Auto merge of #118082 - compiler-errors:rollup-ejsc8yd, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #117828 (Avoid iterating over hashmaps in astconv)
 - #117832 (interpret: simplify handling of shifts by no longer trying to handle signed and unsigned shift amounts in the same branch)
 - #117891 (Recover `dyn` and `impl` after `for<...>`)
 - #117957 (if available use a Child's pidfd for kill/wait)
 - #117988 (Handle attempts to have multiple `cfg`d tail expressions)
 - #117994 (Ignore but do not assume region obligations from unifying headers in negative coherence)
 - #118000 (Make regionck care about placeholders in outlives components)
 - #118068 (subtree update cg_gcc 2023/11/17)

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

3 files changed, 147 insertions, 3 deletions

diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 262e7b899ad..57bc865a0ee 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -21,6 +21,7 @@ use crate::errors::{
 
 use crate::fluent_generated as fluent;
 use crate::parser;
+use crate::parser::attr::InnerAttrPolicy;
 use rustc_ast as ast;
 use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, Lit, LitKind, TokenKind};
@@ -723,6 +724,101 @@ impl<'a> Parser<'a> {
         Err(err)
     }
 
+    pub(super) fn attr_on_non_tail_expr(&self, expr: &Expr) {
+        // Missing semicolon typo error.
+        let span = self.prev_token.span.shrink_to_hi();
+        let mut err = self.sess.create_err(ExpectedSemi {
+            span,
+            token: self.token.clone(),
+            unexpected_token_label: Some(self.token.span),
+            sugg: ExpectedSemiSugg::AddSemi(span),
+        });
+        let attr_span = match &expr.attrs[..] {
+            [] => unreachable!(),
+            [only] => only.span,
+            [first, rest @ ..] => {
+                for attr in rest {
+                    err.span_label(attr.span, "");
+                }
+                first.span
+            }
+        };
+        err.span_label(
+            attr_span,
+            format!(
+                "only `;` terminated statements or tail expressions are allowed after {}",
+                if expr.attrs.len() == 1 { "this attribute" } else { "these attributes" },
+            ),
+        );
+        if self.token == token::Pound
+            && self.look_ahead(1, |t| t.kind == token::OpenDelim(Delimiter::Bracket))
+        {
+            // We have
+            // #[attr]
+            // expr
+            // #[not_attr]
+            // other_expr
+            err.span_label(span, "expected `;` here");
+            err.multipart_suggestion(
+                "alternatively, consider surrounding the expression with a block",
+                vec![
+                    (expr.span.shrink_to_lo(), "{ ".to_string()),
+                    (expr.span.shrink_to_hi(), " }".to_string()),
+                ],
+                Applicability::MachineApplicable,
+            );
+            let mut snapshot = self.create_snapshot_for_diagnostic();
+            if let [attr] = &expr.attrs[..]
+                && let ast::AttrKind::Normal(attr_kind) = &attr.kind
+                && let [segment] = &attr_kind.item.path.segments[..]
+                && segment.ident.name == sym::cfg
+                && let Ok(next_attr) = snapshot.parse_attribute(InnerAttrPolicy::Forbidden(None))
+                && let ast::AttrKind::Normal(next_attr_kind) = next_attr.kind
+                && let [next_segment] = &next_attr_kind.item.path.segments[..]
+                && segment.ident.name == sym::cfg
+                && let Ok(next_expr) = snapshot.parse_expr()
+            {
+                // We have for sure
+                // #[cfg(..)]
+                // expr
+                // #[cfg(..)]
+                // other_expr
+                // So we suggest using `if cfg!(..) { expr } else if cfg!(..) { other_expr }`.
+                let margin = self.sess.source_map().span_to_margin(next_expr.span).unwrap_or(0);
+                let sugg = vec![
+                    (attr.span.with_hi(segment.span().hi()), "if cfg!".to_string()),
+                    (
+                        attr_kind.item.args.span().unwrap().shrink_to_hi().with_hi(attr.span.hi()),
+                        " {".to_string(),
+                    ),
+                    (expr.span.shrink_to_lo(), "    ".to_string()),
+                    (
+                        next_attr.span.with_hi(next_segment.span().hi()),
+                        "} else if cfg!".to_string(),
+                    ),
+                    (
+                        next_attr_kind
+                            .item
+                            .args
+                            .span()
+                            .unwrap()
+                            .shrink_to_hi()
+                            .with_hi(next_attr.span.hi()),
+                        " {".to_string(),
+                    ),
+                    (next_expr.span.shrink_to_lo(), "    ".to_string()),
