rust-clippy/clippy_lints/src/non_expressive_names.rs

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use crate::utils::{span_lint, span_lint_and_then};
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use rustc_ast::ast::{Arm, AssocItem, AssocItemKind, Attribute, Block, FnDecl, Item, ItemKind, Local, Pat, PatKind};
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use rustc_ast::visit::{walk_block, walk_expr, walk_pat, Visitor};
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use rustc_lint::{EarlyContext, EarlyLintPass};
use rustc_middle::lint::in_external_macro;
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use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::source_map::Span;
use rustc_span::sym;
use rustc_span::symbol::{Ident, Symbol};
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use std::cmp::Ordering;
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declare_clippy_lint! {
/// **What it does:** Checks for names that are very similar and thus confusing.
///
/// **Why is this bad?** It's hard to distinguish between names that differ only
/// by a single character.
///
/// **Known problems:** None?
///
/// **Example:**
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/// ```ignore
/// let checked_exp = something;
/// let checked_expr = something_else;
/// ```
pub SIMILAR_NAMES,
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pedantic,
"similarly named items and bindings"
}
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declare_clippy_lint! {
/// **What it does:** Checks for too many variables whose name consists of a
/// single character.
///
/// **Why is this bad?** It's hard to memorize what a variable means without a
/// descriptive name.
///
/// **Known problems:** None?
///
/// **Example:**
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/// ```ignore
/// let (a, b, c, d, e, f, g) = (...);
/// ```
pub MANY_SINGLE_CHAR_NAMES,
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style,
"too many single character bindings"
}
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declare_clippy_lint! {
/// **What it does:** Checks if you have variables whose name consists of just
/// underscores and digits.
///
/// **Why is this bad?** It's hard to memorize what a variable means without a
/// descriptive name.
///
/// **Known problems:** None?
///
/// **Example:**
/// ```rust
/// let _1 = 1;
/// let ___1 = 1;
/// let __1___2 = 11;
/// ```
pub JUST_UNDERSCORES_AND_DIGITS,
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style,
"unclear name"
}
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#[derive(Copy, Clone)]
pub struct NonExpressiveNames {
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pub single_char_binding_names_threshold: u64,
}
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impl_lint_pass!(NonExpressiveNames => [SIMILAR_NAMES, MANY_SINGLE_CHAR_NAMES, JUST_UNDERSCORES_AND_DIGITS]);
struct ExistingName {
interned: Symbol,
span: Span,
len: usize,
exemptions: &'static [&'static str],
}
struct SimilarNamesLocalVisitor<'a, 'tcx> {
names: Vec<ExistingName>,
cx: &'a EarlyContext<'tcx>,
lint: &'a NonExpressiveNames,
/// A stack of scopes containing the single-character bindings in each scope.
single_char_names: Vec<Vec<Ident>>,
}
impl<'a, 'tcx> SimilarNamesLocalVisitor<'a, 'tcx> {
fn check_single_char_names(&self) {
let num_single_char_names = self.single_char_names.iter().flatten().count();
let threshold = self.lint.single_char_binding_names_threshold;
if num_single_char_names as u64 > threshold {
let span = self
.single_char_names
.iter()
.flatten()
.map(|ident| ident.span)
.collect::<Vec<_>>();
span_lint(
self.cx,
MANY_SINGLE_CHAR_NAMES,
span,
&format!(
"{} bindings with single-character names in scope",
num_single_char_names
),
);
}
}
}
// this list contains lists of names that are allowed to be similar
// the assumption is that no name is ever contained in multiple lists.
