1 use rustc::hir::def::Def;
2 use rustc::hir::def_id::DefId;
4 use rustc::ty::adjustment;
5 use lint::{LateContext, EarlyContext, LintContext, LintArray};
6 use lint::{LintPass, EarlyLintPass, LateLintPass};
10 use syntax::errors::Applicability;
11 use syntax::feature_gate::{BUILTIN_ATTRIBUTES, AttributeType};
12 use syntax::print::pprust;
13 use syntax::symbol::keywords;
14 use syntax::util::parser;
22 "unused result of a type flagged as #[must_use]",
23 report_in_external_macro: true
29 "unused result of an expression in a statement"
32 #[derive(Copy, Clone)]
33 pub struct UnusedResults;
35 impl LintPass for UnusedResults {
36 fn get_lints(&self) -> LintArray {
37 lint_array!(UNUSED_MUST_USE, UNUSED_RESULTS)
41 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
42 fn check_stmt(&mut self, cx: &LateContext, s: &hir::Stmt) {
43 let expr = match s.node {
44 hir::StmtKind::Semi(ref expr, _) => &**expr,
48 if let hir::ExprKind::Ret(..) = expr.node {
52 let t = cx.tables.expr_ty(&expr);
53 let type_permits_lack_of_use = if t.is_unit()
54 || cx.tcx.is_ty_uninhabited_from(cx.tcx.hir().get_module_parent(expr.id), t) {
58 ty::Adt(def, _) => check_must_use(cx, def.did, s.span, "", ""),
59 ty::Opaque(def, _) => {
60 let mut must_use = false;
61 for (predicate, _) in &cx.tcx.predicates_of(def).predicates {
62 if let ty::Predicate::Trait(ref poly_trait_predicate) = predicate {
63 let trait_ref = poly_trait_predicate.skip_binder().trait_ref;
64 if check_must_use(cx, trait_ref.def_id, s.span, "implementer of ", "") {
72 ty::Dynamic(binder, _) => {
73 let mut must_use = false;
74 for predicate in binder.skip_binder().iter() {
75 if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate {
76 if check_must_use(cx, trait_ref.def_id, s.span, "", " trait object") {
88 let mut fn_warned = false;
89 let mut op_warned = false;
90 let maybe_def = match expr.node {
91 hir::ExprKind::Call(ref callee, _) => {
93 hir::ExprKind::Path(ref qpath) => {
94 let def = cx.tables.qpath_def(qpath, callee.hir_id);
96 Def::Fn(_) | Def::Method(_) => Some(def),
97 // `Def::Local` if it was a closure, for which we
98 // do not currently support must-use linting
105 hir::ExprKind::MethodCall(..) => {
106 cx.tables.type_dependent_defs().get(expr.hir_id).cloned()
110 if let Some(def) = maybe_def {
111 let def_id = def.def_id();
112 fn_warned = check_must_use(cx, def_id, s.span, "return value of ", "");
113 } else if type_permits_lack_of_use {
114 // We don't warn about unused unit or uninhabited types.
115 // (See https://github.com/rust-lang/rust/issues/43806 for details.)
119 let must_use_op = match expr.node {
120 // Hardcoding operators here seemed more expedient than the
121 // refactoring that would be needed to look up the `#[must_use]`
122 // attribute which does exist on the comparison trait methods
123 hir::ExprKind::Binary(bin_op, ..) => {
130 hir::BinOpKind::Gt => {
133 hir::BinOpKind::Add |
134 hir::BinOpKind::Sub |
135 hir::BinOpKind::Div |
136 hir::BinOpKind::Mul |
137 hir::BinOpKind::Rem => {
138 Some("arithmetic operation")
140 hir::BinOpKind::And | hir::BinOpKind::Or => {
141 Some("logical operation")
143 hir::BinOpKind::BitXor |
144 hir::BinOpKind::BitAnd |
145 hir::BinOpKind::BitOr |
146 hir::BinOpKind::Shl |
147 hir::BinOpKind::Shr => {
148 Some("bitwise operation")
152 hir::ExprKind::Unary(..) => Some("unary operation"),
156 if let Some(must_use_op) = must_use_op {
157 cx.span_lint(UNUSED_MUST_USE, expr.span,
158 &format!("unused {} that must be used", must_use_op));
162 if !(type_permits_lack_of_use || fn_warned || op_warned) {
163 cx.span_lint(UNUSED_RESULTS, s.span, "unused result");
170 descr_pre_path: &str,
171 descr_post_path: &str,
173 for attr in cx.tcx.get_attrs(def_id).iter() {
174 if attr.check_name("must_use") {
175 let msg = format!("unused {}`{}`{} that must be used",
176 descr_pre_path, cx.tcx.item_path_str(def_id), descr_post_path);
177 let mut err = cx.struct_span_lint(UNUSED_MUST_USE, sp, &msg);
178 // check for #[must_use = "..."]
