span, msg);
295 debug!("Attr was used: {:?}", attr);
301 pub(super) UNUSED_PARENS,
303 "`if`, `match`, `while` and `return` do not need parentheses"
306 #[derive(Copy, Clone)]
307 pub struct UnusedParens;
310 fn check_unused_parens_expr(&self,
311 cx: &EarlyContext<'_>,
314 followed_by_block: bool) {
315 if let ast::ExprKind::Paren(ref inner) = value.node {
316 let necessary = followed_by_block && match inner.node {
317 ast::ExprKind::Ret(_) | ast::ExprKind::Break(..) => true,
318 _ => parser::contains_exterior_struct_lit(&inner),
321 let expr_text = if let Ok(snippet) = cx.sess().source_map()
322 .span_to_snippet(value.span) {
325 pprust::expr_to_string(value)
327 Self::remove_outer_parens(cx, value.span, &expr_text, msg);
332 fn check_unused_parens_pat(&self,
333 cx: &EarlyContext<'_>,
336 if let ast::PatKind::Paren(_) = value.node {
337 let pattern_text = if let Ok(snippet) = cx.sess().source_map()
338 .span_to_snippet(value.span) {
341 pprust::pat_to_string(value)
343 Self::remove_outer_parens(cx, value.span, &pattern_text, msg);
347 fn remove_outer_parens(cx: &EarlyContext<'_>, span: Span, pattern: &str, msg: &str) {
348 let span_msg = format!("unnecessary parentheses around {}", msg);
349 let mut err = cx.struct_span_lint(UNUSED_PARENS, span, &span_msg);
350 let mut ate_left_paren = false;
351 let mut ate_right_paren = false;
352 let parens_removed = pattern
359 ate_left_paren = true;
367 ate_right_paren = true;
374 err.span_suggestion_short(
376 "remove these parentheses",
378 Applicability::MachineApplicable,
384 impl LintPass for UnusedParens {
385 fn name(&self) -> &'static str {
389 fn get_lints(&self) -> LintArray {
390 lint_array!(UNUSED_PARENS)
394 impl EarlyLintPass for UnusedParens {
395 fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
396 use syntax::ast::ExprKind::*;
397 let (value, msg, followed_by_block) = match e.node {
398 If(ref cond, ..) => (cond, "`if` condition", true),
399 While(ref cond, ..) => (cond, "`while` condition", true),
400 IfLet(_, ref cond, ..) => (cond, "`if let` head expression", true),
401 WhileLet(_, ref cond, ..) => (cond, "`while let` head expression", true),
402 ForLoop(_, ref cond, ..) => (cond, "`for` head expression", true),
403 Match(ref head, _) => (head, "`match` head expression", true),
404 Ret(Some(ref value)) => (value, "`return` value", false),
405 Assign(_, ref value) => (value, "assigned value", false),
406 AssignOp(.., ref value) => (value, "assigned value", false),
407 // either function/method call, or something this lint doesn't care about
408 ref call_or_other => {
409 let (args_to_check, call_kind) = match *call_or_other {
410 Call(_, ref args) => (&args[..], "function"),
411 // first "argument" is self (which sometimes needs parens)
412 MethodCall(_, ref args) => (&args[1..], "method"),
413 // actual catch-all arm
418 // Don't lint if this is a nested macro expansion: otherwise, the lint could
419 // trigger in situations that macro authors shouldn't have to care about, e.g.,
420 // when a parenthesized token tree matched in one macro expansion is matched as
421 // an expression in another and used as a fn/method argument (Issue #47775)
422 if e.span.ctxt().outer().expn_info()
423 .map_or(false, |info| info.call_site.ctxt().outer()
424 .expn_info().is_some()) {
427 let msg = format!("{} argument", call_kind);
428 for arg in args_to_check {
429 self.check_unused_parens_expr(cx, arg, &msg, false);
434 self.check_unused_parens_expr(cx, &value, msg, followed_by_block);
437 fn check_pat(&mut self, cx: &EarlyContext<'_>, p: &ast::Pat, _: &mut bool) {
438 use ast::PatKind::{Paren, Range};
439 // The lint visitor will visit each subpattern of `p`. We do not want to lint any range
440 // pattern no matter where it occurs in the pattern. For something like `&(a..=b)`, there
441 // is a recursive `check_pat` on `a` and `b`, but we will assume that if there are
442 // unnecessary parens they serve a purpose of readability.
443 if let Paren(ref pat) = p.node {
446 _ => self.check_unused_parens_pat(cx, &p, "pattern")
451 fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) {
452 if let ast::StmtKind::Local(ref local) = s.node {
453 if let Some(ref value) = local.init {
454 self.check_unused_parens_expr(cx, &value, "assigned value", false);
461 UNUSED_IMPORT_BRACES,
463 "unnecessary braces around an imported item"
466 #[derive(Copy, Clone)]
467 pub struct UnusedImportBraces;
469 impl UnusedImportBraces {
470 fn check_use_tree(&self, cx: &EarlyContext<'_>, use_tree: &ast::UseTree, item: &ast::Item) {
471 if let ast::UseTreeKind::Nested(ref items) = use_tree.kind {
472 // Recursively check nested UseTrees
473 for &(ref tree, _) in items {
474 self.check_use_tree(cx, tree, item);
477 // Trigger the lint only if there is one nested item
478 if items.len() != 1 {
482 // Trigger the lint if the nested item is a non-self single item
484 match items[0].0.kind {
485 ast::UseTreeKind::Simple(rename, ..) => {
486 let orig_ident = items[0].0.prefix.segments.last().unwrap().ident;
487 if orig_ident.name == keywords::SelfLower.name() {
490 node_ident = rename.unwrap_or(orig_ident);
492 ast::UseTreeKind::Glob => {
493 node_ident = ast::Ident::from_str("*");
495 ast::UseTreeKind::Nested(_) => {
500 let msg = format!("braces around {} is unnecessary", node_ident.name);
501 cx.span_lint(UNUSED_IMPORT_BRACES, item.span, &msg);
506 impl LintPass for UnusedImportBraces {
507 fn name(&self) -> &'static str {
511 fn get_lints(&self) -> LintArray {
512 lint_array!(UNUSED_IMPORT_BRACES)
516 impl EarlyLintPass for UnusedImportBraces {
517 fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
518 if let ast::ItemKind::Use(ref use_tree) = item.node {
519 self.check_use_tree(cx, use_tree, item);
525 pub(super) UNUSED_ALLOCATION,
527 "detects unnecessary allocations that can be eliminated"
530 #[derive(Copy, Clone)]
531 pub struct UnusedAllocation;
533 impl LintPass for UnusedAllocation {
534 fn name(&self) -> &'static str {
538 fn get_lints(&self) -> LintArray {
539 lint_array!(UNUSED_ALLOCATION)
543 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAllocation {
544 fn check_expr(&mut self, cx: &LateContext<'_, '_>, e: &hir::Expr) {
546 hir::ExprKind::Box(_) => {}
550 for adj in cx.tables.expr_adjustments(e) {
551 if let adjustment::Adjust::Borrow(adjustment::AutoBorrow::Ref(_, m)) = adj.kind {
553 adjustment::AutoBorrowMutability::Immutable =>
554 "unnecessary allocation, use & instead",
555 adjustment::AutoBorrowMutability::Mutable { .. }=>
556 "unnecessary allocation, use &mut instead"
558 cx.span_lint(UNUSED_ALLOCATION, e.span, msg);