diff --git a/compiler/rustc_parse/src/parser/attr.rs b/compiler/rustc_parse/src/parser/attr.rs
index 379e47077ea18..a90eff0221082 100644
--- a/compiler/rustc_parse/src/parser/attr.rs
+++ b/compiler/rustc_parse/src/parser/attr.rs
@@ -151,7 +151,7 @@ impl<'a> Parser<'a> {
         span: Span,
         attr_type: OuterAttributeType,
     ) -> Option<Span> {
-        let mut snapshot = self.clone();
+        let mut snapshot = self.create_snapshot_for_diagnostic();
         let lo = span.lo()
             + BytePos(match attr_type {
                 OuterAttributeType::Attribute => 1,
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 40daf4eb28fc1..250050a48f0a9 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -5,6 +5,7 @@ use super::{
     SemiColonMode, SeqSep, TokenExpectType, TokenType,
 };
 
+use crate::lexer::UnmatchedBrace;
 use rustc_ast as ast;
 use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Lit, LitKind, TokenKind};
@@ -21,6 +22,7 @@ use rustc_errors::{Applicability, DiagnosticBuilder, Handler, PResult};
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, Ident};
 use rustc_span::{MultiSpan, Span, SpanSnippetError, DUMMY_SP};
+use std::ops::{Deref, DerefMut};
 
 use std::mem::take;
 
@@ -154,6 +156,28 @@ impl AttemptLocalParseRecovery {
     }
 }
 
+// SnapshotParser is used to create a snapshot of the parser
+// without causing duplicate errors being emitted when the `Parser`
+// is dropped.
+pub(super) struct SnapshotParser<'a> {
+    parser: Parser<'a>,
+    unclosed_delims: Vec<UnmatchedBrace>,
+}
+
+impl<'a> Deref for SnapshotParser<'a> {
+    type Target = Parser<'a>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.parser
+    }
+}
+
+impl<'a> DerefMut for SnapshotParser<'a> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.parser
+    }
+}
+
 impl<'a> Parser<'a> {
     pub(super) fn span_err<S: Into<MultiSpan>>(
         &self,
@@ -179,6 +203,25 @@ impl<'a> Parser<'a> {
         &self.sess.span_diagnostic
     }
 
