compare-method lint

src/librustc/infer/error_reporting.rs

@@ -646,13 +646,14 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         };
 
         if let SubregionOrigin::CompareImplMethodObligation {
-            span, item_name, impl_item_def_id, trait_item_def_id
+            span, item_name, impl_item_def_id, trait_item_def_id, lint_id
         } = origin {
             self.report_extra_impl_obligation(span,
                                               item_name,
                                               impl_item_def_id,
                                               trait_item_def_id,
-                                              &format!("`{}: {}`", bound_kind, sub))
+                                              &format!("`{}: {}`", bound_kind, sub),
+                                              lint_id)
                 .emit();
             return;
         }
@@ -977,12 +978,14 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             infer::CompareImplMethodObligation { span,
                                                  item_name,
                                                  impl_item_def_id,
-                                                 trait_item_def_id } => {
+                                                 trait_item_def_id,
+                                                 lint_id } => {
                 self.report_extra_impl_obligation(span,
                                                   item_name,
                                                   impl_item_def_id,
                                                   trait_item_def_id,
-                                                  &format!("`{}: {}`", sup, sub))
+                                                  &format!("`{}: {}`", sup, sub),
+                                                  lint_id)
             }
         }
     }

src/librustc/infer/mod.rs

@@ -368,6 +368,10 @@ pub enum SubregionOrigin<'tcx> {
         item_name: ast::Name,
         impl_item_def_id: DefId,
         trait_item_def_id: DefId,
+
+        // this is `Some(_)` if this error arises from the bug fix for
+        // #18937. This is a temporary measure.
+        lint_id: Option<ast::NodeId>,
     },
 }
 
@@ -1816,12 +1820,14 @@ impl<'tcx> SubregionOrigin<'tcx> {
 
             traits::ObligationCauseCode::CompareImplMethodObligation { item_name,
                                                                        impl_item_def_id,
-                                                                       trait_item_def_id } =>
+                                                                       trait_item_def_id,
+                                                                       lint_id } =>
                 SubregionOrigin::CompareImplMethodObligation {
                     span: cause.span,
                     item_name: item_name,
                     impl_item_def_id: impl_item_def_id,
                     trait_item_def_id: trait_item_def_id,
+                    lint_id: lint_id,
                 },
 
             _ => default(),

src/librustc/lint/builtin.rs

@@ -198,6 +198,12 @@ declare_lint! {
     "patterns in functions without body were erroneously allowed"
 }
 
+declare_lint! {
+    pub EXTRA_REQUIREMENT_IN_IMPL,
+    Warn,
+    "detects extra requirements in impls that were erroneously allowed"
+}
+
 /// Does nothing as a lint pass, but registers some `Lint`s
 /// which are used by other parts of the compiler.
 #[derive(Copy, Clone)]
@@ -235,7 +241,8 @@ impl LintPass for HardwiredLints {
             HR_LIFETIME_IN_ASSOC_TYPE,
             LIFETIME_UNDERSCORE,
             SAFE_EXTERN_STATICS,
-            PATTERNS_IN_FNS_WITHOUT_BODY
+            PATTERNS_IN_FNS_WITHOUT_BODY,
+            EXTRA_REQUIREMENT_IN_IMPL
         )
     }
 }

src/librustc/lint/context.rs

@@ -42,7 +42,7 @@ use std::fmt;
 use syntax::attr;
 use syntax::parse::token::InternedString;
 use syntax::ast;
-use syntax_pos::Span;
+use syntax_pos::{MultiSpan, Span};
 use errors::{self, Diagnostic, DiagnosticBuilder};
 use hir;
 use hir::intravisit as hir_visit;
@@ -107,9 +107,12 @@ impl fmt::Debug for EarlyLint {
 }
 
 impl EarlyLint {
-    pub fn new(id: LintId, span: Span, msg: String) -> Self {
-        let mut diagnostic = Diagnostic::new(errors::Level::Warning, &msg);
-        diagnostic.set_span(span);
+    pub fn new<M: EarlyLintMessage>(id: LintId, span: Span, msg: M) -> Self {
+        let diagnostic = msg.into_diagnostic(span);
+        EarlyLint { id: id, span: span, diagnostic: diagnostic }
+    }
+
+    pub fn with_diagnostic(id: LintId, span: Span, diagnostic: Diagnostic) -> Self {
         EarlyLint { id: id, span: span, diagnostic: diagnostic }
     }
 
@@ -120,7 +123,23 @@ impl EarlyLint {
     }
 }
 
+pub trait EarlyLintMessage {
+    fn into_diagnostic(self, span: Span) -> Diagnostic;
+}
 
+impl EarlyLintMessage for String {
+    fn into_diagnostic(self, span: Span) -> Diagnostic {
+        let mut diagnostic = Diagnostic::new(errors::Level::Warning, &self);
+        diagnostic.set_span(span);
+        diagnostic
+    }
+}
+
+impl EarlyLintMessage for Diagnostic {
+    fn into_diagnostic(self, _span: Span) -> Diagnostic {
+        self
+    }
+}
 
 /// Extra information for a future incompatibility lint. See the call
 /// to `register_future_incompatible` in `librustc_lint/lib.rs` for
@@ -439,13 +458,15 @@ pub fn raw_emit_lint(sess: &Session,
     raw_struct_lint(sess, lints, lint, lvlsrc, span, msg).emit();
 }
 
