Auto merge of rust-lang#91517 - matthiaskrgr:rollup-3fmp4go, r=matthiaskrgr

Rollup of 3 pull requests

Successful merges:

 - rust-lang#87054 (Add a `try_reduce` method to the Iterator trait)
 - rust-lang#89701 (Updated error message for accidental uses of derive attribute as a crate attribute)
 - rust-lang#90519 (Keep spans for generics in `#[derive(_)]` desugaring)

Failed merges:

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

Author: bors

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -211,14 +211,6 @@ fn mk_ty_param(
     cx.typaram(span, Ident::new(name, span), attrs.to_owned(), bounds, None)
 }
 
-fn mk_generics(params: Vec<ast::GenericParam>, span: Span) -> Generics {
-    Generics {
-        params,
-        where_clause: ast::WhereClause { has_where_token: false, predicates: Vec::new(), span },
-        span,
-    }
-}
-
 /// Bounds on type parameters.
 #[derive(Clone)]
 pub struct Bounds {
@@ -236,7 +228,7 @@ impl Bounds {
         self_ty: Ident,
         self_generics: &Generics,
     ) -> Generics {
-        let generic_params = self
+        let params = self
             .bounds
             .iter()
             .map(|t| {
@@ -245,7 +237,11 @@ impl Bounds {
             })
             .collect();
 
-        mk_generics(generic_params, span)
+        Generics {
+            params,
+            where_clause: ast::WhereClause { has_where_token: false, predicates: Vec::new(), span },
+            span,
+        }
     }
 }
 

compiler/rustc_builtin_macros/src/deriving/generic/ty.rs

@@ -17,8 +17,7 @@ use rustc_index::vec::IndexVec;
 use rustc_macros::HashStable_Generic;
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
-use rustc_span::{def_id::LocalDefId, BytePos};
-use rustc_span::{MultiSpan, Span, DUMMY_SP};
+use rustc_span::{def_id::LocalDefId, BytePos, MultiSpan, Span, DUMMY_SP};
 use rustc_target::asm::InlineAsmRegOrRegClass;
 use rustc_target::spec::abi::Abi;
 
@@ -526,12 +525,20 @@ pub struct GenericParam<'hir> {
 }
 
 impl GenericParam<'hir> {
-    pub fn bounds_span(&self) -> Option<Span> {
-        self.bounds.iter().fold(None, |span, bound| {
-            let span = span.map(|s| s.to(bound.span())).unwrap_or_else(|| bound.span());
-
-            Some(span)
-        })
+    pub fn bounds_span_for_suggestions(&self) -> Option<Span> {
+        self.bounds
+            .iter()
+            .fold(None, |span: Option<Span>, bound| {
+                // We include bounds that come from a `#[derive(_)]` but point at the user's code,
+                // as we use this method to get a span appropriate for suggestions.
+                if !bound.span().can_be_used_for_suggestions() {
+                    None
+                } else {
+                    let span = span.map(|s| s.to(bound.span())).unwrap_or_else(|| bound.span());
+                    Some(span)
+                }
+            })
+            .map(|sp| sp.shrink_to_hi())
     }
 }
 

compiler/rustc_hir/src/hir.rs

@@ -270,7 +270,7 @@ pub fn suggest_constraining_type_param(
         // `where` clause instead of `trait Base<T: Copy = String>: Super<T>`.
         && !matches!(param.kind, hir::GenericParamKind::Type { default: Some(_), .. })
     {
-        if let Some(bounds_span) = param.bounds_span() {
+        if let Some(span) = param.bounds_span_for_suggestions() {
             // If user has provided some bounds, suggest restricting them:
             //
             //   fn foo<T: Foo>(t: T) { ... }
@@ -284,7 +284,7 @@ pub fn suggest_constraining_type_param(
             //          --
             //          |
             //          replace with: `T: Bar +`
-            suggest_restrict(bounds_span.shrink_to_hi());
+            suggest_restrict(span);
         } else {
             // If user hasn't provided any bounds, suggest adding a new one:
             //

compiler/rustc_middle/src/ty/diagnostics.rs

@@ -1953,28 +1953,52 @@ fn is_c_like_enum(item: &Item<'_>) -> bool {
     }
 }
 
+// FIXME: Fix "Cannot determine resolution" error and remove built-in macros
+// from this check.
 fn check_invalid_crate_level_attr(tcx: TyCtxt<'_>, attrs: &[Attribute]) {
+    // Check for builtin attributes at the crate level
+    // which were unsuccessfully resolved due to cannot determine
+    // resolution for the attribute macro error.
     const ATTRS_TO_CHECK: &[Symbol] = &[
         sym::macro_export,
         sym::repr,
         sym::path,
         sym::automatically_derived,
         sym::start,
         sym::rustc_main,
+        sym::derive,
+        sym::test,
+        sym::test_case,
+        sym::global_allocator,
+        sym::bench,
     ];
 
