Add outlives suggestions for some lifetime errors

src/librustc_errors/diagnostic.rs

@@ -6,7 +6,7 @@ use crate::Applicability;
 use crate::Level;
 use crate::snippet::Style;
 use std::fmt;
-use syntax_pos::{MultiSpan, Span};
+use syntax_pos::{MultiSpan, Span, DUMMY_SP};
 
 #[must_use]
 #[derive(Clone, Debug, PartialEq, Hash, RustcEncodable, RustcDecodable)]
@@ -17,6 +17,11 @@ pub struct Diagnostic {
     pub span: MultiSpan,
     pub children: Vec<SubDiagnostic>,
     pub suggestions: Vec<CodeSuggestion>,
+
+    /// This is not used for highlighting or rendering any error message.  Rather, it can be used
+    /// as a sort key to sort a buffer of diagnostics.  By default, it is the primary span of
+    /// `span` if there is one.  Otherwise, it is `DUMMY_SP`.
+    pub sort_span: Span,
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
@@ -87,6 +92,7 @@ impl Diagnostic {
             span: MultiSpan::new(),
             children: vec![],
             suggestions: vec![],
+            sort_span: DUMMY_SP,
         }
     }
 
@@ -118,6 +124,11 @@ impl Diagnostic {
         self.level == Level::Cancelled
     }
 
+    /// Set the sorting span.
+    pub fn set_sort_span(&mut self, sp: Span) {
+        self.sort_span = sp;
+    }
+
     /// Adds a span/label to be included in the resulting snippet.
     /// This label will be shown together with the original span/label used when creating the
     /// diagnostic, *not* a span added by one of the `span_*` methods.
@@ -457,6 +468,9 @@ impl Diagnostic {
 
     pub fn set_span<S: Into<MultiSpan>>(&mut self, sp: S) -> &mut Self {
         self.span = sp.into();
+        if let Some(span) = self.span.primary_span() {
+            self.sort_span = span;
+        }
         self
     }
 

src/librustc_errors/lib.rs

@@ -619,6 +619,11 @@ impl Handler {
         DiagnosticBuilder::new(self, Level::Fatal, msg)
     }
 
+    /// Construct a builder at the `Help` level with the `msg`.
+    pub fn struct_help(&self, msg: &str) -> DiagnosticBuilder<'_> {
+        DiagnosticBuilder::new(self, Level::Help, msg)
+    }
+
     pub fn span_fatal(&self, span: impl Into<MultiSpan>, msg: &str) -> FatalError {
         self.emit_diag_at_span(Diagnostic::new(Fatal, msg), span);
         FatalError

src/librustc_mir/borrow_check/mod.rs

@@ -367,7 +367,7 @@ fn do_mir_borrowck<'a, 'tcx>(
     }
 
     if !mbcx.errors_buffer.is_empty() {
-        mbcx.errors_buffer.sort_by_key(|diag| diag.span.primary_span());
+        mbcx.errors_buffer.sort_by_key(|diag| diag.sort_span);
 
         for diag in mbcx.errors_buffer.drain(..) {
             mbcx.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);

src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs

@@ -18,6 +18,10 @@ use syntax::errors::Applicability;
 use syntax::symbol::kw;
 use syntax_pos::Span;
 
+use self::outlives_suggestion::OutlivesSuggestionBuilder;
+
+pub mod outlives_suggestion;
+
 mod region_name;
 mod var_name;
 
@@ -56,7 +60,6 @@ enum Trace {
 /// Various pieces of state used when reporting borrow checker errors.
 pub struct ErrorReportingCtx<'a, 'b, 'tcx> {
     /// The region inference context used for borrow chekcing this MIR body.
-    #[allow(dead_code)] // FIXME(mark-i-m): used by outlives suggestions
     region_infcx: &'b RegionInferenceContext<'tcx>,
 
     /// The inference context used for type checking.
@@ -370,6 +373,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         fr: RegionVid,
         fr_origin: NLLRegionVariableOrigin,
         outlived_fr: RegionVid,
+        outlives_suggestion: &mut OutlivesSuggestionBuilder,
         renctx: &mut RegionErrorNamingCtx,
     ) -> DiagnosticBuilder<'a> {
         debug!("report_error(fr={:?}, outlived_fr={:?})", fr, outlived_fr);
@@ -415,9 +419,22 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 self.report_fnmut_error(&errctx, &errci, renctx)
             }
             (ConstraintCategory::Assignment, true, false)
-            | (ConstraintCategory::CallArgument, true, false) =>
-                self.report_escaping_data_error(&errctx, &errci, renctx),
-            _ => self.report_general_error(&errctx, &errci, renctx),
+            | (ConstraintCategory::CallArgument, true, false) => {
+                let mut db = self.report_escaping_data_error(&errctx, &errci, renctx);
+
+                outlives_suggestion.intermediate_suggestion(&errctx, &errci, renctx, &mut db);
+                outlives_suggestion.collect_constraint(fr, outlived_fr);
+
+                db
+            }
+            _ => {
+                let mut db = self.report_general_error(&errctx, &errci, renctx);
+
+                outlives_suggestion.intermediate_suggestion(&errctx, &errci, renctx, &mut db);
+                outlives_suggestion.collect_constraint(fr, outlived_fr);
+
+                db
+            }
         }
     }