create suggestions for mismatched consts

Author: b-naber

Cargo.lock

@@ -276,7 +276,7 @@ dependencies = [
 
 [[package]]
 name = "cargo"
-version = "0.60.0"
+version = "0.59.0"
 dependencies = [
  "anyhow",
  "atty",
@@ -419,7 +419,7 @@ dependencies = [
 
 [[package]]
 name = "cargo-util"
-version = "0.1.2"
+version = "0.1.1"
 dependencies = [
  "anyhow",
  "core-foundation",
@@ -768,7 +768,7 @@ checksum = "8aebca1129a03dc6dc2b127edd729435bbc4a37e1d5f4d7513165089ceb02634"
 
 [[package]]
 name = "crates-io"
-version = "0.33.1"
+version = "0.33.0"
 dependencies = [
  "anyhow",
  "curl",

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -11,6 +11,7 @@ use super::{
 use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use crate::infer::{self, InferCtxt, TyCtxtInferExt};
+use crate::traits::const_evaluatable::AbstractConst;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, ErrorReported};
 use rustc_hir as hir;
@@ -19,6 +20,7 @@ use rustc_hir::intravisit::Visitor;
 use rustc_hir::GenericParam;
 use rustc_hir::Item;
 use rustc_hir::Node;
+//use rustc_middle::mir::interpret::ConstValue;
 use rustc_middle::thir::abstract_const::NotConstEvaluatable;
 use rustc_middle::ty::error::ExpectedFound;
 use rustc_middle::ty::fast_reject::{self, SimplifyParams, StripReferences};
@@ -1173,6 +1175,11 @@ trait InferCtxtPrivExt<'hir, 'tcx> {
         obligated_types: &mut Vec<&ty::TyS<'tcx>>,
         cause_code: &ObligationCauseCode<'tcx>,
     ) -> bool;
+
+    fn try_create_suggestion_for_mismatched_const(
+        &self,
+        expected_found: ExpectedFound<&'tcx ty::Const<'tcx>>,
+    ) -> Option<String>;
 }
 
 impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
@@ -1246,6 +1253,11 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
                 .emit();
             }
             FulfillmentErrorCode::CodeConstEquateError(ref expected_found, ref err) => {
+                debug!(
+                    "expected: {:?}, found: {:?}",
+                    expected_found.expected, expected_found.found
+                );
+
                 self.report_mismatched_consts(
                     &error.obligation.cause,
                     expected_found.expected,
@@ -1489,6 +1501,16 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
         }
     }
 
+    fn try_create_suggestion_for_mismatched_const(
+        &self,
+        expected_found: ExpectedFound<&'tcx ty::Const<'tcx>>,
+    ) -> Option<String> {
+        match AbstractConst::from_const(self.tcx, expected_found.found) {
+            Ok(Some(f_abstract)) => f_abstract.try_print_with_replacing_substs(self.tcx),
+            _ => None,
+        }
+    }
+
     fn report_similar_impl_candidates(
         &self,
         impl_candidates: Vec<ty::TraitRef<'tcx>>,