Refactor Unitful.jl usage to use package extensions

This commit moves all Unitful.jl-specific functionality into a ModelingToolkitUnitfulExt
extension to reduce required dependencies and improve loading times.

Major changes:
- Move Unitful from dependencies to weakdeps in Project.toml
- Create ModelingToolkitUnitfulExt extension with all Unitful-specific functionality
- Remove UnitfulUnitCheck module from main codebase, moved to extension
- Update unit checking functions to be extensible
- Remove direct Unitful imports from main module
- Add extensible error handling for dimension errors

The extension provides backward compatibility by recreating the UnitfulUnitCheck
module when Unitful is loaded.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: ChrisRackauckas

Project.toml

@@ -64,7 +64,6 @@ SymbolicUtils = "d1185830-fcd6-423d-90d6-eec64667417b"
 Symbolics = "0c5d862f-8b57-4792-8d23-62f2024744c7"
 URIs = "5c2747f8-b7ea-4ff2-ba2e-563bfd36b1d4"
 UnPack = "3a884ed6-31ef-47d7-9d2a-63182c4928ed"
-Unitful = "1986cc42-f94f-5a68-af5c-568840ba703d"
 
 [weakdeps]
 BifurcationKit = "0f109fa4-8a5d-4b75-95aa-f515264e7665"
@@ -74,6 +73,7 @@ FMI = "14a09403-18e3-468f-ad8a-74f8dda2d9ac"
 InfiniteOpt = "20393b10-9daf-11e9-18c9-8db751c92c57"
 LabelledArrays = "2ee39098-c373-598a-b85f-a56591580800"
 Pyomo = "0e8e1daf-01b5-4eba-a626-3897743a3816"
+Unitful = "1986cc42-f94f-5a68-af5c-568840ba703d"
 
 [extensions]
 MTKBifurcationKitExt = "BifurcationKit"
@@ -83,6 +83,7 @@ MTKFMIExt = "FMI"
 MTKInfiniteOptExt = "InfiniteOpt"
 MTKLabelledArraysExt = "LabelledArrays"
 MTKPyomoDynamicOptExt = "Pyomo"
+ModelingToolkitUnitfulExt = "Unitful"
 
 [compat]
 ADTypes = "1.14.0"
@@ -165,7 +166,6 @@ SymbolicUtils = "3.26.1"
 Symbolics = "6.40"
 URIs = "1"
 UnPack = "0.1, 1.0"
-Unitful = "1.1"
 julia = "1.9"
 
 [extras]

