rust/src/non_expressive_names.rs

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use rustc::lint::*;
use syntax::codemap::Span;
use syntax::parse::token::InternedString;
use syntax::ast::*;
use syntax::visit::{self, FnKind};
use utils::{span_lint_and_then, in_macro, span_lint};
use strsim::levenshtein;
/// **What it does:** This lint warns about 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:** `checked_exp` and `checked_expr`
declare_lint! {
pub SIMILAR_NAMES,
Warn,
"similarly named items and bindings"
}
/// **What it does:** This lint warns about having 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:** let (a, b, c, d, e, f, g) = (...);
declare_lint! {
pub MANY_SINGLE_CHAR_NAMES,
Warn,
"too many single character bindings"
}
pub struct NonExpressiveNames {
pub similarity_threshold: usize,
pub max_single_char_names: usize,
}
impl LintPass for NonExpressiveNames {
fn get_lints(&self) -> LintArray {
lint_array!(SIMILAR_NAMES, MANY_SINGLE_CHAR_NAMES)
}
}
struct SimilarNamesLocalVisitor<'a, 'b: 'a> {
names: Vec<(InternedString, Span)>,
cx: &'a EarlyContext<'b>,
lint: &'a NonExpressiveNames,
single_char_names: Vec<char>,
}
const WHITELIST: &'static [&'static str] = &[
"lhs", "rhs",
];
struct SimilarNamesNameVisitor<'a, 'b: 'a, 'c: 'b>(&'a mut SimilarNamesLocalVisitor<'b, 'c>);
impl<'v, 'a, 'b, 'c> visit::Visitor<'v> for SimilarNamesNameVisitor<'a, 'b, 'c> {
fn visit_pat(&mut self, pat: &'v Pat) {
if let PatKind::Ident(_, id, _) = pat.node {
self.check_name(id.span, id.node.name);
}
visit::walk_pat(self, pat);
}
}
impl<'a, 'b, 'c> SimilarNamesNameVisitor<'a, 'b, 'c> {
fn check_name(&mut self, span: Span, name: Name) {
if in_macro(self.0.cx, 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 {
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if count != 1 {
return;
}
let c = interned_name.chars().next().expect("already checked");
// make sure we ignore shadowing
if self.0.single_char_names.contains(&c) {
return;
}
self.0.single_char_names.push(c);
if self.0.single_char_names.len() < self.0.lint.max_single_char_names {
return;
}
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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()));
return;
}
for &allow in WHITELIST {
if interned_name == allow {
return;
}
if interned_name.len() <= allow.len() {
continue;
}
// allow_*
let allow_start = allow.chars().chain(Some('_'));
if interned_name.chars().zip(allow_start).all(|(l, r)| l == r) {
return;
}
// *_allow
let allow_end = Some('_').into_iter().chain(allow.chars());
if interned_name.chars().rev().zip(allow_end.rev()).all(|(l, r)| l == r) {
return;
}
}
for &(ref existing_name, sp) in &self.0.names {
let dist = levenshtein(&interned_name, &existing_name);
// equality is caught by shadow lints
if dist == 0 {
continue;
}
// if they differ enough it's all good
if dist > self.0.lint.similarity_threshold {
continue;
}
// are we doing stuff like `for item in items`?
if interned_name.starts_with(&**existing_name) ||
existing_name.starts_with(&*interned_name) ||
interned_name.ends_with(&**existing_name) ||
existing_name.ends_with(&*interned_name) {
continue;
}
let mut split_at = None;
if dist == 1 {
// are we doing stuff like a_bar, b_bar, c_bar?
if interned_name.chars().next() != existing_name.chars().next() {
if interned_name.chars().nth(1) == Some('_') {
continue;
}
split_at = interned_name.chars().next().map(|c| c.len_utf8());
}
// are we doing stuff like foo_x, foo_y, foo_z?
if interned_name.chars().rev().next() != existing_name.chars().rev().next() {
if interned_name.chars().rev().nth(1) == Some('_') {
continue;
}
split_at = interned_name.char_indices().rev().next().map(|(i, _)| i);
}
}
span_lint_and_then(self.0.cx,
SIMILAR_NAMES,
span,
"binding's name is too similar to existing binding",
|diag| {
diag.span_note(sp, "existing binding defined here");
if let Some(split) = split_at {
diag.span_help(span, &format!("separate the discriminating character \
by an underscore like: `{}_{}`",
&interned_name[..split],
&interned_name[split..]));
}
});
return;
}
self.0.names.push((interned_name, span));
}
}
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<'v, 'a, 'b> visit::Visitor<'v> for SimilarNamesLocalVisitor<'a, 'b> {
fn visit_local(&mut self, local: &'v Local) {
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if let Some(ref init) = local.init {
self.apply(|this| visit::walk_expr(this, &**init));
}
// add the pattern after the expression because the bindings aren't available yet in the init expression
SimilarNamesNameVisitor(self).visit_pat(&*local.pat);
}
fn visit_block(&mut self, blk: &'v Block) {
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self.apply(|this| visit::walk_block(this, blk));
}
fn visit_arm(&mut self, arm: &'v 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
SimilarNamesNameVisitor(this).visit_pat(&arm.pats[0]);
this.apply(|this| visit::walk_expr(this, &arm.body));
});
}
fn visit_item(&mut self, _: &'v Item) {
// do nothing
}
}
impl EarlyLintPass for NonExpressiveNames {
fn check_fn(&mut self, cx: &EarlyContext, _: FnKind, decl: &FnDecl, blk: &Block, _: Span, _: NodeId) {
let mut visitor = SimilarNamesLocalVisitor {
names: Vec::new(),
cx: cx,
lint: &self,
single_char_names: Vec::new(),
};
// initialize with function arguments
for arg in &decl.inputs {
visit::walk_pat(&mut SimilarNamesNameVisitor(&mut visitor), &arg.pat);
}
// walk all other bindings
visit::walk_block(&mut visitor, blk);
}
}