Rollup merge of #108854 - Ezrashaw:improve-int-idents, r=oli-obk

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

Improve parser code when we parse a integer (or float) literal but expect an identifier. We emit an error message saying that identifiers can't begin with numbers. This PR just improves that code and expands it to all identifiers. Note that I haven't implemented error recovery (this didn't exist before anyway), I might do that in a follow up PR.

9 files changed, 68 insertions, 45 deletions

diff --git a/compiler/rustc_parse/locales/en-US.ftl b/compiler/rustc_parse/locales/en-US.ftl
index e76e91fc1b1..5c7dc1e2abf 100644
--- a/compiler/rustc_parse/locales/en-US.ftl
+++ b/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
diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index 1662db36d10..63e5bc50513 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/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,
@@ -1208,14 +1217,6 @@ pub(crate) struct SelfParamNotFirst {
 }
 
 #[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 {
     #[primary_span]
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 0a65c37ea7b..5b12bcc1822 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/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],
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
index 8e920f1c421..fc9f1d1330a 100644
--- a/compiler/rustc_parse/src/parser/pat.rs
+++ b/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)) {
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index 92a22ffc2b0..fbe5b88c49e 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/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() {
diff --git a/tests/ui/parser/integer-literal-start-ident.rs b/tests/ui/parser/integer-literal-start-ident.rs
new file mode 100644
index 00000000000..12537482e0f
--- /dev/null
+++ b/tests/ui/parser/integer-literal-start-ident.rs
@@ -0,0 +1,2 @@
+fn 1main() {}
+//~^ ERROR expected identifier, found `1main`
diff --git a/tests/ui/parser/integer-literal-start-ident.stderr b/tests/ui/parser/integer-literal-start-ident.stderr
new file mode 100644
index 00000000000..51c37a0d24c
--- /dev/null
+++ b/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
+
diff --git a/tests/ui/parser/issues/issue-104088.rs b/tests/ui/parser/issues/issue-104088.rs
index 5f794fe2dc9..86988c8cd21 100644
--- a/tests/ui/parser/issues/issue-104088.rs
+++ b/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() {}
diff --git a/tests/ui/parser/issues/issue-104088.stderr b/tests/ui/parser/issues/issue-104088.stderr
index ff4b4bdb695..6511a313149 100644
--- a/tests/ui/parser/issues/issue-104088.stderr
+++ b/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