rust-clippy/clippy_lints/src/non_expressive_names.rs

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use rustc::lint::*;
use syntax::codemap::Span;
use syntax::symbol::InternedString;
use syntax::ast::*;
use syntax::attr;
use syntax::visit::{Visitor, walk_block, walk_pat, walk_expr};
use utils::{span_lint_and_then, in_macro, span_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:**
/// ```rust
/// let checked_exp = something;
/// let checked_expr = something_else;
/// ```
declare_lint! {
pub SIMILAR_NAMES,
Allow,
"similarly named items and bindings"
}
/// **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?
///
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/// **Example:**
/// ```rust
/// let (a, b, c, d, e, f, g) = (...);
/// ```
declare_lint! {
pub MANY_SINGLE_CHAR_NAMES,
Warn,
"too many single character bindings"
}
pub struct NonExpressiveNames {
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pub single_char_binding_names_threshold: u64,
}
impl LintPass for NonExpressiveNames {
fn get_lints(&self) -> LintArray {
lint_array!(SIMILAR_NAMES, MANY_SINGLE_CHAR_NAMES)
}
}
struct ExistingName {
interned: InternedString,
span: Span,
len: usize,
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whitelist: &'static [&'static str],
}
struct SimilarNamesLocalVisitor<'a, 'tcx: 'a> {
names: Vec<ExistingName>,
cx: &'a EarlyContext<'tcx>,
lint: &'a NonExpressiveNames,
single_char_names: Vec<char>,
}
// 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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#[cfg_attr(rustfmt, rustfmt_skip)]
const WHITELIST: &'static [&'static [&'static str]] = &[
&["parsed", "parser"],
&["lhs", "rhs"],
&["tx", "rx"],
&["set", "get"],
];
struct SimilarNamesNameVisitor<'a: 'b, 'tcx: 'a, 'b>(&'b mut SimilarNamesLocalVisitor<'a, 'tcx>);
impl<'a, 'tcx: 'a, 'b> Visitor<'tcx> for SimilarNamesNameVisitor<'a, 'tcx, 'b> {
fn visit_pat(&mut self, pat: &'tcx Pat) {
match pat.node {
PatKind::Ident(_, id, _) => self.check_name(id.span, id.node.name),
PatKind::Struct(_, ref fields, _) => {
for field in fields {
if !field.node.is_shorthand {
self.visit_pat(&field.node.pat);
}
}
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},
_ => walk_pat(self, pat),
}
}
}
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fn get_whitelist(interned_name: &str) -> Option<&'static [&'static str]> {
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for &allow in WHITELIST {
if whitelisted(interned_name, allow) {
return Some(allow);
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}
}
None
}
fn whitelisted(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> {
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fn check_short_name(&mut self, c: char, span: Span) {
// make sure we ignore shadowing
if self.0.single_char_names.contains(&c) {
return;
}
self.0.single_char_names.push(c);
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if self.0.single_char_names.len() as u64 >= self.0.lint.single_char_binding_names_threshold {
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span_lint(
self.0.cx,
MANY_SINGLE_CHAR_NAMES,
span,
&format!("{}th binding whose name is just one char", self.0.single_char_names.len()),
);
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}
}
fn check_name(&mut self, span: Span, name: Name) {
if in_macro(span) {
return;
}
let interned_name = name.as_str();
if interned_name.chars().any(char::is_uppercase) {
return;
}
let count = interned_name.chars().count();
if count < 3 {
if count == 1 {
let c = interned_name.chars().next().expect("already checked");
self.check_short_name(c, span);
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}
return;
}
for existing_name in &self.0.names {
if whitelisted(&interned_name, existing_name.whitelist) {
continue;
}
let mut split_at = None;
if existing_name.len > count {
if existing_name.len - count != 1 || levenstein_not_1(&interned_name, &existing_name.interned) {
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continue;
}
} else if existing_name.len < count {
if count - existing_name.len != 1 || levenstein_not_1(&existing_name.interned, &interned_name) {
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continue;
}
} else {
let mut interned_chars = interned_name.chars();
let mut existing_chars = existing_name.interned.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)) {
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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)) {
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if interned_chars
.zip(existing_chars)
.filter(|&ie| !eq_or_numeric(ie))
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.count() != 1
{
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continue;
}
} else {
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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)
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{
// allowed similarity foo_x, foo_y
// or too many chars differ (foo_x, boo_y) or (foox, booy)
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continue;
}
split_at = interned_name.char_indices().rev().next().map(|(i, _)| i);
}
} 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 == '_' ||
!interned_chars.zip(existing_chars).all(eq_or_numeric)
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{
// allowed similarity x_foo, y_foo
// or too many chars differ (x_foo, y_boo) or (xfoo, yboo)
continue;
}
split_at = interned_name.chars().next().map(|c| c.len_utf8());
}
}
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span_lint_and_then(
self.0.cx,
SIMILAR_NAMES,
span,
"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(
span,
&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 {
whitelist: get_whitelist(&interned_name).unwrap_or(&[]),
interned: interned_name,
span: 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.apply(|this| walk_block(this, blk));
}
fn visit_arm(&mut self, arm: &'tcx Arm) {
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self.apply(|this| {
// just go through the first pattern, as either all patterns
// bind the same bindings or rustc would have errored much earlier
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SimilarNamesNameVisitor(this).visit_pat(&arm.pats[0]);
this.apply(|this| walk_expr(this, &arm.body));
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});
}
fn visit_item(&mut self, _: &Item) {
// do not recurse into inner items
}
}
impl EarlyLintPass for NonExpressiveNames {
fn check_item(&mut self, cx: &EarlyContext, item: &Item) {
if let ItemKind::Fn(ref decl, _, _, _, _, ref blk) = item.node {
if !attr::contains_name(&item.attrs, "test") {
let mut visitor = SimilarNamesLocalVisitor {
names: Vec::new(),
cx: cx,
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lint: self,
single_char_names: Vec::new(),
};
// initialize with function arguments
for arg in &decl.inputs {
SimilarNamesNameVisitor(&mut visitor).visit_pat(&arg.pat);
}
// walk all other bindings
walk_block(&mut visitor, blk);
}
}
}
}
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/// Precondition: `a_name.chars().count() < b_name.chars().count()`.
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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
}