Various diagnostics clean ups/tweaks

compiler/rustc_builtin_macros/src/derive.rs

@@ -84,8 +84,10 @@ fn report_bad_target(sess: &Session, item: &Annotatable, span: Span) -> bool {
             sess,
             span,
             E0774,
-            "`derive` may only be applied to structs, enums and unions",
+            "`derive` may only be applied to `struct`s, `enum`s and `union`s",
         )
+        .span_label(span, "not applicable here")
+        .span_label(item.span(), "not a `struct`, `enum` or `union`")
         .emit();
     }
     bad_target
@@ -99,6 +101,7 @@ fn report_unexpected_literal(sess: &Session, lit: &ast::Lit) {
         _ => "for example, write `#[derive(Debug)]` for `Debug`".to_string(),
     };
     struct_span_err!(sess, lit.span, E0777, "expected path to a trait, found literal",)
+        .span_label(lit.span, "not a trait")
         .help(&help_msg)
         .emit();
 }

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -148,11 +148,7 @@ fn cs_clone_shallow(
             }
             _ => cx.span_bug(
                 trait_span,
-                &format!(
-                    "unexpected substructure in \
-                                                    shallow `derive({})`",
-                    name
-                ),
+                &format!("unexpected substructure in shallow `derive({})`", name),
             ),
         }
     }

compiler/rustc_errors/src/emitter.rs

@@ -365,10 +365,7 @@ pub trait Emitter {
                     continue;
                 }
 
-                if matches!(trace.kind, ExpnKind::Inlined) {
-                    new_labels
-                        .push((trace.call_site, "in the inlined copy of this code".to_string()));
-                } else if always_backtrace {
+                if always_backtrace && !matches!(trace.kind, ExpnKind::Inlined) {
                     new_labels.push((
                         trace.def_site,
                         format!(
@@ -398,13 +395,27 @@ pub trait Emitter {
                 // and it needs an "in this macro invocation" label to match that.
                 let redundant_span = trace.call_site.contains(sp);
 
-                if !redundant_span && matches!(trace.kind, ExpnKind::Macro(MacroKind::Bang, _))
-                    || always_backtrace
-                {
+                if !redundant_span || always_backtrace {
+                    let msg: Cow<'static, _> = match trace.kind {
+                        ExpnKind::Macro(MacroKind::Attr, _) => {
+                            "this procedural macro expansion".into()
+                        }
+                        ExpnKind::Macro(MacroKind::Derive, _) => {
+                            "this derive macro expansion".into()
+                        }
+                        ExpnKind::Macro(MacroKind::Bang, _) => "this macro invocation".into(),
+                        ExpnKind::Inlined => "the inlined copy of this code".into(),
+                        ExpnKind::Root => "in the crate root".into(),
+                        ExpnKind::AstPass(kind) => kind.descr().into(),
+                        ExpnKind::Desugaring(kind) => {
+                            format!("this {} desugaring", kind.descr()).into()
+                        }
+                    };
                     new_labels.push((
                         trace.call_site,
                         format!(
-                            "in this macro invocation{}",
+                            "in {}{}",
+                            msg,
                             if macro_backtrace.len() > 1 && always_backtrace {
                                 // only specify order when the macro
                                 // backtrace is multiple levels deep

compiler/rustc_span/src/hygiene.rs

@@ -952,7 +952,7 @@ pub enum AstPass {
 }
 
 impl AstPass {
-    fn descr(self) -> &'static str {
+    pub fn descr(self) -> &'static str {
         match self {
             AstPass::StdImports => "standard library imports",
             AstPass::TestHarness => "test harness",
@@ -989,7 +989,7 @@ pub enum ForLoopLoc {
 
 impl DesugaringKind {
     /// The description wording should combine well with "desugaring of {}".
-    fn descr(self) -> &'static str {
+    pub fn descr(self) -> &'static str {
         match self {
             DesugaringKind::CondTemporary => "`if` or `while` condition",
             DesugaringKind::Async => "`async` block or function",

