Rollup merge of #67538 - varkor:lhs-assign-diagnostics, r=Centril

Improve diagnostics for invalid assignment

- Improve wording and span information for invalid assignment diagnostics.
- Link to https://github.com/rust-lang/rfcs/issues/372 when it appears the user is trying a destructuring assignment.
- Make the equality constraint in `where` clauses error consistent with the invalid assignment error.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/librustc_parse/parser/expr.rs b/src/librustc_parse/parser/expr.rs
index fa68ddf272a..e0eb841f2c0 100644
--- a/src/librustc_parse/parser/expr.rs
+++ b/src/librustc_parse/parser/expr.rs
@@ -281,7 +281,9 @@ impl<'a> Parser<'a> {
                     let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs);
                     self.mk_expr(span, binary, AttrVec::new())
                 }
-                AssocOp::Assign => self.mk_expr(span, ExprKind::Assign(lhs, rhs), AttrVec::new()),
+                AssocOp::Assign => {
+                    self.mk_expr(span, ExprKind::Assign(lhs, rhs, cur_op_span), AttrVec::new())
+                }
                 AssocOp::AssignOp(k) => {
                     let aop = match k {
                         token::Plus => BinOpKind::Add,