Add Suggestions for Misspelled Keywords

compiler/rustc_parse/messages.ftl

@@ -381,6 +381,7 @@ parse_invalid_char_in_escape_msg = invalid character in {$is_hex ->
     *[false] unicode
     } escape
 
+
 parse_invalid_comparison_operator = invalid comparison operator `{$invalid}`
     .use_instead = `{$invalid}` is not a valid comparison operator, use `{$correct}`
     .spaceship_operator_invalid = `<=>` is not a valid comparison operator, use `std::cmp::Ordering`
@@ -581,6 +582,11 @@ parse_missing_trait_in_trait_impl = missing trait in a trait impl
     .suggestion_add_trait = add a trait here
     .suggestion_remove_for = for an inherent impl, drop this `for`
 
+parse_misspelled_kw = {$is_incorrect_case ->
+                    [true] write keyword `{$similar_kw}` in lowercase
+                    *[false] there is a keyword `{$similar_kw}` with a similar name
+}
+
 parse_modifier_lifetime = `{$modifier}` may only modify trait bounds, not lifetime bounds
     .suggestion = remove the `{$modifier}`
 

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -19,8 +19,9 @@ use rustc_errors::{
     Subdiagnostic,
 };
 use rustc_session::errors::ExprParenthesesNeeded;
+use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::source_map::Spanned;
-use rustc_span::symbol::{kw, sym, Ident};
+use rustc_span::symbol::{kw, sym, AllKeywords, Ident};
 use rustc_span::{BytePos, Span, SpanSnippetError, Symbol, DUMMY_SP};
 use thin_vec::{thin_vec, ThinVec};
 use tracing::{debug, trace};
@@ -203,6 +204,37 @@ impl std::fmt::Display for UnaryFixity {
     }
 }
 
+#[derive(Debug, rustc_macros::Subdiagnostic)]
+#[suggestion(
+    parse_misspelled_kw,
+    applicability = "machine-applicable",
+    code = "{similar_kw}",
+    style = "verbose"
+)]
+struct MisspelledKw {
+    similar_kw: String,
+    #[primary_span]
+    span: Span,
+    is_incorrect_case: bool,
+}
+
+/// Checks if the given `lookup` identifier is similar to any keyword symbol in `candidates`.
+fn find_similar_kw(lookup: Ident, candidates: &[Symbol]) -> Option<MisspelledKw> {
+    let lowercase = lookup.name.as_str().to_lowercase();
+    let lowercase_sym = Symbol::intern(&lowercase);
+    if candidates.contains(&lowercase_sym) {
+        Some(MisspelledKw { similar_kw: lowercase, span: lookup.span, is_incorrect_case: true })
+    } else if let Some(similar_sym) = find_best_match_for_name(candidates, lookup.name, None) {
+        Some(MisspelledKw {
+            similar_kw: similar_sym.to_string(),
+            span: lookup.span,
+            is_incorrect_case: false,
+        })
+    } else {
+        None
+    }
+}
+
 struct MultiSugg {
     msg: String,
     patches: Vec<(Span, String)>,
@@ -638,9 +670,9 @@ impl<'a> Parser<'a> {
             let concat = Symbol::intern(&format!("{prev}{cur}"));
             let ident = Ident::new(concat, DUMMY_SP);
             if ident.is_used_keyword() || ident.is_reserved() || ident.is_raw_guess() {
-                let span = self.prev_token.span.to(self.token.span);
+                let concat_span = self.prev_token.span.to(self.token.span);
                 err.span_suggestion_verbose(
-                    span,
+                    concat_span,
                     format!("consider removing the space to spell keyword `{concat}`"),
                     concat,
                     Applicability::MachineApplicable,
@@ -741,9 +773,55 @@ impl<'a> Parser<'a> {
             err.span_label(sp, label_exp);
             err.span_label(self.token.span, "unexpected token");
         }
+
+        // Check for misspelled keywords if there are no suggestions added to the diagnostic.
+        if err.suggestions.as_ref().is_ok_and(|code_suggestions| code_suggestions.is_empty()) {
+            self.check_for_misspelled_kw(&mut err, &expected);
+        }
         Err(err)
     }
 
