Add ExpectInto numerological conversion trait. (#357)

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/utils/math.rs

@@ -1,3 +1,4 @@
+mod expect_into;
 mod expected;
 mod tried;
 
@@ -5,7 +6,7 @@ use std::convert::TryFrom;
 
 pub use checked_ops::checked_ops;
 
-pub use self::{expected::Expected, tried::Tried};
+pub use self::{expect_into::ExpectInto, expected::Expected, tried::Tried};
 use crate::{Err, Error, Result, debug::type_name, err};
 
 /// Checked arithmetic expression. Returns a Result<R, Error::Arithmetic>
@@ -100,6 +101,11 @@ pub fn ruma_from_usize(val: usize) -> ruma::UInt {
 #[expect(clippy::as_conversions, clippy::cast_possible_truncation)]
 pub fn usize_from_u64_truncated(val: u64) -> usize { val as usize }
 
+#[inline]
+pub fn expect_into<Dst: TryFrom<Src>, Src>(src: Src) -> Dst {
+	try_into(src).expect("failed conversion from Src to Dst")
+}
+
 #[inline]
 pub fn try_into<Dst: TryFrom<Src>, Src>(src: Src) -> Result<Dst> {
 	Dst::try_from(src).map_err(|_| {

src/core/utils/math/expect_into.rs

@@ -0,0 +1,12 @@
+pub trait ExpectInto {
+	#[inline]
+	#[must_use]
+	fn expect_into<Dst: TryFrom<Self>>(self) -> Dst
+	where
+		Self: Sized,
+	{
+		super::expect_into::<Dst, Self>(self)
+	}
+}
+
+impl<T> ExpectInto for T {}

src/core/utils/sys/limits.rs

@@ -2,7 +2,7 @@
 use nix::sys::resource::{Resource, getrlimit};
 use nix::unistd::{SysconfVar, sysconf};
 
-use crate::{Result, apply, debug, utils::math::usize_from_u64_truncated};
+use crate::{Result, apply, debug, utils::math::ExpectInto};
 
 #[cfg(unix)]
 /// This is needed for opening lots of file descriptors, which tends to
@@ -55,7 +55,7 @@ pub fn maximize_thread_limit() -> Result { Ok(()) }
 #[inline]
 pub fn max_file_descriptors() -> Result<(usize, usize)> {
 	getrlimit(Resource::RLIMIT_NOFILE)
-		.map(apply!(2, usize_from_u64_truncated))
+		.map(apply!(2, ExpectInto::expect_into))
 		.map_err(Into::into)
 }
 
@@ -67,7 +67,7 @@ pub fn max_file_descriptors() -> Result<(usize, usize)> { Ok((usize::MAX, usize:
 #[inline]
 pub fn max_stack_size() -> Result<(usize, usize)> {
 	getrlimit(Resource::RLIMIT_STACK)
-		.map(apply!(2, usize_from_u64_truncated))
+		.map(apply!(2, ExpectInto::expect_into))
 		.map_err(Into::into)
 }
 
@@ -79,7 +79,7 @@ pub fn max_stack_size() -> Result<(usize, usize)> { Ok((usize::MAX, usize::MAX))
 #[inline]
 pub fn max_memory_locked() -> Result<(usize, usize)> {
 	getrlimit(Resource::RLIMIT_MEMLOCK)
-		.map(apply!(2, usize_from_u64_truncated))
+		.map(apply!(2, ExpectInto::expect_into))
 		.map_err(Into::into)
 }
 
@@ -96,7 +96,7 @@ pub fn max_memory_locked() -> Result<(usize, usize)> { Ok((usize::MIN, usize::MI
 #[inline]
 pub fn max_threads() -> Result<(usize, usize)> {
 	getrlimit(Resource::RLIMIT_NPROC)
-		.map(apply!(2, usize_from_u64_truncated))
+		.map(apply!(2, ExpectInto::expect_into))
 		.map_err(Into::into)
 }