114 lines
4.1 KiB
Rust
114 lines
4.1 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::{match_def_path, paths, sugg};
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use if_chain::if_chain;
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use rustc_ast::util::parser::AssocOp;
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use rustc_errors::Applicability;
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use rustc_hir::def::{DefKind, Res};
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use rustc_hir::{BinOpKind, Expr, ExprKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::source_map::Spanned;
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declare_clippy_lint! {
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/// **What it does:** Checks for statements of the form `(a - b) < f32::EPSILON` or
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/// `(a - b) < f64::EPSILON`. Notes the missing `.abs()`.
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///
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/// **Why is this bad?** The code without `.abs()` is more likely to have a bug.
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///
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/// **Known problems:** If the user can ensure that b is larger than a, the `.abs()` is
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/// technically unneccessary. However, it will make the code more robust and doesn't have any
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/// large performance implications. If the abs call was deliberately left out for performance
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/// reasons, it is probably better to state this explicitly in the code, which then can be done
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/// with an allow.
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///
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/// **Example:**
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///
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/// ```rust
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/// pub fn is_roughly_equal(a: f32, b: f32) -> bool {
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/// (a - b) < f32::EPSILON
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/// }
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/// ```
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/// Use instead:
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/// ```rust
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/// pub fn is_roughly_equal(a: f32, b: f32) -> bool {
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/// (a - b).abs() < f32::EPSILON
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/// }
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/// ```
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pub FLOAT_EQUALITY_WITHOUT_ABS,
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correctness,
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"float equality check without `.abs()`"
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}
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declare_lint_pass!(FloatEqualityWithoutAbs => [FLOAT_EQUALITY_WITHOUT_ABS]);
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impl<'tcx> LateLintPass<'tcx> for FloatEqualityWithoutAbs {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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let lhs;
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let rhs;
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// check if expr is a binary expression with a lt or gt operator
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if let ExprKind::Binary(op, left, right) = expr.kind {
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match op.node {
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BinOpKind::Lt => {
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lhs = left;
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rhs = right;
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},
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BinOpKind::Gt => {
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lhs = right;
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rhs = left;
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},
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_ => return,
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};
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} else {
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return;
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}
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if_chain! {
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// left hand side is a substraction
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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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},
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val_l,
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val_r,
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) = lhs.kind;
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// right hand side matches either f32::EPSILON or f64::EPSILON
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if let ExprKind::Path(ref epsilon_path) = rhs.kind;
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if let Res::Def(DefKind::AssocConst, def_id) = cx.qpath_res(epsilon_path, rhs.hir_id);
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if match_def_path(cx, def_id, &paths::F32_EPSILON) || match_def_path(cx, def_id, &paths::F64_EPSILON);
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// values of the substractions on the left hand side are of the type float
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let t_val_l = cx.typeck_results().expr_ty(val_l);
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let t_val_r = cx.typeck_results().expr_ty(val_r);
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if let ty::Float(_) = t_val_l.kind();
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if let ty::Float(_) = t_val_r.kind();
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then {
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let sug_l = sugg::Sugg::hir(cx, val_l, "..");
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let sug_r = sugg::Sugg::hir(cx, val_r, "..");
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// format the suggestion
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let suggestion = format!("{}.abs()", sugg::make_assoc(AssocOp::Subtract, &sug_l, &sug_r).maybe_par());
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// spans the lint
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span_lint_and_then(
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cx,
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FLOAT_EQUALITY_WITHOUT_ABS,
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expr.span,
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"float equality check without `.abs()`",
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| diag | {
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diag.span_suggestion(
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lhs.span,
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"add `.abs()`",
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suggestion,
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Applicability::MaybeIncorrect,
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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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