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Diffstat (limited to '')
| -rw-r--r-- | src/tools/clippy/clippy_lints/src/pattern_type_mismatch.rs | 194 |
1 files changed, 194 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/pattern_type_mismatch.rs b/src/tools/clippy/clippy_lints/src/pattern_type_mismatch.rs new file mode 100644 index 000000000..a4d265111 --- /dev/null +++ b/src/tools/clippy/clippy_lints/src/pattern_type_mismatch.rs @@ -0,0 +1,194 @@ +use clippy_utils::diagnostics::span_lint_and_help; +use rustc_hir::{ + intravisit, Body, Expr, ExprKind, FnDecl, HirId, Let, LocalSource, Mutability, Pat, PatKind, Stmt, StmtKind, +}; +use rustc_lint::{LateContext, LateLintPass, LintContext}; +use rustc_middle::lint::in_external_macro; +use rustc_middle::ty; +use rustc_session::{declare_lint_pass, declare_tool_lint}; +use rustc_span::source_map::Span; + +declare_clippy_lint! { + /// ### What it does + /// Checks for patterns that aren't exact representations of the types + /// they are applied to. + /// + /// To satisfy this lint, you will have to adjust either the expression that is matched + /// against or the pattern itself, as well as the bindings that are introduced by the + /// adjusted patterns. For matching you will have to either dereference the expression + /// with the `*` operator, or amend the patterns to explicitly match against `&<pattern>` + /// or `&mut <pattern>` depending on the reference mutability. For the bindings you need + /// to use the inverse. You can leave them as plain bindings if you wish for the value + /// to be copied, but you must use `ref mut <variable>` or `ref <variable>` to construct + /// a reference into the matched structure. + /// + /// If you are looking for a way to learn about ownership semantics in more detail, it + /// is recommended to look at IDE options available to you to highlight types, lifetimes + /// and reference semantics in your code. The available tooling would expose these things + /// in a general way even outside of the various pattern matching mechanics. Of course + /// this lint can still be used to highlight areas of interest and ensure a good understanding + /// of ownership semantics. + /// + /// ### Why is this bad? + /// It isn't bad in general. But in some contexts it can be desirable + /// because it increases ownership hints in the code, and will guard against some changes + /// in ownership. + /// + /// ### Example + /// This example shows the basic adjustments necessary to satisfy the lint. Note how + /// the matched expression is explicitly dereferenced with `*` and the `inner` variable + /// is bound to a shared borrow via `ref inner`. + /// + /// ```rust,ignore + /// // Bad + /// let value = &Some(Box::new(23)); + /// match value { + /// Some(inner) => println!("{}", inner), + /// None => println!("none"), + /// } + /// + /// // Good + /// let value = &Some(Box::new(23)); + /// match *value { + /// Some(ref inner) => println!("{}", inner), + /// None => println!("none"), + /// } + /// ``` + /// + /// The following example demonstrates one of the advantages of the more verbose style. + /// Note how the second version uses `ref mut a` to explicitly declare `a` a shared mutable + /// borrow, while `b` is simply taken by value. This ensures that the loop body cannot + /// accidentally modify the wrong part of the structure. + /// + /// ```rust,ignore + /// // Bad + /// let mut values = vec![(2, 3), (3, 4)]; + /// for (a, b) in &mut values { + /// *a += *b; + /// } + /// + /// // Good + /// let mut values = vec![(2, 3), (3, 4)]; + /// for &mut (ref mut a, b) in &mut values { + /// *a += b; + /// } + /// ``` + #[clippy::version = "1.47.0"] + pub PATTERN_TYPE_MISMATCH, + restriction, + "type of pattern does not match the expression type" +} + +declare_lint_pass!(PatternTypeMismatch => [PATTERN_TYPE_MISMATCH]); + +impl<'tcx> LateLintPass<'tcx> for PatternTypeMismatch { + fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) { + if let StmtKind::Local(local) = stmt.kind { + if in_external_macro(cx.sess(), local.pat.span) { + return; + } + let deref_possible = match local.source { + LocalSource::Normal => DerefPossible::Possible, + _ => DerefPossible::Impossible, + }; + apply_lint(cx, local.pat, deref_possible); + } + } + + fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { + if let ExprKind::Match(_, arms, _) = expr.kind { + for arm in arms { + let pat = &arm.pat; + if apply_lint(cx, pat, DerefPossible::Possible) { + break; + } + } + } + if let ExprKind::Let(Let { pat, .. }) = expr.kind { + apply_lint(cx, pat, DerefPossible::Possible); + } + } + + fn check_fn( + &mut self, + cx: &LateContext<'tcx>, + _: intravisit::FnKind<'tcx>, + _: &'tcx FnDecl<'_>, + body: &'tcx Body<'_>, + _: Span, + _: HirId, + ) { + for param in body.params { + apply_lint(cx, param.pat, DerefPossible::Impossible); + } + } +} + +#[derive(Debug, Clone, Copy)] +enum DerefPossible { + Possible, + Impossible, +} + +fn apply_lint<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'_>, deref_possible: DerefPossible) -> bool { + let maybe_mismatch = find_first_mismatch(cx, pat); + if let Some((span, mutability, level)) = maybe_mismatch { + span_lint_and_help( + cx, + PATTERN_TYPE_MISMATCH, + span, + "type of pattern does not match the expression type", + None, + &format!( + "{}explicitly match against a `{}` pattern and adjust the enclosed variable bindings", + match (deref_possible, level) { + (DerefPossible::Possible, Level::Top) => "use `*` to dereference the match expression or ", + _ => "", + }, + match mutability { + Mutability::Mut => "&mut _", + Mutability::Not => "&_", + }, + ), + ); + true + } else { + false + } +} + +#[derive(Debug, Copy, Clone)] +enum Level { + Top, + Lower, +} + +fn find_first_mismatch<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'_>) -> Option<(Span, Mutability, Level)> { + let mut result = None; + pat.walk(|p| { + if result.is_some() { + return false; + } + if in_external_macro(cx.sess(), p.span) { + return true; + } + let adjust_pat = match p.kind { + PatKind::Or([p, ..]) => p, + _ => p, + }; + if let Some(adjustments) = cx.typeck_results().pat_adjustments().get(adjust_pat.hir_id) { + if let [first, ..] = **adjustments { + if let ty::Ref(.., mutability) = *first.kind() { + let level = if p.hir_id == pat.hir_id { + Level::Top + } else { + Level::Lower + }; + result = Some((p.span, mutability, level)); + } + } + } + result.is_none() + }); + result +} |