diff options
Diffstat (limited to 'src/tools/clippy/clippy_lints/src/manual_strip.rs')
-rw-r--r-- | src/tools/clippy/clippy_lints/src/manual_strip.rs | 252 |
1 files changed, 252 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/manual_strip.rs b/src/tools/clippy/clippy_lints/src/manual_strip.rs new file mode 100644 index 000000000..dfb3efc4e --- /dev/null +++ b/src/tools/clippy/clippy_lints/src/manual_strip.rs @@ -0,0 +1,252 @@ +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 +} |