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

@@ -1928,12 +1928,12 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             ObligationCauseCode::ItemObligation(item_def_id) => {
                 let item_name = tcx.def_path_str(item_def_id);
                 let msg = format!("required by `{}`", item_name);
-                if let Some(sp) = tcx.hir().span_if_local(item_def_id) {
-                    let sp = tcx.sess.source_map().guess_head_span(sp);
-                    err.span_label(sp, &msg);
-                } else {
-                    err.note(&msg);
-                }
+                let sp = tcx
+                    .hir()
+                    .span_if_local(item_def_id)
+                    .unwrap_or_else(|| tcx.def_span(item_def_id));
+                let sp = tcx.sess.source_map().guess_head_span(sp);
+                err.span_note(sp, &msg);
             }
             ObligationCauseCode::BindingObligation(item_def_id, span) => {
                 let item_name = tcx.def_path_str(item_def_id);
@@ -1952,7 +1952,10 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 if span != DUMMY_SP {
                     err.span_label(span, &msg);
                 } else {
-                    err.note(&msg);
+                    err.span_note(
+                        tcx.def_span(item_def_id),
+                        &format!("required by a bound in `{}`", item_name),
+                    );
                 }
             }
             ObligationCauseCode::ObjectCastObligation(object_ty) => {
@@ -1979,9 +1982,8 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
 
                 if self.tcx.sess.is_nightly_build() && is_const_fn {
                     err.help(
-                        "create an inline `const` block, see RFC \
-                        #2920 <https://github.com/rust-lang/rfcs/pull/2920> \
-                        for more information",
+                        "create an inline `const` block, see RFC #2920 \
+                         <https://github.com/rust-lang/rfcs/pull/2920> for more information",
                     );
                 }
             }
@@ -2168,8 +2170,14 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 self.tcx.for_each_relevant_impl(
                     parent_def_id,
                     parent_trait_ref.self_ty().skip_binder(),
-                    |impl_def_id| {
-                        candidates.push(impl_def_id);
+                    |impl_def_id| match self.tcx.hir().get_if_local(impl_def_id) {
+                        Some(Node::Item(hir::Item {
+                            kind: hir::ItemKind::Impl(hir::Impl { .. }),
+                            ..
+                        })) => {
+                            candidates.push(impl_def_id);
+                        }
+                        _ => {}
                     },
                 );
                 match &candidates[..] {

compiler/rustc_typeck/src/check/method/suggest.rs

@@ -933,6 +933,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     item_name
                 );
                 err.span_label(item_name.span, &format!("private {}", kind));
+                let sp = self
+                    .tcx
+                    .hir()
+                    .span_if_local(def_id)
+                    .unwrap_or_else(|| self.tcx.def_span(def_id));
+                err.span_label(sp, &format!("private {} defined here", kind));
                 self.suggest_valid_traits(&mut err, out_of_scope_traits);
                 err.emit();
             }

src/test/ui-fulldeps/session-derive-errors.stderr

@@ -56,6 +56,8 @@ LL | #[message = "This error has a field, and references {name}"]
 error: invalid format string: expected `'}'` but string was terminated
   --> $DIR/session-derive-errors.rs:116:1
    |
+LL | #[derive(SessionDiagnostic)]
+   |          ----------------- in this derive macro expansion
 LL | #[error = "E0123"]
    |               - because of this opening brace
 LL | #[message = "This is missing a closing brace: {name"]
@@ -67,6 +69,9 @@ LL | #[message = "This is missing a closing brace: {name"]
 error: invalid format string: unmatched `}` found
   --> $DIR/session-derive-errors.rs:125:1
    |
+LL | #[derive(SessionDiagnostic)]
+   |          ----------------- in this derive macro expansion
+LL | #[error = "E0123"]
 LL | #[message = "This is missing an opening brace: name}"]
    | ^ unmatched `}` in format string
    |

src/test/ui/allocator/not-an-allocator.stderr

@@ -1,37 +1,61 @@
 error[E0277]: the trait bound `usize: GlobalAlloc` is not satisfied
   --> $DIR/not-an-allocator.rs:2:1
    |
+LL | #[global_allocator]
+   | ------------------- in this procedural macro expansion
 LL | static A: usize = 0;
    | ^^^^^^^^^^^^^^^^^^^^ the trait `GlobalAlloc` is not implemented for `usize`
    |
-   = note: required by `std::alloc::GlobalAlloc::alloc`
+note: required by `std::alloc::GlobalAlloc::alloc`
+  --> $SRC_DIR/core/src/alloc/global.rs:LL:COL
+   |
+LL |     unsafe fn alloc(&self, layout: Layout) -> *mut u8;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the attribute macro `global_allocator` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the trait bound `usize: GlobalAlloc` is not satisfied
   --> $DIR/not-an-allocator.rs:2:1
    |
+LL | #[global_allocator]
+   | ------------------- in this procedural macro expansion
 LL | static A: usize = 0;
    | ^^^^^^^^^^^^^^^^^^^^ the trait `GlobalAlloc` is not implemented for `usize`
    |
-   = note: required by `std::alloc::GlobalAlloc::dealloc`
+note: required by `std::alloc::GlobalAlloc::dealloc`
+  --> $SRC_DIR/core/src/alloc/global.rs:LL:COL
+   |
+LL |     unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the attribute macro `global_allocator` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the trait bound `usize: GlobalAlloc` is not satisfied
   --> $DIR/not-an-allocator.rs:2:1
    |
+LL | #[global_allocator]
+   | ------------------- in this procedural macro expansion
 LL | static A: usize = 0;
    | ^^^^^^^^^^^^^^^^^^^^ the trait `GlobalAlloc` is not implemented for `usize`
    |
-   = note: required by `std::alloc::GlobalAlloc::realloc`
+note: required by `std::alloc::GlobalAlloc::realloc`
+  --> $SRC_DIR/core/src/alloc/global.rs:LL:COL
+   |
+LL |     unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the attribute macro `global_allocator` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the trait bound `usize: GlobalAlloc` is not satisfied
   --> $DIR/not-an-allocator.rs:2:1
    |
+LL | #[global_allocator]
+   | ------------------- in this procedural macro expansion
 LL | static A: usize = 0;
    | ^^^^^^^^^^^^^^^^^^^^ the trait `GlobalAlloc` is not implemented for `usize`
    |
-   = note: required by `std::alloc::GlobalAlloc::alloc_zeroed`
+note: required by `std::alloc::GlobalAlloc::alloc_zeroed`
+  --> $SRC_DIR/core/src/alloc/global.rs:LL:COL
+   |
+LL |     unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the attribute macro `global_allocator` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 4 previous errors

src/test/ui/allocator/two-allocators.stderr

@@ -4,6 +4,7 @@ error: cannot define multiple global allocators
 LL | static A: System = System;
    | -------------------------- previous global allocator defined here
 LL | #[global_allocator]
+   | ------------------- in this procedural macro expansion
 LL | static B: System = System;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot define a new global allocator
    |

src/test/ui/associated-consts/associated-const-array-len.stderr

@@ -1,11 +1,14 @@
 error[E0277]: the trait bound `i32: Foo` is not satisfied
   --> $DIR/associated-const-array-len.rs:5:16
    |
-LL |     const ID: usize;
-   |     ---------------- required by `Foo::ID`
-...
 LL | const X: [i32; <i32 as Foo>::ID] = [0, 1, 2];
    |                ^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `i32`
+   |
+note: required by `Foo::ID`
+  --> $DIR/associated-const-array-len.rs:2:5
+   |
+LL |     const ID: usize;
+   |     ^^^^^^^^^^^^^^^^
 
 error: aborting due to previous error
 

src/test/ui/associated-consts/associated-const-private-impl.stderr

@@ -1,6 +1,9 @@
 error[E0624]: associated constant `ID` is private
   --> $DIR/associated-const-private-impl.rs:13:30
    |
+LL |             const ID: i32 = 1;
+   |             ------------------ private associated constant defined here
+...
 LL |     assert_eq!(1, bar1::Foo::ID);
    |                              ^^ private associated constant
 

