fix(core): AD-friendly to_out_of_place buffers + harmonise changelog filenames

CHANGELOGS.md → CHANGELOG.md

@@ -5,6 +5,29 @@ All notable changes to CTBase will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.27.4-beta] - 2026-07-10
+
+### 🐛 Bug Fixes
+
+#### **Core** — `to_out_of_place` produces AD-friendly functors
+
+- **`Core.to_out_of_place` now widens the output buffer element type from the call
+  arguments** instead of always allocating a `Float64` buffer. The buffer type is
+  `promote_type(T, <arguments' element types>)`, so the resulting out-of-place function is
+  differentiable (its buffer can hold `ForwardDiff.Dual` numbers). The `T` keyword still
+  acts as a floor (default `Float64`), so plain numeric calls — including `Int` arguments —
+  keep their previous behaviour.
+- **Why**: functors produced by `to_out_of_place` (e.g. constraint-by-label functors in
+  CTModels) previously threw `MethodError: Float64(::Dual)` when differentiated through
+  (e.g. a path constraint in a constrained CTFlows `:total` flow).
+- **No breaking changes**: purely additive widening; existing behaviour on `Float64`/`Int`
+  arguments is unchanged. See [BREAKING.md](BREAKING.md).
+
+#### **Housekeeping**
+
+- Renamed `CHANGELOGS.md` → `CHANGELOG.md` and `BREAKINGS.md` → `BREAKING.md` to match the
+  singular naming used across the control-toolbox ecosystem (CTModels, CTFlows, CTSolvers).
+
 ## [0.27.3-beta] - 2026-07-09
 
 ### ✨ New Features
@@ -146,7 +169,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### ✅ Compatibility
 
-- **No breaking changes**: purely additive. Existing code unaffected. See [BREAKINGS.md](BREAKINGS.md).
+- **No breaking changes**: purely additive. Existing code unaffected. See [BREAKING.md](BREAKING.md).
 
 ## [0.26.1-beta] - 2026-07-04
 
@@ -202,7 +225,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### ✅ Compatibility
 
-- **No breaking changes**: purely additive. Existing code unaffected. See [BREAKINGS.md](BREAKINGS.md).
+- **No breaking changes**: purely additive. Existing code unaffected. See [BREAKING.md](BREAKING.md).
 
 ## [0.26.0-beta] - 2026-06-28
 
@@ -235,7 +258,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### ✅ Compatibility
 
-- **No breaking changes**: purely additive. Existing predicates and trait families are unchanged. See [BREAKINGS.md](BREAKINGS.md).
+- **No breaking changes**: purely additive. Existing predicates and trait families are unchanged. See [BREAKING.md](BREAKING.md).
 
 ## [0.25.0-beta] - 2026-06-26
 
@@ -963,7 +986,7 @@ ext/
 
 ### 🎯 Breaking Changes
 
-See [BREAKINGS.md](BREAKINGS.md) for detailed migration guide.
+See [BREAKING.md](BREAKING.md) for detailed migration guide.
 
 ### 🙏 Acknowledgments
 

Project.toml

@@ -1,6 +1,6 @@
 name = "CTBase"
 uuid = "54762871-cc72-4466-b8e8-f6c8b58076cd"
-version = "0.27.3-beta"
+version = "0.27.4-beta"
 authors = ["Olivier Cots <olivier.cots@irit.fr>", "Jean-Baptiste Caillau <caillau@univ-cotedazur.fr>"]
 
 [deps]

src/Core/function_utils.jl

@@ -22,9 +22,26 @@ julia> f = to_out_of_place(f!, 2)
 julia> f(π/4)  # returns approximately [0.707, 0.707]
 ```
 """
+# Promote the element type of the numeric arguments (scalars and arrays), so the
+# allocated buffer can hold e.g. ForwardDiff.Dual values during differentiation. Falls
+# back to `Union{}` for non-numeric arguments (e.g. `nothing`), which is neutral under
+# `promote_type`. Combined with the `T` floor below, non-numeric-only calls keep `T`.
+_promote_arg_eltype() = Union{}
+function _promote_arg_eltype(x::Number, rest...)
+    return promote_type(typeof(x), _promote_arg_eltype(rest...))
+end
+function _promote_arg_eltype(x::AbstractArray, rest...)
+    return promote_type(eltype(x), _promote_arg_eltype(rest...))
+end
+_promote_arg_eltype(_, rest...) = _promote_arg_eltype(rest...)
+
 function to_out_of_place(f!, n; T=Float64)
     function f(args...; kwargs...)
-        r = zeros(T, n)
+        # Widen the floor type `T` with the arguments' element types so the buffer can
+        # hold Dual numbers under AD; `promote_type(Float64, Int) == Float64` keeps the
+        # existing behaviour for plain numeric calls.
+        TT = promote_type(T, _promote_arg_eltype(args...))
+        r = zeros(TT, n)
         f!(r, args...; kwargs...)
         return n == 1 ? r[1] : r
     end

test/suite/core/test_function_utils.jl

@@ -2,6 +2,7 @@ module TestCoreFunctionUtils
 
 using Test: Test
 import CTBase.Core
+import ForwardDiff
 
 const VERBOSE = isdefined(Main, :TestData) ? Main.TestData.VERBOSE : true
 const SHOWTIMING = isdefined(Main, :TestData) ? Main.TestData.SHOWTIMING : true
@@ -68,6 +69,26 @@ function test_function_utils()
             Test.@test length(result) == 5
             Test.@test result == [2.0, 4.0, 6.0, 8.0, 10.0]
         end
+
+        # Regression: the allocated buffer widens its element type from the arguments so
+        # the out-of-place function is differentiable (buffer holds ForwardDiff.Dual).
+        Test.@testset "to_out_of_place - AD-friendly buffer (ForwardDiff)" begin
+            p!(r, x) = (r[1]=x[1]^2; r[2]=sin(x[1]); nothing)
+            p = Core.to_out_of_place(p!, 2)
+            J = ForwardDiff.jacobian(p, [1.3])
+            Test.@test J[1, 1] ≈ 2 * 1.3
+            Test.@test J[2, 1] ≈ cos(1.3)
+
+            # scalar (n=1) output differentiable via `derivative`
+            q!(r, x) = (r[1]=x^3; nothing)
+            q = Core.to_out_of_place(q!, 1)
+            Test.@test ForwardDiff.derivative(q, 2.0) ≈ 3 * 2.0^2
+
+            # the `T` floor is preserved: Int args keep the Float64 buffer (no narrowing)
+            s!(r, x) = (r[1]=x / 2; nothing)
+            s = Core.to_out_of_place(s!, 1)
+            Test.@test s(3) ≈ 1.5
+        end
     end
     return nothing
 end