Support Literal as result of paste

src/lib.rs

@@ -155,10 +155,13 @@ mod segment;
 use crate::attr::expand_attr;
 use crate::error::{Error, Result};
 use crate::segment::Segment;
-use proc_macro::{Delimiter, Group, Ident, Punct, Spacing, Span, TokenStream, TokenTree};
+use proc_macro::{
+    Delimiter, Group, Ident, LexError, Literal, Punct, Spacing, Span, TokenStream, TokenTree,
+};
 use std::char;
 use std::iter;
 use std::panic;
+use std::str::FromStr;
 
 #[proc_macro]
 pub fn paste(input: TokenStream) -> TokenStream {
@@ -416,6 +419,18 @@ fn pasted_to_tokens(mut pasted: String, span: Span) -> Result<TokenStream> {
         apostrophe.set_span(span);
         tokens.extend(iter::once(apostrophe));
         pasted.remove(0);
+    } else if pasted.starts_with(|ch: char| ch.is_ascii_digit()) {
+        let literal = match panic::catch_unwind(|| Literal::from_str(&pasted)) {
+            Ok(Ok(literal)) => TokenTree::Literal(literal),
+            Ok(Err(LexError { .. })) | Err(_) => {
+                return Err(Error::new(
+                    span,
+                    &format!("`{:?}` is not a valid literal", pasted),
+                ));
+            }
+        };
+        tokens.extend(iter::once(literal));
+        return Ok(tokens);
     }
 
     let ident = match panic::catch_unwind(|| Ident::new(&pasted, span)) {

tests/ui/invalid-ident.stderr

@@ -1,8 +1,12 @@
-error: `"0f"` is not a valid identifier
- --> tests/ui/invalid-ident.rs:4:8
+error: expected identifier, found `0f`
+ --> tests/ui/invalid-ident.rs:3:1
   |
-4 |     fn [<0 f>]() {}
-  |        ^^^^^^^
+3 | / paste! {
+4 | |     fn [<0 f>]() {}
+5 | | }
+  | |_^ expected identifier
+  |
+  = note: this error originates in the macro `paste` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `"f\""` is not a valid identifier
  --> tests/ui/invalid-ident.rs:8:8