fix false positive len_zero in is_empty()

src/len_zero.rs

@@ -5,7 +5,7 @@ use syntax::codemap::{Span, Spanned};
 use rustc::middle::def_id::DefId;
 use rustc::middle::ty::{self, MethodTraitItemId, ImplOrTraitItemId};
 
-use utils::{span_lint, walk_ptrs_ty, snippet};
+use utils::{snippet, span_lint, walk_ptrs_ty, with_item_name};
 
 declare_lint!(pub LEN_ZERO, Warn,
               "checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` \
@@ -33,14 +33,14 @@ impl LintPass for LenZero {
     }
 
     fn check_expr(&mut self, cx: &Context, expr: &Expr) {
-        if let &ExprBinary(Spanned{node: cmp, ..}, ref left, ref right) =
-            &expr.node {
-                match cmp {
-                    BiEq => check_cmp(cx, expr.span, left, right, ""),
-                    BiGt | BiNe => check_cmp(cx, expr.span, left, right, "!"),
-                    _ => ()
-                }
+        if let ExprBinary(Spanned{node: cmp, ..}, ref left, ref right) =
+                expr.node {
+            match cmp {
+                BiEq => check_cmp(cx, expr.span, left, right, ""),
+                BiGt | BiNe => check_cmp(cx, expr.span, left, right, "!"),
+                _ => ()
             }
+        }
     }
 }
 
@@ -89,7 +89,11 @@ fn is_self_sig(sig: &MethodSig) -> bool {
         false } else { sig.decl.inputs.len() == 1 }
 }
 
-fn check_cmp(cx: &Context, span: Span, left: &Expr, right: &Expr, op: &str) {
+fn check_cmp(cx: &Context, span: Span, left: &Expr, right: &Expr, op: &str) {    
+    // check if we are in an is_empty() method 
+    if let Some(true) = with_item_name(cx, left, |n| n == "is_empty") {
+        return;
+    }
     match (&left.node, &right.node) {
         (&ExprLit(ref lit), &ExprMethodCall(ref method, _, ref args)) =>
             check_len_zero(cx, span, method, args, lit, op),

src/misc.rs

@@ -5,10 +5,9 @@ use reexport::*;
 use rustc_front::util::{is_comparison_binop, binop_to_string};
 use syntax::codemap::{Span, Spanned};
 use rustc_front::visit::FnKind;
-use rustc::front::map::Node::*;
 use rustc::middle::ty;
 
-use utils::{match_path, snippet, span_lint, walk_ptrs_ty};
+use utils::{match_path, snippet, span_lint, walk_ptrs_ty, with_item_name};
 use consts::constant;
 
 declare_lint!(pub TOPLEVEL_REF_ARG, Warn,
@@ -93,19 +92,11 @@ impl LintPass for FloatCmp {
                         false, |c| c.0.as_float().map_or(false, |f| f == 0.0)) {
                     return;
                 }
-                let parent_id = cx.tcx.map.get_parent(expr.id);
-                match cx.tcx.map.find(parent_id) {
-                    Some(NodeItem(&Item{ ref ident, .. })) |
-                    Some(NodeTraitItem(&TraitItem{ id: _, ref ident, .. })) |
-                    Some(NodeImplItem(&ImplItem{ id: _, ref ident, .. })) => {
-                        let name = ident.name.as_str();
-                        if &*name == "eq" || &*name == "ne" ||
-                                name.starts_with("eq_") ||
-                                name.ends_with("_eq") {
-                            return;
-                        }
-                    },
-                    _ => (),
+                if let Some(true) = with_item_name(cx, expr, |name|
+                        name == "eq" || name == "ne" ||
+                        name.as_str().starts_with("eq_") ||
+                        name.as_str().ends_with("_eq")) {
+                    return;
                 }
                 span_lint(cx, FLOAT_CMP, expr.span, &format!(
                     "{}-comparison of f32 or f64 detected. Consider changing this to \

src/utils.rs

@@ -2,7 +2,7 @@ use rustc::lint::*;
 use rustc_front::hir::*;
 use reexport::*;
 use syntax::codemap::{ExpnInfo, Span, ExpnFormat};
-use rustc::front::map::Node::NodeExpr;
+use rustc::front::map::Node::*;
 use rustc::middle::def_id::DefId;
 use rustc::middle::ty;
 use std::borrow::Cow;
@@ -100,6 +100,19 @@ pub fn match_path(path: &Path, segments: &[&str]) -> bool {
         |(a, b)| &a.identifier.name == b)
 }
 
+pub fn with_item_name<T, F>(cx: &Context, expr: &Expr, f: F) -> Option<T>
+where F: FnOnce(Name) -> T {
+    let parent_id = cx.tcx.map.get_parent(expr.id);
+    match cx.tcx.map.find(parent_id) {
+        Some(NodeItem(&Item{ ref ident, .. })) |
+        Some(NodeTraitItem(&TraitItem{ id: _, ref ident, .. })) |
+        Some(NodeImplItem(&ImplItem{ id: _, ref ident, .. })) => {
+            Some(f(ident.name))
+        },
+        _ => None,
+    }
+}
+
 /// convert a span to a code snippet if available, otherwise use default, e.g.
 /// `snippet(cx, expr.span, "..")`
 pub fn snippet<'a>(cx: &Context, span: Span, default: &'a str) -> Cow<'a, str> {