+    /// Checks if the current token or the previous token are misspelled keywords
+    /// and adds a helpful suggestion.
+    fn check_for_misspelled_kw(&self, err: &mut Diag<'_>, expected: &[TokenType]) {
+        let Some((curr_ident, _)) = self.token.ident() else {
+            return;
+        };
+        let expected_tokens: &[TokenType] =
+            expected.len().checked_sub(10).map_or(&expected, |index| &expected[index..]);
+        let expected_keywords: Vec<Symbol> = expected_tokens
+            .iter()
+            .filter_map(|token| if let TokenType::Keyword(kw) = token { Some(*kw) } else { None })
+            .collect();
+
+        // When there are a few keywords in the last ten elements of `self.expected_tokens` and the current
+        // token is an identifier, it's probably a misspelled keyword.
+        // This handles code like `async Move {}`, misspelled `if` in match guard, misspelled `else` in `if`-`else`
+        // and mispelled `where` in a where clause.
+        if !expected_keywords.is_empty()
+            && !curr_ident.is_used_keyword()
+            && let Some(misspelled_kw) = find_similar_kw(curr_ident, &expected_keywords)
+        {
+            err.subdiagnostic(misspelled_kw);
+        } else if let Some((prev_ident, _)) = self.prev_token.ident()
+            && !prev_ident.is_used_keyword()
+        {
+            // We generate a list of all keywords at runtime rather than at compile time
+            // so that it gets generated only when the diagnostic needs it.
+            // Also, it is unlikely that this list is generated multiple times because the
+            // parser halts after execution hits this path.
+            let all_keywords = AllKeywords::new().collect_used(|| prev_ident.span.edition());
+
+            // Otherwise, check the previous token with all the keywords as possible candidates.
+            // This handles code like `Struct Human;` and `While a < b {}`.
+            // We check the previous token only when the current token is an identifier to avoid false
+            // positives like suggesting keyword `for` for `extern crate foo {}`.
+            if let Some(misspelled_kw) = find_similar_kw(prev_ident, &all_keywords) {
+                err.subdiagnostic(misspelled_kw);
+            }
+        }
+    }
+
     /// The user has written `#[attr] expr` which is unsupported. (#106020)
     pub(super) fn attr_on_non_tail_expr(&self, expr: &Expr) -> ErrorGuaranteed {
         // Missing semicolon typo error.
@@ -846,6 +924,7 @@ impl<'a> Parser<'a> {
                 );
             }
         }
+
         err.emit()
     }
 

compiler/rustc_span/src/symbol.rs

@@ -20,7 +20,8 @@ mod tests;
 
 // The proc macro code for this is in `compiler/rustc_macros/src/symbols.rs`.
 symbols! {
-    // If you modify this list, adjust `is_special` and `is_used_keyword`/`is_unused_keyword`.
+    // If you modify this list, adjust `is_special`, `is_used_keyword`/`is_unused_keyword`
+    // and `AllKeywords`.
     // But this should rarely be necessary if the keywords are kept in alphabetic order.
     Keywords {
         // Special reserved identifiers used internally for elided lifetimes,
@@ -2577,3 +2578,42 @@ impl Ident {
         self.name.can_be_raw() && self.is_reserved()
     }
 }
+
+/// An iterator over all the keywords in Rust.
+#[derive(Copy, Clone)]
+pub struct AllKeywords {
+    curr_idx: u32,
+    end_idx: u32,
+}
+
+impl AllKeywords {
+    /// Initialize a new iterator over all the keywords.
+    ///
+    /// *Note:* Please update this if a new keyword is added beyond the current
+    /// range.
+    pub fn new() -> Self {
+        AllKeywords { curr_idx: kw::Empty.as_u32(), end_idx: kw::Yeet.as_u32() }
+    }
+
+    /// Collect all the keywords in a given edition into a vector.
+    pub fn collect_used(&self, edition: impl Copy + FnOnce() -> Edition) -> Vec<Symbol> {
+        self.filter(|&keyword| {
+            keyword.is_used_keyword_always() || keyword.is_used_keyword_conditional(edition)
+        })
+        .collect()
+    }
+}
+
+impl Iterator for AllKeywords {
+    type Item = Symbol;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.curr_idx <= self.end_idx {
+            let keyword = Symbol::new(self.curr_idx);
+            self.curr_idx += 1;
+            Some(keyword)
+        } else {
+            None
+        }
+    }
+}