+    /// Relace `self` with `snapshot.parser` and extend `unclosed_delims` with `snapshot.unclosed_delims`.
+    /// This is to avoid losing unclosed delims errors `create_snapshot_for_diagnostic` clears.
+    pub(super) fn restore_snapshot(&mut self, snapshot: SnapshotParser<'a>) {
+        *self = snapshot.parser;
+        self.unclosed_delims.extend(snapshot.unclosed_delims.clone());
+    }
+
+    /// Create a snapshot of the `Parser`.
+    pub(super) fn create_snapshot_for_diagnostic(&self) -> SnapshotParser<'a> {
+        let mut snapshot = self.clone();
+        let unclosed_delims = self.unclosed_delims.clone();
+        // Clear `unclosed_delims` in snapshot to avoid
+        // duplicate errors being emitted when the `Parser`
+        // is dropped (which may or may not happen, depending
+        // if the parsing the snapshot is created for is successful)
+        snapshot.unclosed_delims.clear();
+        SnapshotParser { parser: snapshot, unclosed_delims }
+    }
+
     pub(super) fn span_to_snippet(&self, span: Span) -> Result<String, SpanSnippetError> {
         self.sess.source_map().span_to_snippet(span)
     }
@@ -438,7 +481,7 @@ impl<'a> Parser<'a> {
             // fn foo() -> Foo {
             //     field: value,
             // }
-            let mut snapshot = self.clone();
+            let mut snapshot = self.create_snapshot_for_diagnostic();
             let path =
                 Path { segments: vec![], span: self.prev_token.span.shrink_to_lo(), tokens: None };
             let struct_expr = snapshot.parse_struct_expr(None, path, AttrVec::new(), false);
@@ -464,7 +507,7 @@ impl<'a> Parser<'a> {
                             Applicability::MaybeIncorrect,
                         )
                         .emit();
-                    *self = snapshot;
+                    self.restore_snapshot(snapshot);
                     let mut tail = self.mk_block(
                         vec![self.mk_stmt_err(expr.span)],
                         s,
@@ -678,7 +721,7 @@ impl<'a> Parser<'a> {
     /// angle brackets.
     pub(super) fn check_turbofish_missing_angle_brackets(&mut self, segment: &mut PathSegment) {
         if token::ModSep == self.token.kind && segment.args.is_none() {
-            let snapshot = self.clone();
+            let snapshot = self.create_snapshot_for_diagnostic();
             self.bump();
             let lo = self.token.span;
             match self.parse_angle_args(None) {
@@ -712,14 +755,14 @@ impl<'a> Parser<'a> {
                         .emit();
                     } else {
                         // This doesn't look like an invalid turbofish, can't recover parse state.
-                        *self = snapshot;
+                        self.restore_snapshot(snapshot);
                     }
                 }
                 Err(err) => {
                     // We couldn't parse generic parameters, unlikely to be a turbofish. Rely on
                     // generic parse error instead.
                     err.cancel();
-                    *self = snapshot;
+                    self.restore_snapshot(snapshot);
                 }
             }
         }
@@ -825,7 +868,7 @@ impl<'a> Parser<'a> {
                 // `x == y < z`
                 (BinOpKind::Eq, AssocOp::Less | AssocOp::LessEqual | AssocOp::Greater | AssocOp::GreaterEqual) => {
                     // Consume `z`/outer-op-rhs.
-                    let snapshot = self.clone();
+                    let snapshot = self.create_snapshot_for_diagnostic();
                     match self.parse_expr() {
                         Ok(r2) => {
                             // We are sure that outer-op-rhs could be consumed, the suggestion is
@@ -835,14 +878,14 @@ impl<'a> Parser<'a> {
                         }
                         Err(expr_err) => {
                             expr_err.cancel();
-                            *self = snapshot;
+                            self.restore_snapshot(snapshot);
                             false
                         }
                     }
                 }
                 // `x > y == z`
                 (BinOpKind::Lt | BinOpKind::Le | BinOpKind::Gt | BinOpKind::Ge, AssocOp::Equal) => {
-                    let snapshot = self.clone();
+                    let snapshot = self.create_snapshot_for_diagnostic();
                     // At this point it is always valid to enclose the lhs in parentheses, no
                     // further checks are necessary.
                     match self.parse_expr() {
@@ -852,7 +895,7 @@ impl<'a> Parser<'a> {
                         }
                         Err(expr_err) => {
                             expr_err.cancel();
-                            *self = snapshot;
+                            self.restore_snapshot(snapshot);
                             false
                         }
                     }
@@ -917,7 +960,7 @@ impl<'a> Parser<'a> {
                     || outer_op.node == AssocOp::Greater
                 {
                     if outer_op.node == AssocOp::Less {
-                        let snapshot = self.clone();
+                        let snapshot = self.create_snapshot_for_diagnostic();
                         self.bump();
                         // So far we have parsed `foo<bar<`, consume the rest of the type args.
                         let modifiers =
@@ -929,7 +972,7 @@ impl<'a> Parser<'a> {
                         {
                             // We don't have `foo< bar >(` or `foo< bar >::`, so we rewind the
                             // parser and bail out.
-                            *self = snapshot.clone();
+                            self.restore_snapshot(snapshot);
                         }
                     }
                     return if token::ModSep == self.token.kind {
@@ -937,7 +980,7 @@ impl<'a> Parser<'a> {
                         // `foo< bar >::`
                         suggest(&mut err);
 
-                        let snapshot = self.clone();
+                        let snapshot = self.create_snapshot_for_diagnostic();
                         self.bump(); // `::`
 
