vstd_build: Allow disabling std and alloc

source/vstd_build/src/main.rs

@@ -29,6 +29,8 @@ fn main() {
 
     let mut release = false;
     let mut no_verify = false;
+    let mut no_std = false;
+    let mut no_alloc = false;
     let mut verbose = false;
     for arg in args {
         if arg == "--release" {
@@ -37,11 +39,19 @@ fn main() {
             no_verify = true;
         } else if arg == "--verbose" {
             verbose = true;
+        } else if arg == "--no-std" {
+            no_std = true;
+        } else if arg == "--no-alloc" {
+            no_alloc = true;
         } else {
             panic!("unexpected argument: {:}", arg)
         }
     }
 
+    if !no_std && no_alloc {
+        panic!("--no-alloc must be specified along with --no-std");
+    }
+
     #[cfg(target_os = "macos")]
     let (pre, dl) = ("lib", "dylib");
 
@@ -89,6 +99,14 @@ fn main() {
         child_args.push("-C".to_string());
         child_args.push("opt-level=3".to_string());
     }
+    if !no_std {
+        child_args.push("--cfg".to_string());
+        child_args.push("feature=\"std\"".to_string());
+    }
+    if !no_alloc {
+        child_args.push("--cfg".to_string());
+        child_args.push("feature=\"alloc\"".to_string());
+    }
     child_args.push(VSTD_RS_PATH.to_string());
 
     let cmd = verus_target_path.join("rust_verify");