unable to detect rust without extension

[rupansh]

tested against:

use std::collections::HashMap;
use std::fmt::{self, Debug, Formatter};
use std::path::{Path, PathBuf};
use crate::core::{Dependency, Package, PackageId, Source, SourceId, Summary};
use crate::sources::PathSource;

use crate::util::errors::CargoResult;
use crate::util::Config;
use anyhow::Context as _;
use cargo_util::{paths, Sha256};
use serde::Deserialize;

pub struct DirectorySource<'cfg> {
    source_id: SourceId,
    root: PathBuf,
    packages: HashMap<PackageId, (Package, Checksum)>,
    config: &'cfg Config,
}

#[derive(Deserialize)]
struct Checksum {
    package: Option<String>,
    files: HashMap<String, String>,
}

impl<'cfg> DirectorySource<'cfg> {
    pub fn new(path: &Path, id: SourceId, config: &'cfg Config) -> DirectorySource<'cfg> {
        DirectorySource {
            source_id: id,
            root: path.to_path_buf(),
            config,
            packages: HashMap::new(),
        }
    }
}

filename: code

Expected result: Rust
Actual result: