From a1062b9bdcf691fc09f8683ae36d2b31c06c3d8f Mon Sep 17 00:00:00 2001
From: Rageking8 <106309953+Rageking8@users.noreply.github.com>
Date: Thu, 22 Sep 2022 23:41:38 +0800
Subject: [PATCH 1/3] recover from struct nested in struct

---
 compiler/rustc_parse/src/parser/item.rs       | 17 +++++++++++++++++
 src/test/ui/parser/issues/issue-101540.rs     |  7 +++++++
 src/test/ui/parser/issues/issue-101540.stderr | 10 ++++++++++
 3 files changed, 34 insertions(+)
 create mode 100644 src/test/ui/parser/issues/issue-101540.rs
 create mode 100644 src/test/ui/parser/issues/issue-101540.stderr

diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index e55b5ce71cded..e385ac44113a6 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -1715,6 +1715,7 @@ impl<'a> Parser<'a> {
     fn parse_field_ident(&mut self, adt_ty: &str, lo: Span) -> PResult<'a, Ident> {
         let (ident, is_raw) = self.ident_or_err()?;
         if !is_raw && ident.is_reserved() {
+            let snapshot = self.create_snapshot_for_diagnostic();
             let err = if self.check_fn_front_matter(false) {
                 let inherited_vis = Visibility {
                     span: rustc_span::DUMMY_SP,
@@ -1735,6 +1736,22 @@ impl<'a> Parser<'a> {
                 err.help("unlike in C++, Java, and C#, functions are declared in `impl` blocks");
                 err.help("see https://doc.rust-lang.org/book/ch05-03-method-syntax.html for more information");
                 err
+            } else if self.eat_keyword(kw::Struct) {
+                match self.parse_item_struct() {
+                    Ok((ident, _)) => {
+                        let mut err = self.struct_span_err(
+                            lo.with_hi(ident.span.hi()),
+                            &format!("structs are not allowed in {adt_ty} definitions"),
+                        );
+                        err.help("consider creating a new `struct` definition instead of nesting");
+                        err
+                    }
+                    Err(err) => {
+                        err.cancel();
+                        self.restore_snapshot(snapshot);
+                        self.expected_ident_found()
+                    }
+                }
             } else {
                 self.expected_ident_found()
             };
diff --git a/src/test/ui/parser/issues/issue-101540.rs b/src/test/ui/parser/issues/issue-101540.rs
new file mode 100644
index 0000000000000..328ec6f906b1f
--- /dev/null
+++ b/src/test/ui/parser/issues/issue-101540.rs
@@ -0,0 +1,7 @@
+struct S1 {
+    struct S2 {
+    //~^ ERROR structs are not allowed in struct definitions
+    }
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/issues/issue-101540.stderr b/src/test/ui/parser/issues/issue-101540.stderr
new file mode 100644
index 0000000000000..42e471cc13504
--- /dev/null
+++ b/src/test/ui/parser/issues/issue-101540.stderr
@@ -0,0 +1,10 @@
+error: structs are not allowed in struct definitions
+  --> $DIR/issue-101540.rs:2:5
+   |
+LL |       struct S2 {
+   |  _____-^^^^^
+LL | |
+LL | |     }
+   | |_____- help: consider creating a new `struct` definition instead of nesting
+
+error: aborting due to previous error

From f4170b38c8735daa9e764ea395c6c32cd7b9ffa3 Mon Sep 17 00:00:00 2001
From: Rageking8 <106309953+Rageking8@users.noreply.github.com>
Date: Fri, 23 Sep 2022 00:02:50 +0800
Subject: [PATCH 2/3] Change UI test stderr

---
 src/test/ui/parser/issues/issue-101540.stderr | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/src/test/ui/parser/issues/issue-101540.stderr b/src/test/ui/parser/issues/issue-101540.stderr
index 42e471cc13504..d4e861b6061fa 100644
--- a/src/test/ui/parser/issues/issue-101540.stderr
+++ b/src/test/ui/parser/issues/issue-101540.stderr
@@ -2,9 +2,8 @@ error: structs are not allowed in struct definitions
   --> $DIR/issue-101540.rs:2:5
    |
 LL |       struct S2 {
-   |  _____-^^^^^
-LL | |
-LL | |     }
-   | |_____- help: consider creating a new `struct` definition instead of nesting
+   |       ^^^^^^^^^
+   |
+   = help: consider creating a new `struct` definition instead of nesting
 
 error: aborting due to previous error

From c66c2e82c1a405ed3fff99953ab96de03806ca09 Mon Sep 17 00:00:00 2001
From: Rageking8 <106309953+Rageking8@users.noreply.github.com>
Date: Fri, 23 Sep 2022 00:24:30 +0800
Subject: [PATCH 3/3] Fix slight issues with stderr

---
 src/test/ui/parser/issues/issue-101540.stderr | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/test/ui/parser/issues/issue-101540.stderr b/src/test/ui/parser/issues/issue-101540.stderr
index d4e861b6061fa..53c7c9590e6ca 100644
--- a/src/test/ui/parser/issues/issue-101540.stderr
+++ b/src/test/ui/parser/issues/issue-101540.stderr
@@ -1,9 +1,10 @@
 error: structs are not allowed in struct definitions
   --> $DIR/issue-101540.rs:2:5
    |
-LL |       struct S2 {
-   |       ^^^^^^^^^
+LL |     struct S2 {
+   |     ^^^^^^^^^
    |
    = help: consider creating a new `struct` definition instead of nesting
 
 error: aborting due to previous error
+