[BradyPlanden]

Description

Function.create_copy(perform_simplifications=False) built a generic pybamm.Function instead of a copy of the original class. ParameterValues takes this path for every function in a parameter set loaded with Serialise.load_parameters, since it rebuilds the tree with simplify=False (#5779). After processing, pybamm.exp, pybamm.tanh and the other specific functions were generic Function nodes, and a copied Arcsinh2 could not be evaluated.

create_copy always goes through _function_new_copy(children, perform_simplifications), which gains the flag on Function, SpecificFunction and RegPower. With the flag off, a copy keeps its class, RegPower.delta and Arcsinh2.eps. Arcsinh2 is never simplified, so it ignores the flag.

_function_new_copy is private, but a subclass outside PyBaMM that overrides it with the old one-argument signature raises TypeError on every copy. A Function subclass with no override still copies as a generic pybamm.Function, as on main.

This is the base of the Rust execution engine stack (#5732). The lowering in #5959 dispatches on a function's class and rejects a generic Function, so without this fix a reloaded parameter set cannot be solved once #5966 makes "rust" the default. It uses nothing else from the stack and can merge on its own.

Type of change

Bug fix, under ## Bug fixes in CHANGELOG.md.

Key checklist

• No style issues: pre-commit run
• Unit tests pass (N)
• Tests added: a copy of Exp, Tanh, Arcsinh2 and RegPower keeps its class, its replaced child and delta, with and without simplification, and a copied Arcsinh2 evaluates as the original; a saved and reloaded Marquis2019 parameter set keeps Exp in a processed SPM, with no generic Function left

Rust execution engine stack: proposal #5667, showcase #5732

Each PR is one commit on the one above it.

#	PR	Adds
0	#5954	Function.create_copy keeps the function's class ← this PR
0b	#5955	CasADi's RegPower and uniform-grid interpolant lookups match evaluate
1	#5956	pybamm-core: expression graph, typed IR, interpreters, forward-mode AD
2	#5957	pybamm-core: CompiledModel, coloured Jacobians, the C ABI
3	#5958	pybamm.rust bindings, built into the pybamm wheel
4	#5959	Symbol.to_rust
5	#5960	convert_to_format = "rust" for ScipySolver, AlgebraicSolver and EIS
6	#5961	pybammsolvers: IDAKLU over the C ABI
7	#5962	IDAKLUSolver on rust models
8	#5963	variables and sensitivities read in Rust
9	#5964	pybamm-core: diffsol DAE solver
10	#5965	pybamm.DiffsolSolver
11	#5966	"rust" as the default convert_to_format

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.25%. Comparing base (e50fd5c) to head (743663a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5954   +/-   ##
=======================================
  Coverage   98.25%   98.25%           
=======================================
  Files         350      350           
  Lines       36102    36109    +7     
=======================================
+ Hits        35471    35478    +7     
  Misses        631      631           

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[github-actions]

Bencher Report

Project	PyBaMM
Branch	stack/00-function-copy-fix
Testbed	bare-metal

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