rust/src/librustc_lint/unused.rs
Zack M. Davis 0981211c62 hard feature-gate for #[must_use] on functions
We'll actually want a new "soft" warning-only gate to maintain
backwards-compatibility, but it's cleaner to start out with the established,
well-understood gate before implementing the alternative warn-only behavior in
a later commit.

This is in the matter of #43302.
2017-08-22 17:30:39 -07:00

514 lines
17 KiB
Rust

// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use rustc::hir::def_id::DefId;
use rustc::ty;
use rustc::ty::adjustment;
use util::nodemap::FxHashMap;
use lint::{LateContext, EarlyContext, LintContext, LintArray};
use lint::{LintPass, EarlyLintPass, LateLintPass};
use std::collections::hash_map::Entry::{Occupied, Vacant};
use syntax::ast;
use syntax::attr;
use syntax::feature_gate::{BUILTIN_ATTRIBUTES, AttributeType};
use syntax::symbol::keywords;
use syntax::ptr::P;
use syntax_pos::Span;
use rustc_back::slice;
use rustc::hir;
use rustc::hir::intravisit::FnKind;
declare_lint! {
pub UNUSED_MUT,
Warn,
"detect mut variables which don't need to be mutable"
}
#[derive(Copy, Clone)]
pub struct UnusedMut;
impl UnusedMut {
fn check_unused_mut_pat(&self, cx: &LateContext, pats: &[P<hir::Pat>]) {
// collect all mutable pattern and group their NodeIDs by their Identifier to
// avoid false warnings in match arms with multiple patterns
let mut mutables = FxHashMap();
for p in pats {
p.each_binding(|_, id, span, path1| {
let hir_id = cx.tcx.hir.node_to_hir_id(id);
let bm = match cx.tables.pat_binding_modes().get(hir_id) {
Some(&bm) => bm,
None => span_bug!(span, "missing binding mode"),
};
let name = path1.node;
if let ty::BindByValue(hir::MutMutable) = bm {
if !name.as_str().starts_with("_") {
match mutables.entry(name) {
Vacant(entry) => {
entry.insert(vec![id]);
}
Occupied(mut entry) => {
entry.get_mut().push(id);
}
}
}
}
});
}
let used_mutables = cx.tcx.used_mut_nodes.borrow();
for (_, v) in &mutables {
if !v.iter().any(|e| used_mutables.contains(e)) {
cx.span_lint(UNUSED_MUT,
cx.tcx.hir.span(v[0]),
"variable does not need to be mutable");
}
}
}
}
impl LintPass for UnusedMut {
fn get_lints(&self) -> LintArray {
lint_array!(UNUSED_MUT)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedMut {
fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
if let hir::ExprMatch(_, ref arms, _) = e.node {
for a in arms {
self.check_unused_mut_pat(cx, &a.pats)
}
}
}
fn check_stmt(&mut self, cx: &LateContext, s: &hir::Stmt) {
if let hir::StmtDecl(ref d, _) = s.node {
if let hir::DeclLocal(ref l) = d.node {
self.check_unused_mut_pat(cx, slice::ref_slice(&l.pat));
}
}
}
fn check_fn(&mut self,
cx: &LateContext,
_: FnKind,
_: &hir::FnDecl,
body: &hir::Body,
_: Span,
_: ast::NodeId) {
for a in &body.arguments {
self.check_unused_mut_pat(cx, slice::ref_slice(&a.pat));
}
}
}
declare_lint! {
pub UNUSED_MUST_USE,
Warn,
