288 lines
11 KiB
Rust
288 lines
11 KiB
Rust
use clippy_config::Conf;
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use clippy_utils::consts::{ConstEvalCtxt, Constant};
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use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::msrvs::{self, Msrv};
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use clippy_utils::source::snippet_with_applicability;
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use clippy_utils::usage::mutated_variables;
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use clippy_utils::{eq_expr_value, higher};
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use rustc_ast::BindingMode;
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use rustc_ast::ast::LitKind;
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use rustc_data_structures::fx::FxHashMap;
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use rustc_errors::Applicability;
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use rustc_hir::def::Res;
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use rustc_hir::intravisit::{Visitor, walk_expr, walk_pat};
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use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, Node, PatKind};
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use rustc_lint::{LateContext, LateLintPass, LintContext as _};
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use rustc_middle::ty;
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use rustc_session::impl_lint_pass;
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use rustc_span::source_map::Spanned;
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use rustc_span::{Symbol, sym};
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use std::iter;
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declare_clippy_lint! {
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/// ### What it does
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/// Suggests using `strip_{prefix,suffix}` over `str::{starts,ends}_with` and slicing using
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/// the pattern's length.
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///
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/// ### Why is this bad?
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/// Using `str:strip_{prefix,suffix}` is safer and may have better performance as there is no
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/// slicing which may panic and the compiler does not need to insert this panic code. It is
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/// also sometimes more readable as it removes the need for duplicating or storing the pattern
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/// used by `str::{starts,ends}_with` and in the slicing.
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///
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/// ### Example
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/// ```no_run
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/// let s = "hello, world!";
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/// if s.starts_with("hello, ") {
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/// assert_eq!(s["hello, ".len()..].to_uppercase(), "WORLD!");
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/// }
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/// ```
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/// Use instead:
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/// ```no_run
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/// let s = "hello, world!";
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/// if let Some(end) = s.strip_prefix("hello, ") {
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/// assert_eq!(end.to_uppercase(), "WORLD!");
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/// }
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/// ```
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#[clippy::version = "1.48.0"]
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pub MANUAL_STRIP,
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complexity,
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"suggests using `strip_{prefix,suffix}` over `str::{starts,ends}_with` and slicing"
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}
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pub struct ManualStrip {
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msrv: Msrv,
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}
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impl ManualStrip {
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pub fn new(conf: &'static Conf) -> Self {
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Self { msrv: conf.msrv }
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}
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}
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impl_lint_pass!(ManualStrip => [MANUAL_STRIP]);
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#[derive(Clone, Copy, Debug, Eq, PartialEq)]
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enum StripKind {
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Prefix,
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Suffix,
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}
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impl<'tcx> LateLintPass<'tcx> for ManualStrip {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if let Some(higher::If { cond, then, .. }) = higher::If::hir(expr)
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&& let ExprKind::MethodCall(_, target_arg, [pattern], _) = cond.kind
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&& let ExprKind::Path(target_path) = &target_arg.kind
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&& let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(cond.hir_id)
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{
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let strip_kind = if cx.tcx.is_diagnostic_item(sym::str_starts_with, method_def_id) {
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StripKind::Prefix
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} else if cx.tcx.is_diagnostic_item(sym::str_ends_with, method_def_id) {
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StripKind::Suffix
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} else {
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return;
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};
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let target_res = cx.qpath_res(target_path, target_arg.hir_id);
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if target_res == Res::Err {
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return;
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}
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if let Res::Local(hir_id) = target_res
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&& let Some(used_mutably) = mutated_variables(then, cx)
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&& used_mutably.contains(&hir_id)
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{
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return;
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}
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let (strippings, bindings) = find_stripping(cx, strip_kind, target_res, pattern, then);
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if !strippings.is_empty() && self.msrv.meets(cx, msrvs::STR_STRIP_PREFIX) {
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let kind_word = match strip_kind {
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StripKind::Prefix => "prefix",
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StripKind::Suffix => "suffix",
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};
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let test_span = expr.span.until(then.span);
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// If the first use is a simple `let` statement, reuse its identifier in the `if let Some(…)` and
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// remove the `let` statement as long as the identifier is never bound again within the lexical
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// scope of interest.
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let (ident_name, let_stmt_span, skip, mut app) = if let Node::LetStmt(let_stmt) =
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cx.tcx.parent_hir_node(strippings[0].hir_id)
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&& let PatKind::Binding(BindingMode::NONE, _, ident, None) = &let_stmt.pat.kind
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&& bindings.get(&ident.name) == Some(&1)
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{
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(
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ident.name.as_str(),
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Some(cx.sess().source_map().span_extend_while_whitespace(let_stmt.span)),
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1,
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Applicability::MachineApplicable,
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)
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} else {
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("<stripped>", None, 0, Applicability::HasPlaceholders)
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};
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span_lint_and_then(
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cx,
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MANUAL_STRIP,
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strippings[0].span,
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format!("stripping a {kind_word} manually"),
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|diag| {
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diag.span_note(test_span, format!("the {kind_word} was tested here"));
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diag.multipart_suggestion(
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format!("try using the `strip_{kind_word}` method"),
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iter::once((
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test_span,
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format!(
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"if let Some({ident_name}) = {}.strip_{kind_word}({}) ",
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snippet_with_applicability(cx, target_arg.span, "_", &mut app),
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snippet_with_applicability(cx, pattern.span, "_", &mut app)
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),
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))
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.chain(let_stmt_span.map(|span| (span, String::new())))
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.chain(
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strippings
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.into_iter()
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.skip(skip)
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.map(|expr| (expr.span, ident_name.into())),
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)
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.collect(),
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app,
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);
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},
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);
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}
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}
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}
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}
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// Returns `Some(arg)` if `expr` matches `arg.len()` and `None` otherwise.
