Rollup merge of rust-lang#124778 - fmease:fix-diag-msg-parse-meta-item, r=nnethercote

Fix parse error message for meta items

Addresses rust-lang#122796 (comment), cc [`@]Thomasdezeeuw.`

For attrs inside of a macro like `#[doc(alias = $ident)]` or `#[cfg(feature = $ident)]` where `$ident` is a macro metavariable of fragment kind `ident`, we used to say the following when expanded (with `$ident` ⟼ `ident`):

```
error: expected unsuffixed literal or identifier, found `ident`
  --> weird.rs:6:19
   |
6  |      #[cfg(feature = $ident)]
   |                      ^^^^^^
...
11 | m!(id);
   | ------ in this macro invocation
   |
   = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
```

This was incorrect and caused confusion, justifiably so (see rust-lang#122796).

In this position, we only accept/expect *unsuffixed literals* which consist of numeric & string literals as well as the boolean literals / the keywords / the reserved identifiers `false` & `true` **but not** arbitrary identifiers.

Furthermore, we used to suggest garbage when encountering unexpected non-identifier tokens:

```
error: expected unsuffixed literal, found `-`
  --> weird.rs:16:17
   |
16 | #[cfg(feature = -1)]
   |                 ^
   |
help: surround the identifier with quotation marks to parse it as a string
   |
16 | #[cfg(feature =" "-1)]
   |                + +
```

Now we no longer do.

Author: matthiaskrgr

compiler/rustc_parse/messages.ftl

@@ -401,10 +401,8 @@ parse_invalid_logical_operator = `{$incorrect}` is not a logical operator
     .use_amp_amp_for_conjunction = use `&&` to perform logical conjunction
     .use_pipe_pipe_for_disjunction = use `||` to perform logical disjunction
 
-parse_invalid_meta_item = expected unsuffixed literal or identifier, found `{$token}`
-
-parse_invalid_meta_item_unquoted_ident = expected unsuffixed literal, found `{$token}`
-    .suggestion = surround the identifier with quotation marks to parse it as a string
+parse_invalid_meta_item = expected unsuffixed literal, found `{$token}`
+    .quote_ident_sugg = surround the identifier with quotation marks to make it into a string literal
 
 parse_invalid_offset_of = offset_of expects dot-separated field and variant names
 

compiler/rustc_parse/src/errors.rs

@@ -978,21 +978,13 @@ pub(crate) struct InvalidMetaItem {
     #[primary_span]
     pub span: Span,
     pub token: Token,
-}
-
-#[derive(Diagnostic)]
-#[diag(parse_invalid_meta_item_unquoted_ident)]
-pub(crate) struct InvalidMetaItemUnquotedIdent {
-    #[primary_span]
-    pub span: Span,
-    pub token: Token,
     #[subdiagnostic]
-    pub sugg: InvalidMetaItemSuggQuoteIdent,
+    pub quote_ident_sugg: Option<InvalidMetaItemQuoteIdentSugg>,
 }
 
 #[derive(Subdiagnostic)]
-#[multipart_suggestion(parse_suggestion, applicability = "machine-applicable")]
-pub(crate) struct InvalidMetaItemSuggQuoteIdent {
+#[multipart_suggestion(parse_quote_ident_sugg, applicability = "machine-applicable")]
+pub(crate) struct InvalidMetaItemQuoteIdentSugg {
     #[suggestion_part(code = "\"")]
     pub before: Span,
     #[suggestion_part(code = "\"")]

compiler/rustc_parse/src/parser/attr.rs

@@ -1,7 +1,4 @@
-use crate::errors::{
-    InvalidMetaItem, InvalidMetaItemSuggQuoteIdent, InvalidMetaItemUnquotedIdent,
-    SuffixedLiteralInAttribute,
-};
+use crate::errors;
 use crate::fluent_generated as fluent;
 use crate::maybe_whole;
 
@@ -318,7 +315,7 @@ impl<'a> Parser<'a> {
         debug!("checking if {:?} is unsuffixed", lit);
 
         if !lit.kind.is_unsuffixed() {
-            self.dcx().emit_err(SuffixedLiteralInAttribute { span: lit.span });
+            self.dcx().emit_err(errors::SuffixedLiteralInAttribute { span: lit.span });
         }
 
