Auto merge of #44908 - nikomatsakis:beta-20170928, r=alexcrichton

Beta 20170928

Backports of:

- Allow unused extern crate again #44825
- macros: fix bug in collecting trait and impl items with derives. #44757
-  `--cap-lints allow` switches off `can_emit_warnings` #44627
-  Update the libc submodule #44116
- limit and clear cache obligations opportunistically #44269
- clear out projection subobligations after they are processed #43999

src/bootstrap/channel.rs

@@ -29,7 +29,7 @@ pub const CFG_RELEASE_NUM: &str = "1.21.0";
 // An optional number to put after the label, e.g. '.2' -> '-beta.2'
 // Be sure to make this starts with a dot to conform to semver pre-release
 // versions (section 9)
-pub const CFG_PRERELEASE_VERSION: &str = ".3";
+pub const CFG_PRERELEASE_VERSION: &str = ".4";
 
 pub struct GitInfo {
     inner: Option<Info>,

src/librustc/infer/mod.rs

@@ -1160,6 +1160,18 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         value.fold_with(&mut r)
     }
 
+    /// Returns true if `T` contains unresolved type variables. In the
+    /// process of visiting `T`, this will resolve (where possible)
+    /// type variables in `T`, but it never constructs the final,
+    /// resolved type, so it's more efficient than
+    /// `resolve_type_vars_if_possible()`.
+    pub fn any_unresolved_type_vars<T>(&self, value: &T) -> bool
+        where T: TypeFoldable<'tcx>
+    {
+        let mut r = resolve::UnresolvedTypeFinder::new(self);
+        value.visit_with(&mut r)
+    }
+
     pub fn resolve_type_and_region_vars_if_possible<T>(&self, value: &T) -> T
         where T: TypeFoldable<'tcx>
     {

src/librustc/infer/resolve.rs

@@ -10,7 +10,7 @@
 
 use super::{InferCtxt, FixupError, FixupResult};
 use ty::{self, Ty, TyCtxt, TypeFoldable};
-use ty::fold::TypeFolder;
+use ty::fold::{TypeFolder, TypeVisitor};
 
 ///////////////////////////////////////////////////////////////////////////
 // OPPORTUNISTIC TYPE RESOLVER
@@ -80,6 +80,43 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for OpportunisticTypeAndRegionResolv
     }
 }
 
+///////////////////////////////////////////////////////////////////////////
+// UNRESOLVED TYPE FINDER
+
+/// The unresolved type **finder** walks your type and searches for
+/// type variables that don't yet have a value. They get pushed into a
+/// vector. It does not construct the fully resolved type (which might
+/// involve some hashing and so forth).
+pub struct UnresolvedTypeFinder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
+    infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
+}
+
+impl<'a, 'gcx, 'tcx> UnresolvedTypeFinder<'a, 'gcx, 'tcx> {
+    pub fn new(infcx: &'a InferCtxt<'a, 'gcx, 'tcx>) -> Self {
+        UnresolvedTypeFinder { infcx }
+    }
+}
+
+impl<'a, 'gcx, 'tcx> TypeVisitor<'tcx> for UnresolvedTypeFinder<'a, 'gcx, 'tcx> {
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
+        let t = self.infcx.shallow_resolve(t);
+        if t.has_infer_types() {
+            if let ty::TyInfer(_) = t.sty {
+                // Since we called `shallow_resolve` above, this must
+                // be an (as yet...) unresolved inference variable.
+                true
+            } else {
+                // Otherwise, visit its contents.
+                t.super_visit_with(self)
+            }
+        } else {
+            // Micro-optimize: no inference types at all Can't have unresolved type
+            // variables, no need to visit the contents.
+            false
+        }
+    }
+}
+
 ///////////////////////////////////////////////////////////////////////////
 // FULL TYPE RESOLUTION
 

src/librustc/lint/builtin.rs

@@ -30,7 +30,7 @@ declare_lint! {
 
 declare_lint! {
     pub UNUSED_EXTERN_CRATES,
-    Warn,
+    Allow,
     "extern crates that are never used"
 }
 

src/librustc/session/mod.rs

@@ -642,12 +642,16 @@ pub fn build_session_with_codemap(sopts: config::Options,
     // FIXME: This is not general enough to make the warning lint completely override
     // normal diagnostic warnings, since the warning lint can also be denied and changed
     // later via the source code.
-    let can_print_warnings = sopts.lint_opts
+    let warnings_allow = sopts.lint_opts
         .iter()
         .filter(|&&(ref key, _)| *key == "warnings")
-        .map(|&(_, ref level)| *level != lint::Allow)
+        .map(|&(_, ref level)| *level == lint::Allow)
         .last()
-        .unwrap_or(true);
+        .unwrap_or(false);
+    let cap_lints_allow = sopts.lint_cap.map_or(false, |cap| cap == lint::Allow);
+
+    let can_print_warnings = !(warnings_allow || cap_lints_allow);
+
     let treat_err_as_bug = sopts.debugging_opts.treat_err_as_bug;
 
     let emitter: Box<Emitter> = match (sopts.error_format, emitter_dest) {

src/librustc/traits/fulfill.rs

@@ -251,6 +251,9 @@ impl<'a, 'gcx, 'tcx> FulfillmentContext<'tcx> {
             });
             debug!("select: outcome={:?}", outcome);
 
+            // FIXME: if we kept the original cache key, we could mark projection
+            // obligations as complete for the projection cache here.
+
             errors.extend(
                 outcome.errors.into_iter()
                               .map(|e| to_fulfillment_error(e)));