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fn len_arg<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
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if let ExprKind::MethodCall(_, arg, [], _) = expr.kind
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&& let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
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&& cx.tcx.is_diagnostic_item(sym::str_len, method_def_id)
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{
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Some(arg)
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} else {
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None
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}
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}
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// Returns the length of the `expr` if it's a constant string or char.
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fn constant_length(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<u128> {
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let value = ConstEvalCtxt::new(cx).eval(expr)?;
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match value {
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Constant::Str(value) => Some(value.len() as u128),
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Constant::Char(value) => Some(value.len_utf8() as u128),
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_ => None,
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}
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}
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// Tests if `expr` equals the length of the pattern.
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fn eq_pattern_length<'tcx>(cx: &LateContext<'tcx>, pattern: &Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
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if let ExprKind::Lit(Spanned {
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node: LitKind::Int(n, _),
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..
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}) = expr.kind
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{
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constant_length(cx, pattern).is_some_and(|length| *n == length)
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} else {
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len_arg(cx, expr).is_some_and(|arg| eq_expr_value(cx, pattern, arg))
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}
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}
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// Tests if `expr` is a `&str`.
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fn is_ref_str(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
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match cx.typeck_results().expr_ty_adjusted(expr).kind() {
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ty::Ref(_, ty, _) => ty.is_str(),
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_ => false,
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}
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}
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// Removes the outer `AddrOf` expression if needed.
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fn peel_ref<'a>(expr: &'a Expr<'_>) -> &'a Expr<'a> {
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if let ExprKind::AddrOf(BorrowKind::Ref, _, unref) = &expr.kind {
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unref
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} else {
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expr
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}
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}
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/// Find expressions where `target` is stripped using the length of `pattern`.
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/// We'll suggest replacing these expressions with the result of the `strip_{prefix,suffix}`
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/// method.
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/// Also, all bindings found during the visit are counted and returned.
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fn find_stripping<'tcx>(
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cx: &LateContext<'tcx>,
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strip_kind: StripKind,
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target: Res,
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pattern: &'tcx Expr<'_>,
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expr: &'tcx Expr<'tcx>,
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) -> (Vec<&'tcx Expr<'tcx>>, FxHashMap<Symbol, usize>) {
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struct StrippingFinder<'a, 'tcx> {
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cx: &'a LateContext<'tcx>,
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strip_kind: StripKind,
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target: Res,
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pattern: &'tcx Expr<'tcx>,
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results: Vec<&'tcx Expr<'tcx>>,
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bindings: FxHashMap<Symbol, usize>,
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}
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impl<'tcx> Visitor<'tcx> for StrippingFinder<'_, 'tcx> {
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fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
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if is_ref_str(self.cx, ex)
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&& let unref = peel_ref(ex)
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&& let ExprKind::Index(indexed, index, _) = &unref.kind
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&& let Some(higher::Range { start, end, .. }) = higher::Range::hir(index)
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&& let ExprKind::Path(path) = &indexed.kind
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&& self.cx.qpath_res(path, ex.hir_id) == self.target
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{
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match (self.strip_kind, start, end) {
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(StripKind::Prefix, Some(start), None) => {
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if eq_pattern_length(self.cx, self.pattern, start) {
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self.results.push(ex);
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return;
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}
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},
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(StripKind::Suffix, None, Some(end)) => {
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if let ExprKind::Binary(
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Spanned {
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node: BinOpKind::Sub, ..
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},
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left,
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right,
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) = end.kind
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&& let Some(left_arg) = len_arg(self.cx, left)
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&& let ExprKind::Path(left_path) = &left_arg.kind
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&& self.cx.qpath_res(left_path, left_arg.hir_id) == self.target
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&& eq_pattern_length(self.cx, self.pattern, right)
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{
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self.results.push(ex);
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return;
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}
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},
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_ => {},
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}
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}
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walk_expr(self, ex);
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}
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fn visit_pat(&mut self, pat: &'tcx rustc_hir::Pat<'tcx>) -> Self::Result {
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if let PatKind::Binding(_, _, ident, _) = pat.kind {
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*self.bindings.entry(ident.name).or_default() += 1;
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}
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walk_pat(self, pat);
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}
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}
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let mut finder = StrippingFinder {
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cx,
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strip_kind,
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target,
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pattern,
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results: vec![],
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bindings: FxHashMap::default(),
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};
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walk_expr(&mut finder, expr);
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(finder.results, finder.bindings)
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}
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