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use clippy_utils::diagnostics::span_lint_and_help;
use rustc_ast::ast::{GenericParam, GenericParamKind};
use rustc_lint::{EarlyContext, EarlyLintPass};
use rustc_middle::lint::in_external_macro;
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
/// Checks for lifetimes with names which are one character
/// long.
///
/// ### Why is this bad?
/// A single character is likely not enough to express the
/// purpose of a lifetime. Using a longer name can make code
/// easier to understand, especially for those who are new to
/// Rust.
///
/// ### Known problems
/// Rust programmers and learning resources tend to use single
/// character lifetimes, so this lint is at odds with the
/// ecosystem at large. In addition, the lifetime's purpose may
/// be obvious or, rarely, expressible in one character.
///
/// ### Example
/// ```rust
/// struct DiagnosticCtx<'a> {
/// source: &'a str,
/// }
/// ```
/// Use instead:
/// ```rust
/// struct DiagnosticCtx<'src> {
/// source: &'src str,
/// }
/// ```
#[clippy::version = "1.59.0"]
pub SINGLE_CHAR_LIFETIME_NAMES,
restriction,
"warns against single-character lifetime names"
}
declare_lint_pass!(SingleCharLifetimeNames => [SINGLE_CHAR_LIFETIME_NAMES]);
impl EarlyLintPass for SingleCharLifetimeNames {
fn check_generic_param(&mut self, ctx: &EarlyContext<'_>, param: &GenericParam) {
if in_external_macro(ctx.sess, param.ident.span) {
return;
}
if let GenericParamKind::Lifetime = param.kind {
if !param.is_placeholder && param.ident.as_str().len() <= 2 {
span_lint_and_help(
ctx,
SINGLE_CHAR_LIFETIME_NAMES,
param.ident.span,
"single-character lifetime names are likely uninformative",
None,
"use a more informative name",
);
}
}
}
}
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