         Ok(lit)
@@ -356,10 +353,11 @@ impl<'a> Parser<'a> {
         Ok(nmis)
     }
 
-    /// Matches the following grammar (per RFC 1559).
+    /// Parse a meta item per RFC 1559.
+    ///
     /// ```ebnf
-    /// meta_item : PATH ( '=' UNSUFFIXED_LIT | '(' meta_item_inner? ')' )? ;
-    /// meta_item_inner : (meta_item | UNSUFFIXED_LIT) (',' meta_item_inner)? ;
+    /// MetaItem = SimplePath ( '=' UNSUFFIXED_LIT | '(' MetaSeq? ')' )? ;
+    /// MetaSeq = MetaItemInner (',' MetaItemInner)* ','? ;
     /// ```
     pub fn parse_meta_item(&mut self) -> PResult<'a, ast::MetaItem> {
         // We can't use `maybe_whole` here because it would bump in the `None`
@@ -387,46 +385,52 @@ impl<'a> Parser<'a> {
         Ok(if self.eat(&token::Eq) {
             ast::MetaItemKind::NameValue(self.parse_unsuffixed_meta_item_lit()?)
         } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
-            // Matches `meta_seq = ( COMMASEP(meta_item_inner) )`.
             let (list, _) = self.parse_paren_comma_seq(|p| p.parse_meta_item_inner())?;
             ast::MetaItemKind::List(list)
         } else {
             ast::MetaItemKind::Word
         })
     }
 
-    /// Matches `meta_item_inner : (meta_item | UNSUFFIXED_LIT) ;`.
+    /// Parse an inner meta item per RFC 1559.
+    ///
+    /// ```ebnf
+    /// MetaItemInner = UNSUFFIXED_LIT | MetaItem ;
+    /// ```
     fn parse_meta_item_inner(&mut self) -> PResult<'a, ast::NestedMetaItem> {
         match self.parse_unsuffixed_meta_item_lit() {
             Ok(lit) => return Ok(ast::NestedMetaItem::Lit(lit)),
-            Err(err) => err.cancel(),
+            Err(err) => err.cancel(), // we provide a better error below
         }
 
         match self.parse_meta_item() {
             Ok(mi) => return Ok(ast::NestedMetaItem::MetaItem(mi)),
-            Err(err) => err.cancel(),
+            Err(err) => err.cancel(), // we provide a better error below
         }
 
-        let token = self.token.clone();
+        let mut err = errors::InvalidMetaItem {
+            span: self.token.span,
+            token: self.token.clone(),
+            quote_ident_sugg: None,
+        };
 
-        // Check for unquoted idents in meta items, e.g.: #[cfg(key = foo)]
-        // `from_expansion()` ensures we don't suggest for cases such as
-        // `#[cfg(feature = $expr)]` in macros
-        if self.prev_token == token::Eq && !self.token.span.from_expansion() {
+        // Suggest quoting idents, e.g. in `#[cfg(key = value)]`. We don't use `Token::ident` and
+        // don't `uninterpolate` the token to avoid suggesting anything butchered or questionable
+        // when macro metavariables are involved.
+        if self.prev_token == token::Eq
+            && let token::Ident(..) = self.token.kind
+        {
             let before = self.token.span.shrink_to_lo();
-            while matches!(self.token.kind, token::Ident(..)) {
+            while let token::Ident(..) = self.token.kind {
                 self.bump();
             }
-            let after = self.prev_token.span.shrink_to_hi();
-            let sugg = InvalidMetaItemSuggQuoteIdent { before, after };
-            return Err(self.dcx().create_err(InvalidMetaItemUnquotedIdent {
-                span: token.span,
-                token,
-                sugg,
-            }));
+            err.quote_ident_sugg = Some(errors::InvalidMetaItemQuoteIdentSugg {
+                before,
+                after: self.prev_token.span.shrink_to_hi(),
+            });
         }
 
-        Err(self.dcx().create_err(InvalidMetaItem { span: token.span, token }))
+        Err(self.dcx().create_err(err))
     }
 }
 

tests/ui/attributes/nonterminal-expansion.rs

@@ -5,7 +5,7 @@
 macro_rules! pass_nonterminal {
     ($n:expr) => {
         #[repr(align($n))]
-        //~^ ERROR expected unsuffixed literal or identifier, found `n!()`
+        //~^ ERROR expected unsuffixed literal, found `n!()`
         struct S;
     };
 }

tests/ui/attributes/nonterminal-expansion.stderr

@@ -1,4 +1,4 @@
-error: expected unsuffixed literal or identifier, found `n!()`
+error: expected unsuffixed literal, found `n!()`
   --> $DIR/nonterminal-expansion.rs:7:22
    |
 LL |         #[repr(align($n))]

