Auto merge of #97356 - Dylan-DPC:rollup-bhceawj, r=Dylan-DPC

Rollup of 4 pull requests

Successful merges:

 - #97288 (Lifetime variance fixes for rustdoc)
 - #97298 (Parse expression after `else` as a condition if followed by `{`)
 - #97308 (Stabilize `cell_filter_map`)
 - #97321 (explain how to turn integers into fn ptrs)

Failed merges:

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

Author: bors

compiler/rustc_hir/src/hir.rs

@@ -343,12 +343,12 @@ pub struct GenericArgs<'hir> {
     pub span_ext: Span,
 }
 
-impl GenericArgs<'_> {
+impl<'hir> GenericArgs<'hir> {
     pub const fn none() -> Self {
         Self { args: &[], bindings: &[], parenthesized: false, span_ext: DUMMY_SP }
     }
 
-    pub fn inputs(&self) -> &[Ty<'_>] {
+    pub fn inputs(&self) -> &[Ty<'hir>] {
         if self.parenthesized {
             for arg in self.args {
                 match arg {
@@ -549,7 +549,7 @@ impl<'hir> Generics<'hir> {
         &NOPE
     }
 
-    pub fn get_named(&self, name: Symbol) -> Option<&GenericParam<'_>> {
+    pub fn get_named(&self, name: Symbol) -> Option<&GenericParam<'hir>> {
         for param in self.params {
             if name == param.name.ident().name {
                 return Some(param);
@@ -608,7 +608,7 @@ impl<'hir> Generics<'hir> {
     pub fn bounds_for_param(
         &self,
         param_def_id: LocalDefId,
-    ) -> impl Iterator<Item = &WhereBoundPredicate<'_>> {
+    ) -> impl Iterator<Item = &WhereBoundPredicate<'hir>> {
         self.predicates.iter().filter_map(move |pred| match pred {
             WherePredicate::BoundPredicate(bp) if bp.is_param_bound(param_def_id.to_def_id()) => {
                 Some(bp)

compiler/rustc_parse/src/parser/expr.rs

@@ -2010,6 +2010,12 @@ impl<'a> Parser<'a> {
         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs))
     }
 
+    /// Parse a block which takes no attributes and has no label
+    fn parse_simple_block(&mut self) -> PResult<'a, P<Expr>> {
+        let blk = self.parse_block()?;
+        Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new()))
+    }
+
     /// Recover on an explicitly quantified closure expression, e.g., `for<'a> |x: &'a u8| *x + 1`.
     fn recover_quantified_closure_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
         let lo = self.token.span;
@@ -2157,14 +2163,22 @@ impl<'a> Parser<'a> {
         let lo = self.prev_token.span;
         let cond = self.parse_cond_expr()?;
 
+        self.parse_if_after_cond(attrs, lo, cond)
+    }
+
+    fn parse_if_after_cond(
+        &mut self,
+        attrs: AttrVec,
+        lo: Span,
+        cond: P<Expr>,
+    ) -> PResult<'a, P<Expr>> {
         let missing_then_block_binop_span = || {
             match cond.kind {
                 ExprKind::Binary(Spanned { span: binop_span, .. }, _, ref right)
                     if let ExprKind::Block(..) = right.kind => Some(binop_span),
                 _ => None
             }
         };
-
         // Verify that the parsed `if` condition makes sense as a condition. If it is a block, then
         // verify that the last statement is either an implicit return (no `;`) or an explicit
         // return. This won't catch blocks with an explicit `return`, but that would be caught by
@@ -2256,15 +2270,53 @@ impl<'a> Parser<'a> {
 
     /// Parses an `else { ... }` expression (`else` token already eaten).
     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
-        let ctx_span = self.prev_token.span; // `else`
+        let else_span = self.prev_token.span; // `else`
         let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
         let expr = if self.eat_keyword(kw::If) {
             self.parse_if_expr(AttrVec::new())?
+        } else if self.check(&TokenKind::OpenDelim(Delimiter::Brace)) {
+            self.parse_simple_block()?
         } else {
-            let blk = self.parse_block()?;
-            self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new())
+            let snapshot = self.create_snapshot_for_diagnostic();
+            let first_tok = super::token_descr(&self.token);
+            let first_tok_span = self.token.span;
+            match self.parse_expr() {
+                Ok(cond)
+                // If it's not a free-standing expression, and is followed by a block,
+                // then it's very likely the condition to an `else if`.
+                    if self.check(&TokenKind::OpenDelim(Delimiter::Brace))
+                        && classify::expr_requires_semi_to_be_stmt(&cond) =>
+                {
+                    self.struct_span_err(first_tok_span, format!("expected `{{`, found {first_tok}"))
+                        .span_label(else_span, "expected an `if` or a block after this `else`")
+                        .span_suggestion(
+                            cond.span.shrink_to_lo(),
+                            "add an `if` if this is the condition to an chained `if` statement after the `else`",
+                            "if ".to_string(),
+                            Applicability::MaybeIncorrect,
+                        ).multipart_suggestion(
+                            "... otherwise, place this expression inside of a block if it is not an `if` condition",
+                            vec![
+                                (cond.span.shrink_to_lo(), "{ ".to_string()),
+                                (cond.span.shrink_to_hi(), " }".to_string()),
+                            ],
+                            Applicability::MaybeIncorrect,
+                        )
+                        .emit();
+                    self.parse_if_after_cond(AttrVec::new(), cond.span.shrink_to_lo(), cond)?
+                }
+                Err(e) => {
+                    e.cancel();
+                    self.restore_snapshot(snapshot);
+                    self.parse_simple_block()?
+                },
+                Ok(_) => {
+                    self.restore_snapshot(snapshot);
+                    self.parse_simple_block()?
+                },
+            }
         };
-        self.error_on_if_block_attrs(ctx_span, true, expr.span, &attrs);
+        self.error_on_if_block_attrs(else_span, true, expr.span, &attrs);
         Ok(expr)
     }
 

library/core/src/cell.rs

@@ -1390,16 +1390,14 @@ impl<'b, T: ?Sized> Ref<'b, T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(cell_filter_map)]
-    ///
     /// use std::cell::{RefCell, Ref};
     ///
     /// let c = RefCell::new(vec![1, 2, 3]);
     /// let b1: Ref<Vec<u32>> = c.borrow();
     /// let b2: Result<Ref<u32>, _> = Ref::filter_map(b1, |v| v.get(1));
     /// assert_eq!(*b2.unwrap(), 2);
     /// ```
-    #[unstable(feature = "cell_filter_map", reason = "recently added", issue = "81061")]
+    #[stable(feature = "cell_filter_map", since = "1.63.0")]
     #[inline]
     pub fn filter_map<U: ?Sized, F>(orig: Ref<'b, T>, f: F) -> Result<Ref<'b, U>, Self>
     where
@@ -1538,8 +1536,6 @@ impl<'b, T: ?Sized> RefMut<'b, T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(cell_filter_map)]
-    ///
     /// use std::cell::{RefCell, RefMut};
     ///
     /// let c = RefCell::new(vec![1, 2, 3]);
@@ -1555,7 +1551,7 @@ impl<'b, T: ?Sized> RefMut<'b, T> {
     ///
     /// assert_eq!(*c.borrow(), vec![1, 4, 3]);
     /// ```
-    #[unstable(feature = "cell_filter_map", reason = "recently added", issue = "81061")]
+    #[stable(feature = "cell_filter_map", since = "1.63.0")]
     #[inline]
     pub fn filter_map<U: ?Sized, F>(mut orig: RefMut<'b, T>, f: F) -> Result<RefMut<'b, U>, Self>
     where

