Rewrite and move comment to the correct place

Author: jakebailey

src/compiler/checker.ts

@@ -22480,18 +22480,26 @@ namespace ts {
                     target = getActualTypeVariable(target);
                 }
                 if (target.flags & TypeFlags.TypeVariable) {
-                    // If target is a type parameter, make an inference, unless the source type contains
-                    // the anyFunctionType (the wildcard type that's used to avoid contextually typing functions).
-                    // Because the anyFunctionType is internal, it should not be exposed to the user by adding
-                    // it as an inference candidate. Hopefully, a better candidate will come along that does
-                    // not contain anyFunctionType when we come back to this argument for its second round
-                    // of inference. Also, we exclude inferences for silentNeverType (which is used as a wildcard
-                    // when constructing types from type parameters that had no inference candidates).
+                    // Skip inference if the source is "blocked", which is used by the language service to
+                    // prevent inference on nodes currently being edited.
                     if (isFromInferenceBlockedSource(source)) {
                         return;
                     }
                     const inference = getInferenceInfoForType(target);
                     if (inference) {
+                        // If target is a type parameter, make an inference, unless the source type contains
+                        // a "non-inferrable" type. Types with this flag set are markers used to prevent inference.
+                        //
+                        // For example:
+                        //     - anyFunctionType is a wildcard type that's used to avoid contextually typing functions;
+                        //       it's internal, so should not be exposed to the user by adding it as a candidate.
+                        //     - autoType (and autoArrayType) is a special "any" used in control flow; like anyFunctionType,
+                        //       it's internal and should not be observable.
+                        //     - silentNeverType is returned by getInferredType when instantiating a generic function for
+                        //       inference (and a type variable has no mapping).
+                        //
+                        // This flag is infectious; if we produce Box<never> (where never is silentNeverType), Box<never> is
+                        // also non-inferrable.
                         if (getObjectFlags(source) & ObjectFlags.NonInferrableType) {
                             return;
                         }