From 73c82030e893ab259081bf38b4259e05156c32d0 Mon Sep 17 00:00:00 2001
From: Rakshith Ravi <rakshith.ravi@gmx.com>
Date: Thu, 26 Mar 2020 10:36:52 +0530
Subject: Throw error when encountering `...` instead of `..` while destructing
 a pattern

Added tests and stderr output
---
 src/librustc_parse/parser/pat.rs | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

(limited to 'src/librustc_parse')

diff --git a/src/librustc_parse/parser/pat.rs b/src/librustc_parse/parser/pat.rs
index f7f7ac89a18..983aa43916f 100644
--- a/src/librustc_parse/parser/pat.rs
+++ b/src/librustc_parse/parser/pat.rs
@@ -295,6 +295,8 @@ impl<'a> Parser<'a> {
             // A rest pattern `..`.
             self.bump(); // `..`
             PatKind::Rest
+        } else if self.check(&token::DotDotDot) && !self.is_pat_range_end_start(1) {
+            self.recover_dotdotdot_rest_pat(lo)
         } else if let Some(form) = self.parse_range_end() {
             self.parse_pat_range_to(form)? // `..=X`, `...X`, or `..X`.
         } else if self.eat_keyword(kw::Underscore) {
@@ -362,6 +364,25 @@ impl<'a> Parser<'a> {
         Ok(pat)
     }
 
+    /// Recover from a typoed `...` pattern that was encountered
+    /// Ref: Issue #70388
+    fn recover_dotdotdot_rest_pat(&mut self, lo: Span) -> PatKind {
+        // A typoed rest pattern `...`.
+        self.bump(); // `...`
+
+        // The user probably mistook `...` for a rest pattern `..`.
+        self.struct_span_err(lo, "unexpected `...`")
+            .span_label(lo, "not a valid pattern")
+            .span_suggestion_short(
+                lo,
+                "for a rest pattern, use `..` instead of `...`",
+                "..".to_owned(),
+                Applicability::MachineApplicable,
+            )
+            .emit();
+        PatKind::Rest
+    }
+
     /// Try to recover the more general form `intersect ::= $pat_lhs @ $pat_rhs`.
     ///
     /// Allowed binding patterns generated by `binding ::= ref? mut? $ident @ $pat_rhs`
-- 
cgit 1.4.1-3-g733a5