"unused result of a type flagged as #[must_use]"
}
declare_lint! {
pub UNUSED_RESULTS,
Allow,
"unused result of an expression in a statement"
}
#[derive(Copy, Clone)]
pub struct UnusedResults;
impl LintPass for UnusedResults {
fn get_lints(&self) -> LintArray {
lint_array!(UNUSED_MUST_USE, UNUSED_RESULTS)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
fn check_stmt(&mut self, cx: &LateContext, s: &hir::Stmt) {
let expr = match s.node {
hir::StmtSemi(ref expr, _) => &**expr,
_ => return,
};
if let hir::ExprRet(..) = expr.node {
return;
}
let t = cx.tables.expr_ty(&expr);
let ty_warned = match t.sty {
ty::TyTuple(ref tys, _) if tys.is_empty() => return,
ty::TyNever => return,
ty::TyAdt(def, _) => {
if def.variants.is_empty() {
return;
} else {
check_must_use(cx, def.did, s.span, "")
}
},
_ => false,
};
let mut fn_warned = false;
if cx.tcx.sess.features.borrow().fn_must_use {
let maybe_def = match expr.node {
hir::ExprCall(ref callee, _) => {
match callee.node {
hir::ExprPath(ref qpath) => {
Some(cx.tables.qpath_def(qpath, callee.hir_id))
},
_ => None
}
},
hir::ExprMethodCall(..) => {
cx.tables.type_dependent_defs().get(expr.hir_id).cloned()
},
_ => None
};
if let Some(def) = maybe_def {
let def_id = def.def_id();
fn_warned = check_must_use(cx, def_id, s.span, "return value of ");
}
}
if !(ty_warned || fn_warned) {
cx.span_lint(UNUSED_RESULTS, s.span, "unused result");
}
fn check_must_use(cx: &LateContext, def_id: DefId, sp: Span, describe_path: &str) -> bool {
for attr in cx.tcx.get_attrs(def_id).iter() {
if attr.check_name("must_use") {
let mut msg = format!("unused {}`{}` which must be used",
describe_path, cx.tcx.item_path_str(def_id));
// check for #[must_use="..."]
if let Some(s) = attr.value_str() {
msg.push_str(": ");
msg.push_str(&s.as_str());
}
cx.span_lint(UNUSED_MUST_USE, sp, &msg);
return true;
}
}
false
}
}
}
declare_lint! {
pub UNUSED_UNSAFE,
Warn,
"unnecessary use of an `unsafe` block"
}
#[derive(Copy, Clone)]
pub struct UnusedUnsafe;
impl LintPass for UnusedUnsafe {
fn get_lints(&self) -> LintArray {
lint_array!(UNUSED_UNSAFE)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedUnsafe {
fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
/// Return the NodeId for an enclosing scope that is also `unsafe`
fn is_enclosed(cx: &LateContext, id: ast::NodeId) -> Option<(String, ast::NodeId)> {
let parent_id = cx.tcx.hir.get_parent_node(id);
if parent_id != id {
if cx.tcx.used_unsafe.borrow().contains(&parent_id) {
Some(("block".to_string(), parent_id))
} else if let Some(hir::map::NodeItem(&hir::Item {
node: hir::ItemFn(_, hir::Unsafety::Unsafe, _, _, _, _),
..
})) = cx.tcx.hir.find(parent_id) {
Some(("fn".to_string(), parent_id))
} else {
is_enclosed(cx, parent_id)
}
} else {
None
}
}
if let hir::ExprBlock(ref blk) = e.node {
// Don't warn about generated blocks, that'll just pollute the output.
