Insert parentheses around binary operation with attribute

compiler/rustc_ast_pretty/src/pprust/state/expr.rs

@@ -386,18 +386,43 @@ impl<'a> State<'a> {
 
         let ib = self.ibox(INDENT_UNIT);
 
-        // The Match subexpression in `match x {} - 1` must be parenthesized if
-        // it is the leftmost subexpression in a statement:
-        //
-        //     (match x {}) - 1;
-        //
-        // But not otherwise:
-        //
-        //     let _ = match x {} - 1;
-        //
-        // Same applies to a small set of other expression kinds which eagerly
-        // terminate a statement which opens with them.
-        let needs_par = fixup.would_cause_statement_boundary(expr);
+        let needs_par = {
+            // The Match subexpression in `match x {} - 1` must be parenthesized
+            // if it is the leftmost subexpression in a statement:
+            //
+            //     (match x {}) - 1;
+            //
+            // But not otherwise:
+            //
+            //     let _ = match x {} - 1;
+            //
+            // Same applies to a small set of other expression kinds which
+            // eagerly terminate a statement which opens with them.
+            fixup.would_cause_statement_boundary(expr)
+        } || {
+            // If a binary operation ends up with an attribute, such as
+            // resulting from the following macro expansion, then parentheses
+            // are required so that the attribute encompasses the right
+            // subexpression and not just the left one.
+            //
+            //     #![feature(stmt_expr_attributes)]
+            //
+            //     macro_rules! add_attr {
+            //         ($e:expr) => { #[attr] $e };
+            //     }
+            //
+            //     let _ = add_attr!(1 + 1);
+            //
+            // We must pretty-print `#[attr] (1 + 1)` not `#[attr] 1 + 1`.
+            !attrs.is_empty()
+                && matches!(
+                    expr.kind,
+                    ast::ExprKind::Binary(..)
+                        | ast::ExprKind::Cast(..)
+                        | ast::ExprKind::Assign(..)
+                        | ast::ExprKind::AssignOp(..)
+                )
+        };
         if needs_par {
             self.popen();
             fixup = FixupContext::default();

tests/ui-fulldeps/auxiliary/parser.rs

@@ -7,15 +7,17 @@ extern crate rustc_parse;
 extern crate rustc_session;
 extern crate rustc_span;
 
-use rustc_ast::ast::{DUMMY_NODE_ID, Expr};
-use rustc_ast::mut_visit::MutVisitor;
+use rustc_ast::ast::{AttrKind, Attribute, DUMMY_NODE_ID, Expr};
+use rustc_ast::mut_visit::{self, MutVisitor};
 use rustc_ast::node_id::NodeId;
 use rustc_ast::ptr::P;
-use rustc_ast::token;
+use rustc_ast::token::{self, Token};
+use rustc_ast::tokenstream::{AttrTokenStream, AttrTokenTree, LazyAttrTokenStream};
 use rustc_errors::Diag;
 use rustc_parse::parser::Recovery;
 use rustc_session::parse::ParseSess;
-use rustc_span::{DUMMY_SP, FileName, Span};
+use rustc_span::{AttrId, DUMMY_SP, FileName, Span};
+use std::sync::Arc;
 
 pub fn parse_expr(psess: &ParseSess, source_code: &str) -> Option<P<Expr>> {
     let parser = rustc_parse::unwrap_or_emit_fatal(rustc_parse::new_parser_from_source_str(
@@ -46,4 +48,36 @@ impl MutVisitor for Normalize {
     fn visit_span(&mut self, span: &mut Span) {
         *span = DUMMY_SP;
     }
+
+    fn visit_attribute(&mut self, attr: &mut Attribute) {
+        attr.id = AttrId::from_u32(0);
+        if let AttrKind::Normal(normal_attr) = &mut attr.kind {
+            if let Some(tokens) = &mut normal_attr.tokens {
+                let mut stream = tokens.to_attr_token_stream();
+                normalize_attr_token_stream(&mut stream);
+                *tokens = LazyAttrTokenStream::new_direct(stream);
+            }
+        }
+        mut_visit::walk_attribute(self, attr);
+    }
+}
+
+fn normalize_attr_token_stream(stream: &mut AttrTokenStream) {
+    Arc::make_mut(&mut stream.0)
+        .iter_mut()
+        .for_each(normalize_attr_token_tree);
+}
+
+fn normalize_attr_token_tree(token: &mut AttrTokenTree) {
+    match token {
+        AttrTokenTree::Token(token, _spacing) => {
+            Normalize.visit_span(&mut token.span);
+        }
+        AttrTokenTree::Delimited(dspan, _spacing, _delim, stream) => {
+            normalize_attr_token_stream(stream);
+            Normalize.visit_span(&mut dspan.open);
+            Normalize.visit_span(&mut dspan.close);
+        }
+        AttrTokenTree::AttrsTarget(_) => unimplemented!("AttrTokenTree::AttrsTarget"),
+    }
 }

tests/ui-fulldeps/pprust-parenthesis-insertion.rs

@@ -88,6 +88,18 @@ static EXPRS: &[&str] = &[
     // expressions.
     "match 2 { _ => 1 - 1 }",
     "match 2 { _ => ({ 1 }) - 1 }",
+    // Attributes on a Binary, Cast, Assign, and AssignOp expression require
+    // parentheses.
+    "#[attr] (1 + 1)",
+    "#[attr] (1 as T)",
+    "#[attr] (x = 1)",
+    "#[attr] (x += 1)",
+    // If the attribute were not present on the binary operation, it would be
+    // legal to render this without not just the inner parentheses, but also the
+    // outer ones. `return x + .. .field` (Yes, really.) Currently the
+    // pretty-printer does not take advantage of this edge case.
+    "(return #[attr] (x + ..)).field",
+    "(return x + ..).field",
     // Grammar restriction: break value starting with a labeled loop is not
     // allowed, except if the break is also labeled.
     "break 'outer 'inner: loop {} + 2",
@@ -154,7 +166,12 @@ struct Unparenthesize;
 impl MutVisitor for Unparenthesize {
     fn visit_expr(&mut self, e: &mut P<Expr>) {
         while let ExprKind::Paren(paren) = &mut e.kind {
+            let paren_attrs = mem::take(&mut e.attrs);
             *e = mem::replace(paren, Expr::dummy());
+            if !paren_attrs.is_empty() {
+                assert!(e.attrs.is_empty());
+                e.attrs = paren_attrs;
+            }
         }
         mut_visit::walk_expr(self, e);
     }