From 0e67c0134fbb7764ed7bd1532b0e15f1bfd17044 Mon Sep 17 00:00:00 2001
From: llogiq <bogusandre@gmail.com>
Date: Mon, 17 Aug 2015 12:06:56 +0200
Subject: [PATCH] make float_cmp check for zero

---
 src/misc.rs                     |  5 +++++
 tests/compile-fail/float_cmp.rs | 20 ++++++++++++++------
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/src/misc.rs b/src/misc.rs
index 82ea78d97e1..33c34eb9b84 100644
--- a/src/misc.rs
+++ b/src/misc.rs
@@ -9,6 +9,7 @@ use rustc::middle::ty;
 use std::borrow::Cow;
 
 use utils::{match_path, snippet, snippet_block, span_lint, span_help_and_lint, walk_ptrs_ty};
+use consts::constant;
 
 /// Handles uncategorized lints
 /// Currently handles linting of if-let-able matches
@@ -147,6 +148,10 @@ impl LintPass for FloatCmp {
         if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
             let op = cmp.node;
             if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
+                if constant(cx, left).or_else(|| constant(cx, right)).map_or(
+                        false, |c| c.as_float().map_or(false, |f| f == 0.0)) {
+                    return;
+                }
                 span_lint(cx, FLOAT_CMP, expr.span, &format!(
                     "{}-comparison of f32 or f64 detected. Consider changing this to \
                      `abs({} - {}) < epsilon` for some suitable value of epsilon",
diff --git a/tests/compile-fail/float_cmp.rs b/tests/compile-fail/float_cmp.rs
index 419e500d0fc..067ec2818bf 100755
--- a/tests/compile-fail/float_cmp.rs
+++ b/tests/compile-fail/float_cmp.rs
@@ -13,22 +13,30 @@ fn twice<T>(x : T) -> T where T : Add<T, Output = T>, T : Copy {
 #[deny(float_cmp)]
 #[allow(unused)]
 fn main() {
-    ZERO == 0f32; //~ERROR ==-comparison of f32 or f64
-    ZERO == 0.0; //~ERROR ==-comparison of f32 or f64
+    ZERO == 0f32; //no error, comparison with zero is ok
+    ZERO == 0.0; //no error, comparison with zero is ok
     ZERO + ZERO != 1.0; //~ERROR !=-comparison of f32 or f64
 
-    ONE != 0.0; //~ERROR
+    ONE == 1f32; //~ERROR ==-comparison of f32 or f64
+    ONE == (1.0 + 0.0); //~ERROR ==-comparison of f32 or f64
+
+    ONE + ONE == (ZERO + ONE + ONE); //~ERROR ==-comparison of f32 or f64
+
+    ONE != 2.0; //~ERROR !=-comparison of f32 or f64
+    ONE != 0.0; // no error, comparison with zero is ok
     twice(ONE) != ONE; //~ERROR !=-comparison of f32 or f64
-    ONE as f64 != 0.0; //~ERROR !=-comparison of f32 or f64
+    ONE as f64 != 2.0; //~ERROR !=-comparison of f32 or f64
+    ONE as f64 != 0.0; // no error, comparison with zero is ok
 
     let x : f64 = 1.0;
 
     x == 1.0; //~ERROR ==-comparison of f32 or f64
-    x != 0f64; //~ERROR !=-comparison of f32 or f64
+    x != 0f64; // no error, comparison with zero is ok
 
     twice(x) != twice(ONE as f64); //~ERROR !=-comparison of f32 or f64
 
-    x < 0.0;
+
+    x < 0.0; // no errors, lower or greater comparisons need no fuzzyness
     x > 0.0;
     x <= 0.0;
     x >= 0.0;