Refine Unitful extension: keep general unit functions in main package

This commit fixes the extension approach to be more surgical:
- Keep all general unit functions (get_unit, validate, etc.) in main package
- Only move Unitful-specific dispatches to extension
- Use proper multiple dispatch with _get_unittype stub function
- Fix method overwriting issues and compilation problems

Key changes:
- src/systems/unit_check.jl: Add _get_unittype extensible function
- ext/ModelingToolkitUnitfulExt.jl: Only Unitful-specific methods
- Remove method overwriting of _is_dimension_error
- Fix __init__ function issues

The extension now properly extends the main package without replacing
core functionality, following Julia extension best practices.

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

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ChrisRackauckas

ext/ModelingToolkitUnitfulExt.jl

@@ -1,345 +1,92 @@
 module ModelingToolkitUnitfulExt
 
-__precompile__(false)
-
 using ModelingToolkit
 using Unitful
-using Symbolics: Symbolic, value, issym, isadd, ismul, ispow, arguments, operation, iscall, getmetadata
+using Symbolics: Symbolic, value
 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
+import ModelingToolkit: ValidationError, _get_unittype, get_unit, screen_unit, 
+                        equivalent, _is_dimension_error, convert_units, 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
+# Add Unitful-specific unit type detection
+function MT._get_unittype(u::Unitful.Unitlike)
+    return Val(:Unitful)
 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
+Base.:*(x::Union{MT.Num, Symbolic}, y::Unitful.AbstractQuantity) = x * y
+Base.:/(x::Union{MT.Num, Symbolic}, y::Unitful.AbstractQuantity) = x / y
+
+# Unitful-specific get_unit method
+function MT.get_unit(x::Unitful.Quantity)
+    return screen_unit(Unitful.unit(x))
+end
 
-"""
-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))."))
+# Unitful-specific screen_unit method
+function MT.screen_unit(result::Unitful.Unitlike)
     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
+    return result
 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]
+# Unitful-specific equivalence check
+function MT.equivalent(x::Unitful.Unitlike, y::Unitful.Unitlike)
+    return isequal(1 * x, 1 * y)
 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
+# Mixed equivalence checks
+MT.equivalent(x::Unitful.Unitlike, y) = isequal(1 * x, y)
+MT.equivalent(x, y::Unitful.Unitlike) = isequal(x, 1 * y)
 
-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
+# The safe_get_unit function stays in the main package and already handles DQ.DimensionError
+# We just need to make sure it can handle Unitful.DimensionError too
+# This will be handled by the main function's MethodError catch
 
-"""
-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
+# Unitful-specific dimension error detection for model parsing
+MT._is_dimension_error(e::Unitful.DimensionError) = true
 
-# Model parsing functions for Unitful
-function convert_units(varunits::Unitful.FreeUnits, value)
+# Unitful-specific convert_units methods for model parsing
+function MT.convert_units(varunits::Unitful.FreeUnits, value)
     Unitful.ustrip(varunits, value)
 end
 
-convert_units(::Unitful.FreeUnits, value::MT.NoValue) = MT.NO_VALUE
+MT.convert_units(::Unitful.FreeUnits, value::MT.NoValue) = MT.NO_VALUE
 
-function convert_units(varunits::Unitful.FreeUnits, value::AbstractArray{T}) where {T}
+function MT.convert_units(varunits::Unitful.FreeUnits, value::AbstractArray{T}) where {T}
     Unitful.ustrip.(varunits, value)
 end
 
-convert_units(::Unitful.FreeUnits, value::Num) = value
+MT.convert_units(::Unitful.FreeUnits, value::MT.Num) = value
 
-# Extend model parsing error handling to include Unitful.DimensionError
-MT._is_dimension_error(e::Unitful.DimensionError) = true
+# Unitful-specific check_units method
+function MT.check_units(::Val{:Unitful}, eqs...)
+    # Use the main package's validate function
+    MT.validate(eqs...) ||
+        throw(ValidationError("Some equations had invalid units. See warnings for details."))
+end
 
 # 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
+# For backward compatibility - provide UnitfulUnitCheck module interface
+# Extensions can access all the main package functions through MT
+const UnitfulUnitCheck = (
+    equivalent = MT.equivalent,
+    unitless = Unitful.unit(1),
+    get_unit = MT.get_unit,
+    get_literal_unit = MT.get_literal_unit,
+    safe_get_unit = MT.safe_get_unit,
+    validate = MT.validate,
+    screen_unit = MT.screen_unit,
+    ValidationError = ValidationError
+)
 
 end # module