feat/refactor: improve errors in case of ident with number at start

compiler/rustc_parse/locales/en-US.ftl

@@ -412,8 +412,7 @@ parse_fn_ptr_with_generics = function pointer types may not have generic paramet
         *[false] a
     } `for` parameter list
 
-parse_invalid_identifier_with_leading_number = expected identifier, found number literal
-    .label = identifiers cannot start with a number
+parse_invalid_identifier_with_leading_number = identifiers cannot start with a number
 
 parse_maybe_fn_typo_with_impl = you might have meant to write `impl` instead of `fn`
     .suggestion = replace `fn` with `impl` here

compiler/rustc_parse/src/errors.rs

@@ -939,6 +939,7 @@ pub(crate) struct ExpectedIdentifier {
     pub token: Token,
     pub suggest_raw: Option<SuggEscapeToUseAsIdentifier>,
     pub suggest_remove_comma: Option<SuggRemoveComma>,
+    pub help_cannot_start_number: Option<HelpIdentifierStartsWithNumber>,
 }
 
 impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for ExpectedIdentifier {
@@ -975,10 +976,18 @@ impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for ExpectedIdentifier {
             sugg.add_to_diagnostic(&mut diag);
         }
 
+        if let Some(help) = self.help_cannot_start_number {
+            help.add_to_diagnostic(&mut diag);
+        }
+
         diag
     }
 }
 
+#[derive(Subdiagnostic)]
+#[help(parse_invalid_identifier_with_leading_number)]
+pub(crate) struct HelpIdentifierStartsWithNumber;
+
 pub(crate) struct ExpectedSemi {
     pub span: Span,
     pub token: Token,
@@ -1207,14 +1216,6 @@ pub(crate) struct SelfParamNotFirst {
     pub span: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag(parse_invalid_identifier_with_leading_number)]
-pub(crate) struct InvalidIdentiferStartsWithNumber {
-    #[primary_span]
-    #[label]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag(parse_const_generic_without_braces)]
 pub(crate) struct ConstGenericWithoutBraces {

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -8,14 +8,14 @@ use crate::errors::{
     ComparisonOperatorsCannotBeChained, ComparisonOperatorsCannotBeChainedSugg,
     ConstGenericWithoutBraces, ConstGenericWithoutBracesSugg, DocCommentOnParamType,
     DoubleColonInBound, ExpectedIdentifier, ExpectedSemi, ExpectedSemiSugg,
-    GenericParamsWithoutAngleBrackets, GenericParamsWithoutAngleBracketsSugg, InInTypo,
-    IncorrectAwait, IncorrectSemicolon, IncorrectUseOfAwait, ParenthesesInForHead,
-    ParenthesesInForHeadSugg, PatternMethodParamWithoutBody, QuestionMarkInType,
-    QuestionMarkInTypeSugg, SelfParamNotFirst, StructLiteralBodyWithoutPath,
-    StructLiteralBodyWithoutPathSugg, StructLiteralNeedingParens, StructLiteralNeedingParensSugg,
-    SuggEscapeToUseAsIdentifier, SuggRemoveComma, UnexpectedConstInGenericParam,
-    UnexpectedConstParamDeclaration, UnexpectedConstParamDeclarationSugg, UnmatchedAngleBrackets,
-    UseEqInstead,
+    GenericParamsWithoutAngleBrackets, GenericParamsWithoutAngleBracketsSugg,
+    HelpIdentifierStartsWithNumber, InInTypo, IncorrectAwait, IncorrectSemicolon,
+    IncorrectUseOfAwait, ParenthesesInForHead, ParenthesesInForHeadSugg,
+    PatternMethodParamWithoutBody, QuestionMarkInType, QuestionMarkInTypeSugg, SelfParamNotFirst,
+    StructLiteralBodyWithoutPath, StructLiteralBodyWithoutPathSugg, StructLiteralNeedingParens,
+    StructLiteralNeedingParensSugg, SuggEscapeToUseAsIdentifier, SuggRemoveComma,
+    UnexpectedConstInGenericParam, UnexpectedConstParamDeclaration,
+    UnexpectedConstParamDeclarationSugg, UnmatchedAngleBrackets, UseEqInstead,
 };
 
 use crate::fluent_generated as fluent;
@@ -280,6 +280,7 @@ impl<'a> Parser<'a> {
             TokenKind::CloseDelim(Delimiter::Brace),
             TokenKind::CloseDelim(Delimiter::Parenthesis),
         ];
+
         let suggest_raw = match self.token.ident() {
             Some((ident, false))
                 if ident.is_raw_guess()
@@ -295,18 +296,19 @@ impl<'a> Parser<'a> {
             _ => None,
         };
 
-        let suggest_remove_comma =
-            if self.token == token::Comma && self.look_ahead(1, |t| t.is_ident()) {
-                Some(SuggRemoveComma { span: self.token.span })
-            } else {
-                None
-            };
+        let suggest_remove_comma = (self.token == token::Comma
+            && self.look_ahead(1, |t| t.is_ident()))
+        .then_some(SuggRemoveComma { span: self.token.span });
+
+        let help_cannot_start_number =
+            self.is_lit_bad_ident().then_some(HelpIdentifierStartsWithNumber);
 
         let err = ExpectedIdentifier {
             span: self.token.span,
             token: self.token.clone(),
             suggest_raw,
             suggest_remove_comma,
+            help_cannot_start_number,
         };
         let mut err = err.into_diagnostic(&self.sess.span_diagnostic);
 