                         // Consume the rest of the likely `foo<bar>::new()` or return at `foo<bar>`.
@@ -954,7 +997,7 @@ impl<'a> Parser<'a> {
                                 expr_err.cancel();
                                 // Not entirely sure now, but we bubble the error up with the
                                 // suggestion.
-                                *self = snapshot;
+                                self.restore_snapshot(snapshot);
                                 Err(err)
                             }
                         }
@@ -1008,7 +1051,7 @@ impl<'a> Parser<'a> {
     }
 
     fn consume_fn_args(&mut self) -> Result<(), ()> {
-        let snapshot = self.clone();
+        let snapshot = self.create_snapshot_for_diagnostic();
         self.bump(); // `(`
 
         // Consume the fn call arguments.
@@ -1018,7 +1061,7 @@ impl<'a> Parser<'a> {
 
         if self.token.kind == token::Eof {
             // Not entirely sure that what we consumed were fn arguments, rollback.
-            *self = snapshot;
+            self.restore_snapshot(snapshot);
             Err(())
         } else {
             // 99% certain that the suggestion is correct, continue parsing.
@@ -1959,12 +2002,12 @@ impl<'a> Parser<'a> {
     }
 
     fn recover_const_param_decl(&mut self, ty_generics: Option<&Generics>) -> Option<GenericArg> {
-        let snapshot = self.clone();
+        let snapshot = self.create_snapshot_for_diagnostic();
         let param = match self.parse_const_param(vec![]) {
             Ok(param) => param,
             Err(err) => {
                 err.cancel();
-                *self = snapshot;
+                self.restore_snapshot(snapshot);
                 return None;
             }
         };
@@ -2056,7 +2099,7 @@ impl<'a> Parser<'a> {
             // We perform these checks and early return to avoid taking a snapshot unnecessarily.
             return Err(err);
         }
-        let snapshot = self.clone();
+        let snapshot = self.create_snapshot_for_diagnostic();
         if is_op_or_dot {
             self.bump();
         }
@@ -2088,7 +2131,7 @@ impl<'a> Parser<'a> {
                 err.cancel();
             }
         }
-        *self = snapshot;
+        self.restore_snapshot(snapshot);
         Err(err)
     }
 
@@ -2148,7 +2191,7 @@ impl<'a> Parser<'a> {
         let span = self.token.span;
         // We only emit "unexpected `:`" error here if we can successfully parse the
         // whole pattern correctly in that case.
-        let snapshot = self.clone();
+        let snapshot = self.create_snapshot_for_diagnostic();
 
         // Create error for "unexpected `:`".
         match self.expected_one_of_not_found(&[], &[]) {
@@ -2160,7 +2203,7 @@ impl<'a> Parser<'a> {
                         // reasonable error.
                         inner_err.cancel();
                         err.cancel();
-                        *self = snapshot;
+                        self.restore_snapshot(snapshot);
                     }
                     Ok(mut pat) => {
                         // We've parsed the rest of the pattern.
@@ -2239,7 +2282,7 @@ impl<'a> Parser<'a> {
             }
             _ => {
                 // Carry on as if we had not done anything. This should be unreachable.
-                *self = snapshot;
+                self.restore_snapshot(snapshot);
             }
         };
         first_pat
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index df865d77b9bb4..e160385d3a4be 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -704,7 +704,7 @@ impl<'a> Parser<'a> {
                         ExprKind::Path(None, ast::Path { segments, .. }),
                         TokenKind::Ident(kw::For | kw::Loop | kw::While, false),
                     ) if segments.len() == 1 => {
-                        let snapshot = self.clone();
+                        let snapshot = self.create_snapshot_for_diagnostic();
                         let label = Label {
                             ident: Ident::from_str_and_span(
                                 &format!("'{}", segments[0].ident),
@@ -726,7 +726,7 @@ impl<'a> Parser<'a> {
                             }
                             Err(err) => {
                                 err.cancel();
-                                *self = snapshot;
+                                self.restore_snapshot(snapshot);
                             }
                         }
                     }
@@ -1886,7 +1886,7 @@ impl<'a> Parser<'a> {
         lo: Span,
         attrs: AttrVec,
     ) -> Option<P<Expr>> {
-        let mut snapshot = self.clone();
+        let mut snapshot = self.create_snapshot_for_diagnostic();
         match snapshot.parse_array_or_repeat_expr(attrs, token::Brace) {
             Ok(arr) => {
                 let hi = snapshot.prev_token.span;
@@ -1902,7 +1902,7 @@ impl<'a> Parser<'a> {
                 .note("to define an array, one would use square brackets instead of curly braces")
                 .emit();
 
