1 use rustc::hir::def::{Res, DefKind};
2 use rustc::hir::def_id::DefId;
5 use rustc::ty::adjustment;
6 use rustc_data_structures::fx::FxHashMap;
7 use lint::{LateContext, EarlyContext, LintContext, LintArray};
8 use lint::{LintPass, EarlyLintPass, LateLintPass};
12 use syntax::errors::Applicability;
13 use syntax::feature_gate::{AttributeType, BuiltinAttribute, BUILTIN_ATTRIBUTE_MAP};
14 use syntax::print::pprust;
15 use syntax::symbol::{kw, sym};
16 use syntax::symbol::Symbol;
17 use syntax::util::parser;
27 "unused result of a type flagged as #[must_use]",
28 report_in_external_macro: true
34 "unused result of an expression in a statement"
37 declare_lint_pass!(UnusedResults => [UNUSED_MUST_USE, UNUSED_RESULTS]);
39 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
40 fn check_stmt(&mut self, cx: &LateContext<'_, '_>, s: &hir::Stmt) {
41 let expr = match s.node {
42 hir::StmtKind::Semi(ref expr) => &**expr,
46 if let hir::ExprKind::Ret(..) = expr.node {
50 let t = cx.tables.expr_ty(&expr);
51 let type_permits_lack_of_use = if t.is_unit()
52 || cx.tcx.is_ty_uninhabited_from(
53 cx.tcx.hir().get_module_parent_by_hir_id(expr.hir_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_id = match expr.node {
91 hir::ExprKind::Call(ref callee, _) => {
93 hir::ExprKind::Path(ref qpath) => {
94 match cx.tables.qpath_res(qpath, callee.hir_id) {
95 Res::Def(DefKind::Fn, def_id)
96 | Res::Def(DefKind::Method, def_id) => Some(def_id),
97 // `Res::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_def_id(expr.hir_id)
110 if let Some(def_id) = maybe_def_id {
111 fn_warned = check_must_use(cx, def_id, s.span, "return value of ", "");
112 } else if type_permits_lack_of_use {
113 // We don't warn about unused unit or uninhabited types.
114 // (See https://github.com/rust-lang/rust/issues/43806 for details.)
118 let must_use_op = match expr.node {
119 // Hardcoding operators here seemed more expedient than the
120 // refactoring that would be needed to look up the `#[must_use]`
121 // attribute which does exist on the comparison trait methods
122 hir::ExprKind::Binary(bin_op, ..) => {
129 hir::BinOpKind::Gt => {
132 hir::BinOpKind::Add |
133 hir::BinOpKind::Sub |
134 hir::BinOpKind::Div |
135 hir::BinOpKind::Mul |
136 hir::BinOpKind::Rem => {
137 Some("arithmetic operation")
139 hir::BinOpKind::And | hir::BinOpKind::Or => {
140 Some("logical operation")
142 hir::BinOpKind::BitXor |
143 hir::BinOpKind::BitAnd |
144 hir::BinOpKind::BitOr |
145 hir::BinOpKind::Shl |
146 hir::BinOpKind::Shr => {
147 Some("bitwise operation")
151 hir::ExprKind::Unary(..) => Some("unary operation"),
155 if let Some(must_use_op) = must_use_op {
156 cx.span_lint(UNUSED_MUST_USE, expr.span,
157 &format!("unused {} that must be used", must_use_op));
161 if !(type_permits_lack_of_use || fn_warned || op_warned) {
162 cx.span_lint(UNUSED_RESULTS, s.span, "unused result");
166 cx: &LateContext<'_, '_>,
169 descr_pre_path: &str,
170 descr_post_path: &str,
172 for attr in cx.tcx.get_attrs(def_id).iter() {
173 if attr.check_name(sym::must_use) {
174 let msg = format!("unused {}`{}`{} that must be used",
175 descr_pre_path, cx.tcx.def_path_str(def_id), descr_post_path);
176 let mut err = cx.struct_span_lint(UNUSED_MUST_USE, sp, &msg);
177 // check for #[must_use = "..."]
