rust-clippy/clippy_lints/src/get_first.rs

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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::{is_slice_of_primitives, match_def_path, paths};
use if_chain::if_chain;
use rustc_ast::LitKind;
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Spanned;
declare_clippy_lint! {
/// ### What it does
/// Checks for using `x.get(0)` instead of
/// `x.first()`.
///
/// ### Why is this bad?
/// Using `x.first()` is easier to read and has the same
/// result.
///
/// ### Example
/// ```rust
/// let x = vec![2, 3, 5];
/// let first_element = x.get(0);
/// ```
2022-06-05 19:24:41 +00:00
///
/// Use instead:
/// ```rust
/// let x = vec![2, 3, 5];
/// let first_element = x.first();
/// ```
#[clippy::version = "1.63.0"]
pub GET_FIRST,
style,
"Using `x.get(0)` when `x.first()` is simpler"
}
declare_lint_pass!(GetFirst => [GET_FIRST]);
impl<'tcx> LateLintPass<'tcx> for GetFirst {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
if_chain! {
if let hir::ExprKind::MethodCall(_, [struct_calling_on, method_arg], _) = &expr.kind;
if let Some(expr_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
if match_def_path(cx, expr_def_id, &paths::SLICE_GET);
if let Some(_) = is_slice_of_primitives(cx, struct_calling_on);
if let hir::ExprKind::Lit(Spanned { node: LitKind::Int(0, _), .. }) = method_arg.kind;
then {
let mut applicability = Applicability::MachineApplicable;
let slice_name = snippet_with_applicability(
cx,
struct_calling_on.span, "..",
&mut applicability,
);
span_lint_and_sugg(
cx,
GET_FIRST,
expr.span,
&format!("accessing first element with `{0}.get(0)`", slice_name),
"try",
format!("{}.first()", slice_name),
applicability,
);
}
}
}
}