if blk.rules == hir::UnsafeBlock(hir::UserProvided) &&
!cx.tcx.used_unsafe.borrow().contains(&blk.id) {
let mut db = cx.struct_span_lint(UNUSED_UNSAFE, blk.span,
"unnecessary `unsafe` block");
db.span_label(blk.span, "unnecessary `unsafe` block");
if let Some((kind, id)) = is_enclosed(cx, blk.id) {
db.span_note(cx.tcx.hir.span(id),
&format!("because it's nested under this `unsafe` {}", kind));
}
db.emit();
}
}
}
}
declare_lint! {
pub PATH_STATEMENTS,
Warn,
"path statements with no effect"
}
#[derive(Copy, Clone)]
pub struct PathStatements;
impl LintPass for PathStatements {
fn get_lints(&self) -> LintArray {
lint_array!(PATH_STATEMENTS)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PathStatements {
fn check_stmt(&mut self, cx: &LateContext, s: &hir::Stmt) {
if let hir::StmtSemi(ref expr, _) = s.node {
if let hir::ExprPath(_) = expr.node {
cx.span_lint(PATH_STATEMENTS, s.span, "path statement with no effect");
}
}
}
}
declare_lint! {
pub UNUSED_ATTRIBUTES,
Warn,
"detects attributes that were not used by the compiler"
}
#[derive(Copy, Clone)]
pub struct UnusedAttributes;
impl LintPass for UnusedAttributes {
fn get_lints(&self) -> LintArray {
lint_array!(UNUSED_ATTRIBUTES)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAttributes {
fn check_attribute(&mut self, cx: &LateContext, attr: &ast::Attribute) {
debug!("checking attribute: {:?}", attr);
let name = unwrap_or!(attr.name(), return);
// Note that check_name() marks the attribute as used if it matches.
for &(ref name, ty, _) in BUILTIN_ATTRIBUTES {
match ty {
AttributeType::Whitelisted if attr.check_name(name) => {
debug!("{:?} is Whitelisted", name);
break;
}
_ => (),
}
}
let plugin_attributes = cx.sess().plugin_attributes.borrow_mut();
for &(ref name, ty) in plugin_attributes.iter() {
if ty == AttributeType::Whitelisted && attr.check_name(&name) {
debug!("{:?} (plugin attr) is whitelisted with ty {:?}", name, ty);
break;
}
}
if !attr::is_used(attr) {
debug!("Emitting warning for: {:?}", attr);
cx.span_lint(UNUSED_ATTRIBUTES, attr.span, "unused attribute");
// Is it a builtin attribute that must be used at the crate level?
let known_crate = BUILTIN_ATTRIBUTES.iter()
.find(|&&(builtin, ty, _)| name == builtin && ty == AttributeType::CrateLevel)
.is_some();
// Has a plugin registered this attribute as one which must be used at
// the crate level?
let plugin_crate = plugin_attributes.iter()
.find(|&&(ref x, t)| name == &**x && AttributeType::CrateLevel == t)
.is_some();
if known_crate || plugin_crate {
let msg = match attr.style {
ast::AttrStyle::Outer => {
"crate-level attribute should be an inner attribute: add an exclamation \
mark: #![foo]"
}
ast::AttrStyle::Inner => "crate-level attribute should be in the root module",
};
cx.span_lint(UNUSED_ATTRIBUTES, attr.span, msg);
}
} else {
debug!("Attr was used: {:?}", attr);
}
}
}
declare_lint! {
UNUSED_PARENS,
Warn,
"`if`, `match`, `while` and `return` do not need parentheses"
}
#[derive(Copy, Clone)]
pub struct UnusedParens;
impl UnusedParens {
fn check_unused_parens_core(&self,
cx: &EarlyContext,
value: &ast::Expr,
msg: &str,
struct_lit_needs_parens: bool) {
if let ast::ExprKind::Paren(ref inner) = value.node {
let necessary = struct_lit_needs_parens && contains_exterior_struct_lit(&inner);
if !necessary {
cx.span_lint(UNUSED_PARENS,
value.span,
&format!("unnecessary parentheses around {}", msg))
}
}
/// Expressions that syntactically contain an "exterior" struct
/// literal i.e. not surrounded by any parens or other
/// delimiters, e.g. `X { y: 1 }`, `X { y: 1 }.method()`, `foo
/// == X { y: 1 }` and `X { y: 1 } == foo` all do, but `(X {
/// y: 1 }) == foo` does not.
