From d92c68393323359d30a8ee2478b314853a39ba34 Mon Sep 17 00:00:00 2001
From: Fabian Wolff <fabian.wolff@alumni.ethz.ch>
Date: Fri, 1 Oct 2021 23:03:28 +0200
Subject: [PATCH] Improve error message for missing angle brackets in
 `[_]::method`

---
 compiler/rustc_ast/src/ast.rs         | 2 ++
 src/test/ui/parser/issue-89388.rs     | 7 +++++++
 src/test/ui/parser/issue-89388.stderr | 8 ++++++++
 3 files changed, 17 insertions(+)
 create mode 100644 src/test/ui/parser/issue-89388.rs
 create mode 100644 src/test/ui/parser/issue-89388.stderr

diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index c27ab810a4c60..e2424e7d7ad90 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -1211,6 +1211,8 @@ impl Expr {
                 }
             }
 
+            ExprKind::Underscore => TyKind::Infer,
+
             // This expression doesn't look like a type syntactically.
             _ => return None,
         };
diff --git a/src/test/ui/parser/issue-89388.rs b/src/test/ui/parser/issue-89388.rs
new file mode 100644
index 0000000000000..9153c071e8e1a
--- /dev/null
+++ b/src/test/ui/parser/issue-89388.rs
@@ -0,0 +1,7 @@
+// Regression test for #89388.
+
+fn main() {
+    let option: Option<&[u8]> = Some(b"...");
+    let _ = option.map([_]::to_vec);
+    //~^ ERROR: missing angle brackets in associated item path
+}
diff --git a/src/test/ui/parser/issue-89388.stderr b/src/test/ui/parser/issue-89388.stderr
new file mode 100644
index 0000000000000..cf28bef0f4ab0
--- /dev/null
+++ b/src/test/ui/parser/issue-89388.stderr
@@ -0,0 +1,8 @@
+error: missing angle brackets in associated item path
+  --> $DIR/issue-89388.rs:5:24
+   |
+LL |     let _ = option.map([_]::to_vec);
+   |                        ^^^^^^^^^^^ help: try: `<[_]>::to_vec`
+
+error: aborting due to previous error
+