179 if let Some(note) = attr.value_str() {
180 err.note(¬e.as_str());
194 "path statements with no effect"
197 #[derive(Copy, Clone)]
198 pub struct PathStatements;
200 impl LintPass for PathStatements {
201 fn get_lints(&self) -> LintArray {
202 lint_array!(PATH_STATEMENTS)
206 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PathStatements {
207 fn check_stmt(&mut self, cx: &LateContext, s: &hir::Stmt) {
208 if let hir::StmtKind::Semi(ref expr, _) = s.node {
209 if let hir::ExprKind::Path(_) = expr.node {
210 cx.span_lint(PATH_STATEMENTS, s.span, "path statement with no effect");
217 pub UNUSED_ATTRIBUTES,
219 "detects attributes that were not used by the compiler"
222 #[derive(Copy, Clone)]
223 pub struct UnusedAttributes;
225 impl LintPass for UnusedAttributes {
226 fn get_lints(&self) -> LintArray {
227 lint_array!(UNUSED_ATTRIBUTES)
231 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAttributes {
232 fn check_attribute(&mut self, cx: &LateContext, attr: &ast::Attribute) {
233 debug!("checking attribute: {:?}", attr);
234 // Note that check_name() marks the attribute as used if it matches.
235 for &(ref name, ty, _) in BUILTIN_ATTRIBUTES {
237 AttributeType::Whitelisted if attr.check_name(name) => {
238 debug!("{:?} is Whitelisted", name);
245 let plugin_attributes = cx.sess().plugin_attributes.borrow_mut();
246 for &(ref name, ty) in plugin_attributes.iter() {
247 if ty == AttributeType::Whitelisted && attr.check_name(&name) {
248 debug!("{:?} (plugin attr) is whitelisted with ty {:?}", name, ty);
253 let name = attr.name();
254 if !attr::is_used(attr) {
255 debug!("Emitting warning for: {:?}", attr);
256 cx.span_lint(UNUSED_ATTRIBUTES, attr.span, "unused attribute");
257 // Is it a builtin attribute that must be used at the crate level?
258 let known_crate = BUILTIN_ATTRIBUTES.iter()
259 .find(|&&(builtin, ty, _)| name == builtin && ty == AttributeType::CrateLevel)
262 // Has a plugin registered this attribute as one that must be used at
264 let plugin_crate = plugin_attributes.iter()
265 .find(|&&(ref x, t)| name == &**x && AttributeType::CrateLevel == t)
267 if known_crate || plugin_crate {
268 let msg = match attr.style {
269 ast::AttrStyle::Outer => {
270 "crate-level attribute should be an inner attribute: add an exclamation \
273 ast::AttrStyle::Inner => "crate-level attribute should be in the root module",
275 cx.span_lint(UNUSED_ATTRIBUTES, attr.span, msg);
278 debug!("Attr was used: {:?}", attr);
284 pub(super) UNUSED_PARENS,
286 "`if`, `match`, `while` and `return` do not need parentheses"
289 #[derive(Copy, Clone)]
290 pub struct UnusedParens;
293 fn check_unused_parens_expr(&self,
297 followed_by_block: bool) {
298 if let ast::ExprKind::Paren(ref inner) = value.node {
299 let necessary = followed_by_block && match inner.node {
300 ast::ExprKind::Ret(_) | ast::ExprKind::Break(..) => true,
301 _ => parser::contains_exterior_struct_lit(&inner),
304 let expr_text = if let Ok(snippet) = cx.sess().source_map()
305 .span_to_snippet(value.span) {
308 pprust::expr_to_string(value)
310 Self::remove_outer_parens(cx, value.span, &expr_text, msg);
315 fn check_unused_parens_pat(&self,
319 if let ast::PatKind::Paren(_) = value.node {
320 let pattern_text = if let Ok(snippet) = cx.sess().source_map()
321 .span_to_snippet(value.span) {
324 pprust::pat_to_string(value)
326 Self::remove_outer_parens(cx, value.span, &pattern_text, msg);
330 fn remove_outer_parens(cx: &EarlyContext, span: Span, pattern: &str, msg: &str) {
331 let span_msg = format!("unnecessary parentheses around {}", msg);
332 let mut err = cx.struct_span_lint(UNUSED_PARENS, span, &span_msg);
333 let mut ate_left_paren = false;
334 let mut ate_right_paren = false;
335 let parens_removed = pattern
342 ate_left_paren = true;
350 ate_right_paren = true;
357 err.span_suggestion_short_with_applicability(
359 "remove these parentheses",
361 Applicability::MachineApplicable
367 impl LintPass for UnusedParens {
368 fn get_lints(&self) -> LintArray {
369 lint_array!(UNUSED_PARENS)
373 impl EarlyLintPass for UnusedParens {
374 fn check_expr(&mut self, cx: &EarlyContext, e: &ast::Expr) {
375 use syntax::ast::ExprKind::*;
376 let (value, msg, followed_by_block) = match e.node {
377 If(ref cond, ..) => (cond, "`if` condition", true),
378 While(ref cond, ..) => (cond, "`while` condition", true),
379 IfLet(_, ref cond, ..) => (cond, "`if let` head expression", true),