ext/ModelingToolkitUnitfulExt.jl

@@ -0,0 +1,345 @@
+module ModelingToolkitUnitfulExt
+
+__precompile__(false)
+
+using ModelingToolkit
+using Unitful
+using Symbolics: Symbolic, value, issym, isadd, ismul, ispow, arguments, operation, iscall, getmetadata
+using SciMLBase
+using RecursiveArrayTools
+using JumpProcesses: MassActionJump, ConstantRateJump, VariableRateJump
+
+# Import necessary types and functions from ModelingToolkit
+import ModelingToolkit: ValidationError, Connection, instream, JumpType, VariableUnit,
+                        get_systems, Conditional, Comparison, Differential, 
+                        Integral, Num, check_units
+
+const MT = ModelingToolkit
+
+# Method extension for Unitful unit detection
+# This adds a method for the specific case where we have a Unitful unit
+function MT.__get_scalar_unit_type(v)
+    u = MT.__get_literal_unit(v)
+    if u isa MT.DQ.AbstractQuantity
+        return Val(:DynamicQuantities)
+    elseif u isa Unitful.Unitlike
+        return Val(:Unitful)  
+    end
+    return nothing
+end
+
+# Base operations for mixing Symbolic and Unitful
+Base.:*(x::Union{Num, Symbolic}, y::Unitful.AbstractQuantity) = x * y
+Base.:/(x::Union{Num, Symbolic}, y::Unitful.AbstractQuantity) = x / y
+
+"""
+Throw exception on invalid unit types, otherwise return argument.
+"""
+function screen_unit(result)
+    result isa Unitful.Unitlike ||
+        throw(ValidationError("Unit must be a subtype of Unitful.Unitlike, not $(typeof(result))."))
+    result isa Unitful.ScalarUnits ||
+        throw(ValidationError("Non-scalar units such as $result are not supported. Use a scalar unit instead."))
+    result == Unitful.u"°" &&
+        throw(ValidationError("Degrees are not supported. Use radians instead."))
+    result
+end
+
+"""
+Test unit equivalence.
+
+Example of implemented behavior:
+
+```julia
+using ModelingToolkit, Unitful
+MT = ModelingToolkit
+@parameters γ P [unit = u"MW"] E [unit = u"kJ"] τ [unit = u"ms"]
+@test MT.equivalent(u"MW", u"kJ/ms") # Understands prefixes
+@test !MT.equivalent(u"m", u"cm") # Units must be same magnitude
+@test MT.equivalent(MT.get_unit(P^γ), MT.get_unit((E / τ)^γ)) # Handles symbolic exponents
+```
+"""
+equivalent(x, y) = isequal(1 * x, 1 * y)
+const unitless = Unitful.unit(1)
+
+"""
+Find the unit of a symbolic item.
+"""
+get_unit(x::Real) = unitless
+get_unit(x::Unitful.Quantity) = screen_unit(Unitful.unit(x))
+get_unit(x::AbstractArray) = map(get_unit, x)
+get_unit(x::Num) = get_unit(value(x))
+function get_unit(x::Union{Symbolics.ArrayOp, Symbolics.Arr, Symbolics.CallWithMetadata})
+    get_literal_unit(x)
+end
+get_unit(op::Differential, args) = get_unit(args[1]) / get_unit(op.x)
+get_unit(op::typeof(getindex), args) = get_unit(args[1])
+get_unit(x::SciMLBase.NullParameters) = unitless
+get_unit(op::typeof(instream), args) = get_unit(args[1])
+
+get_literal_unit(x) = screen_unit(getmetadata(x, VariableUnit, unitless))
+
+function get_unit(op, args) # Fallback
+    result = op(1 .* get_unit.(args)...)
+    try
+        Unitful.unit(result)
+    catch
+        throw(ValidationError("Unable to get unit for operation $op with arguments $args."))
+    end
+end
+
+function get_unit(op::Integral, args)
+    unit = 1
+    if op.domain.variables isa Vector
+        for u in op.domain.variables
+            unit *= get_unit(u)
+        end
+    else
+        unit *= get_unit(op.domain.variables)
+    end
+    return get_unit(args[1]) * unit
+end
+
+function get_unit(op::Conditional, args)
+    terms = get_unit.(args)
+    terms[1] == unitless ||
+        throw(ValidationError(", in $op, [$(terms[1])] is not dimensionless."))
+    equivalent(terms[2], terms[3]) ||
+        throw(ValidationError(", in $op, units [$(terms[2])] and [$(terms[3])] do not match."))
+    return terms[2]
+end
+
+function get_unit(op::typeof(Symbolics._mapreduce), args)
+    if args[2] == +
+        get_unit(args[3])
+    else
+        throw(ValidationError("Unsupported array operation $op"))
+    end
+end
+
+function get_unit(op::Comparison, args)
+    terms = get_unit.(args)
+    equivalent(terms[1], terms[2]) ||
+        throw(ValidationError(", in comparison $op, units [$(terms[1])] and [$(terms[2])] do not match."))
