feat: support multiple extend statements in MTKModel

Author: ven-k

docs/src/basics/MTKLanguage.md

@@ -147,9 +147,9 @@ julia> ModelingToolkit.getdefault(model_c1.v)
 2.0
 ```
 
-#### `@extend` begin block
+#### `@extend` statement
 
-Partial systems can be extended in a higher system in two ways:
+One or more partial systems can be extended in a higher system with `@extend` statements. This can be done in two ways:
 
   - `@extend PartialSystem(var1 = value1)`
 
@@ -313,7 +313,8 @@ end
   - `:components`: The list of sub-components in the form of [[name, sub_component_name],...].
   - `:constants`: Dictionary of constants mapped to its metadata.
   - `:defaults`: Dictionary of variables and default values specified in the `@defaults`.
-  - `:extend`: The list of extended unknowns, name given to the base system, and name of the base system.
+  - `:extend`: The list of extended unknowns, parameters and components, name given to the base system, and name of the base system.
+    When multiple extend statements are present, latter two are returned as lists.
   - `:structural_parameters`: Dictionary of structural parameters mapped to their metadata.
   - `:parameters`: Dictionary of symbolic parameters mapped to their metadata. For
     parameter arrays, length is added to the metadata as `:size`.

src/systems/abstractsystem.jl

@@ -918,7 +918,7 @@ Mark a system as completed. A completed system is a system which is done being
 defined/modified and is ready for structural analysis or other transformations.
 This allows for analyses and optimizations to be performed which require knowing
 the global structure of the system.
-        
+
 One property to note is that if a system is complete, the system will no longer
 namespace its subsystems or variables, i.e. `isequal(complete(sys).v.i, v.i)`.
 """
@@ -1933,7 +1933,7 @@ function Base.show(
         end
     end
     limited = nrows < nsubs
-    limited && print(io, "\n  ⋮") # too many to print 
+    limited && print(io, "\n  ⋮") # too many to print
 
     # Print equations
     eqs = equations(sys)
@@ -3043,10 +3043,19 @@ function extend(sys::AbstractSystem, basesys::AbstractSystem;
     return T(args...; kwargs...)
 end
 
+function extend(sys, basesys::Vector{T}) where {T <: AbstractSystem}
+    foldl(extend, basesys, init = sys)
+end
+
 function Base.:(&)(sys::AbstractSystem, basesys::AbstractSystem; kwargs...)
     extend(sys, basesys; kwargs...)
 end
 
+function Base.:(&)(
+        sys::AbstractSystem, basesys::Vector{T}; kwargs...) where {T <: AbstractSystem}
+    extend(sys, basesys; kwargs...)
+end
+
 """
 $(SIGNATURES)
 

src/systems/model_parsing.jl

@@ -50,7 +50,7 @@ function _model_macro(mod, name, expr, isconnector)
         :structural_parameters => Dict{Symbol, Dict}()
     )
     comps = Union{Symbol, Expr}[]
-    ext = Ref{Any}(nothing)
+    ext = []
     eqs = Expr[]
     icon = Ref{Union{String, URI}}()
     ps, sps, vs, = [], [], []
@@ -115,10 +115,10 @@ function _model_macro(mod, name, expr, isconnector)
     sys = :($ODESystem($(flatten_equations)(equations), $iv, variables, parameters;
         name, systems, gui_metadata = $gui_metadata, defaults))
 
-    if ext[] === nothing
+    if length(ext) == 0
         push!(exprs.args, :(var"#___sys___" = $sys))
     else
-        push!(exprs.args, :(var"#___sys___" = $extend($sys, $(ext[]))))
+        push!(exprs.args, :(var"#___sys___" = $extend($sys, [$(ext...)])))
     end
 
     isconnector && push!(exprs.args,
@@ -240,7 +240,7 @@ function unit_handled_variable_value(meta, varname)
 end
 
 # This function parses various variable/parameter definitions.
-# 
+#
 # The comments indicate the syntax matched by a block; either when parsed directly
 # when it is called recursively for parsing a part of an expression.
 # These variable definitions are part of test suite in `test/model_parsing.jl`
@@ -286,7 +286,7 @@ function parse_variable_def!(dict, mod, arg, varclass, kwargs, where_types;
         # `(l2(t)[1:N, 1:M] = 2), [description = "l is more than 1D, with arbitrary length"]`
         # `(l3(t)[1:3] = 3), [description = "l2 is 1D"]`
         # `(l4(t)[1:N] = 4), [description = "l2 is 1D, with arbitrary length"]`
-        # 
+        #
         # Condition 2 parses:
         # `(l5(t)[1:3]::Int = 5), [description = "l3 is 1D and has a type"]`
         # `(l6(t)[1:N]::Int = 6), [description = "l3 is 1D and has a type, with arbitrary length"]`
@@ -373,7 +373,7 @@ function parse_variable_def!(dict, mod, arg, varclass, kwargs, where_types;
         # Condition 1 is recursively called by:
         # `par5[1:3]::BigFloat`
         # `par6(t)[1:3]::BigFloat`
-        # 
+        #
         # Condition 2 parses:
         # `b2(t)[1:2]`
         # `a2[1:2]`
@@ -791,11 +791,17 @@ function _parse_extend!(ext, a, b, dict, expr, kwargs, vars, implicit_arglist)
         end
     end
 
-    ext[] = a
+    push!(ext, a)
     push!(b.args, Expr(:kw, :name, Meta.quot(a)))
     push!(expr.args, :($a = $b))
 
-    dict[:extend] = [Symbol.(vars.args), a, b.args[1]]
+    if !haskey(dict, :extend)
+        dict[:extend] = [Symbol.(vars.args), a, b.args[1]]
+    else
+        push!(dict[:extend][1], Symbol.(vars.args)...)
+        dict[:extend][2] = vcat(dict[:extend][2], a)
+        dict[:extend][3] = vcat(dict[:extend][3], b.args[1])
+    end
 
     push!(expr.args, :(@unpack $vars = $a))
 end

test/model_parsing.jl

@@ -945,6 +945,15 @@ end
     end
 end
 
+@mtkmodel MidModelB begin
+    @parameters begin
+        b
+    end
+    @components begin
+        inmodel_b = InnerModel()
+    end
+end
+
 @mtkmodel OuterModel begin
     @extend MidModel()
     @equations begin
@@ -958,3 +967,15 @@ end
     @named out = OuterModel()
     @test OuterModel.structure[:extend][1] == [:inmodel]
 end
+
+@mtkmodel MultipleExtend begin
+    @extend MidModel()
+    @extend MidModelB()
+end
+
+@testset "Multiple extend statements" begin
+    @named multiple_extend = MultipleExtend()
+    @test collect(nameof.(multiple_extend.systems)) == [:inmodel_b, :inmodel]
+    @test MultipleExtend.structure[:extend][1] == [:inmodel, :b, :inmodel_b]
+    @test tosymbol.(parameters(multiple_extend)) == [:b, :inmodel_b₊p, :inmodel₊p]
+end