Add ability for hardwired lints to operate on the diagnostic builder

src/librustc/lint/builtin.rs

@@ -14,8 +14,11 @@
 //! compiler code, rather than using their own custom pass. Those
 //! lints are all available in `rustc_lint::builtin`.
 
+use errors::DiagnosticBuilder;
 use lint::{LintPass, LateLintPass, LintArray};
+use session::Session;
 use session::config::Epoch;
+use syntax::codemap::Span;
 
 declare_lint! {
     pub CONST_ERR,
@@ -312,4 +315,27 @@ impl LintPass for HardwiredLints {
     }
 }
 
+// this could be a closure, but then implementing derive traits
+// becomes hacky (and it gets allocated)
+#[derive(PartialEq, RustcEncodable, RustcDecodable, Debug)]
+pub enum BuiltinLintDiagnostics {
+    Normal,
+    BareTraitObject(Span)
+}
+
+impl BuiltinLintDiagnostics {
+    pub fn run(self, sess: &Session, db: &mut DiagnosticBuilder) {
+        match self {
+            BuiltinLintDiagnostics::Normal => (),
+            BuiltinLintDiagnostics::BareTraitObject(span) => {
+                let sugg = match sess.codemap().span_to_snippet(span) {
+                    Ok(s) => format!("dyn {}", s),
+                    Err(_) => format!("dyn <type>")
+                };
+                db.span_suggestion(span, "use `dyn`", sugg);
+            }
+        }
+    }
+}
+
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for HardwiredLints {}

src/librustc/lint/context.rs

@@ -29,6 +29,7 @@ use self::TargetLint::*;
 use std::slice;
 use lint::{EarlyLintPassObject, LateLintPassObject};
 use lint::{Level, Lint, LintId, LintPass, LintBuffer};
+use lint::builtin::BuiltinLintDiagnostics;
 use lint::levels::{LintLevelSets, LintLevelsBuilder};
 use middle::privacy::AccessLevels;
 use rustc_serialize::{Decoder, Decodable, Encoder, Encodable};
@@ -92,6 +93,7 @@ pub struct BufferedEarlyLint {
     pub ast_id: ast::NodeId,
     pub span: MultiSpan,
     pub msg: String,
+    pub diagnostic: BuiltinLintDiagnostics,
 }
 
 /// Extra information for a future incompatibility lint. See the call
@@ -446,6 +448,16 @@ pub trait LintContext<'tcx>: Sized {
         self.lookup(lint, span, msg).emit();
     }
 
+    fn lookup_and_emit_with_diagnostics<S: Into<MultiSpan>>(&self,
+                                                            lint: &'static Lint,
+                                                            span: Option<S>,
+                                                            msg: &str,
+                                                            diagnostic: BuiltinLintDiagnostics) {
+        let mut db = self.lookup(lint, span, msg);
+        diagnostic.run(self.sess(), &mut db);
+        db.emit();
+    }
+
     fn lookup<S: Into<MultiSpan>>(&self,
                                   lint: &'static Lint,
                                   span: Option<S>,
@@ -516,9 +528,10 @@ impl<'a> EarlyContext<'a> {
 
     fn check_id(&mut self, id: ast::NodeId) {
         for early_lint in self.buffered.take(id) {
-            self.lookup_and_emit(early_lint.lint_id.lint,
-                                 Some(early_lint.span.clone()),
-                                 &early_lint.msg);
+            self.lookup_and_emit_with_diagnostics(early_lint.lint_id.lint,
+                                                  Some(early_lint.span.clone()),
+                                                  &early_lint.msg,
+                                                  early_lint.diagnostic);
         }
     }
 }

src/librustc/lint/mod.rs

@@ -37,6 +37,7 @@ use errors::{DiagnosticBuilder, DiagnosticId};
 use hir::def_id::{CrateNum, LOCAL_CRATE};
 use hir::intravisit::{self, FnKind};
 use hir;
+use lint::builtin::BuiltinLintDiagnostics;
 use session::{config, Session, DiagnosticMessageId};
 use std::hash;
 use syntax::ast;
@@ -399,12 +400,14 @@ impl LintBuffer {
                     lint: &'static Lint,
                     id: ast::NodeId,
                     sp: MultiSpan,
-                    msg: &str) {
+                    msg: &str,
+                    diagnostic: BuiltinLintDiagnostics) {
         let early_lint = BufferedEarlyLint {
             lint_id: LintId::of(lint),
             ast_id: id,
             span: sp,
             msg: msg.to_string(),
+            diagnostic
         };
         let arr = self.map.entry(id).or_insert(Vec::new());
         if !arr.contains(&early_lint) {

src/librustc/session/mod.rs

@@ -16,6 +16,7 @@ use ich::Fingerprint;
 
 use ich;
 use lint;
+use lint::builtin::BuiltinLintDiagnostics;
 use middle::allocator::AllocatorKind;
 use middle::dependency_format;
 use session::search_paths::PathKind;
@@ -341,7 +342,18 @@ impl Session {
                                            sp: S,
                                            msg: &str) {
         match *self.buffered_lints.borrow_mut() {
-            Some(ref mut buffer) => buffer.add_lint(lint, id, sp.into(), msg),
+            Some(ref mut buffer) => buffer.add_lint(lint, id, sp.into(),
+                                                    msg, BuiltinLintDiagnostics::Normal),
+            None => bug!("can't buffer lints after HIR lowering"),
+        }
+    }
+
+    pub fn buffer_lint_with_diagnostic<S: Into<MultiSpan>>(&self,
+        lint: &'static lint::Lint, id: ast::NodeId, sp: S,
+        msg: &str, diagnostic: BuiltinLintDiagnostics) {
+        match *self.buffered_lints.borrow_mut() {
+            Some(ref mut buffer) => buffer.add_lint(lint, id, sp.into(),
+                                                    msg, diagnostic),
             None => bug!("can't buffer lints after HIR lowering"),
         }
     }