fix gen_rust_project

Author: bobozaur

tools/rust_analyzer/bin/gen_rust_project.rs

@@ -1,6 +1,6 @@
 use std::{
     env,
-    fs::File,
+    fs::OpenOptions,
     io::{BufWriter, ErrorKind},
 };
 
@@ -36,11 +36,14 @@ fn write_rust_project(
     }
 
     // Write the new rust-project.json file.
-    let file = File::open(rust_project_path)
-        .with_context(|| "could not open: {rust_project_path}")
+    let file = OpenOptions::new()
+        .write(true)
+        .create(true)
+        .open(rust_project_path)
+        .with_context(|| format!("could not open: {rust_project_path}"))
         .map(BufWriter::new)?;
-    serde_json::to_writer(file, &rust_project)?;
 
+    serde_json::to_writer(file, &rust_project)?;
     Ok(())
 }