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 declare_lint_pass!(UnusedResults => [UNUSED_MUST_USE, UNUSED_RESULTS]);
37 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
38 fn check_stmt(&mut self, cx: &LateContext<'_, '_>, s: &hir::Stmt) {
39 let expr = match s.node {
40 hir::StmtKind::Semi(ref expr) => &**expr,
44 if let hir::ExprKind::Ret(..) = expr.node {
48 let t = cx.tables.expr_ty(&expr);
49 let type_permits_lack_of_use = if t.is_unit()
50 || cx.tcx.is_ty_uninhabited_from(
51 cx.tcx.hir().get_module_parent_by_hir_id(expr.hir_id), t)
56 ty::Adt(def, _) => check_must_use(cx, def.did, s.span, "", ""),
57 ty::Opaque(def, _) => {
58 let mut must_use = false;
59 for (predicate, _) in &cx.tcx.predicates_of(def).predicates {
60 if let ty::Predicate::Trait(ref poly_trait_predicate) = predicate {
61 let trait_ref = poly_trait_predicate.skip_binder().trait_ref;
62 if check_must_use(cx, trait_ref.def_id, s.span, "implementer of ", "") {
70 ty::Dynamic(binder, _) => {
71 let mut must_use = false;
72 for predicate in binder.skip_binder().iter() {
73 if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate {
74 if check_must_use(cx, trait_ref.def_id, s.span, "", " trait object") {
86 let mut fn_warned = false;
87 let mut op_warned = false;
88 let maybe_def = match expr.node {
89 hir::ExprKind::Call(ref callee, _) => {
91 hir::ExprKind::Path(ref qpath) => {
92 let def = cx.tables.qpath_def(qpath, callee.hir_id);
94 Def::Fn(_) | Def::Method(_) => Some(def),
95 // `Def::Local` if it was a closure, for which we
96 // do not currently support must-use linting
103 hir::ExprKind::MethodCall(..) => {
104 cx.tables.type_dependent_def(expr.hir_id)
108 if let Some(def) = maybe_def {
109 let def_id = def.def_id();
110 fn_warned = check_must_use(cx, def_id, s.span, "return value of ", "");
111 } else if type_permits_lack_of_use {
112 // We don't warn about unused unit or uninhabited types.
113 // (See https://github.com/rust-lang/rust/issues/43806 for details.)
117 let must_use_op = match expr.node {
118 // Hardcoding operators here seemed more expedient than the
119 // refactoring that would be needed to look up the `#[must_use]`
120 // attribute which does exist on the comparison trait methods
121 hir::ExprKind::Binary(bin_op, ..) => {
128 hir::BinOpKind::Gt => {
131 hir::BinOpKind::Add |
132 hir::BinOpKind::Sub |
133 hir::BinOpKind::Div |
134 hir::BinOpKind::Mul |
135 hir::BinOpKind::Rem => {
136 Some("arithmetic operation")
138 hir::BinOpKind::And | hir::BinOpKind::Or => {
139 Some("logical operation")
141 hir::BinOpKind::BitXor |
142 hir::BinOpKind::BitAnd |
143 hir::BinOpKind::BitOr |
144 hir::BinOpKind::Shl |
145 hir::BinOpKind::Shr => {
146 Some("bitwise operation")
150 hir::ExprKind::Unary(..) => Some("unary operation"),
154 if let Some(must_use_op) = must_use_op {
155 cx.span_lint(UNUSED_MUST_USE, expr.span,
156 &format!("unused {} that must be used", must_use_op));
160 if !(type_permits_lack_of_use || fn_warned || op_warned) {
161 cx.span_lint(UNUSED_RESULTS, s.span, "unused result");
165 cx: &LateContext<'_, '_>,
168 descr_pre_path: &str,
169 descr_post_path: &str,
171 for attr in cx.tcx.get_attrs(def_id).iter() {
172 if attr.check_name("must_use") {
173 let msg = format!("unused {}`{}`{} that must be used",
174 descr_pre_path, cx.tcx.def_path_str(def_id), descr_post_path);
175 let mut err = cx.struct_span_lint(UNUSED_MUST_USE, sp, &msg);
176 // check for #[must_use = "..."]
