Distinguish boolean literals more precisely

This avoids taking the slow path for things like `0usize` or `0x7e`.

src/runtime.rs

@@ -281,7 +281,7 @@ pub fn push_lifetime_spanned(tokens: &mut TokenStream, span: Span, lifetime: &st
 pub fn push_literal(tokens: &mut TokenStream, repr: &str) {
     // Macro_rules's $literal matcher also matches `true`, `-true`, `false`,
     // `-false` which are not considered valid values for a proc_macro::Literal.
-    if repr.ends_with('e') {
+    if is_boolean_literal(repr) {
         parse(tokens, repr);
     } else {
         let literal = unsafe { Literal::from_str_unchecked(repr) };
@@ -290,7 +290,7 @@ pub fn push_literal(tokens: &mut TokenStream, repr: &str) {
 }
 
 pub fn push_literal_spanned(tokens: &mut TokenStream, span: Span, repr: &str) {
-    if repr.ends_with('e') {
+    if is_boolean_literal(repr) {
         parse_spanned(tokens, span, repr);
     } else {
         let mut literal = unsafe { Literal::from_str_unchecked(repr) };
@@ -299,6 +299,13 @@ pub fn push_literal_spanned(tokens: &mut TokenStream, span: Span, repr: &str) {
     }
 }
 
+fn is_boolean_literal(mut repr: &str) -> bool {
+    if repr.starts_with('-') {
+        repr = &repr[1..];
+    }
+    repr.starts_with(&['t', 'f'])
+}
+
 macro_rules! push_punct {
     ($name:ident $spanned:ident $char1:tt) => {
         pub fn $name(tokens: &mut TokenStream) {