Rollup merge of #126101 - lqd:revert-124099, r=wesleywiser

Revert "Disallow ambiguous attributes on expressions" on nightly

As discussed in [today's t-compiler meeting](https://rust-lang.zulipchat.com/#narrow/stream/238009-t-compiler.2Fmeetings/topic/.5Bweekly.5D.202024-06-06/near/443079505), this reverts PR #124099 to fix P-critical beta regressions #125199.

r? ``@wesleywiser``

Opening as draft so that ``@wesleywiser`` and ``@apiraino,`` you can tell me whether you wanted:
1. a `beta-accepted` revert of #124099 on nightly (this PR)? That will need to be backported to beta (even though #126093 may be the last of those)
2. a revert of #124099 on beta?
3. all of the above?

I also opened #126102, another draft PR to revert #124099 on beta, should you choose options 2 or 3.

compiler/rustc_parse/messages.ftl

@@ -622,8 +622,6 @@ parse_or_pattern_not_allowed_in_let_binding = top-level or-patterns are not allo
 parse_out_of_range_hex_escape = out of range hex escape
     .label = must be a character in the range [\x00-\x7f]
 
-parse_outer_attr_ambiguous = ambiguous outer attributes
-
 parse_outer_attr_explanation = outer attributes, like `#[test]`, annotate the item following them
 
 parse_outer_attribute_not_allowed_on_if_else = outer attributes are not allowed on `if` and `else` branches

compiler/rustc_parse/src/errors.rs

@@ -495,15 +495,6 @@ pub(crate) struct OuterAttributeNotAllowedOnIfElse {
     pub attributes: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag(parse_outer_attr_ambiguous)]
-pub(crate) struct AmbiguousOuterAttributes {
-    #[primary_span]
-    pub span: Span,
-    #[subdiagnostic]
-    pub sugg: WrapInParentheses,
-}
-
 #[derive(Diagnostic)]
 #[diag(parse_missing_in_in_for_loop)]
 pub(crate) struct MissingInInForLoop {

compiler/rustc_parse/src/parser/expr.rs

@@ -328,9 +328,7 @@ pub(super) fn parse_expr_assoc_with(
                 this.parse_expr_assoc_with(prec + prec_adjustment, LhsExpr::NotYetParsed)
             })?;
 
-            self.error_ambiguous_outer_attrs(&lhs, lhs_span, rhs.span);
-            let span = lhs_span.to(rhs.span);
-
+            let span = self.mk_expr_sp(&lhs, lhs_span, rhs.span);
             lhs = match op {
                 AssocOp::Add
                 | AssocOp::Subtract
@@ -429,18 +427,6 @@ fn error_found_expr_would_be_stmt(&self, lhs: &Expr) {
         });
     }
 
-    fn error_ambiguous_outer_attrs(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) {
-        if let Some(attr) = lhs.attrs.iter().find(|a| a.style == AttrStyle::Outer) {
-            self.dcx().emit_err(errors::AmbiguousOuterAttributes {
-                span: attr.span.to(rhs_span),
-                sugg: errors::WrapInParentheses::Expression {
-                    left: attr.span.shrink_to_lo(),
-                    right: lhs_span.shrink_to_hi(),
-                },
-            });
-        }
-    }
-
     /// Possibly translate the current token to an associative operator.
     /// The method does not advance the current token.
     ///
@@ -520,8 +506,7 @@ fn parse_expr_range(
             None
         };
         let rhs_span = rhs.as_ref().map_or(cur_op_span, |x| x.span);
-        self.error_ambiguous_outer_attrs(&lhs, lhs.span, rhs_span);
-        let span = lhs.span.to(rhs_span);
+        let span = self.mk_expr_sp(&lhs, lhs.span, rhs_span);
         let limits =
             if op == AssocOp::DotDot { RangeLimits::HalfOpen } else { RangeLimits::Closed };
         let range = self.mk_range(Some(lhs), rhs, limits);
@@ -739,8 +724,7 @@ fn parse_assoc_op_cast(
         expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind,
     ) -> PResult<'a, P<Expr>> {
         let mk_expr = |this: &mut Self, lhs: P<Expr>, rhs: P<Ty>| {
-            this.error_ambiguous_outer_attrs(&lhs, lhs_span, rhs.span);
-            this.mk_expr(lhs_span.to(rhs.span), expr_kind(lhs, rhs))
+            this.mk_expr(this.mk_expr_sp(&lhs, lhs_span, rhs.span), expr_kind(lhs, rhs))
         };
 