+    return unitless
+end
+
+function get_unit(x::Symbolic)
+    if issym(x)
+        get_literal_unit(x)
+    elseif isadd(x)
+        terms = get_unit.(arguments(x))
+        firstunit = terms[1]
+        for other in terms[2:end]
+            termlist = join(map(repr, terms), ", ")
+            equivalent(other, firstunit) ||
+                throw(ValidationError(", in sum $x, units [$termlist] do not match."))
+        end
+        return firstunit
+    elseif ispow(x)
+        pargs = arguments(x)
+        base, expon = get_unit.(pargs)
+        @assert expon isa Unitful.DimensionlessUnits
+        if base == unitless
+            unitless
+        else
+            pargs[2] isa Number ? base^pargs[2] : (1 * base)^pargs[2]
+        end
+    elseif iscall(x)
+        op = operation(x)
+        if issym(op) || (iscall(op) && iscall(operation(op))) # Dependent variables, not function calls
+            return screen_unit(getmetadata(x, VariableUnit, unitless)) # Like x(t) or x[i]
+        elseif iscall(op) && !iscall(operation(op))
+            gp = getmetadata(x, Symbolics.GetindexParent, nothing) # Like x[1](t)
+            return screen_unit(getmetadata(gp, VariableUnit, unitless))
+        end  # Actual function calls:
+        args = arguments(x)
+        return get_unit(op, args)
+    else # This function should only be reached by Terms, for which `iscall` is true
+        throw(ArgumentError("Unsupported value $x."))
+    end
+end
+
+"""
+Get unit of term, returning nothing & showing warning instead of throwing errors.
+"""
+function safe_get_unit(term, info)
+    side = nothing
+    try
+        side = get_unit(term)
+    catch err
+        if err isa Unitful.DimensionError
+            @warn("$info: $(err.x) and $(err.y) are not dimensionally compatible.")
+        elseif err isa ValidationError
+            @warn(info*err.message)
+        elseif err isa MethodError
+            @warn("$info: no method matching $(err.f) for arguments $(typeof.(err.args)).")
+        else
+            rethrow()
+        end
+    end
+    side
+end
+
+function _validate(terms::Vector, labels::Vector{String}; info::String = "")
+    valid = true
+    first_unit = nothing
+    first_label = nothing
+    for (term, label) in zip(terms, labels)
+        equnit = safe_get_unit(term, info * label)
+        if equnit === nothing
+            valid = false
+        elseif !isequal(term, 0)
+            if first_unit === nothing
+                first_unit = equnit
+                first_label = label
+            elseif !equivalent(first_unit, equnit)
+                valid = false
+                @warn("$info: units [$(first_unit)] for $(first_label) and [$(equnit)] for $(label) do not match.")
+            end
+        end
+    end
+    valid
+end
+
+function _validate(conn::Connection; info::String = "")
+    valid = true
+    syss = get_systems(conn)
+    sys = first(syss)
+    unks = MT.unknowns(sys)
+    for i in 2:length(syss)
+        s = syss[i]
+        _unks = MT.unknowns(s)
+        if length(unks) != length(_unks)
+            valid = false
+            @warn("$info: connected systems $(MT.nameof(sys)) and $(MT.nameof(s)) have $(length(unks)) and $(length(_unks)) unknowns, cannot connect.")
+            continue
+        end
+        for (i, x) in enumerate(unks)
+            j = findfirst(isequal(x), _unks)
+            if j == nothing
+                valid = false
+                @warn("$info: connected systems $(MT.nameof(sys)) and $(MT.nameof(s)) do not have the same unknowns.")
+            else
+                aunit = safe_get_unit(x, info * string(MT.nameof(sys)) * "#$i")
+                bunit = safe_get_unit(_unks[j], info * string(MT.nameof(s)) * "#$j")
+                if !equivalent(aunit, bunit)
+                    valid = false
+                    @warn("$info: connected system unknowns $x and $(_unks[j]) have mismatched units.")
+                end
+            end
+        end
+    end
+    valid
+end
+
+function validate(jump::Union{VariableRateJump, ConstantRateJump}, t::Symbolic; info::String = "")
+    newinfo = replace(info, "eq." => "jump")