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#[rustfmt::skip]
const ALLOWED_TO_BE_SIMILAR: &[&[&str]] = &[
&["parsed", "parser"],
&["lhs", "rhs"],
&["tx", "rx"],
&["set", "get"],
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&["args", "arms"],
&["qpath", "path"],
&["lit", "lint"],
];
struct SimilarNamesNameVisitor<'a, 'tcx, 'b>(&'b mut SimilarNamesLocalVisitor<'a, 'tcx>);
impl<'a, 'tcx, 'b> Visitor<'tcx> for SimilarNamesNameVisitor<'a, 'tcx, 'b> {
fn visit_pat(&mut self, pat: &'tcx Pat) {
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match pat.kind {
PatKind::Ident(_, ident, _) => {
if !pat.span.from_expansion() {
self.check_ident(ident);
}
},
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PatKind::Struct(_, ref fields, _) => {
for field in fields {
if !field.is_shorthand {
self.visit_pat(&field.pat);
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}
}
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},
// just go through the first pattern, as either all patterns
// bind the same bindings or rustc would have errored much earlier
PatKind::Or(ref pats) => self.visit_pat(&pats[0]),
_ => walk_pat(self, pat),
}
}
}
#[must_use]
fn get_exemptions(interned_name: &str) -> Option<&'static [&'static str]> {
for &list in ALLOWED_TO_BE_SIMILAR {
if allowed_to_be_similar(interned_name, list) {
return Some(list);
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}
}
None
}
#[must_use]
fn allowed_to_be_similar(interned_name: &str, list: &[&str]) -> bool {
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list.iter()
.any(|&name| interned_name.starts_with(name) || interned_name.ends_with(name))
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}
impl<'a, 'tcx, 'b> SimilarNamesNameVisitor<'a, 'tcx, 'b> {
fn check_short_ident(&mut self, ident: Ident) {
// Ignore shadowing
if self
.0
.single_char_names
.iter()
.flatten()
.any(|id| id.name == ident.name)
{
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return;
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}
if let Some(scope) = &mut self.0.single_char_names.last_mut() {
scope.push(ident);
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}
}
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#[allow(clippy::too_many_lines)]
fn check_ident(&mut self, ident: Ident) {
let interned_name = ident.name.as_str();
if interned_name.chars().any(char::is_uppercase) {
return;
}
if interned_name.chars().all(|c| c.is_digit(10) || c == '_') {
span_lint(
self.0.cx,
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JUST_UNDERSCORES_AND_DIGITS,
ident.span,
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"consider choosing a more descriptive name",
);
return;
}
let count = interned_name.chars().count();
if count < 3 {
if count == 1 {
self.check_short_ident(ident);
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}
return;
}
for existing_name in &self.0.names {
if allowed_to_be_similar(&interned_name, existing_name.exemptions) {
continue;
}
let mut split_at = None;
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match existing_name.len.cmp(&count) {
Ordering::Greater => {
if existing_name.len - count != 1
|| levenstein_not_1(&interned_name, &existing_name.interned.as_str())
{
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continue;
}
},
Ordering::Less => {
if count - existing_name.len != 1
|| levenstein_not_1(&existing_name.interned.as_str(), &interned_name)
{
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continue;
}
},
Ordering::Equal => {
let mut interned_chars = interned_name.chars();
let interned_str = existing_name.interned.as_str();
let mut existing_chars = interned_str.chars();
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let first_i = interned_chars.next().expect("we know we have at least one char");
let first_e = existing_chars.next().expect("we know we have at least one char");
let eq_or_numeric = |(a, b): (char, char)| a == b || a.is_numeric() && b.is_numeric();
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if eq_or_numeric((first_i, first_e)) {
let last_i = interned_chars.next_back().expect("we know we have at least two chars");
let last_e = existing_chars.next_back().expect("we know we have at least two chars");
if eq_or_numeric((last_i, last_e)) {
if interned_chars
.zip(existing_chars)
.filter(|&ie| !eq_or_numeric(ie))
.count()
!= 1
{
continue;
}
} else {
let second_last_i = interned_chars
.next_back()
.expect("we know we have at least three chars");
let second_last_e = existing_chars
.next_back()
.expect("we know we have at least three chars");
if !eq_or_numeric((second_last_i, second_last_e))
|| second_last_i == '_'
|| !interned_chars.zip(existing_chars).all(eq_or_numeric)
{
// allowed similarity foo_x, foo_y
// or too many chars differ (foo_x, boo_y) or (foox, booy)
continue;
}
split_at = interned_name.char_indices().rev().next().map(|(i, _)| i);
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}
} else {
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let second_i = interned_chars.next().expect("we know we have at least two chars");
let second_e = existing_chars.next().expect("we know we have at least two chars");
if !eq_or_numeric((second_i, second_e))
|| second_i == '_'
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|| !interned_chars.zip(existing_chars).all(eq_or_numeric)
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{
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// allowed similarity x_foo, y_foo
// or too many chars differ (x_foo, y_boo) or (xfoo, yboo)
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continue;
}
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split_at = interned_name.chars().next().map(char::len_utf8);
}
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},
}
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span_lint_and_then(
self.0.cx,
SIMILAR_NAMES,
ident.span,
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"binding's name is too similar to existing binding",
|diag| {
diag.span_note(existing_name.span, "existing binding defined here");
if let Some(split) = split_at {
diag.span_help(
ident.span,
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&format!(
"separate the discriminating character by an \
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underscore like: `{}_{}`",
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&interned_name[..split],
&interned_name[split..]
