Account for Self as a type param

src/librustc_infer/infer/error_reporting/nice_region_error/trait_impl_difference.rs

@@ -6,6 +6,7 @@ use crate::infer::{Subtype, TyCtxtInferExt, ValuePairs};
 use crate::traits::ObligationCauseCode::CompareImplMethodObligation;
 use rustc_errors::ErrorReported;
 use rustc_hir as hir;
+use rustc_hir::def::Res;
 use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::Visitor;
 use rustc_middle::ty::error::ExpectedFound;
@@ -124,15 +125,17 @@ impl Visitor<'tcx> for TypeParamSpanVisitor<'tcx> {
 
     fn visit_ty(&mut self, arg: &'tcx hir::Ty<'tcx>) {
         match arg.kind {
-            hir::TyKind::Slice(_) | hir::TyKind::Tup(_) | hir::TyKind::Array(..) => {
-                hir::intravisit::walk_ty(self, arg);
+            hir::TyKind::Rptr(_, ref mut_ty) => {
+                // We don't want to suggest looking into borrowing `&T` or `&Self`.
+                hir::intravisit::walk_ty(self, mut_ty.ty);
+                return;
             }
             hir::TyKind::Path(hir::QPath::Resolved(None, path)) => match &path.segments {
                 [segment]
                     if segment
                         .res
                         .map(|res| match res {
-                            hir::def::Res::Def(hir::def::DefKind::TyParam, _) => true,
+                            Res::SelfTy(_, _) | Res::Def(hir::def::DefKind::TyParam, _) => true,
                             _ => false,
                         })
                         .unwrap_or(false) =>
@@ -143,5 +146,6 @@ impl Visitor<'tcx> for TypeParamSpanVisitor<'tcx> {
             },
             _ => {}
         }
+        hir::intravisit::walk_ty(self, arg);
     }
 }

src/test/ui/traits/self-without-lifetime-constraint.rs

@@ -0,0 +1,53 @@
+use std::error::Error;
+use std::fmt;
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub enum ValueRef<'a> {
+    Null,
+    Integer(i64),
+    Real(f64),
+    Text(&'a [u8]),
+    Blob(&'a [u8]),
+}
+
+impl<'a> ValueRef<'a> {
+    pub fn as_str(&self) -> FromSqlResult<&'a str, &'a &'a str> {
+        match *self {
+            ValueRef::Text(t) => {
+                std::str::from_utf8(t).map_err(|_| FromSqlError::InvalidType).map(|x| (x, &x))
+            }
+            _ => Err(FromSqlError::InvalidType),
+        }
+    }
+}
+
+#[derive(Debug)]
+#[non_exhaustive]
+pub enum FromSqlError {
+    InvalidType
+}
+
+impl fmt::Display for FromSqlError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "InvalidType")
+    }
+}
+
+impl Error for FromSqlError {}
+
+pub type FromSqlResult<T, K> = Result<(T, K), FromSqlError>;
+
+pub trait FromSql: Sized {
+    fn column_result(value: ValueRef<'_>) -> FromSqlResult<Self, &Self>;
+}
+
+impl FromSql for &str {
+    fn column_result(value: ValueRef<'_>) -> FromSqlResult<&str, &&str> {
+    //~^ ERROR `impl` item signature doesn't match `trait` item signature
+        value.as_str()
+    }
+}
+
+pub fn main() {
+    println!("{}", "Hello World");
+}

src/test/ui/traits/self-without-lifetime-constraint.stderr

@@ -0,0 +1,19 @@
+error: `impl` item signature doesn't match `trait` item signature
+  --> $DIR/self-without-lifetime-constraint.rs:45:5
+   |
+LL |     fn column_result(value: ValueRef<'_>) -> FromSqlResult<Self, &Self>;
+   |     -------------------------------------------------------------------- expected `fn(ValueRef<'_>) -> std::result::Result<(&str, &&str), FromSqlError>`
+...
+LL |     fn column_result(value: ValueRef<'_>) -> FromSqlResult<&str, &&str> {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ found `fn(ValueRef<'_>) -> std::result::Result<(&str, &&str), FromSqlError>`
+   |
+   = note: expected `fn(ValueRef<'_>) -> std::result::Result<(&str, &&str), _>`
+              found `fn(ValueRef<'_>) -> std::result::Result<(&str, &&str), _>`
+help: the lifetime requirements from the `impl` do not correspond to the requirements in the `trait`
+  --> $DIR/self-without-lifetime-constraint.rs:41:60
+   |
+LL |     fn column_result(value: ValueRef<'_>) -> FromSqlResult<Self, &Self>;
+   |                                                            ^^^^ consider borrowing this type parameter in the trait
+
+error: aborting due to previous error
+