library/core/src/intrinsics.rs

@@ -930,6 +930,9 @@ extern "rust-intrinsic" {
     /// fn foo() -> i32 {
     ///     0
     /// }
+    /// // Crucially, we `as`-cast to a raw pointer before `transmute`ing to a function pointer.
+    /// // This avoids an integer-to-pointer `transmute`, which can be problematic.
+    /// // Transmuting between raw pointers and function pointers (i.e., two pointer types) is fine.
     /// let pointer = foo as *const ();
     /// let function = unsafe {
     ///     std::mem::transmute::<*const (), fn() -> i32>(pointer)

library/core/src/primitive_docs.rs

@@ -1351,6 +1351,32 @@ mod prim_ref {}
 /// is a reference to the function-specific ZST. `&bar` is basically never what you
 /// want when `bar` is a function.
 ///
+/// ### Casting to and from integers
+///
+/// You cast function pointers directly to integers:
+///
+/// ```rust
+/// let fnptr: fn(i32) -> i32 = |x| x+2;
+/// let fnptr_addr = fnptr as usize;
+/// ```
+///
+/// However, a direct cast back is not possible. You need to use `transmute`:
+///
+/// ```rust
+/// # let fnptr: fn(i32) -> i32 = |x| x+2;
+/// # let fnptr_addr = fnptr as usize;
+/// let fnptr = fnptr_addr as *const ();
+/// let fnptr: fn(i32) -> i32 = unsafe { std::mem::transmute(fnptr) };
+/// assert_eq!(fnptr(40), 42);
+/// ```
+///
+/// Crucially, we `as`-cast to a raw pointer before `transmute`ing to a function pointer.
+/// This avoids an integer-to-pointer `transmute`, which can be problematic.
+/// Transmuting between raw pointers and function pointers (i.e., two pointer types) is fine.
+///
+/// Note that all of this is not portable to platforms where function pointers and data pointers
+/// have different sizes.
+///
 /// ### Traits
 ///
 /// Function pointers implement the following traits:

library/std/src/primitive_docs.rs

@@ -1351,6 +1351,32 @@ mod prim_ref {}
 /// is a reference to the function-specific ZST. `&bar` is basically never what you
 /// want when `bar` is a function.
 ///
+/// ### Casting to and from integers
+///
+/// You cast function pointers directly to integers:
+///
+/// ```rust
+/// let fnptr: fn(i32) -> i32 = |x| x+2;
+/// let fnptr_addr = fnptr as usize;
+/// ```
+///
+/// However, a direct cast back is not possible. You need to use `transmute`:
+///
+/// ```rust
+/// # let fnptr: fn(i32) -> i32 = |x| x+2;
+/// # let fnptr_addr = fnptr as usize;
+/// let fnptr = fnptr_addr as *const ();
+/// let fnptr: fn(i32) -> i32 = unsafe { std::mem::transmute(fnptr) };
+/// assert_eq!(fnptr(40), 42);
+/// ```
+///
+/// Crucially, we `as`-cast to a raw pointer before `transmute`ing to a function pointer.
+/// This avoids an integer-to-pointer `transmute`, which can be problematic.
+/// Transmuting between raw pointers and function pointers (i.e., two pointer types) is fine.
+///
+/// Note that all of this is not portable to platforms where function pointers and data pointers
+/// have different sizes.
+///
 /// ### Traits
 ///
 /// Function pointers implement the following traits:

src/librustdoc/clean/inline.rs

@@ -218,7 +218,7 @@ pub(crate) fn build_external_trait(cx: &mut DocContext<'_>, did: DefId) -> clean
     }
 }
 
-fn build_external_function(cx: &mut DocContext<'_>, did: DefId) -> clean::Function {
+fn build_external_function<'tcx>(cx: &mut DocContext<'tcx>, did: DefId) -> clean::Function {
     let sig = cx.tcx.fn_sig(did);
 
     let predicates = cx.tcx.predicates_of(did);