Why is this extra let binding necessary? See line 13 below. If you remove it, there's an error. (And the source code: https://github.com/killerswan/ovid/blob/b197f03f4b670e25c420751ec3358ead2d42059a/CSVProvider.rs#L139)

gistfile1.txt

ovid $ git ll -1 --oneline
* b197f03 (HEAD, master) cleanup
ovid $ 
ovid $ git diff
diff --git a/CSVProvider.rs b/CSVProvider.rs
index 2b24cd2..2181c0b 100644
--- a/CSVProvider.rs
+++ b/CSVProvider.rs
@@ -205,8 +205,7 @@ fn provide_csv_given_labels(cx: &mut ExtCtxt, sp: Span, tts: &[TokenTree]) -> Bo
 
    println!("Parsing given labels...");
 
-   let labels1 = format!("{}", labels);
-   let labels_iter = parse_csv_row(labels1.as_slice(), None);
+   let labels_iter = parse_csv_row(format!("{}", labels).as_slice(), None);
 
    println!("Defining items in the CSV provider...");
 
ovid $ 
ovid $ ./build.sh 
CSVProvider.rs:208:36: 208:58 error: borrowed value does not live long enough
CSVProvider.rs:208    let labels_iter = parse_csv_row(format!("{}", labels).as_slice(), None);
                                                      ^~~~~~~~~~~~~~~~~~~~~~
CSVProvider.rs:162:94: 252:2 note: reference must be valid for the block at 162:93...
CSVProvider.rs:162 fn provide_csv_given_labels(cx: &mut ExtCtxt, sp: Span, tts: &[TokenTree]) -> Box<MacResult> {
CSVProvider.rs:163    let mut entries = match parse_entries(cx, tts) {
CSVProvider.rs:164       Some(entries) => entries,
CSVProvider.rs:165       None => return DummyResult::expr(sp),
CSVProvider.rs:166    };
CSVProvider.rs:167 
                   ...
CSVProvider.rs:208:8: 208:75 note: ...but borrowed value is only valid for the statement at 208:7; consider using a `let` binding to increase its lifetime
CSVProvider.rs:208    let labels_iter = parse_csv_row(format!("{}", labels).as_slice(), None);
                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error