380 WhileLet(_, ref cond, ..) => (cond, "`while let` head expression", true),
381 ForLoop(_, ref cond, ..) => (cond, "`for` head expression", true),
382 Match(ref head, _) => (head, "`match` head expression", true),
383 Ret(Some(ref value)) => (value, "`return` value", false),
384 Assign(_, ref value) => (value, "assigned value", false),
385 AssignOp(.., ref value) => (value, "assigned value", false),
386 // either function/method call, or something this lint doesn't care about
387 ref call_or_other => {
388 let (args_to_check, call_kind) = match *call_or_other {
389 Call(_, ref args) => (&args[..], "function"),
390 // first "argument" is self (which sometimes needs parens)
391 MethodCall(_, ref args) => (&args[1..], "method"),
392 // actual catch-all arm
397 // Don't lint if this is a nested macro expansion: otherwise, the lint could
398 // trigger in situations that macro authors shouldn't have to care about, e.g.,
399 // when a parenthesized token tree matched in one macro expansion is matched as
400 // an expression in another and used as a fn/method argument (Issue #47775)
401 if e.span.ctxt().outer().expn_info()
402 .map_or(false, |info| info.call_site.ctxt().outer()
403 .expn_info().is_some()) {
406 let msg = format!("{} argument", call_kind);
407 for arg in args_to_check {
408 self.check_unused_parens_expr(cx, arg, &msg, false);
413 self.check_unused_parens_expr(cx, &value, msg, followed_by_block);
416 fn check_pat(&mut self, cx: &EarlyContext, p: &ast::Pat, _: &mut bool) {
417 use ast::PatKind::{Paren, Range};
418 // The lint visitor will visit each subpattern of `p`. We do not want to lint any range
419 // pattern no matter where it occurs in the pattern. For something like `&(a..=b)`, there
420 // is a recursive `check_pat` on `a` and `b`, but we will assume that if there are
421 // unnecessary parens they serve a purpose of readability.
422 if let Paren(ref pat) = p.node {
425 _ => self.check_unused_parens_pat(cx, &p, "pattern")
430 fn check_stmt(&mut self, cx: &EarlyContext, s: &ast::Stmt) {
431 if let ast::StmtKind::Local(ref local) = s.node {
432 if let Some(ref value) = local.init {
433 self.check_unused_parens_expr(cx, &value, "assigned value", false);
440 UNUSED_IMPORT_BRACES,
442 "unnecessary braces around an imported item"
445 #[derive(Copy, Clone)]
446 pub struct UnusedImportBraces;
448 impl UnusedImportBraces {
449 fn check_use_tree(&self, cx: &EarlyContext, use_tree: &ast::UseTree, item: &ast::Item) {
450 if let ast::UseTreeKind::Nested(ref items) = use_tree.kind {
451 // Recursively check nested UseTrees
452 for &(ref tree, _) in items {
453 self.check_use_tree(cx, tree, item);
456 // Trigger the lint only if there is one nested item
457 if items.len() != 1 {
461 // Trigger the lint if the nested item is a non-self single item
463 match items[0].0.kind {
464 ast::UseTreeKind::Simple(rename, ..) => {
465 let orig_ident = items[0].0.prefix.segments.last().unwrap().ident;
466 if orig_ident.name == keywords::SelfLower.name() {
469 node_ident = rename.unwrap_or(orig_ident);
471 ast::UseTreeKind::Glob => {
472 node_ident = ast::Ident::from_str("*");
474 ast::UseTreeKind::Nested(_) => {
479 let msg = format!("braces around {} is unnecessary", node_ident.name);
480 cx.span_lint(UNUSED_IMPORT_BRACES, item.span, &msg);
485 impl LintPass for UnusedImportBraces {
486 fn get_lints(&self) -> LintArray {
487 lint_array!(UNUSED_IMPORT_BRACES)
491 impl EarlyLintPass for UnusedImportBraces {
492 fn check_item(&mut self, cx: &EarlyContext, item: &ast::Item) {
493 if let ast::ItemKind::Use(ref use_tree) = item.node {
494 self.check_use_tree(cx, use_tree, item);
500 pub(super) UNUSED_ALLOCATION,
502 "detects unnecessary allocations that can be eliminated"
505 #[derive(Copy, Clone)]
506 pub struct UnusedAllocation;
508 impl LintPass for UnusedAllocation {
509 fn get_lints(&self) -> LintArray {
510 lint_array!(UNUSED_ALLOCATION)
514 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAllocation {
515 fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
517 hir::ExprKind::Box(_) => {}
521 for adj in cx.tables.expr_adjustments(e) {
522 if let adjustment::Adjust::Borrow(adjustment::AutoBorrow::Ref(_, m)) = adj.kind {
524 adjustment::AutoBorrowMutability::Immutable =>
525 "unnecessary allocation, use & instead",
526 adjustment::AutoBorrowMutability::Mutable { .. }=>
527 "unnecessary allocation, use &mut instead"
529 cx.span_lint(UNUSED_ALLOCATION, e.span, msg);