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use clippy_utils::{diagnostics::span_lint_and_then, source::snippet_opt};
use rustc_ast::ast::{Item, ItemKind, VariantData};
use rustc_errors::Applicability;
use rustc_lexer::TokenKind;
use rustc_lint::{EarlyContext, EarlyLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::Span;
declare_clippy_lint! {
/// ### What it does
/// Finds structs without fields (a so-called "empty struct") that are declared with brackets.
///
/// ### Why is this bad?
/// Empty brackets after a struct declaration can be omitted.
///
/// ### Example
/// ```rust
/// struct Cookie {}
/// ```
/// Use instead:
/// ```rust
/// struct Cookie;
/// ```
#[clippy::version = "1.62.0"]
pub EMPTY_STRUCTS_WITH_BRACKETS,
restriction,
"finds struct declarations with empty brackets"
}
declare_lint_pass!(EmptyStructsWithBrackets => [EMPTY_STRUCTS_WITH_BRACKETS]);
impl EarlyLintPass for EmptyStructsWithBrackets {
fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
let span_after_ident = item.span.with_lo(item.ident.span.hi());
if let ItemKind::Struct(var_data, _) = &item.kind
&& has_brackets(var_data)
&& has_no_fields(cx, var_data, span_after_ident) {
span_lint_and_then(
cx,
EMPTY_STRUCTS_WITH_BRACKETS,
span_after_ident,
"found empty brackets on struct declaration",
|diagnostic| {
diagnostic.span_suggestion_hidden(
span_after_ident,
"remove the brackets",
";",
Applicability::Unspecified);
},
);
}
}
}
fn has_no_ident_token(braces_span_str: &str) -> bool {
!rustc_lexer::tokenize(braces_span_str).any(|t| t.kind == TokenKind::Ident)
}
fn has_brackets(var_data: &VariantData) -> bool {
!matches!(var_data, VariantData::Unit(_))
}
fn has_no_fields(cx: &EarlyContext<'_>, var_data: &VariantData, braces_span: Span) -> bool {
if !var_data.fields().is_empty() {
return false;
}
// there might still be field declarations hidden from the AST
// (conditionally compiled code using #[cfg(..)])
let Some(braces_span_str) = snippet_opt(cx, braces_span) else {
return false;
};
has_no_ident_token(braces_span_str.as_ref())
}
#[cfg(test)]
mod unit_test {
use super::*;
#[test]
fn test_has_no_ident_token() {
let input = "{ field: u8 }";
assert!(!has_no_ident_token(input));
let input = "(u8, String);";
assert!(!has_no_ident_token(input));
let input = " {
// test = 5
}
";
assert!(has_no_ident_token(input));
let input = " ();";
assert!(has_no_ident_token(input));
}
}
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