Adding symmetric lints and test cases

Author: martiansideofthemoon

src/overflow_check_conditional.rs

@@ -1,14 +1,16 @@
+#![allow(cyclomatic_complexity)]
 use rustc::lint::*;
 use rustc_front::hir::*;
 use utils::{span_lint};
 
-/// **What it does:** This lint finds classic overflow checks.
+/// **What it does:** This lint finds classic underflow / overflow checks.
 ///
-/// **Why is this bad?** Most classic C overflow checks will fail in Rust. Users can use functions like `overflowing_*` and `wrapping_*` instead.
+/// **Why is this bad?** Most classic C underflow / overflow checks will fail in Rust. Users can use functions like `overflowing_*` and `wrapping_*` instead.
 ///
 /// **Known problems:** None.
 ///
 /// **Example:** `a + b < a`
+
 declare_lint!(pub OVERFLOW_CHECK_CONDITIONAL, Warn,
               "Using overflow checks which are likely to panic");
 
@@ -22,35 +24,50 @@ impl LintPass for OverflowCheckConditional {
 }
 
 impl LateLintPass for OverflowCheckConditional {
+    // a + b < a, a > a + b, a < a - b, a - b > a
     fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
         if_let_chain! {[
         let Expr_::ExprBinary(ref op, ref first, ref second) = expr.node,
-        let BinOp_::BiLt = op.node,
-        let Expr_::ExprBinary(ref op2, ref add1, ref add2) = first.node,
-        let BinOp_::BiAdd = op2.node,
-        let Expr_::ExprPath(_,ref path1) = add1.node,
-        let Expr_::ExprPath(_, ref path2) = add2.node,
+        let Expr_::ExprBinary(ref op2, ref ident1, ref ident2) = first.node,
+        let Expr_::ExprPath(_,ref path1) = ident1.node,
+        let Expr_::ExprPath(_, ref path2) = ident2.node,
         let Expr_::ExprPath(_, ref path3) = second.node,
         (&path1.segments[0]).identifier == (&path3.segments[0]).identifier || (&path2.segments[0]).identifier == (&path3.segments[0]).identifier,
-        cx.tcx.expr_ty(add1).is_integral(),
-        cx.tcx.expr_ty(add2).is_integral()
+        cx.tcx.expr_ty(ident1).is_integral(),
+        cx.tcx.expr_ty(ident2).is_integral()
         ], {
-            span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span, "You are trying to use classic C overflow conditons that will fail in Rust.");
+            if let BinOp_::BiLt = op.node {
+                if let BinOp_::BiAdd = op2.node {
+                    span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span, "You are trying to use classic C overflow conditons that will fail in Rust.");
+                }
+            }
+            if let BinOp_::BiGt = op.node {
+                if let BinOp_::BiSub = op2.node {
+                    span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span, "You are trying to use classic C underflow conditons that will fail in Rust.");
+                }
+            }
         }}
 
         if_let_chain! {[
         let Expr_::ExprBinary(ref op, ref first, ref second) = expr.node,
-        let BinOp_::BiGt = op.node,
-        let Expr_::ExprBinary(ref op2, ref sub1, ref sub2) = first.node,
-        let BinOp_::BiSub = op2.node,
-        let Expr_::ExprPath(_,ref path1) = sub1.node,
-        let Expr_::ExprPath(_, ref path2) = sub2.node,
-        let Expr_::ExprPath(_, ref path3) = second.node,
+        let Expr_::ExprBinary(ref op2, ref ident1, ref ident2) = second.node,
+        let Expr_::ExprPath(_,ref path1) = ident1.node,
+        let Expr_::ExprPath(_, ref path2) = ident2.node,
+        let Expr_::ExprPath(_, ref path3) = first.node,
         (&path1.segments[0]).identifier == (&path3.segments[0]).identifier || (&path2.segments[0]).identifier == (&path3.segments[0]).identifier,
-        cx.tcx.expr_ty(sub1).is_integral(),
-        cx.tcx.expr_ty(sub2).is_integral()
+        cx.tcx.expr_ty(ident1).is_integral(),
+        cx.tcx.expr_ty(ident2).is_integral()
         ], {
-            span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span, "You are trying to use classic C underflow conditons that will fail in Rust.");
+            if let BinOp_::BiGt = op.node {
+                if let BinOp_::BiAdd = op2.node {
+                    span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span, "You are trying to use classic C overflow conditons that will fail in Rust.");
+                }
+            }
+            if let BinOp_::BiLt = op.node {
+                if let BinOp_::BiSub = op2.node {
+                    span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span, "You are trying to use classic C underflow conditons that will fail in Rust.");
+                }
+            }
         }}
     }
 }

tests/compile-fail/overflow_check_conditional.rs

@@ -9,21 +9,39 @@ fn main() {
 	let c: u32 = 3;
 	if a + b < a { //~ERROR You are trying to use classic C overflow conditons that will fail in Rust.
 
+	}
+	if a > a + b { //~ERROR You are trying to use classic C overflow conditons that will fail in Rust.
+
 	}
 	if a + b < b { //~ERROR You are trying to use classic C overflow conditons that will fail in Rust.
 
+	}
+	if b > a + b { //~ERROR You are trying to use classic C overflow conditons that will fail in Rust.
+
 	}
 	if a - b > b { //~ERROR You are trying to use classic C underflow conditons that will fail in Rust.
 
+	}
+	if b < a - b { //~ERROR You are trying to use classic C underflow conditons that will fail in Rust.
+
 	}
 	if a - b > a { //~ERROR You are trying to use classic C underflow conditons that will fail in Rust.
 
+	}
+	if a < a - b { //~ERROR You are trying to use classic C underflow conditons that will fail in Rust.
+
 	}
 	if a + b < c {
 
+	}
+	if c > a + b {
+
 	}
 	if a - b < c {
 
+	}
+	if c > a - b {
+
 	}
 	let i = 1.1;
 	let j = 2.2;
@@ -32,6 +50,12 @@ fn main() {
 	}
 	if i - j < i {
 
+	}
+	if i > i + j {
+
+	}
+	if i - j < i {
+
 	}
 }