From b2f3df2902fd79cae7311a29d7b1999b18b22542 Mon Sep 17 00:00:00 2001
From: Joe Richey <joerichey@google.com>
Date: Mon, 29 Apr 2024 12:39:15 -0700
Subject: [PATCH 1/2] Add #[track_caller] to methods which panic

This makes it easier to diagnose problems when the preconidtions of
these methods are not met.

Signed-off-by: Joe Richey <joerichey@google.com>
---
 rand_core/src/lib.rs |  1 +
 src/rng.rs           | 27 +++++++++++++++++++--------
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/rand_core/src/lib.rs b/rand_core/src/lib.rs
index 70424e6c9c..6617ea1c80 100644
--- a/rand_core/src/lib.rs
+++ b/rand_core/src/lib.rs
@@ -385,6 +385,7 @@ pub trait SeedableRng: Sized {
     /// [`getrandom`]: https://docs.rs/getrandom
     #[cfg(feature = "getrandom")]
     #[cfg_attr(doc_cfg, doc(cfg(feature = "getrandom")))]
+    #[track_caller]
     fn from_entropy() -> Self {
         let mut seed = Self::Seed::default();
         if let Err(err) = getrandom::getrandom(seed.as_mut()) {
diff --git a/src/rng.rs b/src/rng.rs
index d9927197cc..6c9d4b7eab 100644
--- a/src/rng.rs
+++ b/src/rng.rs
@@ -9,11 +9,11 @@
 
 //! [`Rng`] trait
 
-use rand_core::{Error, RngCore};
 use crate::distributions::uniform::{SampleRange, SampleUniform};
 use crate::distributions::{self, Distribution, Standard};
 use core::num::Wrapping;
 use core::{mem, slice};
+use rand_core::{Error, RngCore};
 
 /// An automatically-implemented extension trait on [`RngCore`] providing high-level
 /// generic methods for sampling values and other convenience methods.
@@ -124,10 +124,11 @@ pub trait Rng: RngCore {
     /// ```
     ///
     /// [`Uniform`]: distributions::uniform::Uniform
+    #[track_caller]
     fn gen_range<T, R>(&mut self, range: R) -> T
     where
         T: SampleUniform,
-        R: SampleRange<T>
+        R: SampleRange<T>,
     {
         assert!(!range.is_empty(), "cannot sample empty range");
         range.sample_single(self).unwrap()
@@ -236,8 +237,9 @@ pub trait Rng: RngCore {
     ///
     /// [`fill_bytes`]: RngCore::fill_bytes
     /// [`try_fill`]: Rng::try_fill
+    #[track_caller]
     fn fill<T: Fill + ?Sized>(&mut self, dest: &mut T) {
-        dest.try_fill(self).unwrap_or_else(|_| panic!("Rng::fill failed"))
+        dest.try_fill(self).expect("Rng::fill failed")
     }
 
     /// Fill any type implementing [`Fill`] with random data
@@ -288,9 +290,12 @@ pub trait Rng: RngCore {
     ///
     /// [`Bernoulli`]: distributions::Bernoulli
     #[inline]
+    #[track_caller]
     fn gen_bool(&mut self, p: f64) -> bool {
-        let d = distributions::Bernoulli::new(p).unwrap();
-        self.sample(d)
+        match distributions::Bernoulli::new(p) {
+            Ok(d) => self.sample(d),
+            Err(_) => panic!("p={:?} is outside range [0.0, 1.0]", p),
+        }
     }
 
     /// Return a bool with a probability of `numerator/denominator` of being
@@ -317,9 +322,15 @@ pub trait Rng: RngCore {
     ///
     /// [`Bernoulli`]: distributions::Bernoulli
     #[inline]
+    #[track_caller]
     fn gen_ratio(&mut self, numerator: u32, denominator: u32) -> bool {
-        let d = distributions::Bernoulli::from_ratio(numerator, denominator).unwrap();
-        self.sample(d)
+        match distributions::Bernoulli::from_ratio(numerator, denominator) {
+            Ok(d) => self.sample(d),
+            Err(_) => panic!(
+                "p={}/{} is outside range [0.0, 1.0]",
+                numerator, denominator
+            ),
+        }
     }
 
     /// Alias for [`Rng::random`].
@@ -432,8 +443,8 @@ where [T]: Fill
 #[cfg(test)]
 mod test {
     use super::*;
-    use crate::test::rng;
     use crate::rngs::mock::StepRng;
+    use crate::test::rng;
     #[cfg(feature = "alloc")] use alloc::boxed::Box;
 
     #[test]

From 10e71184da4cf10a45c340ad60ae7116fccbd200 Mon Sep 17 00:00:00 2001
From: Joe Richey <joerichey@google.com>
Date: Mon, 29 Apr 2024 12:45:16 -0700
Subject: [PATCH 2/2] Update CHANGELOG

Signed-off-by: Joe Richey <joerichey@google.com>
---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 96d9c3eb9a..4499433951 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ You may also find the [Upgrade Guide](https://rust-random.github.io/book/update.
 - Bump the MSRV to 1.61.0
 - Rename `Rng::gen` to `Rng::random` to avoid conflict with the new `gen` keyword in Rust 2024 (#1435)
 - Move all benchmarks to new `benches` crate (#1439)
+- Annotate panicking methods with `#[track_caller]` (#1442)
 
 ## [0.9.0-alpha.1] - 2024-03-18
 - Add the `Slice::num_choices` method to the Slice distribution (#1402)