diff options
Diffstat (limited to 'src/tools/clippy/clippy_lints/src/partialeq_to_none.rs')
-rw-r--r-- | src/tools/clippy/clippy_lints/src/partialeq_to_none.rs | 105 |
1 files changed, 105 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/partialeq_to_none.rs b/src/tools/clippy/clippy_lints/src/partialeq_to_none.rs new file mode 100644 index 000000000..000b0ba7a --- /dev/null +++ b/src/tools/clippy/clippy_lints/src/partialeq_to_none.rs @@ -0,0 +1,105 @@ +use clippy_utils::{ + diagnostics::span_lint_and_sugg, is_lang_ctor, peel_hir_expr_refs, peel_ref_operators, sugg, + ty::is_type_diagnostic_item, +}; +use rustc_errors::Applicability; +use rustc_hir::{BinOpKind, Expr, ExprKind, LangItem}; +use rustc_lint::{LateContext, LateLintPass}; +use rustc_session::{declare_lint_pass, declare_tool_lint}; +use rustc_span::sym; + +declare_clippy_lint! { + /// ### What it does + /// + /// Checks for binary comparisons to a literal `Option::None`. + /// + /// ### Why is this bad? + /// + /// A programmer checking if some `foo` is `None` via a comparison `foo == None` + /// is usually inspired from other programming languages (e.g. `foo is None` + /// in Python). + /// Checking if a value of type `Option<T>` is (not) equal to `None` in that + /// way relies on `T: PartialEq` to do the comparison, which is unneeded. + /// + /// ### Example + /// ```rust + /// fn foo(f: Option<u32>) -> &'static str { + /// if f != None { "yay" } else { "nay" } + /// } + /// ``` + /// Use instead: + /// ```rust + /// fn foo(f: Option<u32>) -> &'static str { + /// if f.is_some() { "yay" } else { "nay" } + /// } + /// ``` + #[clippy::version = "1.64.0"] + pub PARTIALEQ_TO_NONE, + style, + "Binary comparison to `Option<T>::None` relies on `T: PartialEq`, which is unneeded" +} +declare_lint_pass!(PartialeqToNone => [PARTIALEQ_TO_NONE]); + +impl<'tcx> LateLintPass<'tcx> for PartialeqToNone { + fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) { + // Skip expanded code, as we have no control over it anyway... + if e.span.from_expansion() { + return; + } + + // If the expression is of type `Option` + let is_ty_option = + |expr: &Expr<'_>| is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr).peel_refs(), sym::Option); + + // If the expression is a literal `Option::None` + let is_none_ctor = |expr: &Expr<'_>| { + !expr.span.from_expansion() + && matches!(&peel_hir_expr_refs(expr).0.kind, + ExprKind::Path(p) if is_lang_ctor(cx, p, LangItem::OptionNone)) + }; + + let mut applicability = Applicability::MachineApplicable; + + if let ExprKind::Binary(op, left_side, right_side) = e.kind { + // All other comparisons (e.g. `>= None`) have special meaning wrt T + let is_eq = match op.node { + BinOpKind::Eq => true, + BinOpKind::Ne => false, + _ => return, + }; + + // We are only interested in comparisons between `Option` and a literal `Option::None` + let scrutinee = match ( + is_none_ctor(left_side) && is_ty_option(right_side), + is_none_ctor(right_side) && is_ty_option(left_side), + ) { + (true, false) => right_side, + (false, true) => left_side, + _ => return, + }; + + // Peel away refs/derefs (as long as we don't cross manual deref impls), as + // autoref/autoderef will take care of those + let sugg = format!( + "{}.{}", + sugg::Sugg::hir_with_applicability(cx, peel_ref_operators(cx, scrutinee), "..", &mut applicability) + .maybe_par(), + if is_eq { "is_none()" } else { "is_some()" } + ); + + span_lint_and_sugg( + cx, + PARTIALEQ_TO_NONE, + e.span, + "binary comparison to literal `Option::None`", + if is_eq { + "use `Option::is_none()` instead" + } else { + "use `Option::is_some()` instead" + }, + sugg, + applicability, + ); + } + } +} |