From 96be287f12ff4199b3b1005a22a2dd7c1f01f5bf Mon Sep 17 00:00:00 2001
From: Oliver Schneider <git-spam-no-reply9815368754983@oli-obk.de>
Date: Thu, 24 Mar 2016 16:29:20 +0100
Subject: [PATCH] detect negations of terminals like a != b vs a == b

---
 src/booleans.rs                | 27 ++++++++++++++++++++++++++-
 tests/compile-fail/booleans.rs | 18 +++++++++++++++---
 2 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/src/booleans.rs b/src/booleans.rs
index 2de59c9bc597..b43f22973115 100644
--- a/src/booleans.rs
+++ b/src/booleans.rs
@@ -1,7 +1,8 @@
 use rustc::lint::{LintArray, LateLintPass, LateContext, LintPass};
 use rustc_front::hir::*;
 use rustc_front::intravisit::*;
-use syntax::ast::LitKind;
+use syntax::ast::{LitKind, DUMMY_NODE_ID};
+use syntax::codemap::{DUMMY_SP, dummy_spanned};
 use utils::{span_lint_and_then, in_macro, snippet_opt, SpanlessEq};
 
 /// **What it does:** This lint checks for boolean expressions that can be written more concisely
@@ -92,6 +93,30 @@ impl<'a, 'tcx, 'v> Hir2Qmm<'a, 'tcx, 'v> {
                 #[allow(cast_possible_truncation)]
                 return Ok(Bool::Term(n as u8));
             }
+            let negated = match e.node {
+                ExprBinary(binop, ref lhs, ref rhs) => {
+                    let mk_expr = |op| Expr {
+                        id: DUMMY_NODE_ID,
+                        span: DUMMY_SP,
+                        attrs: None,
+                        node: ExprBinary(dummy_spanned(op), lhs.clone(), rhs.clone()),
+                    };
+                    match binop.node {
+                        BiEq => mk_expr(BiNe),
+                        BiNe => mk_expr(BiEq),
+                        BiGt => mk_expr(BiLe),
+                        BiGe => mk_expr(BiLt),
+                        BiLt => mk_expr(BiGe),
+                        BiLe => mk_expr(BiGt),
+                        _ => continue,
+                    }
+                },
+                _ => continue,
+            };
+            if SpanlessEq::new(self.cx).ignore_fn().eq_expr(&negated, expr) {
+                #[allow(cast_possible_truncation)]
+                return Ok(Bool::Not(Box::new(Bool::Term(n as u8))));
+            }
         }
         let n = self.terminals.len();
         self.terminals.push(e);
diff --git a/tests/compile-fail/booleans.rs b/tests/compile-fail/booleans.rs
index 43528f5c5dfc..4ad51226d516 100644
--- a/tests/compile-fail/booleans.rs
+++ b/tests/compile-fail/booleans.rs
@@ -54,14 +54,26 @@ fn equality_stuff() {
     let c: i32 = unimplemented!();
     let d: i32 = unimplemented!();
     let e: i32 = unimplemented!();
-    let _ = a == b && a != b;
+    let _ = a == b && a != b; //~ ERROR this boolean expression contains a logic bug
+    //|~ HELP for further information visit
+    //|~ HELP this expression can be optimized out
+    //|~ HELP it would look like the following
+    //|~ SUGGESTION let _ = false;
     let _ = a == b && c == 5 && a == b; //~ ERROR this boolean expression can be simplified
     //|~ HELP for further information visit
     //|~ SUGGESTION let _ = c == 5 && a == b;
     let _ = a == b && c == 5 && b == a; //~ ERROR this boolean expression can be simplified
     //|~ HELP for further information visit
     //|~ SUGGESTION let _ = c == 5 && a == b;
-    let _ = a < b && a >= b;
-    let _ = a > b && a <= b;
+    let _ = a < b && a >= b; //~ ERROR this boolean expression contains a logic bug
+    //|~ HELP for further information visit
+    //|~ HELP this expression can be optimized out
+    //|~ HELP it would look like the following
+    //|~ SUGGESTION let _ = false;
+    let _ = a > b && a <= b; //~ ERROR this boolean expression contains a logic bug
+    //|~ HELP for further information visit
+    //|~ HELP this expression can be optimized out
+    //|~ HELP it would look like the following
+    //|~ SUGGESTION let _ = false;
     let _ = a > b && a == b;
 }