-pub fn raw_struct_lint<'a>(sess: &'a Session,
-                           lints: &LintStore,
-                           lint: &'static Lint,
-                           lvlsrc: LevelSource,
-                           span: Option<Span>,
-                           msg: &str)
-                           -> DiagnosticBuilder<'a> {
+pub fn raw_struct_lint<'a, S>(sess: &'a Session,
+                              lints: &LintStore,
+                              lint: &'static Lint,
+                              lvlsrc: LevelSource,
+                              span: Option<S>,
+                              msg: &str)
+                              -> DiagnosticBuilder<'a>
+    where S: Into<MultiSpan>
+{
     let (mut level, source) = lvlsrc;
     if level == Allow {
         return sess.diagnostic().struct_dummy();

src/librustc/lint/mod.rs

@@ -41,7 +41,7 @@ use hir;
 
 pub use lint::context::{LateContext, EarlyContext, LintContext, LintStore,
                         raw_emit_lint, check_crate, check_ast_crate, gather_attrs,
-                        raw_struct_lint, FutureIncompatibleInfo, EarlyLint};
+                        raw_struct_lint, FutureIncompatibleInfo, EarlyLint, EarlyLintMessage};
 
 /// Specification of a single lint.
 #[derive(Copy, Clone, Debug)]

src/librustc/session/mod.rs

@@ -258,11 +258,11 @@ impl Session {
     pub fn unimpl(&self, msg: &str) -> ! {
         self.diagnostic().unimpl(msg)
     }
-    pub fn add_lint(&self,
-                    lint: &'static lint::Lint,
-                    id: ast::NodeId,
-                    sp: Span,
-                    msg: String) {
+    pub fn add_lint<M: lint::EarlyLintMessage>(&self,
+                                               lint: &'static lint::Lint,
+                                               id: ast::NodeId,
+                                               sp: Span,
+                                               msg: M) {
         let lint_id = lint::LintId::of(lint);
         let mut lints = self.lints.borrow_mut();
         let early_lint = lint::EarlyLint::new(lint_id, sp, msg);

src/librustc/traits/error_reporting.rs

@@ -27,6 +27,7 @@ use super::{
 use fmt_macros::{Parser, Piece, Position};
 use hir::def_id::DefId;
 use infer::{self, InferCtxt, TypeOrigin};
+use rustc::lint::builtin::EXTRA_REQUIREMENT_IN_IMPL;
 use ty::{self, AdtKind, ToPredicate, ToPolyTraitRef, Ty, TyCtxt, TypeFoldable};
 use ty::error::ExpectedFound;
 use ty::fast_reject;
@@ -423,9 +424,15 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                                         item_name: ast::Name,
                                         _impl_item_def_id: DefId,
                                         trait_item_def_id: DefId,
-                                        requirement: &fmt::Display)
+                                        requirement: &fmt::Display,
+                                        lint_id: Option<ast::NodeId>) // (*)
                                         -> DiagnosticBuilder<'tcx>
     {
+        // (*) This parameter is temporary and used only for phasing
+        // in the bug fix to #18937. If it is `Some`, it has a kind of
+        // weird effect -- the diagnostic is reported as a lint, and
+        // the builder which is returned is marked as canceled.
+
         let mut err =
             struct_span_err!(self.tcx.sess,
                              error_span,
@@ -441,6 +448,12 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             error_span,
             &format!("impl has extra requirement {}", requirement));
 
+        if let Some(node_id) = lint_id {
+            let diagnostic = (*err).clone();
+            self.tcx.sess.add_lint(EXTRA_REQUIREMENT_IN_IMPL, node_id, error_span, diagnostic);
+            err.cancel();
+        }
+
         err
     }
 
@@ -452,14 +465,15 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         let mut err = match *error {
             SelectionError::Unimplemented => {
                 if let ObligationCauseCode::CompareImplMethodObligation {
-                    item_name, impl_item_def_id, trait_item_def_id
+                    item_name, impl_item_def_id, trait_item_def_id, lint_id
                 } = obligation.cause.code {
                     self.report_extra_impl_obligation(
                         span,
                         item_name,
                         impl_item_def_id,
                         trait_item_def_id,
-                        &format!("`{}`", obligation.predicate))
+                        &format!("`{}`", obligation.predicate),
+                        lint_id)
                         .emit();
                     return;
                 } else {

src/librustc/traits/mod.rs

@@ -138,10 +138,12 @@ pub enum ObligationCauseCode<'tcx> {
 
     ImplDerivedObligation(DerivedObligationCause<'tcx>),
 
+    // error derived when matching traits/impls; see ObligationCause for more details
     CompareImplMethodObligation {
         item_name: ast::Name,
         impl_item_def_id: DefId,
-        trait_item_def_id: DefId
+        trait_item_def_id: DefId,
+        lint_id: Option<ast::NodeId>,
     },
 }
 

src/librustc/traits/structural_impls.rs

@@ -197,11 +197,13 @@ impl<'a, 'tcx> Lift<'tcx> for traits::ObligationCauseCode<'a> {
             }
             super::CompareImplMethodObligation { item_name,
                                                  impl_item_def_id,
-                                                 trait_item_def_id } => {
+                                                 trait_item_def_id,
+                                                 lint_id } => {
                 Some(super::CompareImplMethodObligation {
                     item_name: item_name,
                     impl_item_def_id: impl_item_def_id,
                     trait_item_def_id: trait_item_def_id,
+                    lint_id: lint_id,
                 })
             }
         }