177 if let Some(note) = attr.value_str() {
178 err.note(¬e.as_str());
192 "path statements with no effect"
195 declare_lint_pass!(PathStatements => [PATH_STATEMENTS]);
197 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PathStatements {
198 fn check_stmt(&mut self, cx: &LateContext<'_, '_>, s: &hir::Stmt) {
199 if let hir::StmtKind::Semi(ref expr) = s.node {
200 if let hir::ExprKind::Path(_) = expr.node {
201 cx.span_lint(PATH_STATEMENTS, s.span, "path statement with no effect");
208 pub UNUSED_ATTRIBUTES,
210 "detects attributes that were not used by the compiler"
213 declare_lint_pass!(UnusedAttributes => [UNUSED_ATTRIBUTES]);
215 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAttributes {
216 fn check_attribute(&mut self, cx: &LateContext<'_, '_>, attr: &ast::Attribute) {
217 debug!("checking attribute: {:?}", attr);
218 // Note that check_name() marks the attribute as used if it matches.
219 for &(name, ty, ..) in BUILTIN_ATTRIBUTES {
221 AttributeType::Whitelisted if attr.check_name(name) => {
222 debug!("{:?} is Whitelisted", name);
229 let plugin_attributes = cx.sess().plugin_attributes.borrow_mut();
230 for &(ref name, ty) in plugin_attributes.iter() {
231 if ty == AttributeType::Whitelisted && attr.check_name(&**name) {
232 debug!("{:?} (plugin attr) is whitelisted with ty {:?}", name, ty);
237 let name = attr.name_or_empty();
238 if !attr::is_used(attr) {
239 debug!("Emitting warning for: {:?}", attr);
240 cx.span_lint(UNUSED_ATTRIBUTES, attr.span, "unused attribute");
241 // Is it a builtin attribute that must be used at the crate level?
242 let known_crate = BUILTIN_ATTRIBUTES.iter()
243 .find(|&&(builtin, ty, ..)| {
244 name == builtin && ty == AttributeType::CrateLevel
248 // Has a plugin registered this attribute as one that must be used at
250 let plugin_crate = plugin_attributes.iter()
251 .find(|&&(ref x, t)| name == x.as_str() && AttributeType::CrateLevel == t)
253 if known_crate || plugin_crate {
254 let msg = match attr.style {
255 ast::AttrStyle::Outer => {
256 "crate-level attribute should be an inner attribute: add an exclamation \
259 ast::AttrStyle::Inner => "crate-level attribute should be in the root module",
261 cx.span_lint(UNUSED_ATTRIBUTES, attr.span, msg);
264 debug!("Attr was used: {:?}", attr);
270 pub(super) UNUSED_PARENS,
272 "`if`, `match`, `while` and `return` do not need parentheses"
275 declare_lint_pass!(UnusedParens => [UNUSED_PARENS]);
278 fn check_unused_parens_expr(&self,
279 cx: &EarlyContext<'_>,
282 followed_by_block: bool) {
283 if let ast::ExprKind::Paren(ref inner) = value.node {
284 let necessary = followed_by_block && match inner.node {
285 ast::ExprKind::Ret(_) | ast::ExprKind::Break(..) => true,
286 _ => parser::contains_exterior_struct_lit(&inner),
289 let expr_text = if let Ok(snippet) = cx.sess().source_map()
290 .span_to_snippet(value.span) {
293 pprust::expr_to_string(value)
295 Self::remove_outer_parens(cx, value.span, &expr_text, msg);
300 fn check_unused_parens_pat(&self,
301 cx: &EarlyContext<'_>,
304 if let ast::PatKind::Paren(_) = value.node {
305 let pattern_text = if let Ok(snippet) = cx.sess().source_map()
306 .span_to_snippet(value.span) {
309 pprust::pat_to_string(value)
311 Self::remove_outer_parens(cx, value.span, &pattern_text, msg);
315 fn remove_outer_parens(cx: &EarlyContext<'_>, span: Span, pattern: &str, msg: &str) {
316 let span_msg = format!("unnecessary parentheses around {}", msg);
317 let mut err = cx.struct_span_lint(UNUSED_PARENS, span, &span_msg);
318 let mut ate_left_paren = false;
319 let mut ate_right_paren = false;
320 let parens_removed = pattern
327 ate_left_paren = true;
335 ate_right_paren = true;
342 err.span_suggestion_short(
344 "remove these parentheses",
346 Applicability::MachineApplicable,
352 impl EarlyLintPass for UnusedParens {
353 fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
354 use syntax::ast::ExprKind::*;
355 let (value, msg, followed_by_block) = match e.node {
356 If(ref cond, ..) => (cond, "`if` condition", true),
357 While(ref cond, ..) => (cond, "`while` condition", true),
358 IfLet(_, ref cond, ..) => (cond, "`if let` head expression", true),