-                *self = snapshot;
+                self.restore_snapshot(snapshot);
                 Some(self.mk_expr_err(arr.span))
             }
             Err(e) => {
@@ -2370,7 +2370,7 @@ impl<'a> Parser<'a> {
         if self.token.kind != token::Semi {
             return None;
         }
-        let start_snapshot = self.clone();
+        let start_snapshot = self.create_snapshot_for_diagnostic();
         let semi_sp = self.token.span;
         self.bump(); // `;`
         let mut stmts =
@@ -2418,15 +2418,15 @@ impl<'a> Parser<'a> {
                 return Some(err(self, stmts));
             }
             if self.token.kind == token::Comma {
-                *self = start_snapshot;
+                self.restore_snapshot(start_snapshot);
                 return None;
             }
-            let pre_pat_snapshot = self.clone();
+            let pre_pat_snapshot = self.create_snapshot_for_diagnostic();
             match self.parse_pat_no_top_alt(None) {
                 Ok(_pat) => {
                     if self.token.kind == token::FatArrow {
                         // Reached arm end.
-                        *self = pre_pat_snapshot;
+                        self.restore_snapshot(pre_pat_snapshot);
                         return Some(err(self, stmts));
                     }
                 }
@@ -2435,21 +2435,21 @@ impl<'a> Parser<'a> {
                 }
             }
 
