Add lots of static Symbols.

These will be used in the subsequent commits. Many of them are
attributes.

The commit also adds the ability to handle symbols that aren't
identifiers (e.g. "proc-macro").

src/librustc_macros/src/symbols.rs

@@ -11,7 +11,7 @@ use quote::quote;
 #[allow(non_camel_case_types)]
 mod kw {
     syn::custom_keyword!(Keywords);
-    syn::custom_keyword!(Other);
+    syn::custom_keyword!(Symbols);
 }
 
 struct Keyword {
@@ -33,14 +33,24 @@ impl Parse for Keyword {
     }
 }
 
-struct Symbol(Ident);
+struct Symbol {
+    name: Ident,
+    value: Option<LitStr>,
+}
 
 impl Parse for Symbol {
     fn parse(input: ParseStream<'_>) -> Result<Self> {
-        let ident: Ident = input.parse()?;
+        let name = input.parse()?;
+        let value = match input.parse::<Token![:]>() {
+            Ok(_) => Some(input.parse()?),
+            Err(_) => None,
+        };
         input.parse::<Token![,]>()?;
 
-        Ok(Symbol(ident))
+        Ok(Symbol {
+            name,
+            value,
+        })
     }
 }
 
@@ -69,7 +79,7 @@ impl Parse for Input {
         braced!(content in input);
         let keywords = content.parse()?;
 
-        input.parse::<kw::Other>()?;
+        input.parse::<kw::Symbols>()?;
         let content;
         braced!(content in input);
         let symbols = content.parse()?;
@@ -116,19 +126,22 @@ pub fn symbols(input: TokenStream) -> TokenStream {
     }
 
     for symbol in &input.symbols.0 {
-        let value = &symbol.0;
-        let value_str = value.to_string();
-        check_dup(&value_str);
+        let name = &symbol.name;
+        let value = match &symbol.value {
+            Some(value) => value.value(),
+            None => name.to_string(),
+        };
+        check_dup(&value);
         prefill_stream.extend(quote! {
-            #value_str,
+            #value,
         });
         symbols_stream.extend(quote! {
-            pub const #value: Symbol = Symbol::new(#counter);
+            pub const #name: Symbol = Symbol::new(#counter);
         });
         counter += 1;
     }
 
-    TokenStream::from(quote! {
+    let tt = TokenStream::from(quote! {
         macro_rules! keywords {
             () => {
                 #keyword_stream
@@ -159,5 +172,11 @@ pub fn symbols(input: TokenStream) -> TokenStream {
                 ])
             }
         }
-    })
+    });
+
+    // To see the generated code generated, uncomment this line, recompile, and
+    // run the resulting output through `rustfmt`.
+    //eprintln!("{}", tt);
+
+    tt
 }