         // Save the state of the parser before parsing type normally, in case there is a
@@ -3858,6 +3842,16 @@ pub(super) fn mk_expr_err(&self, span: Span, guar: ErrorGuaranteed) -> P<Expr> {
         self.mk_expr(span, ExprKind::Err(guar))
     }
 
+    /// Create expression span ensuring the span of the parent node
+    /// is larger than the span of lhs and rhs, including the attributes.
+    fn mk_expr_sp(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) -> Span {
+        lhs.attrs
+            .iter()
+            .find(|a| a.style == AttrStyle::Outer)
+            .map_or(lhs_span, |a| a.span)
+            .to(rhs_span)
+    }
+
     fn collect_tokens_for_expr(
         &mut self,
         attrs: AttrWrapper,

src/tools/clippy/tests/ui/cfg_attr_rustfmt.fixed

@@ -16,7 +16,7 @@ fn foo(
 
 fn skip_on_statements() {
     #[rustfmt::skip]
-    { 5+3; }
+    5+3;
 }
 
 #[rustfmt::skip]
@@ -33,11 +33,11 @@ mod foo {
 #[clippy::msrv = "1.29"]
 fn msrv_1_29() {
     #[cfg_attr(rustfmt, rustfmt::skip)]
-    { 1+29; }
+    1+29;
 }
 
 #[clippy::msrv = "1.30"]
 fn msrv_1_30() {
     #[rustfmt::skip]
-    { 1+30; }
+    1+30;
 }

src/tools/clippy/tests/ui/cfg_attr_rustfmt.rs

@@ -16,7 +16,7 @@ fn foo(
 
 fn skip_on_statements() {
     #[cfg_attr(rustfmt, rustfmt::skip)]
-    { 5+3; }
+    5+3;
 }
 
 #[cfg_attr(rustfmt, rustfmt_skip)]
@@ -33,11 +33,11 @@ pub fn f() {}
 #[clippy::msrv = "1.29"]
 fn msrv_1_29() {
     #[cfg_attr(rustfmt, rustfmt::skip)]
-    { 1+29; }
+    1+29;
 }
 
 #[clippy::msrv = "1.30"]
 fn msrv_1_30() {
     #[cfg_attr(rustfmt, rustfmt::skip)]
-    { 1+30; }
+    1+30;
 }

src/tools/rustfmt/tests/source/attrib.rs

@@ -214,8 +214,8 @@ pub struct Params {
 // #3313
 fn stmt_expr_attributes() {
     let foo ;
-    (#[must_use]
-   foo) = false ;
+    #[must_use]
+   foo = false ;
 }
 
 // #3509

src/tools/rustfmt/tests/target/attrib.rs

@@ -248,8 +248,8 @@ pub struct Params {
 // #3313
 fn stmt_expr_attributes() {
     let foo;
-    (#[must_use]
-    foo) = false;
+    #[must_use]
+    foo = false;
 }
 
