2020-09-24 12:49:22 +00:00
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use crate::consts::{constant, Constant};
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use crate::utils::usage::mutated_variables;
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2021-03-16 00:55:45 +00:00
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use crate::utils::{eq_expr_value, higher, match_def_path, meets_msrv, paths};
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use clippy_utils::diagnostics::{multispan_sugg, span_lint_and_then};
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2021-03-14 23:17:44 +00:00
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use clippy_utils::source::snippet;
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2020-09-24 12:49:22 +00:00
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use if_chain::if_chain;
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use rustc_ast::ast::LitKind;
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use rustc_hir::def::Res;
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use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
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use rustc_hir::BinOpKind;
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use rustc_hir::{BorrowKind, Expr, ExprKind};
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2020-12-06 14:01:03 +00:00
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use rustc_lint::{LateContext, LateLintPass, LintContext};
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2020-09-24 12:49:22 +00:00
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use rustc_middle::hir::map::Map;
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use rustc_middle::ty;
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2020-12-06 14:01:03 +00:00
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use rustc_semver::RustcVersion;
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use rustc_session::{declare_tool_lint, impl_lint_pass};
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2020-09-24 12:49:22 +00:00
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use rustc_span::source_map::Spanned;
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use rustc_span::Span;
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2020-12-06 14:01:03 +00:00
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const MANUAL_STRIP_MSRV: RustcVersion = RustcVersion::new(1, 45, 0);
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2020-09-24 12:49:22 +00:00
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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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/// **Known problems:**
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/// None.
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///
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/// **Example:**
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///
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/// ```rust
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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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/// ```rust
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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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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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2020-12-06 14:01:03 +00:00
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pub struct ManualStrip {
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msrv: Option<RustcVersion>,
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}
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impl ManualStrip {
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#[must_use]
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pub fn new(msrv: Option<RustcVersion>) -> Self {
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Self { msrv }
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}
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}
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impl_lint_pass!(ManualStrip => [MANUAL_STRIP]);
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2020-09-24 12:49:22 +00:00
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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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2020-12-06 14:01:03 +00:00
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if !meets_msrv(self.msrv.as_ref(), &MANUAL_STRIP_MSRV) {
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return;
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}
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2020-09-24 12:49:22 +00:00
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if_chain! {
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2021-01-01 18:38:11 +00:00
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if let ExprKind::If(cond, then, _) = &expr.kind;
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2020-09-24 12:49:22 +00:00
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if let ExprKind::MethodCall(_, _, [target_arg, pattern], _) = cond.kind;
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if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(cond.hir_id);
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if let ExprKind::Path(target_path) = &target_arg.kind;
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then {
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let strip_kind = if match_def_path(cx, method_def_id, &paths::STR_STARTS_WITH) {
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StripKind::Prefix
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} else if match_def_path(cx, method_def_id, &paths::STR_ENDS_WITH) {
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StripKind::Suffix
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} else {
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return;
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};
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2021-01-18 19:36:32 +00:00
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let target_res = cx.qpath_res(&target_path, target_arg.hir_id);
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2020-09-24 12:49:22 +00:00
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if target_res == Res::Err {
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return;
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};
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if_chain! {
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if let Res::Local(hir_id) = target_res;
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if let Some(used_mutably) = mutated_variables(then, cx);
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if used_mutably.contains(&hir_id);
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then {
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return;
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}
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}
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let strippings = find_stripping(cx, strip_kind, target_res, pattern, then);
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if !strippings.is_empty() {
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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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span_lint_and_then(cx, MANUAL_STRIP, strippings[0], &format!("stripping a {} manually", kind_word), |diag| {
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diag.span_note(test_span, &format!("the {} was tested here", kind_word));
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multispan_sugg(
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diag,
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&format!("try using the `strip_{}` method", kind_word),
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vec![(test_span,
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format!("if let Some(<stripped>) = {}.strip_{}({}) ",
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snippet(cx, target_arg.span, ".."),
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kind_word,
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snippet(cx, pattern.span, "..")))]
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.into_iter().chain(strippings.into_iter().map(|span| (span, "<stripped>".into()))),
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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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2020-12-06 14:01:03 +00:00
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extract_msrv_attr!(LateContext);
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2020-09-24 12:49:22 +00:00
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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_chain! {
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if let ExprKind::MethodCall(_, _, [arg], _) = expr.kind;
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if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
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if match_def_path(cx, method_def_id, &paths::STR_LEN);
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then {
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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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}
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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, _) = constant(cx, cx.typeck_results(), 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).map_or(false, |length| length == n)
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} else {
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len_arg(cx, expr).map_or(false, |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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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<'_>,
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) -> Vec<Span> {
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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<Span>,
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}
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impl<'a, 'tcx> Visitor<'tcx> for StrippingFinder<'a, 'tcx> {
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type Map = Map<'tcx>;
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fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
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NestedVisitorMap::None
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}
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fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
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if_chain! {
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if is_ref_str(self.cx, ex);
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let unref = peel_ref(ex);
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if let ExprKind::Index(indexed, index) = &unref.kind;
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2020-12-06 14:01:03 +00:00
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if let Some(higher::Range { start, end, .. }) = higher::range(index);
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2020-09-24 12:49:22 +00:00
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if let ExprKind::Path(path) = &indexed.kind;
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2021-01-18 19:36:32 +00:00
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if self.cx.qpath_res(path, ex.hir_id) == self.target;
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2020-09-24 12:49:22 +00:00
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then {
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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.span);
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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_chain! {
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if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, left, right) = end.kind;
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if let Some(left_arg) = len_arg(self.cx, left);
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if let ExprKind::Path(left_path) = &left_arg.kind;
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2021-01-18 19:36:32 +00:00
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if self.cx.qpath_res(left_path, left_arg.hir_id) == self.target;
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2020-09-24 12:49:22 +00:00
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if eq_pattern_length(self.cx, self.pattern, right);
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then {
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self.results.push(ex.span);
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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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}
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}
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walk_expr(self, ex);
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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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};
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walk_expr(&mut finder, expr);
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finder.results
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}
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