From 5d4025bebbb59832052ddfc91dd80867128830d3 Mon Sep 17 00:00:00 2001
From: kadmin <julianknodt@gmail.com>
Date: Fri, 14 Jan 2022 06:06:21 +0000
Subject: [PATCH] Better diagnostic for const struct fields

---
 compiler/rustc_parse/src/parser/stmt.rs |  3 +++
 src/test/ui/issues/issue-92776.rs       | 23 +++++++++++++++++++++++
 src/test/ui/issues/issue-92776.stderr   | 22 ++++++++++++++++++++++
 3 files changed, 48 insertions(+)
 create mode 100644 src/test/ui/issues/issue-92776.rs
 create mode 100644 src/test/ui/issues/issue-92776.stderr

diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index d3e7d1690ccf6..90e2d1b55e57a 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -254,6 +254,9 @@ impl<'a> Parser<'a> {
                         err.emit();
                         None
                     } else {
+                        if self.check(&token::Dot) {
+                            err.help("if this was intended as a const argument, wrap it in curly braces: `{ ... }`");
+                        }
                         // Rewind to before attempting to parse the type and continue parsing.
                         let parser_snapshot_after_type =
                             mem::replace(self, parser_snapshot_before_type);
diff --git a/src/test/ui/issues/issue-92776.rs b/src/test/ui/issues/issue-92776.rs
new file mode 100644
index 0000000000000..f9d942aa8db29
--- /dev/null
+++ b/src/test/ui/issues/issue-92776.rs
@@ -0,0 +1,23 @@
+struct Example {
+    foo: usize
+}
+
+struct Example2(u32);
+
+const EXAMPLE: Example = Example { foo: 42 };
+const EXAMPLE_2: Example2 = Example2(42);
+
+struct Wow<const N: usize> {
+    field: [u8; N]
+}
+
+
+fn a() {
+    let _a: Wow<EXAMPLE.foo> = Wow::new();
+    //~^ ERROR expected one of
+}
+
+fn main() {
+    let _b: Wow<EXAMPLE_2.0> = Wow::new();
+    //~^ ERROR expected one of
+}
diff --git a/src/test/ui/issues/issue-92776.stderr b/src/test/ui/issues/issue-92776.stderr
new file mode 100644
index 0000000000000..e0a063cd3a368
--- /dev/null
+++ b/src/test/ui/issues/issue-92776.stderr
@@ -0,0 +1,22 @@
+error: expected one of `!`, `(`, `+`, `,`, `::`, `:`, `<`, `=`, or `>`, found `.`
+  --> $DIR/issue-92776.rs:16:24
+   |
+LL |     let _a: Wow<EXAMPLE.foo> = Wow::new();
+   |         --             ^ expected one of 9 possible tokens
+   |         |
+   |         while parsing the type for `_a`
+   |
+   = help: if this was intended as a const argument, wrap it in curly braces: `{ ... }`
+
+error: expected one of `!`, `(`, `+`, `,`, `::`, `:`, `<`, `=`, or `>`, found `.`
+  --> $DIR/issue-92776.rs:21:26
+   |
+LL |     let _b: Wow<EXAMPLE_2.0> = Wow::new();
+   |         --               ^ expected one of 9 possible tokens
+   |         |
+   |         while parsing the type for `_b`
+   |
+   = help: if this was intended as a const argument, wrap it in curly braces: `{ ... }`
+
+error: aborting due to 2 previous errors
+