make outlives constraints from generic arguments less boring

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -13,7 +13,7 @@ use rustc_hir::{PolyTraitRef, TyKind, WhereBoundPredicate};
 use rustc_infer::infer::{NllRegionVariableOrigin, RelateParamBound};
 use rustc_middle::bug;
 use rustc_middle::hir::place::PlaceBase;
-use rustc_middle::mir::{ConstraintCategory, ReturnConstraint};
+use rustc_middle::mir::{AnnotationSource, ConstraintCategory, ReturnConstraint};
 use rustc_middle::ty::{self, GenericArgs, Region, RegionVid, Ty, TyCtxt, TypeVisitor};
 use rustc_span::{Ident, Span, kw};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
@@ -49,7 +49,8 @@ impl<'tcx> ConstraintDescription for ConstraintCategory<'tcx> {
             ConstraintCategory::Cast { is_implicit_coercion: false, .. } => "cast ",
             ConstraintCategory::Cast { is_implicit_coercion: true, .. } => "coercion ",
             ConstraintCategory::CallArgument(_) => "argument ",
-            ConstraintCategory::TypeAnnotation => "type annotation ",
+            ConstraintCategory::TypeAnnotation(AnnotationSource::GenericArg) => "generic argument ",
+            ConstraintCategory::TypeAnnotation(_) => "type annotation ",
             ConstraintCategory::SizedBound => "proving this value is `Sized` ",
             ConstraintCategory::CopyBound => "copying this value ",
             ConstraintCategory::OpaqueType => "opaque type ",

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -13,9 +13,9 @@ use rustc_infer::infer::region_constraints::{GenericKind, VarInfos, VerifyBound,
 use rustc_infer::infer::{InferCtxt, NllRegionVariableOrigin, RegionVariableOrigin};
 use rustc_middle::bug;
 use rustc_middle::mir::{
-    BasicBlock, Body, ClosureOutlivesRequirement, ClosureOutlivesSubject, ClosureOutlivesSubjectTy,
-    ClosureRegionRequirements, ConstraintCategory, Local, Location, ReturnConstraint,
-    TerminatorKind,
+    AnnotationSource, BasicBlock, Body, ClosureOutlivesRequirement, ClosureOutlivesSubject,
+    ClosureOutlivesSubjectTy, ClosureRegionRequirements, ConstraintCategory, Local, Location,
+    ReturnConstraint, TerminatorKind,
 };
 use rustc_middle::traits::{ObligationCause, ObligationCauseCode};
 use rustc_middle::ty::fold::fold_regions;
@@ -2063,15 +2063,19 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                     // Mimic old logic for this, to minimize false positives in tests.
                     && !path
                         .iter()
-                        .any(|c| matches!(c.category, ConstraintCategory::TypeAnnotation)) =>
+                        .any(|c| matches!(c.category, ConstraintCategory::TypeAnnotation(_))) =>
                 {
                     1
                 }
                 // Between other interesting constraints, order by their position on the `path`.
                 ConstraintCategory::Yield
                 | ConstraintCategory::UseAsConst
                 | ConstraintCategory::UseAsStatic
-                | ConstraintCategory::TypeAnnotation
+                | ConstraintCategory::TypeAnnotation(
+                    AnnotationSource::Ascription
+                    | AnnotationSource::Declaration
+                    | AnnotationSource::OpaqueCast,
+                )
                 | ConstraintCategory::Cast { .. }
                 | ConstraintCategory::CallArgument(_)
                 | ConstraintCategory::CopyBound
@@ -2082,17 +2086,19 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 // Give assignments a lower priority when flagged as less likely to be interesting.
                 // In particular, de-prioritize MIR assignments lowered from argument patterns.
                 ConstraintCategory::Assignment { has_interesting_ty: false } => 3,
+                // Generic arguments are unlikely to be what relates regions together
+                ConstraintCategory::TypeAnnotation(AnnotationSource::GenericArg) => 4,
                 // We handle predicates and opaque types specially; don't prioritize them here.
-                ConstraintCategory::Predicate(_) | ConstraintCategory::OpaqueType => 4,
+                ConstraintCategory::Predicate(_) | ConstraintCategory::OpaqueType => 5,
                 // `Boring` constraints can correspond to user-written code and have useful spans,
                 // but don't provide any other useful information for diagnostics.
-                ConstraintCategory::Boring => 5,
+                ConstraintCategory::Boring => 6,
                 // `BoringNoLocation` constraints can point to user-written code, but are less
                 // specific, and are not used for relations that would make sense to blame.
-                ConstraintCategory::BoringNoLocation => 6,
+                ConstraintCategory::BoringNoLocation => 7,
                 // Do not blame internal constraints.
-                ConstraintCategory::Internal => 7,
-                ConstraintCategory::IllegalUniverse => 8,
+                ConstraintCategory::Internal => 8,
+                ConstraintCategory::IllegalUniverse => 9,
             }
         };
 

