From a362ee86290bc27095efa67703def3e05312709f Mon Sep 17 00:00:00 2001
From: Hiroshi Shinaoka <h.shinaoka@gmail.com>
Date: Fri, 20 Mar 2026 07:57:35 +0900
Subject: [PATCH] Re-export chainrules-core from chainrules and add Neg bound
 to ScalarAd

Downstream crates can now depend on `chainrules` alone to get core
traits (Differentiable, ReverseRule, ForwardRule, etc.). Adding `Neg`
to `ScalarAd` removes the `neg_one()` helper and `from_i32(-1) *`
workarounds, making negation idiomatic (`-x` instead of `-1 * x`).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 crates/chainrules/src/binary.rs     |  6 +++---
 crates/chainrules/src/lib.rs        |  5 +++++
 crates/chainrules/src/scalar_ad.rs  | 10 ++++++++--
 crates/chainrules/src/unary/mod.rs  |  4 ----
 crates/chainrules/src/unary/trig.rs | 10 +++++-----
 5 files changed, 21 insertions(+), 14 deletions(-)

diff --git a/crates/chainrules/src/binary.rs b/crates/chainrules/src/binary.rs
index 3c1756c..9d21d4c 100644
--- a/crates/chainrules/src/binary.rs
+++ b/crates/chainrules/src/binary.rs
@@ -91,7 +91,7 @@ pub fn sub_frule<S: ScalarAd>(x: S, y: S, dx: S, dy: S) -> (S, S) {
 /// assert_eq!(dy, -2.0_f64);
 /// ```
 pub fn sub_rrule<S: ScalarAd>(cotangent: S) -> (S, S) {
-    (cotangent, S::from_i32(-1) * cotangent)
+    (cotangent, -cotangent)
 }
 
 /// Primal `mul`.
@@ -176,7 +176,7 @@ pub fn div_frule<S: ScalarAd>(x: S, y: S, dx: S, dy: S) -> (S, S) {
     let primal = x / y;
     let inv_y = S::from_i32(1) / y;
     let dfdx = inv_y.conj();
-    let dfdy = (S::from_i32(-1) * x * inv_y * inv_y).conj();
+    let dfdy = (-(x * inv_y * inv_y)).conj();
     let tangent = dx * dfdx + dy * dfdy;
     (primal, tangent)
 }
@@ -200,6 +200,6 @@ pub fn div_frule<S: ScalarAd>(x: S, y: S, dx: S, dy: S) -> (S, S) {
 pub fn div_rrule<S: ScalarAd>(x: S, y: S, cotangent: S) -> (S, S) {
     let inv_y = S::from_i32(1) / y;
     let dfdx = inv_y.conj();
-    let dfdy = (S::from_i32(-1) * x * inv_y * inv_y).conj();
+    let dfdy = (-(x * inv_y * inv_y)).conj();
     (cotangent * dfdx, cotangent * dfdy)
 }
diff --git a/crates/chainrules/src/lib.rs b/crates/chainrules/src/lib.rs
index 9cb3863..9fb6fa8 100644
--- a/crates/chainrules/src/lib.rs
+++ b/crates/chainrules/src/lib.rs
@@ -34,6 +34,11 @@
 //! assert_eq!(dx, 12.0);
 //! ```
 
+pub use chainrules_core::{
+    AdResult, AutodiffError, Differentiable, ForwardRule, NodeId, PullbackEntry,
+    PullbackWithTangentsEntry, ReverseRule, SavePolicy,
+};
+
 mod binary;
 mod power;
 mod real_ops;
diff --git a/crates/chainrules/src/scalar_ad.rs b/crates/chainrules/src/scalar_ad.rs
index 1cc5870..7b0a6dd 100644
--- a/crates/chainrules/src/scalar_ad.rs
+++ b/crates/chainrules/src/scalar_ad.rs
@@ -1,4 +1,4 @@
-use core::ops::{Add, Div, Mul, Sub};
+use core::ops::{Add, Div, Mul, Neg, Sub};
 
 use num_complex::{Complex32, Complex64};
 use num_traits::Float;
@@ -16,7 +16,13 @@ use num_traits::Float;
 /// takes_scalar(1.0_f64);
 /// ```
 pub trait ScalarAd:
-    Copy + PartialEq + Add<Output = Self> + Sub<Output = Self> + Mul<Output = Self> + Div<Output = Self>
+    Copy
+    + PartialEq
+    + Neg<Output = Self>
+    + Add<Output = Self>
+    + Sub<Output = Self>
+    + Mul<Output = Self>
+    + Div<Output = Self>
 {
     /// Real exponent type for `powf`.
     type Real: Copy + Float;
diff --git a/crates/chainrules/src/unary/mod.rs b/crates/chainrules/src/unary/mod.rs
index b90eed0..27488f4 100644
--- a/crates/chainrules/src/unary/mod.rs
+++ b/crates/chainrules/src/unary/mod.rs
@@ -9,10 +9,6 @@ fn one<S: ScalarAd>() -> S {
     S::from_i32(1)
 }
 
-fn neg_one<S: ScalarAd>() -> S {
-    S::from_i32(-1)
-}
-
 pub use basic::{conj, conj_frule, conj_rrule, sqrt, sqrt_frule, sqrt_rrule};
 pub use exp_log::{
     exp, exp_frule, exp_rrule, expm1, expm1_frule, expm1_rrule, log, log1p, log1p_frule,
diff --git a/crates/chainrules/src/unary/trig.rs b/crates/chainrules/src/unary/trig.rs
index 4c6a259..e5cdf3c 100644
--- a/crates/chainrules/src/unary/trig.rs
+++ b/crates/chainrules/src/unary/trig.rs
@@ -1,4 +1,4 @@
-use crate::unary::{neg_one, one};
+use crate::unary::one;
 use crate::ScalarAd;
 
 /// Primal `sin`.
@@ -25,12 +25,12 @@ pub fn cos<S: ScalarAd>(x: S) -> S {
 /// Forward rule for `cos`.
 pub fn cos_frule<S: ScalarAd>(x: S, dx: S) -> (S, S) {
     let y = x.cos();
-    (y, dx * (neg_one::<S>() * x.sin()).conj())
+    (y, dx * (-x.sin()).conj())
 }
 
 /// Reverse rule for `cos`.
 pub fn cos_rrule<S: ScalarAd>(x: S, cotangent: S) -> S {
-    cotangent * (neg_one::<S>() * x.sin()).conj()
+    cotangent * (-x.sin()).conj()
 }
 
 fn inverse_sqrt_one_minus_square<S: ScalarAd>(x: S) -> S {
@@ -62,13 +62,13 @@ pub fn acos<S: ScalarAd>(x: S) -> S {
 /// Forward rule for `acos`.
 pub fn acos_frule<S: ScalarAd>(x: S, dx: S) -> (S, S) {
     let y = x.acos();
-    let scale = neg_one::<S>() * inverse_sqrt_one_minus_square(x);
+    let scale = -inverse_sqrt_one_minus_square(x);
     (y, dx * scale.conj())
 }
 
 /// Reverse rule for `acos`.
 pub fn acos_rrule<S: ScalarAd>(x: S, cotangent: S) -> S {
-    cotangent * (neg_one::<S>() * inverse_sqrt_one_minus_square(x)).conj()
+    cotangent * (-inverse_sqrt_one_minus_square(x)).conj()
 }
 
 /// Primal `atan`.