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|
use clippy_utils::consts::{constant, Constant};
use clippy_utils::diagnostics::{multispan_sugg, span_lint_and_then};
use clippy_utils::source::snippet;
use clippy_utils::usage::mutated_variables;
use clippy_utils::{eq_expr_value, higher, match_def_path, meets_msrv, msrvs, paths};
use if_chain::if_chain;
use rustc_ast::ast::LitKind;
use rustc_hir::def::Res;
use rustc_hir::intravisit::{walk_expr, Visitor};
use rustc_hir::BinOpKind;
use rustc_hir::{BorrowKind, Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_semver::RustcVersion;
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::source_map::Spanned;
use rustc_span::Span;
declare_clippy_lint! {
/// ### What it does
/// Suggests using `strip_{prefix,suffix}` over `str::{starts,ends}_with` and slicing using
/// the pattern's length.
///
/// ### Why is this bad?
/// Using `str:strip_{prefix,suffix}` is safer and may have better performance as there is no
/// slicing which may panic and the compiler does not need to insert this panic code. It is
/// also sometimes more readable as it removes the need for duplicating or storing the pattern
/// used by `str::{starts,ends}_with` and in the slicing.
///
/// ### Example
/// ```rust
/// let s = "hello, world!";
/// if s.starts_with("hello, ") {
/// assert_eq!(s["hello, ".len()..].to_uppercase(), "WORLD!");
/// }
/// ```
/// Use instead:
/// ```rust
/// let s = "hello, world!";
/// if let Some(end) = s.strip_prefix("hello, ") {
/// assert_eq!(end.to_uppercase(), "WORLD!");
/// }
/// ```
#[clippy::version = "1.48.0"]
pub MANUAL_STRIP,
complexity,
"suggests using `strip_{prefix,suffix}` over `str::{starts,ends}_with` and slicing"
}
pub struct ManualStrip {
msrv: Option<RustcVersion>,
}
impl ManualStrip {
#[must_use]
pub fn new(msrv: Option<RustcVersion>) -> Self {
Self { msrv }
}
}
impl_lint_pass!(ManualStrip => [MANUAL_STRIP]);
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
enum StripKind {
Prefix,
Suffix,
}
impl<'tcx> LateLintPass<'tcx> for ManualStrip {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if !meets_msrv(self.msrv, msrvs::STR_STRIP_PREFIX) {
return;
}
if_chain! {
if let Some(higher::If { cond, then, .. }) = higher::If::hir(expr);
if let ExprKind::MethodCall(_, target_arg, [pattern], _) = cond.kind;
if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(cond.hir_id);
if let ExprKind::Path(target_path) = &target_arg.kind;
then {
let strip_kind = if match_def_path(cx, method_def_id, &paths::STR_STARTS_WITH) {
StripKind::Prefix
} else if match_def_path(cx, method_def_id, &paths::STR_ENDS_WITH) {
StripKind::Suffix
} else {
return;
};
let target_res = cx.qpath_res(target_path, target_arg.hir_id);
if target_res == Res::Err {
return;
};
if_chain! {
if let Res::Local(hir_id) = target_res;
if let Some(used_mutably) = mutated_variables(then, cx);
if used_mutably.contains(&hir_id);
then {
return;
}
}
let strippings = find_stripping(cx, strip_kind, target_res, pattern, then);
if !strippings.is_empty() {
let kind_word = match strip_kind {
StripKind::Prefix => "prefix",
StripKind::Suffix => "suffix",
};
let test_span = expr.span.until(then.span);
span_lint_and_then(cx, MANUAL_STRIP, strippings[0], &format!("stripping a {} manually", kind_word), |diag| {
diag.span_note(test_span, &format!("the {} was tested here", kind_word));
multispan_sugg(
diag,
&format!("try using the `strip_{}` method", kind_word),
vec![(test_span,
format!("if let Some(<stripped>) = {}.strip_{}({}) ",
snippet(cx, target_arg.span, ".."),
kind_word,
snippet(cx, pattern.span, "..")))]