@@ -365,6 +367,17 @@ impl<'a> Parser<'a> {
         err
     }
 
+    /// Checks if the current token is a integer or float literal and looks like
+    /// it could be a invalid identifier with digits at the start.
+    pub(super) fn is_lit_bad_ident(&mut self) -> bool {
+        matches!(self.token.uninterpolate().kind, token::Literal(Lit { kind: token::LitKind::Integer | token::LitKind::Float, .. })
+            // ensure that the integer literal is followed by a *invalid*
+            // suffix: this is how we know that it is a identifier with an
+            // invalid beginning.
+            if rustc_ast::MetaItemLit::from_token(&self.token).is_none()
+        )
+    }
+
     pub(super) fn expected_one_of_not_found(
         &mut self,
         edible: &[TokenKind],

compiler/rustc_parse/src/parser/pat.rs

@@ -348,6 +348,10 @@ impl<'a> Parser<'a> {
             lo = self.token.span;
         }
 
+        if self.is_lit_bad_ident() {
+            return Err(self.expected_ident_found());
+        }
+
         let pat = if self.check(&token::BinOp(token::And)) || self.token.kind == token::AndAnd {
             self.parse_pat_deref(expected)?
         } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {

compiler/rustc_parse/src/parser/stmt.rs

@@ -273,7 +273,6 @@ impl<'a> Parser<'a> {
             self.bump();
         }
 
-        self.report_invalid_identifier_error()?;
         let (pat, colon) =
             self.parse_pat_before_ty(None, RecoverComma::Yes, PatternLocation::LetBinding)?;
 
@@ -366,17 +365,6 @@ impl<'a> Parser<'a> {
         Ok(P(ast::Local { ty, pat, kind, id: DUMMY_NODE_ID, span: lo.to(hi), attrs, tokens: None }))
     }
 
-    /// report error for `let 1x = 123`
-    pub fn report_invalid_identifier_error(&mut self) -> PResult<'a, ()> {
-        if let token::Literal(lit) = self.token.uninterpolate().kind &&
-            rustc_ast::MetaItemLit::from_token(&self.token).is_none() &&
-            (lit.kind == token::LitKind::Integer || lit.kind == token::LitKind::Float) &&
-            self.look_ahead(1, |t| matches!(t.kind, token::Eq) || matches!(t.kind, token::Colon ) ) {
-                return Err(self.sess.create_err(errors::InvalidIdentiferStartsWithNumber { span: self.token.span }));
-        }
-        Ok(())
-    }
-
     fn check_let_else_init_bool_expr(&self, init: &ast::Expr) {
         if let ast::ExprKind::Binary(op, ..) = init.kind {
             if op.node.lazy() {

tests/ui/parser/integer-literal-start-ident.rs

@@ -0,0 +1,2 @@
+fn 1main() {}
+//~^ ERROR expected identifier, found `1main`

tests/ui/parser/integer-literal-start-ident.stderr

@@ -0,0 +1,10 @@
+error: expected identifier, found `1main`
+  --> $DIR/integer-literal-start-ident.rs:1:4
+   |
+LL | fn 1main() {}
+   |    ^^^^^ expected identifier
+   |
+   = help: identifiers cannot start with a number
+
+error: aborting due to previous error
+

tests/ui/parser/issues/issue-104088.rs

@@ -4,12 +4,12 @@ fn test() {
 
 fn test_2() {
     let 1x = 123;
-    //~^ ERROR expected identifier, found number literal
+    //~^ ERROR expected identifier, found `1x`
 }
 
 fn test_3() {
     let 2x: i32 = 123;
-    //~^ ERROR expected identifier, found number literal
+    //~^ ERROR expected identifier, found `2x`
 }
 
 fn test_4() {
@@ -20,7 +20,7 @@ fn test_4() {
 
 fn test_5() {
     let 23name = 123;
-    //~^ ERROR expected identifier, found number literal
+    //~^ ERROR expected identifier, found `23name`
 }
 
 fn main() {}

tests/ui/parser/issues/issue-104088.stderr

@@ -1,20 +1,26 @@
-error: expected identifier, found number literal
+error: expected identifier, found `1x`
   --> $DIR/issue-104088.rs:6:9
    |
 LL |     let 1x = 123;
-   |         ^^ identifiers cannot start with a number
+   |         ^^ expected identifier
+   |
+   = help: identifiers cannot start with a number
 
-error: expected identifier, found number literal
+error: expected identifier, found `2x`
   --> $DIR/issue-104088.rs:11:9
    |
 LL |     let 2x: i32 = 123;
-   |         ^^ identifiers cannot start with a number
+   |         ^^ expected identifier
+   |
+   = help: identifiers cannot start with a number
 
-error: expected identifier, found number literal
+error: expected identifier, found `23name`
   --> $DIR/issue-104088.rs:22:9
    |
 LL |     let 23name = 123;
-   |         ^^^^^^ identifiers cannot start with a number
+   |         ^^^^^^ expected identifier
+   |
+   = help: identifiers cannot start with a number
 
 error[E0308]: mismatched types
   --> $DIR/issue-104088.rs:16:12