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -298,7 +298,7 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
                         context.ambient_variance(),
                         base_ty.ty,
                         location.to_locations(),
-                        ConstraintCategory::TypeAnnotation,
+                        ConstraintCategory::TypeAnnotation(AnnotationSource::OpaqueCast),
                     )
                     .unwrap();
             }
@@ -333,7 +333,7 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
                 ty::Invariant,
                 &UserTypeProjection { base: annotation_index, projs: vec![] },
                 locations,
-                ConstraintCategory::Boring,
+                ConstraintCategory::TypeAnnotation(AnnotationSource::GenericArg),
             ) {
                 let annotation = &self.typeck.user_type_annotations[annotation_index];
                 span_mirbug!(
@@ -455,7 +455,7 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
                     ty::Invariant,
                     user_ty,
                     Locations::All(*span),
-                    ConstraintCategory::TypeAnnotation,
+                    ConstraintCategory::TypeAnnotation(AnnotationSource::Declaration),
                 ) {
                     span_mirbug!(
                         self,
@@ -938,7 +938,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                         ty::Invariant,
                         &UserTypeProjection { base: annotation_index, projs: vec![] },
                         location.to_locations(),
-                        ConstraintCategory::Boring,
+                        ConstraintCategory::TypeAnnotation(AnnotationSource::GenericArg),
                     ) {
                         let annotation = &self.user_type_annotations[annotation_index];
                         span_mirbug!(
@@ -973,7 +973,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     *variance,
                     projection,
                     Locations::All(stmt.source_info.span),
-                    ConstraintCategory::TypeAnnotation,
+                    ConstraintCategory::TypeAnnotation(AnnotationSource::Ascription),
                 ) {
                     let annotation = &self.user_type_annotations[projection.base];
                     span_mirbug!(

compiler/rustc_middle/src/mir/query.rs

@@ -229,7 +229,7 @@ pub enum ConstraintCategory<'tcx> {
     Yield,
     UseAsConst,
     UseAsStatic,
-    TypeAnnotation,
+    TypeAnnotation(AnnotationSource),
     Cast {
         /// Whether this cast is a coercion that was automatically inserted by the compiler.
         is_implicit_coercion: bool,
@@ -280,6 +280,15 @@ pub enum ReturnConstraint {
     ClosureUpvar(FieldIdx),
 }
 
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
+#[derive(TyEncodable, TyDecodable, HashStable, TypeVisitable, TypeFoldable)]
+pub enum AnnotationSource {
+    Ascription,
+    Declaration,
+    OpaqueCast,
+    GenericArg,
+}
+
 /// The subject of a `ClosureOutlivesRequirement` -- that is, the thing
 /// that must outlive some region.
 #[derive(Copy, Clone, Debug, TyEncodable, TyDecodable, HashStable)]

tests/ui/fn/implied-bounds-unnorm-associated-type-2.stderr

@@ -6,7 +6,7 @@ LL | fn g<'a, 'b>() {
    |      |
    |      lifetime `'a` defined here
 LL |     f::<'a, 'b>(());
-   |     ^^^^^^^^^^^^^^^ requires that `'b` must outlive `'a`
+   |     ^^^^^^^^^^^^^^^ generic argument requires that `'b` must outlive `'a`
    |
    = help: consider adding the following bound: `'b: 'a`
    = note: requirement occurs because of a function pointer to `f`