178 if let Some(note) = attr.value_str() {
179 err.note(¬e.as_str());
193 "path statements with no effect"
196 declare_lint_pass!(PathStatements => [PATH_STATEMENTS]);
198 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PathStatements {
199 fn check_stmt(&mut self, cx: &LateContext<'_, '_>, s: &hir::Stmt) {
200 if let hir::StmtKind::Semi(ref expr) = s.node {
201 if let hir::ExprKind::Path(_) = expr.node {
202 cx.span_lint(PATH_STATEMENTS, s.span, "path statement with no effect");
209 pub UNUSED_ATTRIBUTES,
211 "detects attributes that were not used by the compiler"
214 #[derive(Copy, Clone)]
215 pub struct UnusedAttributes {
216 builtin_attributes: &'static FxHashMap<Symbol, &'static BuiltinAttribute>,
219 impl UnusedAttributes {
220 pub fn new() -> Self {
222 builtin_attributes: &*BUILTIN_ATTRIBUTE_MAP,
227 impl_lint_pass!(UnusedAttributes => [UNUSED_ATTRIBUTES]);
229 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAttributes {
230 fn check_attribute(&mut self, cx: &LateContext<'_, '_>, attr: &ast::Attribute) {
231 debug!("checking attribute: {:?}", attr);
233 let attr_info = attr.ident().and_then(|ident| self.builtin_attributes.get(&ident.name));
235 if let Some(&&(name, ty, ..)) = attr_info {
237 AttributeType::Whitelisted => {
238 debug!("{:?} is Whitelisted", name);
245 let plugin_attributes = cx.sess().plugin_attributes.borrow_mut();
246 for &(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_or_empty();
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 = attr_info.map(|&&(_, ty, ..)| {
259 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(|&&(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 declare_lint_pass!(UnusedParens => [UNUSED_PARENS]);
292 fn check_unused_parens_expr(&self,
293 cx: &EarlyContext<'_>,
296 followed_by_block: bool) {
297 if let ast::ExprKind::Paren(ref inner) = value.node {
298 let necessary = followed_by_block && match inner.node {
299 ast::ExprKind::Ret(_) | ast::ExprKind::Break(..) => true,
300 _ => parser::contains_exterior_struct_lit(&inner),
303 let expr_text = if let Ok(snippet) = cx.sess().source_map()
304 .span_to_snippet(value.span) {
307 pprust::expr_to_string(value)
309 Self::remove_outer_parens(cx, value.span, &expr_text, msg);
314 fn check_unused_parens_pat(&self,
315 cx: &EarlyContext<'_>,
318 if let ast::PatKind::Paren(_) = value.node {
319 let pattern_text = if let Ok(snippet) = cx.sess().source_map()
320 .span_to_snippet(value.span) {
323 pprust::pat_to_string(value)
325 Self::remove_outer_parens(cx, value.span, &pattern_text, msg);
329 fn remove_outer_parens(cx: &EarlyContext<'_>, span: Span, pattern: &str, msg: &str) {
330 let span_msg = format!("unnecessary parentheses around {}", msg);
331 let mut err = cx.struct_span_lint(UNUSED_PARENS, span, &span_msg);
332 let mut ate_left_paren = false;
333 let mut ate_right_paren = false;
334 let parens_removed = pattern
341 ate_left_paren = true;
349 ate_right_paren = true;
356 err.span_suggestion_short(
358 "remove these parentheses",
360 Applicability::MachineApplicable,
366 impl EarlyLintPass for UnusedParens {
367 fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
368 use syntax::ast::ExprKind::*;
369 let (value, msg, followed_by_block) = match e.node {
370 If(ref cond, ..) => (cond, "`if` condition", true),
371 While(ref cond, ..) => (cond, "`while` condition", true),
372 IfLet(_, ref cond, ..) => (cond, "`if let` head expression", true),
373 WhileLet(_, ref cond, ..) => (cond, "`while let` head expression", true),
374 ForLoop(_, ref cond, ..) => (cond, "`for` head expression", true),
375 Match(ref head, _) => (head, "`match` head expression", true),
376 Ret(Some(ref value)) => (value, "`return` value", false),
377 Assign(_, ref value) => (value, "assigned value", false),
378 AssignOp(.., ref value) => (value, "assigned value", false),