tests/ui/conditional-compilation/cfg-attr-syntax-validation.rs

@@ -28,8 +28,8 @@ struct S9;
 macro_rules! generate_s10 {
     ($expr: expr) => {
         #[cfg(feature = $expr)]
-        //~^ ERROR expected unsuffixed literal or identifier, found `concat!("nonexistent")`
-        //~| ERROR expected unsuffixed literal or identifier, found `concat!("nonexistent")`
+        //~^ ERROR expected unsuffixed literal, found `concat!("nonexistent")`
+        //~| ERROR expected unsuffixed literal, found `concat!("nonexistent")`
         struct S10;
     }
 }

tests/ui/conditional-compilation/cfg-attr-syntax-validation.stderr

@@ -54,7 +54,7 @@ LL | #[cfg(a = b"hi")]
    |           |
    |           help: consider removing the prefix
 
-error: expected unsuffixed literal or identifier, found `concat!("nonexistent")`
+error: expected unsuffixed literal, found `concat!("nonexistent")`
   --> $DIR/cfg-attr-syntax-validation.rs:30:25
    |
 LL |         #[cfg(feature = $expr)]
@@ -65,7 +65,7 @@ LL | generate_s10!(concat!("nonexistent"));
    |
    = note: this error originates in the macro `generate_s10` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: expected unsuffixed literal or identifier, found `concat!("nonexistent")`
+error: expected unsuffixed literal, found `concat!("nonexistent")`
   --> $DIR/cfg-attr-syntax-validation.rs:30:25
    |
 LL |         #[cfg(feature = $expr)]

tests/ui/deprecation/issue-66340-deprecated-attr-non-meta-grammar.stderr

@@ -4,7 +4,7 @@ error: expected unsuffixed literal, found `test`
 LL | #[deprecated(note = test)]
    |                     ^^^^
    |
-help: surround the identifier with quotation marks to parse it as a string
+help: surround the identifier with quotation marks to make it into a string literal
    |
 LL | #[deprecated(note = "test")]
    |                     +    +

tests/ui/parser/attribute/attr-bad-meta-4.rs

@@ -1,12 +1,17 @@
 macro_rules! mac {
     ($attr_item: meta) => {
         #[cfg($attr_item)]
-        //~^ ERROR expected unsuffixed literal or identifier, found `an(arbitrary token stream)`
-        //~| ERROR expected unsuffixed literal or identifier, found `an(arbitrary token stream)`
+        //~^ ERROR expected unsuffixed literal, found `an(arbitrary token stream)`
+        //~| ERROR expected unsuffixed literal, found `an(arbitrary token stream)`
         struct S;
     }
 }
 
 mac!(an(arbitrary token stream));
 
+#[cfg(feature = -1)]
+//~^ ERROR expected unsuffixed literal, found `-`
+//~| ERROR expected unsuffixed literal, found `-`
+fn handler() {}
+
 fn main() {}

tests/ui/parser/attribute/attr-bad-meta-4.stderr

@@ -1,4 +1,10 @@
-error: expected unsuffixed literal or identifier, found `an(arbitrary token stream)`
+error: expected unsuffixed literal, found `-`
+  --> $DIR/attr-bad-meta-4.rs:12:17
+   |
+LL | #[cfg(feature = -1)]
+   |                 ^
+
+error: expected unsuffixed literal, found `an(arbitrary token stream)`
   --> $DIR/attr-bad-meta-4.rs:3:15
    |
 LL |         #[cfg($attr_item)]
@@ -9,7 +15,7 @@ LL | mac!(an(arbitrary token stream));
    |
    = note: this error originates in the macro `mac` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: expected unsuffixed literal or identifier, found `an(arbitrary token stream)`
+error: expected unsuffixed literal, found `an(arbitrary token stream)`
   --> $DIR/attr-bad-meta-4.rs:3:15
    |
 LL |         #[cfg($attr_item)]
@@ -21,5 +27,13 @@ LL | mac!(an(arbitrary token stream));
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
    = note: this error originates in the macro `mac` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 2 previous errors
+error: expected unsuffixed literal, found `-`
+  --> $DIR/attr-bad-meta-4.rs:12:17
+   |
+LL | #[cfg(feature = -1)]
+   |                 ^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: aborting due to 4 previous errors