Lint for trait methods without bodies

As discussed in rust-lang/rust#47475 the #[inline] attribute is
currently allowed on trait methods without bodies (i.e. without a
default implementation). This is misleading as it could be interpreted
as affecting the implementations of the trait method. Add a lint for any
use of #[inline] on a trait method without a body.

Fixes rust-lang/rust#47475

clippy_lints/src/lib.rs

@@ -109,6 +109,7 @@ pub mod identity_op;
 pub mod if_let_redundant_pattern_matching;
 pub mod if_not_else;
 pub mod infinite_iter;
+pub mod inline_fn_without_body;
 pub mod int_plus_one;
 pub mod invalid_ref;
 pub mod is_unit_expr;
@@ -359,6 +360,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
     reg.register_late_lint_pass(box use_self::UseSelf);
     reg.register_late_lint_pass(box bytecount::ByteCount);
     reg.register_late_lint_pass(box infinite_iter::Pass);
+    reg.register_late_lint_pass(box inline_fn_without_body::Pass);
     reg.register_late_lint_pass(box invalid_ref::InvalidRef);
     reg.register_late_lint_pass(box identity_conversion::IdentityConversion::default());
     reg.register_late_lint_pass(box types::ImplicitHasher);
@@ -477,6 +479,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
         identity_op::IDENTITY_OP,
         if_let_redundant_pattern_matching::IF_LET_REDUNDANT_PATTERN_MATCHING,
         infinite_iter::INFINITE_ITER,
+        inline_fn_without_body::INLINE_FN_WITHOUT_BODY,
         invalid_ref::INVALID_REF,
         is_unit_expr::UNIT_EXPR,
         large_enum_variant::LARGE_ENUM_VARIANT,