Fix rustdoc run failures by shutting down definitely some lints

src/librustc/lint/levels.rs

@@ -118,6 +118,11 @@ impl LintLevelSets {
         // Ensure that we never exceed the `--cap-lints` argument.
         level = cmp::min(level, self.lint_cap);
 
+        if let Some(driver_level) = sess.driver_lint_caps.get(&LintId::of(lint)) {
+            // Ensure that we never exceed driver level.
+            level = cmp::min(*driver_level, level);
+        }
+
         return (level, src)
     }
 

src/librustc/session/mod.rs

@@ -22,7 +22,7 @@ use middle::dependency_format;
 use session::search_paths::PathKind;
 use session::config::{OutputType};
 use ty::tls;
-use util::nodemap::{FxHashSet};
+use util::nodemap::{FxHashMap, FxHashSet};
 use util::common::{duration_to_secs_str, ErrorReported};
 use util::common::ProfileQueriesMsg;
 
@@ -160,6 +160,9 @@ pub struct Session {
 
     /// Metadata about the allocators for the current crate being compiled
     pub has_global_allocator: Once<bool>,
+
+    /// Cap lint level specified by a driver specifically.
+    pub driver_lint_caps: FxHashMap<lint::LintId, lint::Level>,
 }
 
 pub struct PerfStats {
@@ -1164,6 +1167,7 @@ pub fn build_session_(
             (*GLOBAL_JOBSERVER).clone()
         },
         has_global_allocator: Once::new(),
+        driver_lint_caps: FxHashMap(),
     };
 
     sess

src/librustdoc/core.rs

@@ -235,6 +235,14 @@ pub fn run_core(search_paths: SearchPaths,
         let mut sess = session::build_session_(
             sessopts, cpath, diagnostic_handler, codemap,
         );
+
+        let shutdown_lints = [lint::builtin::UNUSED_IMPORTS,
+                              lint::builtin::UNUSED_EXTERN_CRATES];
+
+        for l in &shutdown_lints {
+            sess.driver_lint_caps.insert(lint::LintId::of(l), lint::Allow);
+        }
+
         let codegen_backend = rustc_driver::get_codegen_backend(&sess);
         let cstore = Rc::new(CStore::new(codegen_backend.metadata_loader()));
         rustc_lint::register_builtins(&mut sess.lint_store.borrow_mut(), Some(&sess));
@@ -299,7 +307,6 @@ pub fn run_core(search_paths: SearchPaths,
                                                             &sess);
 
         let resolver = RefCell::new(resolver);
-
         abort_on_err(driver::phase_3_run_analysis_passes(&*codegen_backend,
                                                         control,
                                                         &sess,

src/test/rustdoc-ui/unused.rs

@@ -0,0 +1,24 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-pass
+
+// This test purpose is to check that unused_imports lint isn't fired
+// by rustdoc. Why would it? Because when rustdoc is running, it uses
+// "everybody-loops" which replaces parts of code with "loop {}" to get
+// huge performance improvements.
+
+#![deny(unused_imports)]
+
+use std::fs::File;
+
+pub fn f() {
+    let _: File;
+}