various: fix clippy warnings

- Adds proper documentation comments with `# Errors` sections for all
  functions returning `Result`
- `cast_precision_loss` on `u64` -> `f64` for disk sizes is acceptable
  since disk sizes won't exceed f64's precision limit in practice.
  Thus, we can suppress those.
- `cast_sign_loss` and `cast_possible_truncation` on the percentage
  calculation is safe since percentages are always 0-100. Once again,
  it's safe to suppress.

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Id4dd7ebc9674407d2be4f38ff4de24bc6a6a6964

src/release.rs

@@ -21,6 +21,11 @@ pub fn get_system_info(utsname: &UtsName) -> String {
   result
 }
 
+/// Gets the pretty name of the OS from `/etc/os-release`.
+///
+/// # Errors
+///
+/// Returns an error if `/etc/os-release` cannot be read.
 #[cfg_attr(feature = "hotpath", hotpath::measure)]
 pub fn get_os_pretty_name() -> Result<String, io::Error> {
   // We use a stack-allocated buffer here, which seems to perform MUCH better

src/system.rs

@@ -49,7 +49,13 @@ pub fn get_shell() -> String {
     .to_owned()
 }
 
+/// Gets the root disk usage information.
+///
+/// # Errors
+///
+/// Returns an error if the filesystem information cannot be retrieved.
 #[cfg_attr(feature = "hotpath", hotpath::measure)]
+#[allow(clippy::cast_precision_loss)]
 pub fn get_root_disk_usage() -> Result<String, io::Error> {
   let vfs = statvfs("/")?;
   let block_size = vfs.block_size() as u64;
@@ -75,6 +81,11 @@ pub fn get_root_disk_usage() -> Result<String, io::Error> {
   Ok(result)
 }
 
+/// Gets the system memory usage information.
+///
+/// # Errors
+///
+/// Returns an error if `/proc/meminfo` cannot be read.
 #[cfg_attr(feature = "hotpath", hotpath::measure)]
 pub fn get_memory_usage() -> Result<String, io::Error> {
   #[cfg_attr(feature = "hotpath", hotpath::measure)]
@@ -109,6 +120,7 @@ pub fn get_memory_usage() -> Result<String, io::Error> {
   }
 
   let (used_memory, total_memory) = parse_memory_info()?;
+  #[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
   let percentage_used = (used_memory / total_memory * 100.0).round() as u64;
 
   let mut result = String::with_capacity(64);

src/uptime.rs

@@ -1,5 +1,10 @@
 use std::{fmt::Write, io, mem::MaybeUninit};
 
+/// Gets the current system uptime.
+///
+/// # Errors
+///
+/// Returns an error if the system uptime cannot be retrieved.
 #[cfg_attr(feature = "hotpath", hotpath::measure)]
 pub fn get_current() -> Result<String, io::Error> {
   let uptime_seconds = {
@@ -7,6 +12,7 @@ pub fn get_current() -> Result<String, io::Error> {
     if unsafe { libc::sysinfo(info.as_mut_ptr()) } != 0 {
       return Err(io::Error::last_os_error());
     }
+    #[allow(clippy::cast_sign_loss)]
     unsafe { info.assume_init().uptime as u64 }
   };