Add @description to @mtkmodel

Author: hersle

docs/src/basics/MTKLanguage.md

@@ -23,6 +23,7 @@ equations.
 
 `@mtkmodel` definition contains begin blocks of
 
+  - `@description`: for describing the whole system with a human-readable string
   - `@components`: for listing sub-components of the system
   - `@constants`: for declaring constants
   - `@defaults`: for passing `defaults` to ODESystem
@@ -42,20 +43,23 @@ using ModelingToolkit
 using ModelingToolkit: t
 
 @mtkmodel ModelA begin
+    @description "A component with parameters `k` and `k_array`."
     @parameters begin
         k
         k_array[1:2]
     end
 end
 
 @mtkmodel ModelB begin
+    @description "A component with parameters `p1` and `p2`."
     @parameters begin
         p1 = 1.0, [description = "Parameter of ModelB"]
         p2 = 1.0, [description = "Parameter of ModelB"]
     end
 end
 
 @mtkmodel ModelC begin
+    @description "A bigger system that contains many more things."
     @icon "https://github.com/SciML/SciMLDocs/blob/main/docs/src/assets/logo.png"
     @constants begin
         c::Int = 1, [description = "Example constant."]
@@ -91,6 +95,10 @@ end
 end
 ```
 
+#### `@description`
+
+A documenting `String` that summarizes and explains what the model is.
+
 #### `@icon`
 
 An icon can be embedded in 3 ways:

docs/src/tutorials/acausal_components.md

@@ -84,6 +84,7 @@ end
 end
 
 @mtkmodel RCModel begin
+    @description "A circuit with a constant voltage source, resistor and capacitor connected in series."
     @components begin
         resistor = Resistor(R = 1.0)
         capacitor = Capacitor(C = 1.0)
@@ -251,6 +252,7 @@ make all of our parameter values 1.0. As `resistor`, `capacitor`, `source` lists
 
 ```@example acausal
 @mtkmodel RCModel begin
+    @description "A circuit with a constant voltage source, resistor and capacitor connected in series."
     @components begin
         resistor = Resistor(R = 1.0)
         capacitor = Capacitor(C = 1.0)

src/systems/model_parsing.jl

@@ -109,11 +109,13 @@ function _model_macro(mod, name, expr, isconnector)
     gui_metadata = isassigned(icon) > 0 ? GUIMetadata(GlobalRef(mod, name), icon[]) :
                    GUIMetadata(GlobalRef(mod, name))
 
+    description = get(dict, :description, "")
+
     @inline pop_structure_dict!.(
         Ref(dict), [:constants, :defaults, :kwargs, :structural_parameters])
 
     sys = :($ODESystem($(flatten_equations)(equations), $iv, variables, parameters;
-        name, systems, gui_metadata = $gui_metadata, defaults))
+        name, description = $description, systems, gui_metadata = $gui_metadata, defaults))
 
     if length(ext) == 0
         push!(exprs.args, :(var"#___sys___" = $sys))
@@ -598,7 +600,9 @@ function parse_model!(exprs, comps, ext, eqs, icon, vs, ps, sps, c_evts, d_evts,
         dict, mod, arg, kwargs, where_types)
     mname = arg.args[1]
     body = arg.args[end]
-    if mname == Symbol("@components")
+    if mname == Symbol("@description")
+        parse_description!(body, dict)
+    elseif mname == Symbol("@components")
         parse_components!(exprs, comps, dict, body, kwargs)
     elseif mname == Symbol("@extend")
         parse_extend!(exprs, ext, dict, mod, body, kwargs)
@@ -1156,6 +1160,14 @@ function parse_icon!(body::Symbol, dict, icon, mod)
     parse_icon!(getfield(mod, body), dict, icon, mod)
 end
 
+function parse_description!(body, dict)
+    if body isa String
+        dict[:description] = body
+    else
+        error("Invalid description string $body")
+    end
+end
+
 ### Parsing Components:
 
 function component_args!(a, b, varexpr, kwargs; index_name = nothing)

test/model_parsing.jl

@@ -127,6 +127,7 @@ end
 end
 
 @mtkmodel RC begin
+    @description "An RC circuit."
     @structural_parameters begin
         R_val = 10u"Ω"
         C_val = 10u"F"
@@ -139,7 +140,6 @@ end
         constant = Constant(; k = k_val)
         ground = MyMockModule.Ground()
     end
-
     @equations begin
         connect(constant.output, source.V)
         connect(source.p, resistor.p)
@@ -157,6 +157,7 @@ sol = solve(prob)
 defs = ModelingToolkit.defaults(rc)
 @test sol[rc.capacitor.v, end] ≈ defs[rc.constant.k]
 resistor = getproperty(rc, :resistor; namespace = false)
+@test ModelingToolkit.description(rc) == "An RC circuit."
 @test getname(rc.resistor) === getname(resistor)
 @test getname(rc.resistor.R) === getname(resistor.R)
 @test getname(rc.resistor.v) === getname(resistor.v)