refactor: move Connection and connect here instead of Symbolics

Author: AayushSabharwal

src/ModelingToolkit.jl

@@ -72,7 +72,7 @@ using RuntimeGeneratedFunctions: drop_expr
 using Symbolics: degree
 using Symbolics: _parse_vars, value, @derivatives, get_variables,
                  exprs_occur_in, symbolic_linear_solve, build_expr, unwrap, wrap,
-                 VariableSource, getname, variable, Connection, connect,
+                 VariableSource, getname, variable,
                  NAMESPACE_SEPARATOR, set_scalar_metadata, setdefaultval,
                  initial_state, transition, activeState, entry, hasnode,
                  ticksInState, timeInState, fixpoint_sub, fast_substitute,

src/systems/analysis_points.jl

@@ -176,7 +176,7 @@ function renamespace(sys, ap::AnalysisPoint)
 end
 
 # create analysis points via `connect`
-function Symbolics.connect(in, ap::AnalysisPoint, outs...; verbose = true)
+function connect(in, ap::AnalysisPoint, outs...; verbose = true)
     return AnalysisPoint() ~ AnalysisPoint(in, ap.name, collect(outs); verbose)
 end
 
@@ -217,11 +217,11 @@ typically is not (unless the model is an inverse model).
 - `verbose`: Warn if an input is connected to an output (reverse causality). Silence this
   warning if you are analyzing an inverse model.
 """
-function Symbolics.connect(in::AbstractSystem, name::Symbol, out, outs...; verbose = true)
+function connect(in::AbstractSystem, name::Symbol, out, outs...; verbose = true)
     return AnalysisPoint() ~ AnalysisPoint(in, name, [out; collect(outs)]; verbose)
 end
 
-function Symbolics.connect(
+function connect(
         in::ConnectableSymbolicT, name::Symbol, out::ConnectableSymbolicT,
         outs::ConnectableSymbolicT...; verbose = true)
     allvars = (in, out, outs...)

src/systems/connectors.jl

@@ -1,4 +1,48 @@
 using Symbolics: StateMachineOperator
+
+"""
+    $(TYPEDEF)
+
+Struct used to represent a connection equation. A connection equation is an `Equation`
+where the LHS is an empty `Connection(nothing)` and the RHS is a `Connection` containing
+the connected connectors.
+
+For special types of connections, the LHS `Connection` can contain relevant metadata.
+"""
+struct Connection
+    systems::Any
+end
+
+Base.broadcastable(x::Connection) = Ref(x)
+Connection() = Connection(nothing)
+Base.hash(c::Connection, seed::UInt) = hash(c.systems, (0xc80093537bdc1311 % UInt) ⊻ seed)
+Symbolics.hide_lhs(_::Connection) = true
+
+"""
+    $(TYPEDSIGNATURES)
+
+Connect multiple connectors created via `@connector`. All connected connectors
+must be unique.
+"""
+function connect(sys1::AbstractSystem, sys2::AbstractSystem, syss::AbstractSystem...)
+    syss = (sys1, sys2, syss...)
+    length(unique(nameof, syss)) == length(syss) || error("connect takes distinct systems!")
+    Equation(Connection(), Connection(syss)) # the RHS are connected systems
+end
+
+function Base.show(io::IO, c::Connection)
+    print(io, "connect(")
+    if c.systems isa AbstractArray || c.systems isa Tuple
+        n = length(c.systems)
+        for (i, s) in enumerate(c.systems)
+            str = join(split(string(nameof(s)), NAMESPACE_SEPARATOR), '.')
+            print(io, str)
+            i != n && print(io, ", ")
+        end
+    end
+    print(io, ")")
+end
+
 isconnection(_) = false
 isconnection(_::Connection) = true
 """
@@ -188,7 +232,7 @@ var1 ~ var3
 # ...
 ```
 """
-function Symbolics.connect(var1::ConnectableSymbolicT, var2::ConnectableSymbolicT,
+function connect(var1::ConnectableSymbolicT, var2::ConnectableSymbolicT,
         vars::ConnectableSymbolicT...)
     allvars = (var1, var2, vars...)
     validate_causal_variables_connection(allvars)

src/systems/systemstructure.jl

@@ -1,11 +1,11 @@
 using DataStructures
-using Symbolics: linear_expansion, unwrap, Connection
+using Symbolics: linear_expansion, unwrap
 using SymbolicUtils: iscall, operation, arguments, Symbolic
 using SymbolicUtils: quick_cancel, maketerm
 using ..ModelingToolkit
 import ..ModelingToolkit: isdiffeq, var_from_nested_derivative, vars!, flatten,
                           value, InvalidSystemException, isdifferential, _iszero,
-                          isparameter,
+                          isparameter, Connection,
                           independent_variables, SparseMatrixCLIL, AbstractSystem,
                           equations, isirreducible, input_timedomain, TimeDomain,
                           InferredTimeDomain,

src/variables.jl

@@ -102,7 +102,7 @@ potential is equated at a junction.
 For more information, refer to the [Connection semantics](@ref connect_semantics) section
 of the docs.
 
-See also: [`Symbolics.connect`](@ref), [`@connector`](@ref), [`Flow`](@ref),
+See also: [`connect`](@ref), [`@connector`](@ref), [`Flow`](@ref),
 [`Stream`](@ref).
 """
 struct Equality <: AbstractConnectType end # Equality connection
@@ -118,7 +118,7 @@ for current flowing in and out of the function).
 For more information, refer to the [Connection semantics](@ref connect_semantics) section
 of the docs.
 
-See also: [`Symbolics.connect`](@ref), [`@connector`](@ref), [`Equality`](@ref),
+See also: [`connect`](@ref), [`@connector`](@ref), [`Equality`](@ref),
 [`Stream`](@ref).
 """
 struct Flow <: AbstractConnectType end     # sum to 0
@@ -132,7 +132,7 @@ the variable is part of a special stream connector.
 For more information, refer to the [Connection semantics](@ref connect_semantics) section
 of the docs.
 
-See also: [`Symbolics.connect`](@ref), [`@connector`](@ref), [`Equality`](@ref),
+See also: [`connect`](@ref), [`@connector`](@ref), [`Equality`](@ref),
 [`Flow`](@ref).
 """
 struct Stream <: AbstractConnectType end   # special stream connector