From c341c7f7d52cdcdbab6f3273d1a7023754e3c188 Mon Sep 17 00:00:00 2001
From: Kartavya Vashishtha <sendtokartavya@gmail.com>
Date: Fri, 22 Jul 2022 00:08:11 +0530
Subject: [PATCH] subscriber: mark builders as must_use (#2239)

## Motivation

Builders not marked `#[must_use]` can not be initialized sometimes, causing silent failures.
Eg.
```rust
fn main() {
    tracing_subscriber::fmt();
    tracing::info!("hello");
}
```
won't print anything.

## Solution

Added `#[must_use]` to builder types in the tracing-subscriber crate.
---
 tracing-subscriber/src/filter/env/builder.rs | 1 +
 tracing-subscriber/src/fmt/mod.rs            | 1 +
 2 files changed, 2 insertions(+)

diff --git a/tracing-subscriber/src/filter/env/builder.rs b/tracing-subscriber/src/filter/env/builder.rs
index 36b5205431..7bc65484ea 100644
--- a/tracing-subscriber/src/filter/env/builder.rs
+++ b/tracing-subscriber/src/filter/env/builder.rs
@@ -11,6 +11,7 @@ use tracing::level_filters::STATIC_MAX_LEVEL;
 ///
 /// [builder]: https://rust-unofficial.github.io/patterns/patterns/creational/builder.html
 #[derive(Debug, Clone)]
+#[must_use]
 pub struct Builder {
     regex: bool,
     env: Option<String>,
diff --git a/tracing-subscriber/src/fmt/mod.rs b/tracing-subscriber/src/fmt/mod.rs
index d7abce1635..f34ff691cd 100644
--- a/tracing-subscriber/src/fmt/mod.rs
+++ b/tracing-subscriber/src/fmt/mod.rs
@@ -240,6 +240,7 @@ pub type Formatter<N = format::DefaultFields, E = format::Format, W = fn() -> io
 /// Configures and constructs `Collector`s.
 #[derive(Debug)]
 #[cfg_attr(docsrs, doc(cfg(all(feature = "fmt", feature = "std"))))]
+#[must_use]
 pub struct CollectorBuilder<
     N = format::DefaultFields,
     E = format::Format,