Feature Request

Summary

I have structs which have fields I'd like to log. So I create a log_context member which holds the kv pairs.
These rarely change, and then only by appending values. The current syntax becomes unwieldy if I use
the field names and values and later refactor the struct and add additional fields I'd like to log.

Motivation

I'm writing server code and would like to efficiently log object information in addition to the normal point in code logging.

Guide-level explanation

Assume a struct has a log_context field consisting of a container of kv pairs and is referenced by something. At some point in the code, you'd like to log some information and include the kv pairs in the log as k=val (tagged data).

info!("some logging state={}", state, something);
or if its easier:
info!("some logging state={}", state, &something);
or if its easier:
info!("some logging state={}", state, Some(something));

or if easier, the log_context field could be an Option<_>

Reference-level explanation

This is another means of specifying kv pairs, and would likely require new macros, e.g., info_kv!(...) or reworking existing macros.

Drawbacks

This could be work that few take advantage of. Although, I suspect once the community starts seeing it in action adoption may occur rapidly.

Rationale and alternatives

The primary alternative is to forgo the macros and build the Record using builder methods, which is at best tedious.

Unresolved Questions

I don't believe this creates unresolved issues.

Bug Report

Your Environment

| Software | Version(s) |
| MacOS 11.04 |
| kv-log-macro 1.0.7 |
| Rustc - rustc 1.53.0-nightly (673d0db5e 2021-03-23 |

Expected Behavior

The last line of the example is:

info!("hello {}", "cats", {
            cat_1: "chashu",
            cat_2: "nori",
        });

I'm expecting this to print key of cat_1 and a value of cats etc.

{"message":"hello cats",level":"INFO", "cat_1": "chahu", ... }

Current Behavior

(removed irrelevant fields)

{"message":"hello cats",level":"INFO", ... }

Nothing related to the key value fields are logged at all.

Code Sample

The code:

use kv_log_macro::info;

#[tokio::main]
async fn main() {
    log4rs::init_file("./config/log4rs.yml", Default::default())
        .expect("Should have logging configuration at config/log4rs.yml");
    info!("hello {}", "cats", {
            cat_1: "chashu",
            cat_2: "nori",
        });
}

Log4rs config:

refresh_rate: 30 seconds

appenders:
  json_file:
    kind: file
    path: 'json.log'
    encoder:
      kind: json

  human_file:
    kind: file
    path: "human.log"
    encoder:
      pattern: "{h({d} {l} - {m}{n})}"

root:
  level: info
  appenders:
    - json_file
    - human_file

I don't know where in the chain this breaks, but when using femme as a logger with this only log::info!("hello", {}) works, but log::info!("hello") gets ignored.

use kv_log_macro::{log_enabled, level::Debug};

if log_enabled!(Debug) {
  // DO THINGs
}

Fails to compile

error[E0425]: cannot find function `__private_api_enabled` in crate `$crate`
   --> src/log/middleware.rs:70:16
    |
70  |               if log_enabled!(Debug) {
    |                  ^^^^^^^^^^^^^^^^^^^ help: a function with a similar name exists: `__private_api_log`
    | 
   ::: /Users/dignifiedquire/.cargo/registry/src/github.com-1ecc6299db9ec823/kv-log-macro-1.0.4/src/lib.rs:228:1
    |
228 | / pub fn __private_api_log(
229 | |     args: fmt::Arguments<'_>,
230 | |     level: Level,
231 | |     &(target, module_path, file, line): &(&str, &'static str, &'static str, u32),
...   |
244 | |     );
245 | | }
    | |_- similarly named function `__private_api_log` defined here
    |
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)