tests/ui/parser/extern-crate-unexpected-token.stderr

@@ -3,6 +3,11 @@ error: expected one of `crate` or `{`, found `crte`
    |
 LL | extern crte foo;
    |        ^^^^ expected one of `crate` or `{`
+   |
+help: there is a keyword `crate` with a similar name
+   |
+LL | extern crate foo;
+   |        ~~~~~
 
 error: aborting due to 1 previous error
 

tests/ui/parser/issues/issue-70549-resolve-after-recovered-self-ctor.stderr

@@ -8,10 +8,16 @@ error: expected one of `:`, `@`, or `|`, found keyword `Self`
   --> $DIR/issue-70549-resolve-after-recovered-self-ctor.rs:4:17
    |
 LL |     fn foo(&mur Self) {}
-   |            -----^^^^
-   |            |    |
-   |            |    expected one of `:`, `@`, or `|`
-   |            help: declare the type after the parameter binding: `<identifier>: <type>`
+   |                 ^^^^ expected one of `:`, `@`, or `|`
+   |
+help: there is a keyword `mut` with a similar name
+   |
+LL |     fn foo(&mut Self) {}
+   |             ~~~
+help: declare the type after the parameter binding
+   |
+LL |     fn foo(<identifier>: <type>) {}
+   |            ~~~~~~~~~~~~~~~~~~~~
 
 error: unexpected lifetime `'static` in pattern
   --> $DIR/issue-70549-resolve-after-recovered-self-ctor.rs:8:13
@@ -35,16 +41,27 @@ error: expected one of `:`, `@`, or `|`, found keyword `Self`
   --> $DIR/issue-70549-resolve-after-recovered-self-ctor.rs:8:25
    |
 LL |     fn bar(&'static mur Self) {}
-   |            -------------^^^^
-   |            |            |
-   |            |            expected one of `:`, `@`, or `|`
-   |            help: declare the type after the parameter binding: `<identifier>: <type>`
+   |                         ^^^^ expected one of `:`, `@`, or `|`
+   |
+help: there is a keyword `mut` with a similar name
+   |
+LL |     fn bar(&'static mut Self) {}
+   |                     ~~~
+help: declare the type after the parameter binding
+   |
+LL |     fn bar(<identifier>: <type>) {}
+   |            ~~~~~~~~~~~~~~~~~~~~
 
 error: expected one of `:`, `@`, or `|`, found keyword `Self`
   --> $DIR/issue-70549-resolve-after-recovered-self-ctor.rs:14:17
    |
 LL |     fn baz(&mur Self @ _) {}
    |                 ^^^^ expected one of `:`, `@`, or `|`
+   |
+help: there is a keyword `mut` with a similar name
+   |
+LL |     fn baz(&mut Self @ _) {}
+   |             ~~~
 
 error[E0533]: expected unit struct, found self constructor `Self`
   --> $DIR/issue-70549-resolve-after-recovered-self-ctor.rs:4:17

tests/ui/parser/misspelled-keywords/assoc-type.rs

@@ -0,0 +1,6 @@
+trait Animal {
+    Type Result = u8;
+    //~^ ERROR expected one of
+}
+
+fn main() {}