359 WhileLet(_, ref cond, ..) => (cond, "`while let` head expression", true),
360 ForLoop(_, ref cond, ..) => (cond, "`for` head expression", true),
361 Match(ref head, _) => (head, "`match` head expression", true),
362 Ret(Some(ref value)) => (value, "`return` value", false),
363 Assign(_, ref value) => (value, "assigned value", false),
364 AssignOp(.., ref value) => (value, "assigned value", false),
365 // either function/method call, or something this lint doesn't care about
366 ref call_or_other => {
367 let (args_to_check, call_kind) = match *call_or_other {
368 Call(_, ref args) => (&args[..], "function"),
369 // first "argument" is self (which sometimes needs parens)
370 MethodCall(_, ref args) => (&args[1..], "method"),
371 // actual catch-all arm
376 // Don't lint if this is a nested macro expansion: otherwise, the lint could
377 // trigger in situations that macro authors shouldn't have to care about, e.g.,
378 // when a parenthesized token tree matched in one macro expansion is matched as
379 // an expression in another and used as a fn/method argument (Issue #47775)
380 if e.span.ctxt().outer().expn_info()
381 .map_or(false, |info| info.call_site.ctxt().outer()
382 .expn_info().is_some()) {
385 let msg = format!("{} argument", call_kind);
386 for arg in args_to_check {
387 self.check_unused_parens_expr(cx, arg, &msg, false);
392 self.check_unused_parens_expr(cx, &value, msg, followed_by_block);
395 fn check_pat(&mut self, cx: &EarlyContext<'_>, p: &ast::Pat, _: &mut bool) {
396 use ast::PatKind::{Paren, Range};
397 // The lint visitor will visit each subpattern of `p`. We do not want to lint any range
398 // pattern no matter where it occurs in the pattern. For something like `&(a..=b)`, there
399 // is a recursive `check_pat` on `a` and `b`, but we will assume that if there are
400 // unnecessary parens they serve a purpose of readability.
401 if let Paren(ref pat) = p.node {
404 _ => self.check_unused_parens_pat(cx, &p, "pattern")
409 fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) {
410 if let ast::StmtKind::Local(ref local) = s.node {
411 if let Some(ref value) = local.init {
412 self.check_unused_parens_expr(cx, &value, "assigned value", false);
419 UNUSED_IMPORT_BRACES,
421 "unnecessary braces around an imported item"
424 declare_lint_pass!(UnusedImportBraces => [UNUSED_IMPORT_BRACES]);
426 impl UnusedImportBraces {
427 fn check_use_tree(&self, cx: &EarlyContext<'_>, use_tree: &ast::UseTree, item: &ast::Item) {
428 if let ast::UseTreeKind::Nested(ref items) = use_tree.kind {
429 // Recursively check nested UseTrees
430 for &(ref tree, _) in items {
431 self.check_use_tree(cx, tree, item);
434 // Trigger the lint only if there is one nested item
435 if items.len() != 1 {
439 // Trigger the lint if the nested item is a non-self single item
441 match items[0].0.kind {
442 ast::UseTreeKind::Simple(rename, ..) => {
443 let orig_ident = items[0].0.prefix.segments.last().unwrap().ident;
444 if orig_ident.name == keywords::SelfLower.name() {
447 node_ident = rename.unwrap_or(orig_ident);
449 ast::UseTreeKind::Glob => {
450 node_ident = ast::Ident::from_str("*");
452 ast::UseTreeKind::Nested(_) => {
457 let msg = format!("braces around {} is unnecessary", node_ident.name);
458 cx.span_lint(UNUSED_IMPORT_BRACES, item.span, &msg);
463 impl EarlyLintPass for UnusedImportBraces {
464 fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
465 if let ast::ItemKind::Use(ref use_tree) = item.node {
466 self.check_use_tree(cx, use_tree, item);
472 pub(super) UNUSED_ALLOCATION,
474 "detects unnecessary allocations that can be eliminated"
477 declare_lint_pass!(UnusedAllocation => [UNUSED_ALLOCATION]);
479 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAllocation {
480 fn check_expr(&mut self, cx: &LateContext<'_, '_>, e: &hir::Expr) {
482 hir::ExprKind::Box(_) => {}
486 for adj in cx.tables.expr_adjustments(e) {
487 if let adjustment::Adjust::Borrow(adjustment::AutoBorrow::Ref(_, m)) = adj.kind {
489 adjustment::AutoBorrowMutability::Immutable =>
490 "unnecessary allocation, use & instead",
491 adjustment::AutoBorrowMutability::Mutable { .. }=>
492 "unnecessary allocation, use &mut instead"
494 cx.span_lint(UNUSED_ALLOCATION, e.span, msg);