     for attr in attrs {
-        for attr_to_check in ATTRS_TO_CHECK {
-            if attr.has_name(*attr_to_check) {
-                tcx.sess
-                    .struct_span_err(
+        // This function should only be called with crate attributes
+        // which are inner attributes always but lets check to make sure
+        if attr.style == AttrStyle::Inner {
+            for attr_to_check in ATTRS_TO_CHECK {
+                if attr.has_name(*attr_to_check) {
+                    let mut err = tcx.sess.struct_span_err(
                         attr.span,
                         &format!(
                             "`{}` attribute cannot be used at crate level",
                             attr_to_check.to_ident_string()
                         ),
-                    )
-                    .emit();
+                    );
+                    // Only emit an error with a suggestion if we can create a
+                    // string out of the attribute span
+                    if let Ok(src) = tcx.sess.source_map().span_to_snippet(attr.span) {
+                        let replacement = src.replace("#!", "#");
+                        err.span_suggestion_verbose(
+                            attr.span,
+                            "perhaps you meant to use an outer attribute",
+                            replacement,
+                            rustc_errors::Applicability::MachineApplicable,
+                        );
+                    }
+                    err.emit()
+                }
             }
         }
     }

compiler/rustc_passes/src/check_attr.rs

@@ -1735,7 +1735,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                         (generics.span, format!("<{}>", ident))
                     };
                     // Do not suggest if this is coming from macro expansion.
-                    if !span.from_expansion() {
+                    if span.can_be_used_for_suggestions() {
                         return Some((
                             span.shrink_to_hi(),
                             msg,
@@ -1803,7 +1803,7 @@ impl<'tcx> LifetimeContext<'_, 'tcx> {
         );
         err.span_label(lifetime_ref.span, "undeclared lifetime");
         let mut suggests_in_band = false;
-        let mut suggest_note = true;
+        let mut suggested_spans = vec![];
         for missing in &self.missing_named_lifetime_spots {
             match missing {
                 MissingLifetimeSpot::Generics(generics) => {
@@ -1821,23 +1821,17 @@ impl<'tcx> LifetimeContext<'_, 'tcx> {
                         suggests_in_band = true;
                         (generics.span, format!("<{}>", lifetime_ref))
                     };
-                    if !span.from_expansion() {
+                    if suggested_spans.contains(&span) {
+                        continue;
+                    }
+                    suggested_spans.push(span);
+                    if span.can_be_used_for_suggestions() {
                         err.span_suggestion(
                             span,
                             &format!("consider introducing lifetime `{}` here", lifetime_ref),
                             sugg,
                             Applicability::MaybeIncorrect,
                         );
-                    } else if suggest_note {
-                        suggest_note = false; // Avoid displaying the same help multiple times.
-                        err.span_label(
-                            span,
-                            &format!(
-                                "lifetime `{}` is missing in item created through this procedural \
-                                 macro",
-                                lifetime_ref,
-                            ),
-                        );
                     }
                 }
                 MissingLifetimeSpot::HigherRanked { span, span_type } => {

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -551,6 +551,16 @@ impl Span {
         matches!(self.ctxt().outer_expn_data().kind, ExpnKind::Macro(MacroKind::Derive, _))
     }
 
+    /// Gate suggestions that would not be appropriate in a context the user didn't write.
+    pub fn can_be_used_for_suggestions(self) -> bool {
+        !self.from_expansion()
+        // FIXME: If this span comes from a `derive` macro but it points at code the user wrote,
+        // the callsite span and the span will be pointing at different places. It also means that
+        // we can safely provide suggestions on this span.
+            || (matches!(self.ctxt().outer_expn_data().kind, ExpnKind::Macro(MacroKind::Derive, _))
+                && self.parent_callsite().map(|p| (p.lo(), p.hi())) != Some((self.lo(), self.hi())))
+    }
+
     #[inline]
     pub fn with_root_ctxt(lo: BytePos, hi: BytePos) -> Span {
         Span::new(lo, hi, SyntaxContext::root(), None)

compiler/rustc_span/src/lib.rs

@@ -262,16 +262,16 @@ fn suggest_restriction(
             match generics
                 .params
                 .iter()
-                .map(|p| p.bounds_span().unwrap_or(p.span))
-                .filter(|&span| generics.span.contains(span) && span.desugaring_kind().is_none())
+                .map(|p| p.bounds_span_for_suggestions().unwrap_or(p.span.shrink_to_hi()))
+                .filter(|&span| generics.span.contains(span) && span.can_be_used_for_suggestions())
                 .max_by_key(|span| span.hi())
             {
                 // `fn foo(t: impl Trait)`
                 //        ^ suggest `<T: Trait>` here
                 None => (generics.span, format!("<{}>", type_param)),
                 // `fn foo<A>(t: impl Trait)`
                 //        ^^^ suggest `<A, T: Trait>` here
-                Some(span) => (span.shrink_to_hi(), format!(", {}", type_param)),
+                Some(span) => (span, format!(", {}", type_param)),
             },
             // `fn foo(t: impl Trait)`
             //                       ^ suggest `where <T as Trait>::A: Bound`