),
);
}
},
);
return;
}
self.0.names.push(ExistingName {
exemptions: get_exemptions(&interned_name).unwrap_or(&[]),
interned: ident.name,
span: ident.span,
len: count,
});
}
}
impl<'a, 'b> SimilarNamesLocalVisitor<'a, 'b> {
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/// ensure scoping rules work
fn apply<F: for<'c> Fn(&'c mut Self)>(&mut self, f: F) {
let n = self.names.len();
let single_char_count = self.single_char_names.len();
f(self);
self.names.truncate(n);
self.single_char_names.truncate(single_char_count);
}
}
impl<'a, 'tcx> Visitor<'tcx> for SimilarNamesLocalVisitor<'a, 'tcx> {
fn visit_local(&mut self, local: &'tcx Local) {
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if let Some(ref init) = local.init {
self.apply(|this| walk_expr(this, &**init));
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}
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// add the pattern after the expression because the bindings aren't available
// yet in the init
// expression
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SimilarNamesNameVisitor(self).visit_pat(&*local.pat);
}
fn visit_block(&mut self, blk: &'tcx Block) {
self.single_char_names.push(vec![]);
self.apply(|this| walk_block(this, blk));
self.check_single_char_names();
self.single_char_names.pop();
}
fn visit_arm(&mut self, arm: &'tcx Arm) {
self.single_char_names.push(vec![]);
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self.apply(|this| {
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SimilarNamesNameVisitor(this).visit_pat(&arm.pat);
this.apply(|this| walk_expr(this, &arm.body));
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});
self.check_single_char_names();
self.single_char_names.pop();
}
fn visit_item(&mut self, _: &Item) {
// do not recurse into inner items
}
}
impl EarlyLintPass for NonExpressiveNames {
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fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
if in_external_macro(cx.sess, item.span) {
return;
}
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if let ItemKind::Fn(_, ref sig, _, Some(ref blk)) = item.kind {
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do_check(self, cx, &item.attrs, &sig.decl, blk);
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}
}
fn check_impl_item(&mut self, cx: &EarlyContext<'_>, item: &AssocItem) {
if in_external_macro(cx.sess, item.span) {
return;
}
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if let AssocItemKind::Fn(_, ref sig, _, Some(ref blk)) = item.kind {
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do_check(self, cx, &item.attrs, &sig.decl, blk);
}
}
}
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fn do_check(lint: &mut NonExpressiveNames, cx: &EarlyContext<'_>, attrs: &[Attribute], decl: &FnDecl, blk: &Block) {
if !attrs.iter().any(|attr| attr.has_name(sym::test)) {
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let mut visitor = SimilarNamesLocalVisitor {
names: Vec::new(),
cx,
lint,
single_char_names: vec![vec![]],
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};
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// initialize with function arguments
for arg in &decl.inputs {
SimilarNamesNameVisitor(&mut visitor).visit_pat(&arg.pat);
}
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// walk all other bindings
walk_block(&mut visitor, blk);
visitor.check_single_char_names();
}
}
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/// Precondition: `a_name.chars().count() < b_name.chars().count()`.
#[must_use]
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fn levenstein_not_1(a_name: &str, b_name: &str) -> bool {
debug_assert!(a_name.chars().count() < b_name.chars().count());
let mut a_chars = a_name.chars();
let mut b_chars = b_name.chars();
while let (Some(a), Some(b)) = (a_chars.next(), b_chars.next()) {
if a == b {
continue;
}
if let Some(b2) = b_chars.next() {
// check if there's just one character inserted
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return a != b2 || a_chars.ne(b_chars);
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} else {
// tuple
// ntuple
return true;
}
}
// for item in items
true
}