Fix #1142 float constant comparison lint
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0c43b60dd4
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@ -357,6 +357,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
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arithmetic::INTEGER_ARITHMETIC,
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array_indexing::INDEXING_SLICING,
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assign_ops::ASSIGN_OPS,
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misc::FLOAT_CMP_CONST,
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]);
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reg.register_lint_group("clippy_pedantic", vec![
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@ -13,6 +13,7 @@ use utils::{get_item_name, get_parent_expr, implements_trait, in_constant, in_ma
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span_lint_and_then, walk_ptrs_ty};
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use utils::sugg::Sugg;
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use syntax::ast::{FloatTy, LitKind, CRATE_NODE_ID};
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use consts::constant;
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/// **What it does:** Checks for function arguments and let bindings denoted as
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/// `ref`.
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@ -200,6 +201,27 @@ declare_lint! {
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"using 0 as *{const, mut} T"
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}
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/// **What it does:** Checks for (in-)equality comparisons on floating-point
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/// value and constant, except in functions called `*eq*` (which probably
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/// implement equality for a type involving floats).
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///
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/// **Why is this bad?** Floating point calculations are usually imprecise, so
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/// asking if two values are *exactly* equal is asking for trouble. For a good
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/// guide on what to do, see [the floating point
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/// guide](http://www.floating-point-gui.de/errors/comparison).
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// const ONE == 1.00f64
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/// x == ONE // where both are floats
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/// ```
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declare_restriction_lint! {
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pub FLOAT_CMP_CONST,
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"using `==` or `!=` on float constants instead of comparing difference with an epsilon"
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}
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#[derive(Copy, Clone)]
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pub struct Pass;
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@ -214,7 +236,8 @@ impl LintPass for Pass {
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REDUNDANT_PATTERN,
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USED_UNDERSCORE_BINDING,
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SHORT_CIRCUIT_STATEMENT,
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ZERO_PTR
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ZERO_PTR,
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FLOAT_CMP_CONST
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)
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}
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}
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@ -334,7 +357,12 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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return;
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}
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}
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span_lint_and_then(cx, FLOAT_CMP, expr.span, "strict comparison of f32 or f64", |db| {
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let (lint, msg) = if is_named_constant(cx, left) || is_named_constant(cx, right) {
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(FLOAT_CMP_CONST, "strict comparison of f32 or f64 constant")
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} else {
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(FLOAT_CMP, "strict comparison of f32 or f64")
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};
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span_lint_and_then(cx, lint, expr.span, msg, |db| {
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let lhs = Sugg::hir(cx, left, "..");
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let rhs = Sugg::hir(cx, right, "..");
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@ -421,6 +449,14 @@ fn check_nan(cx: &LateContext, path: &Path, expr: &Expr) {
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}
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}
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fn is_named_constant<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
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if let Some((_, res)) = constant(cx, expr) {
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res
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} else {
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false
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}
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}
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fn is_allowed<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
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let parent_item = cx.tcx.hir.get_parent(expr.id);
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let parent_def_id = cx.tcx.hir.local_def_id(parent_item);
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31
tests/ui/float_cmp_const.rs
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31
tests/ui/float_cmp_const.rs
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@ -0,0 +1,31 @@
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#![warn(float_cmp_const)]
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#![allow(unused, no_effect, unnecessary_operation)]
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const ONE: f32 = 1.0;
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const TWO: f32 = 2.0;
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fn eq_one(x: f32) -> bool {
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if x.is_nan() { false } else { x == ONE } // no error, inside "eq" fn
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}
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fn main() {
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// has errors
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1f32 == ONE;
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TWO == ONE;
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TWO != ONE;
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ONE + ONE == TWO;
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1 as f32 == ONE;
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let v = 0.9;
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v == ONE;
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v != ONE;
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// no errors, lower than or greater than comparisons
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v < ONE;
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v > ONE;
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v <= ONE;
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v >= ONE;
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}
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85
tests/ui/float_cmp_const.stderr
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85
tests/ui/float_cmp_const.stderr
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@ -0,0 +1,85 @@
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error: strict comparison of f32 or f64 constant
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--> $DIR/float_cmp_const.rs:16:5
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16 | 1f32 == ONE;
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| ^^^^^^^^^^^ help: consider comparing them within some error: `(1f32 - ONE).abs() < error`
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= note: `-D float-cmp-const` implied by `-D warnings`
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note: std::f32::EPSILON and std::f64::EPSILON are available.
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--> $DIR/float_cmp_const.rs:16:5
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16 | 1f32 == ONE;
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| ^^^^^^^^^^^
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error: strict comparison of f32 or f64 constant
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--> $DIR/float_cmp_const.rs:17:5
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17 | TWO == ONE;
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| ^^^^^^^^^^ help: consider comparing them within some error: `(TWO - ONE).abs() < error`
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note: std::f32::EPSILON and std::f64::EPSILON are available.
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--> $DIR/float_cmp_const.rs:17:5
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17 | TWO == ONE;
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| ^^^^^^^^^^
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error: strict comparison of f32 or f64 constant
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--> $DIR/float_cmp_const.rs:18:5
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18 | TWO != ONE;
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| ^^^^^^^^^^ help: consider comparing them within some error: `(TWO - ONE).abs() < error`
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note: std::f32::EPSILON and std::f64::EPSILON are available.
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--> $DIR/float_cmp_const.rs:18:5
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18 | TWO != ONE;
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| ^^^^^^^^^^
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error: strict comparison of f32 or f64 constant
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--> $DIR/float_cmp_const.rs:19:5
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19 | ONE + ONE == TWO;
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| ^^^^^^^^^^^^^^^^ help: consider comparing them within some error: `(ONE + ONE - TWO).abs() < error`
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note: std::f32::EPSILON and std::f64::EPSILON are available.
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--> $DIR/float_cmp_const.rs:19:5
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19 | ONE + ONE == TWO;
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| ^^^^^^^^^^^^^^^^
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error: strict comparison of f32 or f64 constant
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--> $DIR/float_cmp_const.rs:20:5
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20 | 1 as f32 == ONE;
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| ^^^^^^^^^^^^^^^ help: consider comparing them within some error: `(1 as f32 - ONE).abs() < error`
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note: std::f32::EPSILON and std::f64::EPSILON are available.
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--> $DIR/float_cmp_const.rs:20:5
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20 | 1 as f32 == ONE;
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| ^^^^^^^^^^^^^^^
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error: strict comparison of f32 or f64 constant
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--> $DIR/float_cmp_const.rs:23:5
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23 | v == ONE;
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| ^^^^^^^^ help: consider comparing them within some error: `(v - ONE).abs() < error`
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note: std::f32::EPSILON and std::f64::EPSILON are available.
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--> $DIR/float_cmp_const.rs:23:5
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23 | v == ONE;
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| ^^^^^^^^
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error: strict comparison of f32 or f64 constant
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--> $DIR/float_cmp_const.rs:24:5
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24 | v != ONE;
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| ^^^^^^^^ help: consider comparing them within some error: `(v - ONE).abs() < error`
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note: std::f32::EPSILON and std::f64::EPSILON are available.
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--> $DIR/float_cmp_const.rs:24:5
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24 | v != ONE;
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| ^^^^^^^^
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