added `try_find_description` to distinguish no desc from invalid code

1 files changed, 20 insertions, 4 deletions

diff --git a/src/librustc_errors/registry.rs b/src/librustc_errors/registry.rs
index 771542cb06f..c92a9d04775 100644
--- a/src/librustc_errors/registry.rs
+++ b/src/librustc_errors/registry.rs
@@ -1,16 +1,32 @@
 use rustc_data_structures::fx::FxHashMap;
 
+#[derive(Debug)]
+pub struct InvalidErrorCode;
+
 #[derive(Clone)]
 pub struct Registry {
-    descriptions: FxHashMap<&'static str, &'static str>,
+    long_descriptions: FxHashMap<&'static str, Option<&'static str>>,
 }
 
 impl Registry {
-    pub fn new(descriptions: &[(&'static str, &'static str)]) -> Registry {
-        Registry { descriptions: descriptions.iter().cloned().collect() }
+    pub fn new(long_descriptions: &[(&'static str, Option<&'static str>)]) -> Registry {
+        Registry { long_descriptions: long_descriptions.iter().cloned().collect() }
     }
 
+    /// This will panic if an invalid error code is passed in
     pub fn find_description(&self, code: &str) -> Option<&'static str> {
-        self.descriptions.get(code).cloned()
+        self.try_find_description(code).unwrap()
+    }
+    /// Returns `InvalidErrorCode` if the code requested does not exist in the
+    /// registry. Otherwise, returns an `Option` where `None` means the error
+    /// code is valid but has no extended information.
+    pub fn try_find_description(
+        &self,
+        code: &str,
+    ) -> Result<Option<&'static str>, InvalidErrorCode> {
+        if !self.long_descriptions.contains_key(code) {
+            return Err(InvalidErrorCode);
+        }
+        Ok(self.long_descriptions.get(code).unwrap().clone())
     }
 }