Run lint on where bounds

Author: notriddle

clippy_lints/src/drop_bounds.rs

@@ -1,7 +1,6 @@
 use crate::utils::{match_def_path, paths, span_lint};
 use if_chain::if_chain;
 use rustc::hir::*;
-use rustc::hir::GenericBound::Trait;
 use rustc::lint::{LateLintPass, LintArray, LintPass};
 use rustc::{declare_tool_lint, lint_array};
 
@@ -43,19 +42,30 @@ impl LintPass for Pass {
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
     fn check_generic_param(&mut self, cx: &rustc::lint::LateContext<'a, 'tcx>, p: &'tcx GenericParam) {
         for bound in &p.bounds {
-            if_chain! {
-                if let Trait(t, _) = bound;
-                if let Some(def_id) = t.trait_ref.path.def.opt_def_id();
-                if match_def_path(cx.tcx, def_id, &paths::DROP_TRAIT);
-                then {
-                    span_lint(
-                        cx,
-                        DROP_BOUNDS,
-                        t.span,
-                        &DROP_BOUNDS_SUMMARY.to_string()
-                    );
-                }
+            lint_bound(cx, bound);
+        }
+    }
+    fn check_where_predicate(&mut self, cx: &rustc::lint::LateContext<'a, 'tcx>, p: &'tcx WherePredicate) {
+        if let WherePredicate::BoundPredicate(WhereBoundPredicate{bounds, ..}) = p {
+            for bound in bounds {
+                lint_bound(cx, bound);
             }
         }
     }
 }
+
+fn lint_bound<'a, 'tcx>(cx: &rustc::lint::LateContext<'a, 'tcx>, bound: &'tcx GenericBound) {
+    if_chain! {
+        if let GenericBound::Trait(t, _) = bound;
+        if let Some(def_id) = t.trait_ref.path.def.opt_def_id();
+        if match_def_path(cx.tcx, def_id, &paths::DROP_TRAIT);
+        then {
+            span_lint(
+                cx,
+                DROP_BOUNDS,
+                t.span,
+                DROP_BOUNDS_SUMMARY
+            );
+        }
+    }
+}

tests/ui/drop_bounds.rs

@@ -1,8 +1,4 @@
+#![allow(unused)]
 fn foo<T: Drop>() {}
-struct K;
-impl Drop for K {
-    fn drop(&mut self) {}
-}
-fn main() {
-    foo::<K>();
-}
+fn bar<T>() where T: Drop {}
+fn main() {}

tests/ui/drop_bounds.stderr

@@ -1,10 +1,16 @@
 error: Bounds of the form `T: Drop` are useless. Use `std::mem::needs_drop` to detect if a type has drop glue.
-  --> $DIR/drop_bounds.rs:1:11
+  --> $DIR/drop_bounds.rs:2:11
    |
 LL | fn foo<T: Drop>() {}
    |           ^^^^
    |
    = note: #[deny(clippy::drop_bounds)] on by default
 
-error: aborting due to previous error
+error: Bounds of the form `T: Drop` are useless. Use `std::mem::needs_drop` to detect if a type has drop glue.
+  --> $DIR/drop_bounds.rs:3:22
+   |
+LL | fn bar<T>() where T: Drop {}
+   |                      ^^^^
+
+error: aborting due to 2 previous errors