Enable generating track-specific test cases (#1774)

docs/CONTRIBUTING.md

@@ -41,6 +41,9 @@ The tests are generated using the template engine [Tera].
 The input of the template is the canonical data from [`problem-specifications`].
 if you want to exclude certain tests from being generated,
 you have to set `include = false` in `.meta/tests.toml`.
+Please include a comment about the reason for excluding it.
+If you want to add additional track-specific tests, you can do so in a file `.meta/additional-tests.json`.
+Only do this with a good reason for not upstreaming these tests.
 
 Find some tips about writing tera templates [here](#tera-templates).
 

rust-tooling/src/exercise_generation.rs

@@ -8,7 +8,7 @@ use tera::Context;
 
 use crate::{
     exercise_config::{get_excluded_tests, get_test_emplate},
-    problem_spec::{get_canonical_data, SingleTestCase, TestCase},
+    problem_spec::{get_additional_test_cases, get_canonical_data, SingleTestCase, TestCase},
 };
 
 pub struct GeneratedExercise {
@@ -95,7 +95,11 @@ fn to_hex(value: &tera::Value, _args: &HashMap<String, tera::Value>) -> tera::Re
 }
 
 fn generate_tests(slug: &str, fn_names: Vec<String>) -> String {
-    let cases = get_canonical_data(slug).cases;
+    let cases = {
+        let mut cases = get_canonical_data(slug).cases;
+        cases.extend_from_slice(&get_additional_test_cases(slug));
+        cases
+    };
     let excluded_tests = get_excluded_tests(slug);
     let mut template = get_test_emplate(slug).unwrap();
     if template.get_template_names().next().is_none() {

rust-tooling/src/problem_spec.rs

@@ -51,6 +51,25 @@ pub fn get_canonical_data(slug: &str) -> CanonicalData {
     })
 }
 
+/// The Rust track may define additional test cases in
+/// `.meta/additional-tests.json`, which are not appropriate
+/// to upstream for all other languages to implement.
+pub fn get_additional_test_cases(slug: &str) -> Vec<TestCase> {
+    let path = std::path::PathBuf::from("exercises/practice")
+        .join(slug)
+        .join(".meta/additional-tests.json");
+    if !path.exists() {
+        return Vec::new();
+    }
+    let contents = std::fs::read_to_string(&path).unwrap();
+    serde_json::from_str(contents.as_str()).unwrap_or_else(|e| {
+        panic!(
+            "should deserialize additional tests for {}: {e}",
+            path.display()
+        )
+    })
+}
+
 #[test]
 fn deserialize_canonical_data() {
     crate::fs_utils::cd_into_repo_root();