span_to_snippet return value is a Result, not an Option

Author: zackmdavis

src/diag.md

@@ -56,7 +56,7 @@ let mut err = sess.struct_span_err(sp, "oh no! this is an error!");
 // In some cases, you might need to check if `sp` is generated by a macro to
 // avoid printing weird errors about macro-generated code.
 
-if let Some(snippet) = sess.codemap().span_to_snippet(sp) {
+if let Ok(snippet) = sess.codemap().span_to_snippet(sp) {
     // Use the snippet to generate a suggested fix
     err.span_suggestion(suggestion_sp, "try using a qux here", format!("qux {}", snip));
 } else {
@@ -90,7 +90,7 @@ For example, to make our `qux` suggestion machine-applicable, we would do:
 ```rust,ignore
 let mut err = sess.struct_span_err(sp, "oh no! this is an error!");
 
-if let Some(snippet) = sess.codemap().span_to_snippet(sp) {
+if let Ok(snippet) = sess.codemap().span_to_snippet(sp) {
     // Add applicability info!
     err.span_suggestion_with_applicability(
         suggestion_sp,