Deny warning in every main sub-crate

This enables the same warnings that are enabled in `clippy_lints` also
in `clippy_utils` and `clippy_dev`. Then it makes sure, that the
`deny-warnings` feature is passed down to `clippy_lints` and
`clippy_utils` when compiling Clippy.

Cargo.toml

@@ -49,7 +49,7 @@ rustc-workspace-hack = "1.0.0"
 rustc_tools_util = { version = "0.2.0", path = "rustc_tools_util" }
 
 [features]
-deny-warnings = []
+deny-warnings = ["clippy_lints/deny-warnings"]
 integration = ["tempfile"]
 internal-lints = ["clippy_lints/internal-lints"]
 metadata-collector-lint = ["internal-lints", "clippy_lints/metadata-collector-lint"]

clippy_dev/src/lib.rs

@@ -1,5 +1,7 @@
-#![cfg_attr(feature = "deny-warnings", deny(warnings))]
 #![feature(once_cell)]
+#![cfg_attr(feature = "deny-warnings", deny(warnings))]
+// warn on lints, that are included in `rust-lang/rust`s bootstrap
+#![warn(rust_2018_idioms, unused_lifetimes)]
 
 use itertools::Itertools;
 use regex::Regex;

clippy_dev/src/main.rs

@@ -1,4 +1,6 @@
 #![cfg_attr(feature = "deny-warnings", deny(warnings))]
+// warn on lints, that are included in `rust-lang/rust`s bootstrap
+#![warn(rust_2018_idioms, unused_lifetimes)]
 
 use clap::{App, Arg, ArgMatches, SubCommand};
 use clippy_dev::{bless, fmt, ide_setup, new_lint, serve, stderr_length_check, update_lints};

clippy_lints/Cargo.toml

@@ -30,7 +30,7 @@ rustc-semver = "1.1.0"
 url = { version = "2.1.0", features = ["serde"] }
 
 [features]
-deny-warnings = []
+deny-warnings = ["clippy_utils/deny-warnings"]
 # build clippy with internal lints enabled, off by default
 internal-lints = ["clippy_utils/internal-lints"]
 metadata-collector-lint = ["serde_json", "clippy_utils/metadata-collector-lint"]

clippy_utils/Cargo.toml

@@ -14,6 +14,7 @@ unicode-normalization = "0.1"
 rustc-semver="1.1.0"
 
 [features]
+deny-warnings = []
 internal-lints = []
 metadata-collector-lint = []
 

clippy_utils/src/lib.rs

@@ -3,7 +3,14 @@
 #![feature(iter_zip)]
 #![feature(rustc_private)]
 #![recursion_limit = "512"]
+#![cfg_attr(feature = "deny-warnings", deny(warnings))]
 #![allow(clippy::missing_errors_doc, clippy::missing_panics_doc, clippy::must_use_candidate)]
+// warn on the same lints as `clippy_lints`
+#![warn(trivial_casts, trivial_numeric_casts)]
+// warn on lints, that are included in `rust-lang/rust`s bootstrap
+#![warn(rust_2018_idioms, unused_lifetimes)]
+// warn on rustc internal lints
+#![warn(rustc::internal)]
 
 // FIXME: switch to something more ergonomic here, once available.
 // (Currently there is no way to opt into sysroot crates without `extern crate`.)