 // #3509

tests/pretty/ast-stmt-expr-attr.rs

@@ -13,17 +13,17 @@ fn syntax() {
     let _ = #[attr] ();
     let _ = #[attr] (#[attr] 0,);
     let _ = #[attr] (#[attr] 0, 0);
-    let _ = (#[attr] 0) + #[attr] 0;
-    let _ = (#[attr] 0) / #[attr] 0;
-    let _ = (#[attr] 0) & #[attr] 0;
-    let _ = (#[attr] 0) % #[attr] 0;
+    let _ = #[attr] 0 + #[attr] 0;
+    let _ = #[attr] 0 / #[attr] 0;
+    let _ = #[attr] 0 & #[attr] 0;
+    let _ = #[attr] 0 % #[attr] 0;
     let _ = #[attr] (0 + 0);
     let _ = #[attr] !0;
     let _ = #[attr] -0;
     let _ = #[attr] false;
     let _ = #[attr] 0;
     let _ = #[attr] 'c';
-    let _ = (#[attr] x) as Y;
+    let _ = #[attr] x as Y;
     let _ = #[attr] (x as Y);
     let _ =
         #[attr] while true {
@@ -88,9 +88,9 @@ fn syntax() {
             let _ = ();
             foo
         };
-    let _ = (#[attr] x) = y;
+    let _ = #[attr] x = y;
     let _ = #[attr] (x = y);
-    let _ = (#[attr] x) += y;
+    let _ = #[attr] x += y;
     let _ = #[attr] (x += y);
     let _ = #[attr] foo.bar;
     let _ = (#[attr] foo).bar;
@@ -98,8 +98,8 @@ fn syntax() {
     let _ = (#[attr] foo).0;
     let _ = #[attr] foo[bar];
     let _ = (#[attr] foo)[bar];
-    let _ = (#[attr] 0)..#[attr] 0;
-    let _ = (#[attr] 0)..;
+    let _ = #[attr] 0..#[attr] 0;
+    let _ = #[attr] 0..;
     let _ = #[attr] (0..0);
     let _ = #[attr] (0..);
     let _ = #[attr] (..0);

tests/pretty/stmt_expr_attributes.rs

@@ -147,13 +147,13 @@ fn _11() {
     let _ = #[rustc_dummy] (0);
     let _ = #[rustc_dummy] (0,);
     let _ = #[rustc_dummy] (0, 0);
-    let _ = (#[rustc_dummy] 0) + #[rustc_dummy] 0;
+    let _ = #[rustc_dummy] 0 + #[rustc_dummy] 0;
     let _ = #[rustc_dummy] !0;
     let _ = #[rustc_dummy] -0i32;
     let _ = #[rustc_dummy] false;
     let _ = #[rustc_dummy] 'c';
     let _ = #[rustc_dummy] 0;
-    let _ = (#[rustc_dummy] 0) as usize;
+    let _ = #[rustc_dummy] 0 as usize;
     let _ =
         #[rustc_dummy] while false {
             #![rustc_dummy]
@@ -208,8 +208,8 @@ fn _11() {
         };
     let const {} = #[rustc_dummy] const {};
     let mut x = 0;
-    let _ = (#[rustc_dummy] x) = 15;
-    let _ = (#[rustc_dummy] x) += 15;
+    let _ = #[rustc_dummy] x = 15;
+    let _ = #[rustc_dummy] x += 15;
     let s = Foo { data: () };
     let _ = #[rustc_dummy] s.data;
     let _ = (#[rustc_dummy] s).data;
@@ -219,8 +219,8 @@ fn _11() {
     let v = vec!(0);
     let _ = #[rustc_dummy] v[0];
     let _ = (#[rustc_dummy] v)[0];
-    let _ = (#[rustc_dummy] 0)..#[rustc_dummy] 0;
-    let _ = (#[rustc_dummy] 0)..;
+    let _ = #[rustc_dummy] 0..#[rustc_dummy] 0;
+    let _ = #[rustc_dummy] 0..;
     let _ = #[rustc_dummy] (0..0);
     let _ = #[rustc_dummy] (0..);
     let _ = #[rustc_dummy] (..0);

tests/ui/lint/unused/unused-doc-comments-edge-cases.rs

@@ -20,10 +20,10 @@ fn doc_comment_between_if_else(num: u8) -> bool {
 }
 
 fn doc_comment_on_expr(num: u8) -> bool {
-    (/// useless doc comment
+    /// useless doc comment
     //~^ ERROR: attributes on expressions are experimental
     //~| ERROR: unused doc comment
-    num) == 3
+    num == 3
 }
 
 fn doc_comment_on_expr_field() -> bool {

tests/ui/lint/unused/unused-doc-comments-edge-cases.stderr

@@ -5,10 +5,10 @@ LL |     else {
    |     ^^^^ expected expression
 
 error[E0658]: attributes on expressions are experimental
-  --> $DIR/unused-doc-comments-edge-cases.rs:23:6
+  --> $DIR/unused-doc-comments-edge-cases.rs:23:5
    |
-LL |     (/// useless doc comment
-   |      ^^^^^^^^^^^^^^^^^^^^^^^
+LL |     /// useless doc comment
+   |     ^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: see issue #15701 <https://github.com/rust-lang/rust/issues/15701> for more information
    = help: add `#![feature(stmt_expr_attributes)]` to the crate attributes to enable
@@ -32,12 +32,12 @@ LL | #![deny(unused_doc_comments)]
    |         ^^^^^^^^^^^^^^^^^^^
 
