Rust: add optional dependencies to ql tests

Also accept `options.yml` and `options.yaml` files as well for test options,
to get YAML syntax highlighting. In a follow up PR we might make the extension
mandatory.

rust/extractor/src/config.rs

@@ -43,6 +43,7 @@ pub struct Config {
     pub inputs: Vec<PathBuf>,
     pub qltest: bool,
     pub qltest_cargo_check: bool,
+    pub qltest_dependencies: Vec<String>,
 }
 
 impl Config {
@@ -61,7 +62,13 @@ impl Config {
                 .ancestors()
                 // only travel up while we're within the test pack
                 .take_while_inclusive(|p| !p.join("qlpack.yml").exists())
-                .map(|p| p.join("options"))
+                .flat_map(|p| {
+                    [
+                        p.join("options"),
+                        p.join("options.yml"),
+                        p.join("options.yaml"),
+                    ]
+                })
                 .filter(|p| p.exists())
                 .collect_vec();
             option_files.reverse();

rust/extractor/src/qltest.rs

@@ -21,7 +21,7 @@ fn dump_lib() -> anyhow::Result<()> {
     fs::write("lib.rs", lib).context("writing lib.rs")
 }
 
-fn dump_cargo_manifest() -> anyhow::Result<()> {
+fn dump_cargo_manifest(dependencies: &[String]) -> anyhow::Result<()> {
     let mut manifest = String::from(
         r#"[workspace]
 [package]
@@ -40,6 +40,13 @@ path = "main.rs"
 "#,
         );
     }
+    if !dependencies.is_empty() {
+        manifest.push_str("[dependencies]\n");
+        for dep in dependencies {
+            manifest.push_str(dep);
+            manifest.push('\n');
+        }
+    }
     fs::write("Cargo.toml", manifest).context("writing Cargo.toml")
 }
 
@@ -54,7 +61,7 @@ fn set_sources(config: &mut Config) -> anyhow::Result<()> {
 pub(crate) fn prepare(config: &mut Config) -> anyhow::Result<()> {
     dump_lib()?;
     set_sources(config)?;
-    dump_cargo_manifest()?;
+    dump_cargo_manifest(&config.qltest_dependencies)?;
     if config.qltest_cargo_check {
         let status = Command::new("cargo")
             .env("RUSTFLAGS", "-Awarnings")