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

@@ -177,11 +177,9 @@ crate fn placeholder_type_error(
         sugg.push((arg.span, (*type_name).to_string()));
     } else {
         let last = generics.iter().last().unwrap();
-        sugg.push((
-            // Account for bounds, we want `fn foo<T: E, K>(_: K)` not `fn foo<T, K: E>(_: K)`.
-            last.bounds_span().unwrap_or(last.span).shrink_to_hi(),
-            format!(", {}", type_name),
-        ));
+        // Account for bounds, we want `fn foo<T: E, K>(_: K)` not `fn foo<T, K: E>(_: K)`.
+        let span = last.bounds_span_for_suggestions().unwrap_or(last.span.shrink_to_hi());
+        sugg.push((span, format!(", {}", type_name)));
     }
 
     let mut err = bad_placeholder_type(tcx, placeholder_types, kind);

compiler/rustc_typeck/src/collect.rs

@@ -2216,6 +2216,86 @@ pub trait Iterator {
         Some(self.fold(first, f))
     }
 
+    /// Reduces the elements to a single one by repeatedly applying a reducing operation. If the
+    /// closure returns a failure, the failure is propagated back to the caller immediately.
+    ///
+    /// The return type of this method depends on the return type of the closure. If the closure
+    /// returns `Result<Self::Item, E>`, then this function will return `Result<Option<Self::Item>,
+    /// E>`. If the closure returns `Option<Self::Item>`, then this function will return
+    /// `Option<Option<Self::Item>>`.
+    ///
+    /// When called on an empty iterator, this function will return either `Some(None)` or
+    /// `Ok(None)` depending on the type of the provided closure.
+    ///
+    /// For iterators with at least one element, this is essentially the same as calling
+    /// [`try_fold()`] with the first element of the iterator as the initial accumulator value.
+    ///
+    /// [`try_fold()`]: Iterator::try_fold
+    ///
+    /// # Examples
+    ///
+    /// Safely calculate the sum of a series of numbers:
+    ///
+    /// ```
+    /// #![feature(iterator_try_reduce)]
+    ///
+    /// let numbers: Vec<usize> = vec![10, 20, 5, 23, 0];
+    /// let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y));
+    /// assert_eq!(sum, Some(Some(58)));
+    /// ```
+    ///
+    /// Determine when a reduction short circuited:
+    ///
+    /// ```
+    /// #![feature(iterator_try_reduce)]
+    ///
+    /// let numbers = vec![1, 2, 3, usize::MAX, 4, 5];
+    /// let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y));
+    /// assert_eq!(sum, None);
+    /// ```
+    ///
+    /// Determine when a reduction was not performed because there are no elements:
+    ///
+    /// ```
+    /// #![feature(iterator_try_reduce)]
+    ///
+    /// let numbers: Vec<usize> = Vec::new();
+    /// let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y));
+    /// assert_eq!(sum, Some(None));
+    /// ```
+    ///
+    /// Use a [`Result`] instead of an [`Option`]:
+    ///
+    /// ```
+    /// #![feature(iterator_try_reduce)]
+    ///
+    /// let numbers = vec!["1", "2", "3", "4", "5"];
+    /// let max: Result<Option<_>, <usize as std::str::FromStr>::Err> =
+    ///     numbers.into_iter().try_reduce(|x, y| {
+    ///         if x.parse::<usize>()? > y.parse::<usize>()? { Ok(x) } else { Ok(y) }
+    ///     });
+    /// assert_eq!(max, Ok(Some("5")));
+    /// ```
+    #[inline]
+    #[unstable(feature = "iterator_try_reduce", reason = "new API", issue = "87053")]
+    fn try_reduce<F, R>(&mut self, f: F) -> ChangeOutputType<R, Option<R::Output>>
+    where
+        Self: Sized,
+        F: FnMut(Self::Item, Self::Item) -> R,
+        R: Try<Output = Self::Item>,
+        R::Residual: Residual<Option<Self::Item>>,
+    {
+        let first = match self.next() {
+            Some(i) => i,
+            None => return Try::from_output(None),
+        };
+
+        match self.try_fold(first, f).branch() {
+            ControlFlow::Break(r) => FromResidual::from_residual(r),
+            ControlFlow::Continue(i) => Try::from_output(Some(i)),
+        }
+    }
+
     /// Tests if every element of the iterator matches a predicate.
     ///
     /// `all()` takes a closure that returns `true` or `false`. It applies