bazel: Treat Rust warnings as errors

Additionally fix outstanding warnings.

Bug: https://pwbug.dev/329685244
Change-Id: I506d643374552a12f0224dbdb8c779b5d9d03af4
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/196436
Reviewed-by: Ted Pudlik <tpudlik@google.com>
Commit-Queue: Erik Gilling <konkers@google.com>

Author: konkers

pw_format/rust/pw_format_test_macros_test.rs

@@ -42,7 +42,6 @@ pub enum PrintfTestGeneratorOps {
 
 #[cfg(test)]
 mod tests {
-    use pw_format::macros::IntegerDisplayType;
     use pw_format_test_macros::{
         char_sub_core_fmt_generator_test_macro, char_sub_printf_generator_test_macro,
         core_fmt_generator_test_macro, generator_test_macro,

pw_stream/rust/pw_stream/lib.rs

@@ -182,8 +182,6 @@ pub(crate) mod test_utils {
 mod tests {
     use core::cmp::min;
 
-    use pw_status::Error;
-
     use super::test_utils::*;
     use super::*;
 

pw_toolchain/rust/defs.bzl

@@ -65,7 +65,7 @@ EXTRA_TARGETS = [
 CHANNELS = [
     {
         "name": "nightly",
-        "extra_rustc_flags": [],
+        "extra_rustc_flags": ["-Dwarnings"],
         "target_settings": ["@rules_rust//rust/toolchain/channel:nightly"],
     },
     {
@@ -74,7 +74,7 @@ CHANNELS = [
         # disable experimental features with the exception of `proc_macro_span`
         # because the `proc-marcro2` automatically detects the toolchain
         # as nightly and dynamically uses this feature.
-        "extra_rustc_flags": ["-Zallow-features=proc_macro_span"],
+        "extra_rustc_flags": ["-Dwarnings", "-Zallow-features=proc_macro_span"],
         "target_settings": ["@rules_rust//rust/toolchain/channel:stable"],
     },
 ]