tests/ui/parser/misspelled-keywords/assoc-type.stderr

@@ -0,0 +1,18 @@
+error: expected one of `!` or `::`, found `Result`
+  --> $DIR/assoc-type.rs:2:10
+   |
+LL | trait Animal {
+   |              - while parsing this item list starting here
+LL |     Type Result = u8;
+   |          ^^^^^^ expected one of `!` or `::`
+LL |
+LL | }
+   | - the item list ends here
+   |
+help: write keyword `type` in lowercase
+   |
+LL |     type Result = u8;
+   |     ~~~~
+
+error: aborting due to 1 previous error
+

tests/ui/parser/misspelled-keywords/async-move.rs

@@ -0,0 +1,6 @@
+//@ edition: 2018
+
+fn main() {
+    async Move {}
+    //~^ ERROR expected one of
+}

tests/ui/parser/misspelled-keywords/async-move.stderr

@@ -0,0 +1,13 @@
+error: expected one of `move`, `|`, or `||`, found `Move`
+  --> $DIR/async-move.rs:4:11
+   |
+LL |     async Move {}
+   |           ^^^^ expected one of `move`, `|`, or `||`
+   |
+help: write keyword `move` in lowercase
+   |
+LL |     async move {}
+   |           ~~~~
+
+error: aborting due to 1 previous error
+

tests/ui/parser/misspelled-keywords/const-fn.rs

@@ -0,0 +1,5 @@
+cnst fn code() {}
+//~^ ERROR expected one of
+
+fn main() {
+}

tests/ui/parser/misspelled-keywords/const-fn.stderr

@@ -0,0 +1,13 @@
+error: expected one of `!` or `::`, found keyword `fn`
+  --> $DIR/const-fn.rs:1:6
+   |
+LL | cnst fn code() {}
+   |      ^^ expected one of `!` or `::`
+   |
+help: there is a keyword `const` with a similar name
+   |
+LL | const fn code() {}
+   | ~~~~~
+
+error: aborting due to 1 previous error
+

tests/ui/parser/misspelled-keywords/const-generics.rs

@@ -0,0 +1,4 @@
+fn foo<consta N: usize>(_arr: [i32; N]) {}
+//~^ ERROR expected one of
+
+fn main() {}

tests/ui/parser/misspelled-keywords/const-generics.stderr

@@ -0,0 +1,13 @@
+error: expected one of `,`, `:`, `=`, or `>`, found `N`
+  --> $DIR/const-generics.rs:1:15
+   |
+LL | fn foo<consta N: usize>(_arr: [i32; N]) {}
+   |               ^ expected one of `,`, `:`, `=`, or `>`
+   |
+help: there is a keyword `const` with a similar name
+   |
+LL | fn foo<const N: usize>(_arr: [i32; N]) {}
+   |        ~~~~~
+
+error: aborting due to 1 previous error
+

tests/ui/parser/misspelled-keywords/const.rs

@@ -0,0 +1,4 @@
+cons A: u8 = 10;
+//~^ ERROR expected one of
+
+fn main() {}

tests/ui/parser/misspelled-keywords/const.stderr

@@ -0,0 +1,13 @@
+error: expected one of `!` or `::`, found `A`
+  --> $DIR/const.rs:1:6
+   |
+LL | cons A: u8 = 10;
+   |      ^ expected one of `!` or `::`
+   |
+help: there is a keyword `const` with a similar name
+   |
+LL | const A: u8 = 10;
+   | ~~~~~
+
+error: aborting due to 1 previous error
+

tests/ui/parser/misspelled-keywords/for-loop.rs

@@ -0,0 +1,4 @@
+fn main() {
+    form i in 1..10 {}
+    //~^ ERROR expected one of
+}

tests/ui/parser/misspelled-keywords/for-loop.stderr

@@ -0,0 +1,13 @@
+error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `i`
+  --> $DIR/for-loop.rs:2:10
+   |
+LL |     form i in 1..10 {}
+   |          ^ expected one of 8 possible tokens
+   |
+help: there is a keyword `for` with a similar name
+   |
+LL |     for i in 1..10 {}
+   |     ~~~
+
+error: aborting due to 1 previous error
+