-            *self = pre_pat_snapshot;
+            self.restore_snapshot(pre_pat_snapshot);
             match self.parse_stmt_without_recovery(true, ForceCollect::No) {
                 // Consume statements for as long as possible.
                 Ok(Some(stmt)) => {
                     stmts.push(stmt);
                 }
                 Ok(None) => {
-                    *self = start_snapshot;
+                    self.restore_snapshot(start_snapshot);
                     break;
                 }
                 // We couldn't parse either yet another statement missing it's
                 // enclosing block nor the next arm's pattern or closing brace.
                 Err(stmt_err) => {
                     stmt_err.cancel();
-                    *self = start_snapshot;
+                    self.restore_snapshot(start_snapshot);
                     break;
                 }
             }
diff --git a/compiler/rustc_parse/src/parser/path.rs b/compiler/rustc_parse/src/parser/path.rs
index 5e537d7b95c4a..17c57867cf9cf 100644
--- a/compiler/rustc_parse/src/parser/path.rs
+++ b/compiler/rustc_parse/src/parser/path.rs
@@ -624,9 +624,18 @@ impl<'a> Parser<'a> {
             GenericArg::Const(self.parse_const_arg()?)
         } else if self.check_type() {
             // Parse type argument.
+            let is_const_fn = self.look_ahead(1, |t| t.kind == token::OpenDelim(token::Paren));
+            let mut snapshot = self.create_snapshot_for_diagnostic();
             match self.parse_ty() {
                 Ok(ty) => GenericArg::Type(ty),
                 Err(err) => {
+                    if is_const_fn {
+                        if let Ok(expr) = (*snapshot).parse_expr_res(Restrictions::CONST_EXPR, None)
+                        {
+                            self.restore_snapshot(snapshot);
+                            return Ok(Some(self.dummy_const_arg_needs_braces(err, expr.span)));
+                        }
+                    }
                     // Try to recover from possible `const` arg without braces.
                     return self.recover_const_arg(start, err).map(Some);
                 }
@@ -636,7 +645,7 @@ impl<'a> Parser<'a> {
         } else {
             // Fall back by trying to parse a const-expr expression. If we successfully do so,
             // then we should report an error that it needs to be wrapped in braces.
-            let snapshot = self.clone();
+            let snapshot = self.create_snapshot_for_diagnostic();
             match self.parse_expr_res(Restrictions::CONST_EXPR, None) {
                 Ok(expr) => {
                     return Ok(Some(self.dummy_const_arg_needs_braces(
@@ -645,7 +654,7 @@ impl<'a> Parser<'a> {
                     )));
                 }
                 Err(err) => {
-                    *self = snapshot;
+                    self.restore_snapshot(snapshot);
                     err.cancel();
                     return Ok(None);
                 }
diff --git a/src/test/ui/const-generics/const-generic-function.rs b/src/test/ui/const-generics/const-generic-function.rs
new file mode 100644
index 0000000000000..c8d2683e53f47
--- /dev/null
+++ b/src/test/ui/const-generics/const-generic-function.rs
@@ -0,0 +1,21 @@
+fn foo<const N: i32>() -> i32 {
+    N
+}
+
+const fn bar(n: i32, m: i32) -> i32 {
+    n
+}
+
+const fn baz() -> i32 {
+    1
+}
+
+const FOO: i32 = 3;
+
+fn main() {
+    foo::<baz()>(); //~ ERROR expected type, found function `baz`
+    //~| ERROR unresolved item provided when a constant was expected
+    foo::<bar(bar(1, 1), bar(1, 1))>(); //~ ERROR expected type, found `1`
+    foo::<bar(1, 1)>(); //~ ERROR expected type, found `1`
+    foo::<bar(FOO, 2)>(); //~ ERROR expected type, found `2`
+}
diff --git a/src/test/ui/const-generics/const-generic-function.stderr b/src/test/ui/const-generics/const-generic-function.stderr
new file mode 100644
index 0000000000000..5ad3f1006c17d
--- /dev/null
+++ b/src/test/ui/const-generics/const-generic-function.stderr
@@ -0,0 +1,54 @@
+error: expected type, found `1`
+  --> $DIR/const-generic-function.rs:18:19
+   |
+LL |     foo::<bar(bar(1, 1), bar(1, 1))>();
+   |                   ^ expected type
+   |
+help: expressions must be enclosed in braces to be used as const generic arguments
+   |
+LL |     foo::<{ bar(bar(1, 1), bar(1, 1)) }>();
+   |           +                           +
+
+error: expected type, found `1`
+  --> $DIR/const-generic-function.rs:19:15
+   |
+LL |     foo::<bar(1, 1)>();
+   |               ^ expected type
+   |
+help: expressions must be enclosed in braces to be used as const generic arguments
+   |
+LL |     foo::<{ bar(1, 1) }>();
+   |           +           +
+
+error: expected type, found `2`
+  --> $DIR/const-generic-function.rs:20:20
+   |
+LL |     foo::<bar(FOO, 2)>();
+   |                    ^ expected type
+   |
+help: expressions must be enclosed in braces to be used as const generic arguments
+   |
+LL |     foo::<{ bar(FOO, 2) }>();
+   |           +             +
+
+error[E0573]: expected type, found function `baz`
+  --> $DIR/const-generic-function.rs:16:11
+   |
+LL |     foo::<baz()>();
+   |           ^^^^^ not a type
+
+error[E0747]: unresolved item provided when a constant was expected
+  --> $DIR/const-generic-function.rs:16:11
+   |
+LL |     foo::<baz()>();
+   |           ^^^^^
+   |
+help: if this generic argument was intended as a const parameter, surround it with braces
+   |
+LL |     foo::<{ baz() }>();
+   |           +       +
+
+error: aborting due to 5 previous errors
+
+Some errors have detailed explanations: E0573, E0747.
+For more information about an error, try `rustc --explain E0573`.