Add FunctionProperties extension: look through SciMLFunction wrappers#1413
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ChrisRackauckas merged 1 commit intoJun 30, 2026
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`hasbranching` (FunctionProperties.jl) is used by SciMLSensitivity to decide
whether a ReverseDiff tape can be compiled for an ODE right-hand side. It is
called on `unwrapped_f(prob.f)`, i.e. an `AbstractSciMLFunction`, and analyzes
whatever callable it is handed.
Handed the SciMLFunction functor, it scans dispatch plumbing rather than the
user's RHS: the operator-selection branch (`if f.f isa AbstractSciMLOperator`)
and, for an MTK-compiled RHS, splat forwarding into a generated function. The
result is that even a branch-free linear RHS reports `true`, and (without the
companion FunctionProperties changes) genuine branches behind the forwarder are
missed.
This weakdep extension defines
FunctionProperties.hasbranching(f::AbstractSciMLFunction, args...) =
FunctionProperties.hasbranching(f.f, args...)
so the analysis targets the wrapped RHS `f.f`. Loaded only when both packages
are present; no new hard dependency.
Stacked on SciML/FunctionProperties.jl#62 (the value-independent-branch
detection that the unwrapped analysis relies on); compat set to that release.
Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
ChrisRackauckas-Claude
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Summary
hasbranching(FunctionProperties.jl) is how SciMLSensitivity decides whether a ReverseDiff tape can be compiled for an ODE RHS (concrete_solve.jl). It is called onunwrapped_f(prob.f)— anAbstractSciMLFunction— and analyzes whatever callable it is handed.Handed the SciMLFunction functor, it scans dispatch plumbing instead of the user's RHS:
if f.f isa AbstractSciMLOperator(a compile-time-constantisa), andRuntimeGeneratedFunction.The consequence is that even a branch-free linear RHS
ẋ = x − a·xreportshasbranching = true, needlessly disabling ReverseDiff compilation; and a genuine branch (a registeredrelu) behind the forwarder is missed.Change
A weakdep extension that looks through the wrapper to the wrapped RHS:
Loaded only when both packages are present — no new hard dependency on SciMLBase. Follows the existing
ext/SciMLBase*Ext.jlpattern.Tests
test/function_properties_ext.jl(registered in thecoregroup): confirms the method is defined and that a branch-free vs. branchyODEFunctionare scored correctly through the unwrap. Verified locally (3/3) by dev'ing this branch + FunctionProperties#62 into a fresh env — the extension precompiles and dispatches. Runic clean.Stack
Companion to SciML/FunctionProperties.jl#62, which fixes the underlying analysis (compile-time-constant branches ignored, splat forwarders followed, and constant-decided branches — e.g. split-mode
MTKParametersindexing — refuted via constant-propagation-aware inference). With #62 in place this unwrap makes the full MTK RHS table correct through theODEFunctionwith no container-specific overrides. Compat is therefore pinned toFunctionProperties = "0.1.7".Semver
Additive weakdep extension, non-breaking:
3.30.0→3.30.1.