Rust grammar allows trailing commas in most places where a list of
elements are accepted. It simplifies cases when the list is generated
by a macro, allowing the macro to avoid special cases for a one element
list vs longer lists.
As such, it is a common practice to allow trailing commas in macros as
well.
#### Problem
Our existing datapoint macro syntax does directly not support group-by tags.
The existing workaround is to embed the group-by tags into the metric name which does not scale well.
#### Summary of Changes
This PR extends the existing syntax to support group-by tags as follows. The new syntax is also compatible with the existing syntax:
```
datapoint_debug!(
"metric_name",
"tag" => "tag-value",
"tag2" => "tag-value2",
....
("field1", 100, i64), // field syntax is the same as the current syntax.
("field2", "hello", String),
...
);
```
Illia Bobyr
steviez
Yueh-Hsuan Chiang
Michael Vines
behzad nouri
anatoly yakovenko
sakridge