From dcd91d5ceb1990a48c985e01cbe6fca7e274f016 Mon Sep 17 00:00:00 2001
From: Mazdak Farrokhzad <twingoow@gmail.com>
Date: Wed, 13 Nov 2019 12:05:37 +0100
Subject: [PATCH] parser: don't use `unreachable!()` in `fn unexpected`.

---
 src/librustc_parse/parser/mod.rs                 |  4 +++-
 .../parser/issue-66357-unexpected-unreachable.rs | 14 ++++++++++++++
 .../issue-66357-unexpected-unreachable.stderr    | 16 ++++++++++++++++
 3 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/parser/issue-66357-unexpected-unreachable.rs
 create mode 100644 src/test/ui/parser/issue-66357-unexpected-unreachable.stderr

diff --git a/src/librustc_parse/parser/mod.rs b/src/librustc_parse/parser/mod.rs
index a491d91e20f..d5d8604be85 100644
--- a/src/librustc_parse/parser/mod.rs
+++ b/src/librustc_parse/parser/mod.rs
@@ -443,7 +443,9 @@ pub(super) fn this_token_descr(&self) -> String {
     crate fn unexpected<T>(&mut self) -> PResult<'a, T> {
         match self.expect_one_of(&[], &[]) {
             Err(e) => Err(e),
-            Ok(_) => unreachable!(),
+            // We can get `Ok(true)` from `recover_closing_delimiter`
+            // which is called in `expected_one_of_not_found`.
+            Ok(_) => FatalError.raise(),
         }
     }
 
diff --git a/src/test/ui/parser/issue-66357-unexpected-unreachable.rs b/src/test/ui/parser/issue-66357-unexpected-unreachable.rs
new file mode 100644
index 00000000000..1730adfa914
--- /dev/null
+++ b/src/test/ui/parser/issue-66357-unexpected-unreachable.rs
@@ -0,0 +1,14 @@
+// The problem in #66357 was that the call trace:
+//
+// - parse_fn_block_decl
+// - expect_or
+// - unexpected
+// - expect_one_of
+// - expected_one_of_not_found
+// - recover_closing_delimiter
+//
+// ended up bubbling up `Ok(true)` to `unexpected` which then used `unreachable!()`.
+
+fn f() { |[](* }
+//~^ ERROR expected one of `,` or `:`, found `(`
+//~| ERROR expected one of `)`, `-`, `_`, `box`, `mut`, `ref`, `|`, identifier, or path, found `*`
diff --git a/src/test/ui/parser/issue-66357-unexpected-unreachable.stderr b/src/test/ui/parser/issue-66357-unexpected-unreachable.stderr
new file mode 100644
index 00000000000..00d84e2afe3
--- /dev/null
+++ b/src/test/ui/parser/issue-66357-unexpected-unreachable.stderr
@@ -0,0 +1,16 @@
+error: expected one of `,` or `:`, found `(`
+  --> $DIR/issue-66357-unexpected-unreachable.rs:12:13
+   |
+LL | fn f() { |[](* }
+   |             ^ expected one of `,` or `:`
+
+error: expected one of `)`, `-`, `_`, `box`, `mut`, `ref`, `|`, identifier, or path, found `*`
+  --> $DIR/issue-66357-unexpected-unreachable.rs:12:14
+   |
+LL | fn f() { |[](* }
+   |             -^ help: `)` may belong here
+   |             |
+   |             unclosed delimiter
+
+error: aborting due to 2 previous errors
+