 error: unused doc comment
-  --> $DIR/unused-doc-comments-edge-cases.rs:23:6
+  --> $DIR/unused-doc-comments-edge-cases.rs:23:5
    |
-LL |     (/// useless doc comment
-   |      ^^^^^^^^^^^^^^^^^^^^^^^
+LL |     /// useless doc comment
+   |     ^^^^^^^^^^^^^^^^^^^^^^^
 ...
-LL |     num) == 3
+LL |     num == 3
    |     --- rustdoc does not generate documentation for expressions
    |
    = help: use `//` for a plain comment

tests/ui/parser/attribute/attr-binary-expr-ambigous.fixed

@@ -1,15 +0,0 @@
-//@ run-rustfix
-#![feature(stmt_expr_attributes)]
-#![allow(unused_assignments, unused_attributes)]
-
-fn main() {
-    let mut x = (#[deprecated] 1) + 2; //~ ERROR ambiguous
-
-    (#[deprecated] x) = 4; //~ ERROR ambiguous
-
-    x = (#[deprecated] 5) as i32; //~ ERROR ambiguous
-
-    let _r = (#[deprecated] 1)..6; //~ ERROR ambiguous
-
-    println!("{}", x);
-}

tests/ui/parser/attribute/attr-binary-expr-ambigous.rs

@@ -1,15 +0,0 @@
-//@ run-rustfix
-#![feature(stmt_expr_attributes)]
-#![allow(unused_assignments, unused_attributes)]
-
-fn main() {
-    let mut x = #[deprecated] 1 + 2; //~ ERROR ambiguous
-
-    #[deprecated] x = 4; //~ ERROR ambiguous
-
-    x = #[deprecated] 5 as i32; //~ ERROR ambiguous
-
-    let _r = #[deprecated] 1..6; //~ ERROR ambiguous
-
-    println!("{}", x);
-}

tests/ui/parser/attribute/attr-binary-expr-ambigous.stderr

@@ -1,46 +0,0 @@
-error: ambiguous outer attributes
-  --> $DIR/attr-binary-expr-ambigous.rs:6:17
-   |
-LL |     let mut x = #[deprecated] 1 + 2;
-   |                 ^^^^^^^^^^^^^^^^^^^
-   |
-help: wrap the expression in parentheses
-   |
-LL |     let mut x = (#[deprecated] 1) + 2;
-   |                 +               +
-
-error: ambiguous outer attributes
-  --> $DIR/attr-binary-expr-ambigous.rs:8:5
-   |
-LL |     #[deprecated] x = 4;
-   |     ^^^^^^^^^^^^^^^^^^^
-   |
-help: wrap the expression in parentheses
-   |
-LL |     (#[deprecated] x) = 4;
-   |     +               +
-
-error: ambiguous outer attributes
-  --> $DIR/attr-binary-expr-ambigous.rs:10:9
-   |
-LL |     x = #[deprecated] 5 as i32;
-   |         ^^^^^^^^^^^^^^^^^^^^^^
-   |
-help: wrap the expression in parentheses
-   |
-LL |     x = (#[deprecated] 5) as i32;
-   |         +               +
-
-error: ambiguous outer attributes
-  --> $DIR/attr-binary-expr-ambigous.rs:12:14
-   |
-LL |     let _r = #[deprecated] 1..6;
-   |              ^^^^^^^^^^^^^^^^^^
-   |
-help: wrap the expression in parentheses
-   |
-LL |     let _r = (#[deprecated] 1)..6;
-   |              +               +
-
-error: aborting due to 4 previous errors
-

tests/ui/proc-macro/issue-81555.rs

@@ -10,5 +10,6 @@
 fn main() {
     let _x;
     let y = ();
-    (#[identity_attr] _x) = y;
+    #[identity_attr]
+    _x = y;
 }