+    _validate([jump.rate, 1 / t], ["rate", "1/t"], info = newinfo) && # Assuming the rate is per time units
+        validate(jump.affect!, info = newinfo)
+end
+
+function validate(jump::MassActionJump, t::Symbolic; info::String = "")
+    left_symbols = [x[1] for x in jump.reactant_stoch] #vector of pairs of symbol,int -> vector symbols
+    net_symbols = [x[1] for x in jump.net_stoch]
+    all_symbols = vcat(left_symbols, net_symbols)
+    allgood = _validate(all_symbols, string.(all_symbols); info)
+    n = sum(x -> x[2], jump.reactant_stoch, init = 0)
+    base_unitful = all_symbols[1] #all same, get first
+    allgood && _validate([jump.scaled_rates, 1 / (t * base_unitful^n)],
+        ["scaled_rates", "1/(t*reactants^$n))"]; info)
+end
+
+function validate(jumps::Vector{JumpType}, t::Symbolic)
+    labels = ["in Mass Action Jumps,", "in Constant Rate Jumps,", "in Variable Rate Jumps,"]
+    majs = filter(x -> x isa MassActionJump, jumps)
+    crjs = filter(x -> x isa ConstantRateJump, jumps)
+    vrjs = filter(x -> x isa VariableRateJump, jumps)
+    splitjumps = [majs, crjs, vrjs]
+    all([validate(js, t; info) for (js, info) in zip(splitjumps, labels)])
+end
+
+function validate(eq::MT.Equation; info::String = "")
+    if typeof(eq.lhs) == Connection
+        _validate(eq.rhs; info)
+    else
+        _validate([eq.lhs, eq.rhs], ["left", "right"]; info)
+    end
+end
+
+function validate(eq::MT.Equation, term::Union{Symbolic, Unitful.Quantity, Num}; info::String = "")
+    _validate([eq.lhs, eq.rhs, term], ["left", "right", "noise"]; info)
+end
+
+function validate(eq::MT.Equation, terms::Vector; info::String = "")
+    _validate(vcat([eq.lhs, eq.rhs], terms),
+        vcat(["left", "right"], "noise  #" .* string.(1:length(terms))); info)
+end
+
+"""
+Returns true iff units of equations are valid.
+"""
+function validate(eqs::Vector; info::String = "")
+    all([validate(eqs[idx], info = info * " in eq. #$idx") for idx in 1:length(eqs)])
+end
+
+function validate(eqs::Vector, noise::Vector; info::String = "")
+    all([validate(eqs[idx], noise[idx], info = info * " in eq. #$idx")
+         for idx in 1:length(eqs)])
+end
+
+function validate(eqs::Vector, noise::Matrix; info::String = "")
+    all([validate(eqs[idx], noise[idx, :], info = info * " in eq. #$idx")
+         for idx in 1:length(eqs)])
+end
+
+function validate(eqs::Vector, term::Symbolic; info::String = "")
+    all([validate(eqs[idx], term, info = info * " in eq. #$idx") for idx in 1:length(eqs)])
+end
+
+validate(term::Symbolic) = safe_get_unit(term, "") !== nothing
+
+"""
+Throws error if units of equations are invalid.
+"""
+function check_units(::Val{:Unitful}, eqs...)
+    validate(eqs...) ||
+        throw(ValidationError("Some equations had invalid units. See warnings for details."))
+end
+
+# Model parsing functions for Unitful
+function convert_units(varunits::Unitful.FreeUnits, value)
+    Unitful.ustrip(varunits, value)
+end
+
+convert_units(::Unitful.FreeUnits, value::MT.NoValue) = MT.NO_VALUE
+
+function convert_units(varunits::Unitful.FreeUnits, value::AbstractArray{T}) where {T}
+    Unitful.ustrip.(varunits, value)
+end
+
+convert_units(::Unitful.FreeUnits, value::Num) = value
+
+# Extend model parsing error handling to include Unitful.DimensionError
+MT._is_dimension_error(e::Unitful.DimensionError) = true
+
+# Define Unitful time variables (moved from main module)
+const t_unitful = let
+    MT.only(MT.@independent_variables t [unit = Unitful.u"s"])
+end
+const D_unitful = MT.Differential(t_unitful)
+
+# Create a UnitfulUnitCheck module for backward compatibility
+module UnitfulUnitCheck
+    using ..ModelingToolkitUnitfulExt
+    # Re-export all functions from the extension for backward compatibility
+    const equivalent = ModelingToolkitUnitfulExt.equivalent
+    const unitless = ModelingToolkitUnitfulExt.unitless
+    const get_unit = ModelingToolkitUnitfulExt.get_unit
+    const get_literal_unit = ModelingToolkitUnitfulExt.get_literal_unit
+    const safe_get_unit = ModelingToolkitUnitfulExt.safe_get_unit
+    const validate = ModelingToolkitUnitfulExt.validate
+    const screen_unit = ModelingToolkitUnitfulExt.screen_unit
+end
+
+end # module