.into_iter().chain(strippings.into_iter().map(|span| (span, "<stripped>".into()))),
);
});
}
}
}
}
extract_msrv_attr!(LateContext);
}
// Returns `Some(arg)` if `expr` matches `arg.len()` and `None` otherwise.
fn len_arg<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
if_chain! {
if let ExprKind::MethodCall(_, arg, [], _) = expr.kind;
if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
if match_def_path(cx, method_def_id, &paths::STR_LEN);
then {
Some(arg)
} else {
None
}
}
}
// Returns the length of the `expr` if it's a constant string or char.
fn constant_length(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<u128> {
let (value, _) = constant(cx, cx.typeck_results(), expr)?;
match value {
Constant::Str(value) => Some(value.len() as u128),
Constant::Char(value) => Some(value.len_utf8() as u128),
_ => None,
}
}
// Tests if `expr` equals the length of the pattern.
fn eq_pattern_length<'tcx>(cx: &LateContext<'tcx>, pattern: &Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
if let ExprKind::Lit(Spanned {
node: LitKind::Int(n, _),
..
}) = expr.kind
{
constant_length(cx, pattern).map_or(false, |length| length == n)
} else {
len_arg(cx, expr).map_or(false, |arg| eq_expr_value(cx, pattern, arg))
}
}
// Tests if `expr` is a `&str`.
fn is_ref_str(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
match cx.typeck_results().expr_ty_adjusted(expr).kind() {
ty::Ref(_, ty, _) => ty.is_str(),
_ => false,
}
}
// Removes the outer `AddrOf` expression if needed.
fn peel_ref<'a>(expr: &'a Expr<'_>) -> &'a Expr<'a> {
if let ExprKind::AddrOf(BorrowKind::Ref, _, unref) = &expr.kind {
unref
} else {
expr
}
}
// Find expressions where `target` is stripped using the length of `pattern`.
// We'll suggest replacing these expressions with the result of the `strip_{prefix,suffix}`
// method.
fn find_stripping<'tcx>(
cx: &LateContext<'tcx>,
strip_kind: StripKind,
target: Res,
pattern: &'tcx Expr<'_>,
expr: &'tcx Expr<'_>,
) -> Vec<Span> {
struct StrippingFinder<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
strip_kind: StripKind,
target: Res,
pattern: &'tcx Expr<'tcx>,
results: Vec<Span>,
}
impl<'a, 'tcx> Visitor<'tcx> for StrippingFinder<'a, 'tcx> {
fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
if_chain! {
if is_ref_str(self.cx, ex);
let unref = peel_ref(ex);
if let ExprKind::Index(indexed, index) = &unref.kind;
if let Some(higher::Range { start, end, .. }) = higher::Range::hir(index);
if let ExprKind::Path(path) = &indexed.kind;
if self.cx.qpath_res(path, ex.hir_id) == self.target;
then {
match (self.strip_kind, start, end) {
(StripKind::Prefix, Some(start), None) => {
if eq_pattern_length(self.cx, self.pattern, start) {
self.results.push(ex.span);
return;
}
},
(StripKind::Suffix, None, Some(end)) => {
if_chain! {
if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, left, right) = end.kind;
if let Some(left_arg) = len_arg(self.cx, left);
if let ExprKind::Path(left_path) = &left_arg.kind;
if self.cx.qpath_res(left_path, left_arg.hir_id) == self.target;
if eq_pattern_length(self.cx, self.pattern, right);
then {
self.results.push(ex.span);
return;
}
}
},
_ => {}
}
}
}
walk_expr(self, ex);
}
}
let mut finder = StrippingFinder {
cx,
strip_kind,
target,
pattern,
results: vec![],
};
walk_expr(&mut finder, expr);
finder.results
}
|