379 // either function/method call, or something this lint doesn't care about
380 ref call_or_other => {
381 let (args_to_check, call_kind) = match *call_or_other {
382 Call(_, ref args) => (&args[..], "function"),
383 // first "argument" is self (which sometimes needs parens)
384 MethodCall(_, ref args) => (&args[1..], "method"),
385 // actual catch-all arm
390 // Don't lint if this is a nested macro expansion: otherwise, the lint could
391 // trigger in situations that macro authors shouldn't have to care about, e.g.,
392 // when a parenthesized token tree matched in one macro expansion is matched as
393 // an expression in another and used as a fn/method argument (Issue #47775)
394 if e.span.ctxt().outer_expn_info()
395 .map_or(false, |info| info.call_site.ctxt().outer_expn_info().is_some()) {
398 let msg = format!("{} argument", call_kind);
399 for arg in args_to_check {
400 self.check_unused_parens_expr(cx, arg, &msg, false);
405 self.check_unused_parens_expr(cx, &value, msg, followed_by_block);
408 fn check_pat(&mut self, cx: &EarlyContext<'_>, p: &ast::Pat) {
409 use ast::PatKind::{Paren, Range};
410 // The lint visitor will visit each subpattern of `p`. We do not want to lint any range
411 // pattern no matter where it occurs in the pattern. For something like `&(a..=b)`, there
412 // is a recursive `check_pat` on `a` and `b`, but we will assume that if there are
413 // unnecessary parens they serve a purpose of readability.
414 if let Paren(ref pat) = p.node {
417 _ => self.check_unused_parens_pat(cx, &p, "pattern")
422 fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) {
423 if let ast::StmtKind::Local(ref local) = s.node {
424 if let Some(ref value) = local.init {
425 self.check_unused_parens_expr(cx, &value, "assigned value", false);
432 UNUSED_IMPORT_BRACES,
434 "unnecessary braces around an imported item"
437 declare_lint_pass!(UnusedImportBraces => [UNUSED_IMPORT_BRACES]);
439 impl UnusedImportBraces {
440 fn check_use_tree(&self, cx: &EarlyContext<'_>, use_tree: &ast::UseTree, item: &ast::Item) {
441 if let ast::UseTreeKind::Nested(ref items) = use_tree.kind {
442 // Recursively check nested UseTrees
443 for &(ref tree, _) in items {
444 self.check_use_tree(cx, tree, item);
447 // Trigger the lint only if there is one nested item
448 if items.len() != 1 {
452 // Trigger the lint if the nested item is a non-self single item
454 match items[0].0.kind {
455 ast::UseTreeKind::Simple(rename, ..) => {
456 let orig_ident = items[0].0.prefix.segments.last().unwrap().ident;
457 if orig_ident.name == kw::SelfLower {
460 node_ident = rename.unwrap_or(orig_ident);
462 ast::UseTreeKind::Glob => {
463 node_ident = ast::Ident::from_str("*");
465 ast::UseTreeKind::Nested(_) => {
470 let msg = format!("braces around {} is unnecessary", node_ident.name);
471 cx.span_lint(UNUSED_IMPORT_BRACES, item.span, &msg);
476 impl EarlyLintPass for UnusedImportBraces {
477 fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
478 if let ast::ItemKind::Use(ref use_tree) = item.node {
479 self.check_use_tree(cx, use_tree, item);
485 pub(super) UNUSED_ALLOCATION,
487 "detects unnecessary allocations that can be eliminated"
490 declare_lint_pass!(UnusedAllocation => [UNUSED_ALLOCATION]);
492 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAllocation {
493 fn check_expr(&mut self, cx: &LateContext<'_, '_>, e: &hir::Expr) {
495 hir::ExprKind::Box(_) => {}
499 for adj in cx.tables.expr_adjustments(e) {
500 if let adjustment::Adjust::Borrow(adjustment::AutoBorrow::Ref(_, m)) = adj.kind {
502 adjustment::AutoBorrowMutability::Immutable =>
503 "unnecessary allocation, use & instead",
504 adjustment::AutoBorrowMutability::Mutable { .. }=>
505 "unnecessary allocation, use &mut instead"
507 cx.span_lint(UNUSED_ALLOCATION, e.span, msg);