chore: Clean up parse logic for Value

src/cmd.rs

@@ -1,5 +1,10 @@
 use quote::{quote, ToTokens};
-use syn::{braced, bracketed, parse::Parse, punctuated::Punctuated, token, Token};
+use syn::{
+    braced, bracketed,
+    parse::{discouraged::Speculative, Parse},
+    punctuated::Punctuated,
+    token, Token,
+};
 
 pub struct Command {
     program: Value,
@@ -376,15 +381,23 @@ impl Parse for Value {
     fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
         let expr_fork = input.fork();
         expr_fork
-            .parse::<syn::Expr>()
-            .and_then(|_| input.parse().map(Self::Expr))
-            .or_else(|_| {
-                let ident_fork = input.fork();
-                ident_fork
-                    .parse::<syn::Ident>()
-                    .and_then(|_| input.parse().map(Self::Ident))
+            .parse()
+            .map(|expr| {
+                input.advance_to(&expr_fork);
+                Self::Expr(expr)
+            })
+            .or_else(|_| {
+                if input.peek(syn::Ident) {
+                    input.parse().map(Self::Ident)
+                } else if input.peek(syn::Lit) {
+                    input.parse().map(Self::Lit)
+                } else {
+                    Err(syn::Error::new(
+                        input.span(),
+                        "Expected an expression, ident, or literal",
+                    ))
+                }
             })
-            .or_else(|_| input.parse().map(Self::Lit))
     }
 }