1 files changed, 183 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/errors/note_and_explain.rs b/compiler/rustc_trait_selection/src/errors/note_and_explain.rs
new file mode 100644
index 00000000000..1f18cd8c8d8
--- /dev/null
+++ b/compiler/rustc_trait_selection/src/errors/note_and_explain.rs
@@ -0,0 +1,183 @@
+use crate::error_reporting::infer::nice_region_error::find_anon_type;
+use crate::fluent_generated as fluent;
+use rustc_errors::{Diag, EmissionGuarantee, IntoDiagArg, SubdiagMessageOp, Subdiagnostic};
+use rustc_hir::def_id::LocalDefId;
+use rustc_middle::bug;
+use rustc_middle::ty::{self, TyCtxt};
+use rustc_span::{symbol::kw, Span};
+
+struct DescriptionCtx<'a> {
+    span: Option<Span>,
+    kind: &'a str,
+    arg: String,
+}
+
+impl<'a> DescriptionCtx<'a> {
+    fn new<'tcx>(
+        tcx: TyCtxt<'tcx>,
+        generic_param_scope: LocalDefId,
+        region: ty::Region<'tcx>,
+        alt_span: Option<Span>,
+    ) -> Option<Self> {
+        let (span, kind, arg) = match *region {
+            ty::ReEarlyParam(br) => {
+                let scope = tcx
+                    .parent(tcx.generics_of(generic_param_scope).region_param(br, tcx).def_id)
+                    .expect_local();
+                let span = if let Some(param) =
+                    tcx.hir().get_generics(scope).and_then(|generics| generics.get_named(br.name))
+                {
+                    param.span
+                } else {
+                    tcx.def_span(scope)
+                };
+                if br.has_name() {
+                    (Some(span), "as_defined", br.name.to_string())
+                } else {
+                    (Some(span), "as_defined_anon", String::new())
+                }
+            }
+            ty::ReLateParam(ref fr) => {
+                if !fr.bound_region.is_named()
+                    && let Some((ty, _)) =
+                        find_anon_type(tcx, generic_param_scope, region, &fr.bound_region)
+                {
+                    (Some(ty.span), "defined_here", String::new())
+                } else {
+                    let scope = fr.scope.expect_local();
+                    match fr.bound_region {
+                        ty::BoundRegionKind::BrNamed(_, name) => {
+                            let span = if let Some(param) = tcx
+                                .hir()
+                                .get_generics(scope)
+                                .and_then(|generics| generics.get_named(name))
+                            {
+                                param.span
+                            } else {
+                                tcx.def_span(scope)
+                            };
+                            if name == kw::UnderscoreLifetime {
+                                (Some(span), "as_defined_anon", String::new())
+                            } else {
+                                (Some(span), "as_defined", name.to_string())
+                            }
+                        }
+                        ty::BrAnon => {
+                            let span = Some(tcx.def_span(scope));
+                            (span, "defined_here", String::new())
+                        }
+                        _ => (Some(tcx.def_span(scope)), "defined_here_reg", region.to_string()),
+                    }
+                }
+            }
+
+            ty::ReStatic => (alt_span, "restatic", String::new()),
+
+            ty::RePlaceholder(_) | ty::ReError(_) => return None,
+
+            ty::ReVar(_) | ty::ReBound(..) | ty::ReErased => {
+                bug!("unexpected region for DescriptionCtx: {:?}", region);
+            }
+        };
+        Some(DescriptionCtx { span, kind, arg })
+    }
+}
+
+pub enum PrefixKind {
+    Empty,
+    RefValidFor,
+    ContentValidFor,
+    TypeObjValidFor,
+    SourcePointerValidFor,
+    TypeSatisfy,
+    TypeOutlive,
+    LfParamInstantiatedWith,
+    LfParamMustOutlive,
+    LfInstantiatedWith,
+    LfMustOutlive,
+    PointerValidFor,
+    DataValidFor,
+}
+
+pub enum SuffixKind {
+    Empty,
+    Continues,
+    ReqByBinding,
+}
+
+impl IntoDiagArg for PrefixKind {
+    fn into_diag_arg(self) -> rustc_errors::DiagArgValue {
+        let kind = match self {
+            Self::Empty => "empty",
+            Self::RefValidFor => "ref_valid_for",
+            Self::ContentValidFor => "content_valid_for",
+            Self::TypeObjValidFor => "type_obj_valid_for",
+            Self::SourcePointerValidFor => "source_pointer_valid_for",
+            Self::TypeSatisfy => "type_satisfy",
+            Self::TypeOutlive => "type_outlive",
+            Self::LfParamInstantiatedWith => "lf_param_instantiated_with",
+            Self::LfParamMustOutlive => "lf_param_must_outlive",
+            Self::LfInstantiatedWith => "lf_instantiated_with",
+            Self::LfMustOutlive => "lf_must_outlive",
+            Self::PointerValidFor => "pointer_valid_for",
+            Self::DataValidFor => "data_valid_for",
+        }
+        .into();
+        rustc_errors::DiagArgValue::Str(kind)
+    }
+}
+
+impl IntoDiagArg for SuffixKind {
+    fn into_diag_arg(self) -> rustc_errors::DiagArgValue {
+        let kind = match self {
+            Self::Empty => "empty",
+            Self::Continues => "continues",
+            Self::ReqByBinding => "req_by_binding",
+        }
+        .into();
+        rustc_errors::DiagArgValue::Str(kind)
+    }
+}
+
+pub struct RegionExplanation<'a> {
+    desc: DescriptionCtx<'a>,
+    prefix: PrefixKind,
+    suffix: SuffixKind,
+}
+
+impl RegionExplanation<'_> {
+    pub fn new<'tcx>(
+        tcx: TyCtxt<'tcx>,
+        generic_param_scope: LocalDefId,
+        region: ty::Region<'tcx>,
+        alt_span: Option<Span>,
+        prefix: PrefixKind,
+        suffix: SuffixKind,
+    ) -> Option<Self> {
+        Some(Self {
+            desc: DescriptionCtx::new(tcx, generic_param_scope, region, alt_span)?,
+            prefix,
+            suffix,
+        })
+    }
+}
+
+impl Subdiagnostic for RegionExplanation<'_> {
+    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
+        self,
+        diag: &mut Diag<'_, G>,
+        f: &F,
+    ) {
+        diag.arg("pref_kind", self.prefix);
+        diag.arg("suff_kind", self.suffix);
+        diag.arg("desc_kind", self.desc.kind);
+        diag.arg("desc_arg", self.desc.arg);
+
+        let msg = f(diag, fluent::trait_selection_region_explanation.into());
+        if let Some(span) = self.desc.span {
+            diag.span_note(span, msg);
+        } else {
+            diag.note(msg);
+        }
+    }
+}