fn contains_exterior_struct_lit(value: &ast::Expr) -> bool {
match value.node {
ast::ExprKind::Struct(..) => true,
ast::ExprKind::Assign(ref lhs, ref rhs) |
ast::ExprKind::AssignOp(_, ref lhs, ref rhs) |
ast::ExprKind::Binary(_, ref lhs, ref rhs) => {
// X { y: 1 } + X { y: 2 }
contains_exterior_struct_lit(&lhs) || contains_exterior_struct_lit(&rhs)
}
ast::ExprKind::Unary(_, ref x) |
ast::ExprKind::Cast(ref x, _) |
ast::ExprKind::Type(ref x, _) |
ast::ExprKind::Field(ref x, _) |
ast::ExprKind::TupField(ref x, _) |
ast::ExprKind::Index(ref x, _) => {
// &X { y: 1 }, X { y: 1 }.y
contains_exterior_struct_lit(&x)
}
ast::ExprKind::MethodCall(.., ref exprs) => {
// X { y: 1 }.bar(...)
contains_exterior_struct_lit(&exprs[0])
}
_ => false,
}
}
}
}
impl LintPass for UnusedParens {
fn get_lints(&self) -> LintArray {
lint_array!(UNUSED_PARENS)
}
}
impl EarlyLintPass for UnusedParens {
fn check_expr(&mut self, cx: &EarlyContext, e: &ast::Expr) {
use syntax::ast::ExprKind::*;
let (value, msg, struct_lit_needs_parens) = match e.node {
If(ref cond, ..) => (cond, "`if` condition", true),
While(ref cond, ..) => (cond, "`while` condition", true),
IfLet(_, ref cond, ..) => (cond, "`if let` head expression", true),
WhileLet(_, ref cond, ..) => (cond, "`while let` head expression", true),
ForLoop(_, ref cond, ..) => (cond, "`for` head expression", true),
Match(ref head, _) => (head, "`match` head expression", true),
Ret(Some(ref value)) => (value, "`return` value", false),
Assign(_, ref value) => (value, "assigned value", false),
AssignOp(.., ref value) => (value, "assigned value", false),
InPlace(_, ref value) => (value, "emplacement value", false),
_ => return,
};
self.check_unused_parens_core(cx, &value, msg, struct_lit_needs_parens);
}
fn check_stmt(&mut self, cx: &EarlyContext, s: &ast::Stmt) {
let (value, msg) = match s.node {
ast::StmtKind::Local(ref local) => {
match local.init {
Some(ref value) => (value, "assigned value"),
None => return,
}
}
_ => return,
};
self.check_unused_parens_core(cx, &value, msg, false);
}
}
declare_lint! {
UNUSED_IMPORT_BRACES,
Allow,
"unnecessary braces around an imported item"
}
#[derive(Copy, Clone)]
pub struct UnusedImportBraces;
impl LintPass for UnusedImportBraces {
fn get_lints(&self) -> LintArray {
lint_array!(UNUSED_IMPORT_BRACES)
}
}
impl EarlyLintPass for UnusedImportBraces {
fn check_item(&mut self, cx: &EarlyContext, item: &ast::Item) {
if let ast::ItemKind::Use(ref view_path) = item.node {
if let ast::ViewPathList(_, ref items) = view_path.node {
if items.len() == 1 && items[0].node.name.name != keywords::SelfValue.name() {
let msg = format!("braces around {} is unnecessary", items[0].node.name);
cx.span_lint(UNUSED_IMPORT_BRACES, item.span, &msg);
}
}
}
}
}
declare_lint! {
UNUSED_ALLOCATION,
Warn,
"detects unnecessary allocations that can be eliminated"
}
#[derive(Copy, Clone)]
pub struct UnusedAllocation;
impl LintPass for UnusedAllocation {
fn get_lints(&self) -> LintArray {
lint_array!(UNUSED_ALLOCATION)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAllocation {
fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
match e.node {
hir::ExprBox(_) => {}
_ => return,
}
for adj in cx.tables.expr_adjustments(e) {
if let adjustment::Adjust::Borrow(adjustment::AutoBorrow::Ref(_, m)) = adj.kind {
let msg = match m {
hir::MutImmutable => "unnecessary allocation, use & instead",
hir::MutMutable => "unnecessary allocation, use &mut instead"
};
cx.span_lint(UNUSED_ALLOCATION, e.span, msg);
}
}
}
}