Add support for literals

compiler/rustc_expand/src/mbe/metavar_expr.rs

@@ -1,12 +1,12 @@
-use rustc_ast::token::{self, Delimiter, IdentIsRaw};
+use rustc_ast::token::{self, Delimiter, IdentIsRaw, Token};
 use rustc_ast::tokenstream::{RefTokenTreeCursor, TokenStream, TokenTree};
 use rustc_ast::{LitIntType, LitKind};
 use rustc_ast_pretty::pprust;
 use rustc_errors::{Applicability, PResult};
 use rustc_macros::{Decodable, Encodable};
 use rustc_session::parse::ParseSess;
 use rustc_span::symbol::Ident;
-use rustc_span::Span;
+use rustc_span::{Span, Symbol};
 
 pub(crate) const RAW_IDENT_ERR: &str = "`${concat(..)}` currently does not support raw identifiers";
 
@@ -51,11 +51,18 @@ impl MetaVarExpr {
                 let mut result = Vec::new();
                 loop {
                     let is_var = try_eat_dollar(&mut iter);
-                    let element_ident = parse_ident(&mut iter, psess, outer_span)?;
+                    let token = parse_token(&mut iter, psess, outer_span)?;
                     let element = if is_var {
-                        MetaVarExprConcatElem::Var(element_ident)
+                        MetaVarExprConcatElem::Var(parse_ident_from_token(psess, token)?)
+                    } else if let token::TokenKind::Literal(token::Lit {
+                        kind: token::LitKind::Char | token::LitKind::Integer | token::LitKind::Str,
+                        symbol,
+                        suffix: None,
+                    }) = token.kind
+                    {
+                        MetaVarExprConcatElem::Literal(symbol)
                     } else {
-                        MetaVarExprConcatElem::Ident(element_ident)
+                        MetaVarExprConcatElem::Ident(parse_ident_from_token(psess, token)?)
                     };
                     result.push(element);
                     if iter.look_ahead(0).is_none() {
@@ -105,11 +112,13 @@ impl MetaVarExpr {
 
 #[derive(Debug, Decodable, Encodable, PartialEq)]
 pub(crate) enum MetaVarExprConcatElem {
-    /// There is NO preceding dollar sign, which means that this identifier should be interpreted
-    /// as a literal.
+    /// Identifier WITHOUT a preceding dollar sign, which means that this identifier should be
+    /// interpreted as a literal.
     Ident(Ident),
-    /// There is a preceding dollar sign, which means that this identifier should be expanded
-    /// and interpreted as a variable.
+    /// For example, a number or a string.
+    Literal(Symbol),
+    /// Identifier WITH a preceding dollar sign, which means that this identifier should be
+    /// expanded and interpreted as a variable.
     Var(Ident),
 }
 
@@ -180,12 +189,14 @@ fn parse_ident<'psess>(
     psess: &'psess ParseSess,
     fallback_span: Span,
 ) -> PResult<'psess, Ident> {
-    let Some(tt) = iter.next() else {
-        return Err(psess.dcx().struct_span_err(fallback_span, "expected identifier"));
-    };
-    let TokenTree::Token(token, _) = tt else {
-        return Err(psess.dcx().struct_span_err(tt.span(), "expected identifier"));
-    };
+    let token = parse_token(iter, psess, fallback_span)?;
+    parse_ident_from_token(psess, token)
+}
+
+fn parse_ident_from_token<'psess>(
+    psess: &'psess ParseSess,
+    token: &Token,
+) -> PResult<'psess, Ident> {
     if let Some((elem, is_raw)) = token.ident() {
         if let IdentIsRaw::Yes = is_raw {
             return Err(psess.dcx().struct_span_err(elem.span, RAW_IDENT_ERR));
@@ -205,6 +216,20 @@ fn parse_ident<'psess>(
     Err(err)
 }
 
+fn parse_token<'psess, 't>(
+    iter: &mut RefTokenTreeCursor<'t>,
+    psess: &'psess ParseSess,
+    fallback_span: Span,
+) -> PResult<'psess, &'t Token> {
+    let Some(tt) = iter.next() else {
+        return Err(psess.dcx().struct_span_err(fallback_span, "expected identifier"));
+    };
+    let TokenTree::Token(token, _) = tt else {
+        return Err(psess.dcx().struct_span_err(tt.span(), "expected identifier"));
+    };
+    Ok(token)
+}
+
 /// Tries to move the iterator forward returning `true` if there is a comma. If not, then the
 /// iterator is not modified and the result is `false`.
 fn try_eat_comma(iter: &mut RefTokenTreeCursor<'_>) -> bool {

