Auto merge of #106945 - matthiaskrgr:rollup-c5or8z3, r=matthiaskrgr

Rollup of 5 pull requests

Successful merges:

 - #105954 (Update instrument-coverage.md)
 - #106835 (new trait solver: rebase impl substs for gats correctly)
 - #106912 (check -Z query-dep-graph is enabled if -Z dump-dep-graph (#106736))
 - #106940 (Improve a TAIT error and add an error code plus documentation)
 - #106942 (Update books)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -12,6 +12,8 @@ use rustc_span::Span;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
 use rustc_trait_selection::traits::ObligationCtxt;
 
+use crate::session_diagnostics::NonGenericOpaqueTypeParam;
+
 use super::RegionInferenceContext;
 
 impl<'tcx> RegionInferenceContext<'tcx> {
@@ -389,17 +391,13 @@ fn check_opaque_type_parameter_valid(
         } else {
             // Prevent `fn foo() -> Foo<u32>` from being defining.
             let opaque_param = opaque_generics.param_at(i, tcx);
-            tcx.sess
-                .struct_span_err(span, "non-defining opaque type use in defining scope")
-                .span_note(
-                    tcx.def_span(opaque_param.def_id),
-                    &format!(
-                        "used non-generic {} `{}` for generic parameter",
-                        opaque_param.kind.descr(),
-                        arg,
-                    ),
-                )
-                .emit();
+            let kind = opaque_param.kind.descr();
+            tcx.sess.emit_err(NonGenericOpaqueTypeParam {
+                ty: arg,
+                kind,
+                span,
+                param_span: tcx.def_span(opaque_param.def_id),
+            });
             return false;
         }
     }

compiler/rustc_borrowck/src/session_diagnostics.rs

@@ -1,6 +1,6 @@
 use rustc_errors::{IntoDiagnosticArg, MultiSpan};
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
-use rustc_middle::ty::Ty;
+use rustc_middle::ty::{GenericArg, Ty};
 use rustc_span::Span;
 
 use crate::diagnostics::RegionName;
@@ -240,3 +240,14 @@ pub(crate) struct MoveBorrow<'a> {
     #[label]
     pub borrow_span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(borrowck_opaque_type_non_generic_param, code = "E0792")]
+pub(crate) struct NonGenericOpaqueTypeParam<'a, 'tcx> {
+    pub ty: GenericArg<'tcx>,
+    pub kind: &'a str,
+    #[primary_span]
+    pub span: Span,
+    #[label]
+    pub param_span: Span,
+}

compiler/rustc_error_codes/src/error_codes.rs

@@ -508,6 +508,7 @@ E0787: include_str!("./error_codes/E0787.md"),
 E0788: include_str!("./error_codes/E0788.md"),
 E0790: include_str!("./error_codes/E0790.md"),
 E0791: include_str!("./error_codes/E0791.md"),
+E0792: include_str!("./error_codes/E0792.md"),
 ;
 //  E0006, // merged with E0005
 //  E0008, // cannot bind by-move into a pattern guard

compiler/rustc_error_codes/src/error_codes/E0792.md

@@ -0,0 +1,60 @@
+A type alias impl trait can only have its hidden type assigned
+when used fully generically (and within their defining scope).
+This means
+
+```compile_fail,E0792
+#![feature(type_alias_impl_trait)]
+
+type Foo<T> = impl std::fmt::Debug;
+
+fn foo() -> Foo<u32> {
+    5u32
+}
+```
+
+is not accepted. If it were accepted, one could create unsound situations like
+
+```compile_fail,E0792
+#![feature(type_alias_impl_trait)]
+
+type Foo<T> = impl Default;
+
+fn foo() -> Foo<u32> {
+    5u32
+}
+
+fn main() {
+    let x = Foo::<&'static mut String>::default();
+}
+```
+
+
+Instead you need to make the function generic:
+
+```
+#![feature(type_alias_impl_trait)]
+
+type Foo<T> = impl std::fmt::Debug;
+
+fn foo<U>() -> Foo<U> {
+    5u32
+}
+```
+
+This means that no matter the generic parameter to `foo`,
+the hidden type will always be `u32`.
+If you want to link the generic parameter to the hidden type,
+you can do that, too:
+
+
+```
+#![feature(type_alias_impl_trait)]
+
+use std::fmt::Debug;
+
+type Foo<T: Debug> = impl Debug;
+
+fn foo<U: Debug>() -> Foo<U> {
+    Vec::<U>::new()
+}
+```

compiler/rustc_error_messages/locales/en-US/borrowck.ftl

@@ -120,3 +120,7 @@ borrowck_cannot_move_when_borrowed =
         [value] value
         *[other] {$value_place}
     } occurs here
+
+borrowck_opaque_type_non_generic_param =
+    expected generic {$kind} parameter, found `{$ty}`
+    .label = this generic parameter must be used with a generic {$kind} parameter

compiler/rustc_middle/src/ty/diagnostics.rs

@@ -17,7 +17,7 @@ use rustc_type_ir::sty::TyKind::*;
 
 impl<'tcx> IntoDiagnosticArg for Ty<'tcx> {
     fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
-        format!("{}", self).into_diagnostic_arg()
+        self.to_string().into_diagnostic_arg()
     }
 }
 

compiler/rustc_middle/src/ty/subst.rs

@@ -7,6 +7,7 @@ use crate::ty::visit::{TypeVisitable, TypeVisitor};
 use crate::ty::{self, Lift, List, ParamConst, Ty, TyCtxt};
 
 use rustc_data_structures::intern::Interned;
+use rustc_errors::{DiagnosticArgValue, IntoDiagnosticArg};
 use rustc_hir::def_id::DefId;
 use rustc_macros::HashStable;
 use rustc_serialize::{self, Decodable, Encodable};
@@ -36,6 +37,12 @@ pub struct GenericArg<'tcx> {
     marker: PhantomData<(Ty<'tcx>, ty::Region<'tcx>, ty::Const<'tcx>)>,
 }
 
+impl<'tcx> IntoDiagnosticArg for GenericArg<'tcx> {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+        self.to_string().into_diagnostic_arg()
+    }
+}
+
 const TAG_MASK: usize = 0b11;
 const TYPE_TAG: usize = 0b00;
 const REGION_TAG: usize = 0b01;

compiler/rustc_session/src/config.rs

@@ -2459,6 +2459,11 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
 
     let pretty = parse_pretty(&unstable_opts, error_format);
 
+    // query-dep-graph is required if dump-dep-graph is given #106736
+    if unstable_opts.dump_dep_graph && !unstable_opts.query_dep_graph {
+        early_error(error_format, "can't dump dependency graph without `-Z query-dep-graph`");
+    }
+
     // Try to find a directory containing the Rust `src`, for more details see
     // the doc comment on the `real_rust_source_base_dir` field.
     let tmp_buf;

compiler/rustc_trait_selection/src/solve/project_goals.rs

@@ -171,7 +171,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
             let impl_substs_with_gat = goal.predicate.projection_ty.substs.rebase_onto(
                 tcx,
                 goal_trait_ref.def_id,
-                impl_trait_ref.substs,
+                impl_substs,
             );
             let substs = translate_substs(
                 acx.infcx,