writing VCD for combinatorial circuits works!

crates/fayalite/src/cli.rs

@@ -653,19 +653,21 @@ impl FormalArgs {
                 self.sby.display()
             )))
         };
-        fs::write(
-            cache_file,
-            serde_json::to_string_pretty(&FormalCache {
-                version: FormalCacheVersion::CURRENT,
-                contents_hash: contents_hash.unwrap(),
-                stdout_stderr: captured_output,
-                result: match &result {
-                    Ok(FormalOutput { verilog: _ }) => Ok(FormalCacheOutput {}),
-                    Err(error) => Err(error.to_string()),
-                },
-            })
-            .expect("serialization shouldn't ever fail"),
-        )?;
+        if do_cache {
+            fs::write(
+                cache_file,
+                serde_json::to_string_pretty(&FormalCache {
+                    version: FormalCacheVersion::CURRENT,
+                    contents_hash: contents_hash.unwrap(),
+                    stdout_stderr: captured_output,
+                    result: match &result {
+                        Ok(FormalOutput { verilog: _ }) => Ok(FormalCacheOutput {}),
+                        Err(error) => Err(error.to_string()),
+                    },
+                })
+                .expect("serialization shouldn't ever fail"),
+            )?;
+        }
         result
     }
 }