Factor out a repeated expression in lower_attr_args.

Author: nnethercote

compiler/rustc_ast_lowering/src/lib.rs

@@ -941,15 +941,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             AttrArgs::Eq(eq_span, AttrArgsEq::Ast(expr)) => {
                 // In valid code the value always ends up as a single literal. Otherwise, a dummy
                 // literal suffices because the error is handled elsewhere.
-                let lit = if let ExprKind::Lit(token_lit) = expr.kind {
-                    match Lit::from_token_lit(token_lit, expr.span) {
-                        Ok(lit) => lit,
-                        Err(_err) => Lit {
-                            token_lit: token::Lit::new(token::LitKind::Err, kw::Empty, None),
-                            kind: LitKind::Err,
-                            span: DUMMY_SP,
-                        },
-                    }
+                let lit = if let ExprKind::Lit(token_lit) = expr.kind 
+                    && let Ok(lit) = Lit::from_token_lit(token_lit, expr.span)
+                {
+                    lit
                 } else {
                     Lit {
                         token_lit: token::Lit::new(token::LitKind::Err, kw::Empty, None),