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -680,8 +680,9 @@ fn transcribe_metavar_expr<'a>(
             let mut concatenated = String::new();
             for element in elements.into_iter() {
                 let string = match element {
-                    MetaVarExprConcatElem::Ident(ident) => ident.to_string(),
-                    MetaVarExprConcatElem::Var(ident) => extract_ident(dcx, *ident, interp)?,
+                    MetaVarExprConcatElem::Ident(elem) => elem.to_string(),
+                    MetaVarExprConcatElem::Literal(elem) => elem.as_str().into(),
+                    MetaVarExprConcatElem::Var(elem) => extract_ident(dcx, *elem, interp)?,
                 };
                 concatenated.push_str(&string);
             }
@@ -751,6 +752,11 @@ fn extract_ident<'a>(
             }
             return Ok(token_ident.to_string());
         }
+        if let ParseNtResult::Tt(TokenTree::Token(Token { kind: TokenKind::Literal(lit), .. }, _)) =
+            pnr
+        {
+            return Ok(lit.symbol.to_ident_string());
+        }
     }
     Err(dcx.struct_span_err(
         ident.span,

tests/ui/macros/macro-metavar-expr-concat/allowed-operations.rs

@@ -37,6 +37,18 @@ macro_rules! without_dollar_sign_is_an_ident {
     };
 }
 
+macro_rules! literals {
+    ($var:ident) => {{
+        let ${concat(_a, 'b')}: () = ();
+        let ${concat(_a, 1)}: () = ();
+        let ${concat(_a, "b")}: () = ();
+
+        let ${concat($var, 'b')}: () = ();
+        let ${concat($var, 1)}: () = ();
+        let ${concat($var, "b")}: () = ();
+    }};
+}
+
 fn main() {
     create_things!(behold);
     behold_separated_idents_in_a_fn();
@@ -55,4 +67,6 @@ fn main() {
     without_dollar_sign_is_an_ident!(_123);
     assert_eq!(VARident, 1);
     assert_eq!(VAR_123, 2);
+
+    literals!(_hello);
 }

tests/ui/macros/macro-metavar-expr-concat/syntax-errors.rs

@@ -11,9 +11,6 @@ macro_rules! wrong_concat_declarations {
         ${concat(aaaa,)}
         //~^ ERROR expected identifier
 
-        ${concat(aaaa, 1)}
-        //~^ ERROR expected identifier
-
         ${concat(_, aaaa)}
 
         ${concat(aaaa aaaa)}
@@ -30,9 +27,6 @@ macro_rules! wrong_concat_declarations {
 
         ${concat($ex, aaaa,)}
         //~^ ERROR expected identifier
-
-        ${concat($ex, aaaa, 123)}
-        //~^ ERROR expected identifier
     };
 }
 

tests/ui/macros/macro-metavar-expr-concat/syntax-errors.stderr

@@ -16,53 +16,41 @@ error: expected identifier
 LL |         ${concat(aaaa,)}
    |          ^^^^^^^^^^^^^^^
 
-error: expected identifier, found `1`
-  --> $DIR/syntax-errors.rs:14:24
-   |
-LL |         ${concat(aaaa, 1)}
-   |                        ^ help: try removing `1`
-
 error: expected comma
-  --> $DIR/syntax-errors.rs:19:10
+  --> $DIR/syntax-errors.rs:16:10
    |
 LL |         ${concat(aaaa aaaa)}
    |          ^^^^^^^^^^^^^^^^^^^
 
 error: `concat` must have at least two elements
-  --> $DIR/syntax-errors.rs:22:11
+  --> $DIR/syntax-errors.rs:19:11
    |
 LL |         ${concat($ex)}
    |           ^^^^^^
 
 error: expected comma
-  --> $DIR/syntax-errors.rs:28:10
+  --> $DIR/syntax-errors.rs:25:10
    |
 LL |         ${concat($ex, aaaa 123)}
    |          ^^^^^^^^^^^^^^^^^^^^^^^
 
 error: expected identifier
-  --> $DIR/syntax-errors.rs:31:10
+  --> $DIR/syntax-errors.rs:28:10
    |
 LL |         ${concat($ex, aaaa,)}
    |          ^^^^^^^^^^^^^^^^^^^^
 
-error: expected identifier, found `123`
-  --> $DIR/syntax-errors.rs:34:29
-   |
-LL |         ${concat($ex, aaaa, 123)}
-   |                             ^^^ help: try removing `123`
-
 error: `${concat(..)}` currently only accepts identifiers or meta-variables as parameters
-  --> $DIR/syntax-errors.rs:25:19
+  --> $DIR/syntax-errors.rs:22:19
    |
 LL |         ${concat($ex, aaaa)}
    |                   ^^
 
 error: variable `foo` is not recognized in meta-variable expression
-  --> $DIR/syntax-errors.rs:41:30
+  --> $DIR/syntax-errors.rs:35:30
    |
 LL |         const ${concat(FOO, $foo)}: i32 = 2;
    |                              ^^^
 
-error: aborting due to 11 previous errors
+error: aborting due to 9 previous errors