parser will not give wrong help message for 'public'

compiler/rustc_ast/src/token.rs

@@ -436,6 +436,26 @@ impl Token {
             || self == &OpenDelim(Delimiter::Parenthesis)
     }
 
+    /// Returns `true` if the token can appear at the start of a item
+    pub fn can_begin_item(&self) -> bool {
+        self.is_keyword(kw::Use)
+            || self.is_keyword(kw::Fn)
+            || self.is_keyword(kw::Extern)
+            || self.is_keyword(kw::Crate)
+            || self.is_keyword(kw::Mod)
+            || self.is_keyword(kw::Const)
+            || self.is_keyword(kw::Static)
+            || self.is_keyword(kw::Trait)
+            || self.is_keyword(kw::Impl)
+            || self.is_keyword(kw::Mod)
+            || self.is_keyword(kw::Type)
+            || self.is_keyword(kw::Enum)
+            || self.is_keyword(kw::Struct)
+            || self.is_keyword(kw::Union)
+            || self.is_keyword(kw::Macro)
+            || self == &OpenDelim(Delimiter::Parenthesis)
+    }
+
     /// Returns `true` if the token is any literal.
     pub fn is_lit(&self) -> bool {
         matches!(self.kind, Literal(..))

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -22,7 +22,7 @@ use rustc_errors::{
 use rustc_errors::{pluralize, struct_span_err, Diagnostic, EmissionGuarantee, ErrorGuaranteed};
 use rustc_macros::{SessionDiagnostic, SessionSubdiagnostic};
 use rustc_span::source_map::Spanned;
-use rustc_span::symbol::{kw, Ident};
+use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{Span, SpanSnippetError, DUMMY_SP};
 use std::ops::{Deref, DerefMut};
 
@@ -602,15 +602,13 @@ impl<'a> Parser<'a> {
         self.last_unexpected_token_span = Some(self.token.span);
         let mut err = self.struct_span_err(self.token.span, &msg_exp);
 
-        if let TokenKind::Ident(symbol, _) = &self.prev_token.kind {
-            if symbol.as_str() == "public" {
-                err.span_suggestion_short(
-                    self.prev_token.span,
-                    "write `pub` instead of `public` to make the item public",
-                    "pub",
-                    appl,
-                );
-            }
+        if self.prev_token.is_ident_named(sym::public) && self.token.can_begin_item() {
+            err.span_suggestion_short(
+                self.prev_token.span,
+                "write `pub` instead of `public` to make the item public",
+                "pub",
+                appl,
+            );
         }
 
         // Add suggestion for a missing closing angle bracket if '>' is included in expected_tokens

compiler/rustc_span/src/symbol.rs

@@ -1118,6 +1118,7 @@ symbols! {
         ptr_offset_from_unsigned,
         pub_macro_rules,
         pub_restricted,
+        public,
         pure,
         pushpop_unsafe,
         qreg,

src/test/ui/parser/public-instead-of-pub-1.fixed

@@ -0,0 +1,11 @@
+// Checks what happens when `public` is used instead of the correct, `pub`
+// run-rustfix
+
+pub enum Test {
+    //~^ ERROR expected one of `!` or `::`, found keyword `enum`
+    //~^^ HELP write `pub` instead of `public` to make the item public
+    A,
+    B,
+}
+
+fn main() { }

src/test/ui/parser/public-instead-of-pub-1.rs

@@ -0,0 +1,11 @@
+// Checks what happens when `public` is used instead of the correct, `pub`
+// run-rustfix
+
+public enum Test {
+    //~^ ERROR expected one of `!` or `::`, found keyword `enum`
+    //~^^ HELP write `pub` instead of `public` to make the item public
+    A,
+    B,
+}
+
+fn main() { }

src/test/ui/parser/public-instead-of-pub-1.stderr

@@ -0,0 +1,13 @@
+error: expected one of `!` or `::`, found keyword `enum`
+  --> $DIR/public-instead-of-pub-1.rs:4:8
+   |
+LL | public enum Test {
+   |        ^^^^ expected one of `!` or `::`
+   |
+help: write `pub` instead of `public` to make the item public
+   |
+LL | pub enum Test {
+   | ~~~
+
+error: aborting due to previous error
+

src/test/ui/parser/public-instead-of-pub-2.rs

@@ -0,0 +1,7 @@
+// Checks what happens when `public` is used instead of the correct, `pub`
+// Won't give help message for this case
+
+public let x = 1;
+//~^ ERROR expected one of `!` or `::`, found keyword `let`
+
+fn main() { }

src/test/ui/parser/public-instead-of-pub-2.stderr

@@ -0,0 +1,8 @@
+error: expected one of `!` or `::`, found keyword `let`
+  --> $DIR/public-instead-of-pub-2.rs:4:8
+   |
+LL | public let x = 1;
+   |        ^^^ expected one of `!` or `::`
+
+error: aborting due to previous error
+