+                    (next_expr.span.shrink_to_hi(), format!("\n{}}}", " ".repeat(margin))),
+                ];
+                err.multipart_suggestion(
+                    "it seems like you are trying to provide different expressions depending on \
+                     `cfg`, consider using `if cfg!(..)`",
+                    sugg,
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+        err.emit();
+    }
     fn check_too_many_raw_str_terminators(&mut self, err: &mut Diagnostic) -> bool {
         let sm = self.sess.source_map();
         match (&self.prev_token.kind, &self.token.kind) {
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index d1c5ca4b93c..5316dde6096 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -619,6 +619,20 @@ impl<'a> Parser<'a> {
         match &mut stmt.kind {
             // Expression without semicolon.
             StmtKind::Expr(expr)
+                if classify::expr_requires_semi_to_be_stmt(expr)
+                    && !expr.attrs.is_empty()
+                    && ![token::Eof, token::Semi, token::CloseDelim(Delimiter::Brace)]
+                        .contains(&self.token.kind) =>
+            {
+                // The user has written `#[attr] expr` which is unsupported. (#106020)
+                self.attr_on_non_tail_expr(&expr);
+                // We already emitted an error, so don't emit another type error
+                let sp = expr.span.to(self.prev_token.span);
+                *expr = self.mk_expr_err(sp);
+            }
+
+            // Expression without semicolon.
+            StmtKind::Expr(expr)
                 if self.token != token::Eof && classify::expr_requires_semi_to_be_stmt(expr) =>
             {
                 // Just check for errors and recover; do not eat semicolon yet.
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index dc0f1396523..75617b1b3ea 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -287,6 +287,7 @@ impl<'a> Parser<'a> {
             // Function pointer type
             self.parse_ty_bare_fn(lo, ThinVec::new(), None, recover_return_sign)?
         } else if self.check_keyword(kw::For) {
+            let for_span = self.token.span;
             // Function pointer type or bound list (trait object type) starting with a poly-trait.
             //   `for<'lt> [unsafe] [extern "ABI"] fn (&'lt S) -> T`
             //   `for<'lt> Trait1<'lt> + Trait2 + 'a`
@@ -299,9 +300,42 @@ impl<'a> Parser<'a> {
                     recover_return_sign,
                 )?
             } else {
-                let path = self.parse_path(PathStyle::Type)?;
-                let parse_plus = allow_plus == AllowPlus::Yes && self.check_plus();
-                self.parse_remaining_bounds_path(lifetime_defs, path, lo, parse_plus)?
+                // Try to recover `for<'a> dyn Trait` or `for<'a> impl Trait`.
+                if self.may_recover()
+                    && (self.eat_keyword_noexpect(kw::Impl) || self.eat_keyword_noexpect(kw::Dyn))
+                {
+                    let kw = self.prev_token.ident().unwrap().0.name;
+                    let mut err = self.sess.create_err(errors::TransposeDynOrImpl {
+                        span: self.prev_token.span,
+                        kw: kw.as_str(),
+                        sugg: errors::TransposeDynOrImplSugg {
+                            removal_span: self.prev_token.span.with_hi(self.token.span.lo()),
+                            insertion_span: for_span.shrink_to_lo(),
+                            kw: kw.as_str(),
+                        },
+                    });
+                    let path = self.parse_path(PathStyle::Type)?;
+                    let parse_plus = allow_plus == AllowPlus::Yes && self.check_plus();
+                    let kind =
+                        self.parse_remaining_bounds_path(lifetime_defs, path, lo, parse_plus)?;
+                    // Take the parsed bare trait object and turn it either
+                    // into a `dyn` object or an `impl Trait`.
+                    let kind = match (kind, kw) {
+                        (TyKind::TraitObject(bounds, _), kw::Dyn) => {
+                            TyKind::TraitObject(bounds, TraitObjectSyntax::Dyn)
+                        }
+                        (TyKind::TraitObject(bounds, _), kw::Impl) => {
+                            TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds)
+                        }
+                        _ => return Err(err),
+                    };
+                    err.emit();
+                    kind
+                } else {
+                    let path = self.parse_path(PathStyle::Type)?;
+                    let parse_plus = allow_plus == AllowPlus::Yes && self.check_plus();
+                    self.parse_remaining_bounds_path(lifetime_defs, path, lo, parse_plus)?
+                }
             }
         } else if self.eat_keyword(kw::Impl) {
             self.parse_impl_ty(&mut impl_dyn_multi)?