Fix false negative with OK_EXPECT

src/methods.rs

@@ -274,7 +274,6 @@ declare_lint! {
 ///    println!("{:p} {:p}",*y, z); // prints out the same pointer
 /// }
 /// ```
-/// 
 declare_lint! {
     pub CLONE_DOUBLE_REF, Warn, "using `clone` on `&&T`"
 }
@@ -789,26 +788,12 @@ fn get_error_type<'a>(cx: &LateContext, ty: ty::Ty<'a>) -> Option<ty::Ty<'a>> {
     None
 }
 
-/// This checks whether a given type is known to implement Debug. It's
-/// conservative, i.e. it should not return false positives, but will return
-/// false negatives.
+/// This checks whether a given type is known to implement Debug.
 fn has_debug_impl<'a, 'b>(ty: ty::Ty<'a>, cx: &LateContext<'b, 'a>) -> bool {
-    let no_ref_ty = walk_ptrs_ty(ty);
-    let debug = match cx.tcx.lang_items.debug_trait() {
-        Some(debug) => debug,
-        None => return false,
-    };
-    let debug_def = cx.tcx.lookup_trait_def(debug);
-    let mut debug_impl_exists = false;
-    debug_def.for_each_relevant_impl(cx.tcx, no_ref_ty, |d| {
-        let self_ty = &cx.tcx.impl_trait_ref(d).and_then(|im| im.substs.self_ty());
-        if let Some(self_ty) = *self_ty {
-            if !self_ty.flags.get().contains(ty::TypeFlags::HAS_PARAMS) {
-                debug_impl_exists = true;
-            }
-        }
-    });
-    debug_impl_exists
+    match cx.tcx.lang_items.debug_trait() {
+        Some(debug) => implements_trait(cx, ty, debug, Some(vec![])),
+        None => false,
+    }
 }
 
 #[cfg_attr(rustfmt, rustfmt_skip)]

tests/compile-fail/methods.rs

@@ -274,10 +274,8 @@ fn main() {
     // the error type implements `Debug`
     let res2: Result<i32, MyError> = Ok(0);
     res2.ok().expect("oh noes!");
-    // we currently don't warn if the error type has a type parameter
-    // (but it would be nice if we did)
     let res3: Result<u32, MyErrorWithParam<u8>>= Ok(0);
-    res3.ok().expect("whoof");
+    res3.ok().expect("whoof"); //~ERROR called `ok().expect()`
     let res4: Result<u32, io::Error> = Ok(0);
     res4.ok().expect("argh"); //~ERROR called `ok().expect()`
     let res5: io::Result<u32> = Ok(0);