Rollup merge of #108482 - Ezrashaw:force-error-docs, r=GuillaumeGomez

statically guarantee that current error codes are documented

Closes #61137 (that's right!)

Pretty simple refactor (often just a change from `Result<Option<&str>>` to `Result<&str>`)

r? `@GuillaumeGomez` (could you specially look at 53044158ef? I believe you wrote that in the first place, just want to make sure you're happy with the change)

compiler/rustc_errors/src/json.rs

@@ -580,7 +580,7 @@ impl DiagnosticCode {
             let je_result =
                 je.registry.as_ref().map(|registry| registry.try_find_description(&s)).unwrap();
 
-            DiagnosticCode { code: s, explanation: je_result.unwrap_or(None) }
+            DiagnosticCode { code: s, explanation: je_result.ok() }
         })
     }
 }

compiler/rustc_errors/src/lib.rs

@@ -1477,9 +1477,7 @@ impl HandlerInner {
                 .emitted_diagnostic_codes
                 .iter()
                 .filter_map(|x| match &x {
-                    DiagnosticId::Error(s)
-                        if registry.try_find_description(s).map_or(false, |o| o.is_some()) =>
-                    {
+                    DiagnosticId::Error(s) if registry.try_find_description(s).is_ok() => {
                         Some(s.clone())
                     }
                     _ => None,

compiler/rustc_errors/src/registry.rs

@@ -5,21 +5,17 @@ pub struct InvalidErrorCode;
 
 #[derive(Clone)]
 pub struct Registry {
-    long_descriptions: FxHashMap<&'static str, Option<&'static str>>,
+    long_descriptions: FxHashMap<&'static str, &'static str>,
 }
 
 impl Registry {
-    pub fn new(long_descriptions: &[(&'static str, Option<&'static str>)]) -> Registry {
+    pub fn new(long_descriptions: &[(&'static str, &'static str)]) -> Registry {
         Registry { long_descriptions: long_descriptions.iter().copied().collect() }
     }
 
     /// 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> {
+    /// registry.
+    pub fn try_find_description(&self, code: &str) -> Result<&'static str, InvalidErrorCode> {
         self.long_descriptions.get(code).copied().ok_or(InvalidErrorCode)
     }
 }