Add custom error msg for missing crates (#146)

src/main.rs

@@ -80,10 +80,17 @@ fn main() -> Result<()> {
             r#"{"version": 2, "status": "error", "message": "One of the tests timed out"}"#,
         );
     } else if results_json.contains("probable build failure") {
-        results_json = format!(
-            r#"{{"version": 2, "status": "error", "message": "{}"}}"#,
-            results_out.escape_default()
-        );
+        if results_out.contains("error: no matching package named") {
+            results_json = format!(
+                r#"{{"version": 2, "status": "error", "message": "{}"}}"#,
+                escape(MISSING_CRATE_ERR_MSG)
+            );
+        } else {
+            results_json = format!(
+                r#"{{"version": 2, "status": "error", "message": "{}"}}"#,
+                escape(&results_out)
+            );
+        }
     }
 
     // only display relative path in output to students
@@ -118,3 +125,22 @@ fn determine_profile(input_dir: &Path) -> Result<&'static str> {
         Ok("dev")
     }
 }
+
+fn escape(s: &str) -> String {
+    // escape_default turns "'" into "\'" which is incorrect in json
+    // and needs to be reverted
+    s.escape_default().to_string().replace("\\'", "'")
+}
+
+static MISSING_CRATE_ERR_MSG: &str = "\
+It looks like you're using a crate which isn't supported by our test runner.
+Please see the file at the below URL to check which ones are supported.
+Please get in touch if you think your crate should be included
+or something else about the user experience could be improved.
+
+List of available crates:
+https://github.com/exercism/rust-test-runner/blob/main/local-registry/Cargo.toml
+
+Exercism forum (Rust topic):
+https://forum.exercism.org/c/programming/rust
+";

tests/example-missing-crate/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "example-missing-crate"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+lets-hope-nobody-publishes-a-crate-with-a-silly-name-like-this = "*"

tests/example-missing-crate/expected_results.json

@@ -0,0 +1,5 @@
+{
+  "version": 2,
+  "status": "error",
+  "message": "It looks like you're using a crate which isn't supported by our test runner.\nPlease see the file at the below URL to check which ones are supported.\nPlease get in touch if you think your crate should be included\nor something else about the user experience could be improved.\n\nList of available crates:\nhttps://github.com/exercism/rust-test-runner/blob/main/local-registry/Cargo.toml\n\nExercism forum (Rust topic):\nhttps://forum.exercism.org/c/programming/rust\n"
+}

tests/example-missing-crate/src/lib.rs

@@ -0,0 +1 @@
+