src/test/ui/associated-consts/issue-63496.stderr

@@ -1,9 +1,6 @@
 error[E0283]: type annotations needed
   --> $DIR/issue-63496.rs:4:21
    |
-LL |     const C: usize;
-   |     --------------- required by `A::C`
-LL | 
 LL |     fn f() -> ([u8; A::C], [u8; A::C]);
    |                     ^^^^
    |                     |
@@ -12,13 +9,15 @@ LL |     fn f() -> ([u8; A::C], [u8; A::C]);
    |
    = note: cannot satisfy `_: A`
    = note: associated constants cannot be accessed directly on a `trait`, they can only be accessed through a specific `impl`
+note: required by `A::C`
+  --> $DIR/issue-63496.rs:2:5
+   |
+LL |     const C: usize;
+   |     ^^^^^^^^^^^^^^^
 
 error[E0283]: type annotations needed
   --> $DIR/issue-63496.rs:4:33
    |
-LL |     const C: usize;
-   |     --------------- required by `A::C`
-LL | 
 LL |     fn f() -> ([u8; A::C], [u8; A::C]);
    |                                 ^^^^
    |                                 |
@@ -27,6 +26,11 @@ LL |     fn f() -> ([u8; A::C], [u8; A::C]);
    |
    = note: cannot satisfy `_: A`
    = note: associated constants cannot be accessed directly on a `trait`, they can only be accessed through a specific `impl`
+note: required by `A::C`
+  --> $DIR/issue-63496.rs:2:5
+   |
+LL |     const C: usize;
+   |     ^^^^^^^^^^^^^^^
 
 error: aborting due to 2 previous errors
 

src/test/ui/associated-item/issue-48027.stderr

@@ -16,8 +16,6 @@ LL |     const X: usize;
 error[E0283]: type annotations needed
   --> $DIR/issue-48027.rs:3:32
    |
-LL |     const X: usize;
-   |     --------------- required by `Bar::X`
 LL |     fn return_n(&self) -> [u8; Bar::X];
    |                                ^^^^^^
    |                                |
@@ -26,6 +24,11 @@ LL |     fn return_n(&self) -> [u8; Bar::X];
    |
    = note: cannot satisfy `_: Bar`
    = note: associated constants cannot be accessed directly on a `trait`, they can only be accessed through a specific `impl`
+note: required by `Bar::X`
+  --> $DIR/issue-48027.rs:2:5
+   |
+LL |     const X: usize;
+   |     ^^^^^^^^^^^^^^^
 
 error: aborting due to 2 previous errors
 

src/test/ui/associated-types/associated-types-bound-failure.stderr

@@ -1,12 +1,14 @@
 error[E0277]: the trait bound `<G as GetToInt>::R: ToInt` is not satisfied
   --> $DIR/associated-types-bound-failure.rs:19:19
    |
-LL |     fn to_int(&self) -> isize;
-   |     -------------------------- required by `ToInt::to_int`
-...
 LL |     ToInt::to_int(&g.get())
    |                   ^^^^^^^^ the trait `ToInt` is not implemented for `<G as GetToInt>::R`
    |
+note: required by `ToInt::to_int`
+  --> $DIR/associated-types-bound-failure.rs:6:5
+   |
+LL |     fn to_int(&self) -> isize;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
 help: consider further restricting the associated type
    |
 LL |     where G : GetToInt, <G as GetToInt>::R: ToInt

src/test/ui/associated-types/associated-types-unconstrained.stderr

@@ -1,13 +1,15 @@
 error[E0283]: type annotations needed
   --> $DIR/associated-types-unconstrained.rs:14:20
    |
-LL |     fn bar() -> isize;
-   |     ------------------ required by `Foo::bar`
-...
 LL |     let x: isize = Foo::bar();
    |                    ^^^^^^^^ cannot infer type
    |
    = note: cannot satisfy `_: Foo`
+note: required by `Foo::bar`
+  --> $DIR/associated-types-unconstrained.rs:5:5
+   |
+LL |     fn bar() -> isize;
+   |     ^^^^^^^^^^^^^^^^^^
 
 error: aborting due to previous error