Add label metadata to symbolic variables

docs/src/basics/Variable_metadata.md

@@ -39,6 +39,14 @@ help?> u
   Symbolics.VariableSource: (:variables, :u)
 ```
 
+## Label
+
+Label is descriptive name of a symbolic variable. It can be defined as:
+
+```@example metadata
+@parameters R [label = "Resistance"]
+```
+
 ## Connect
 
 Variables in connectors can have `connect` metadata which describes the type of connections.

src/ModelingToolkit.jl

@@ -206,7 +206,7 @@ export @component, @mtkmodel, @mtkbuild
 export isinput, isoutput, getbounds, hasbounds, getguess, hasguess, isdisturbance,
     istunable, getdist, hasdist,
     tunable_parameters, isirreducible, getdescription, hasdescription, isbinaryvar,
-    isintegervar
+    isintegervar, getlabel, haslabel
 export ode_order_lowering, dae_order_lowering, liouville_transform
 export PDESystem
 export Differential, expand_derivatives, @derivatives

src/systems/model_parsing.jl

@@ -110,6 +110,7 @@ function parse_variable_def!(dict, mod, arg, varclass, kwargs;
         def = nothing, indices::Union{Vector{UnitRange{Int}}, Nothing} = nothing)
     metatypes = [(:connection_type, VariableConnectType),
         (:description, VariableDescription),
+        (:label, VariableLabel),
         (:unit, VariableUnit),
         (:bounds, VariableBounds),
         (:noise, VariableNoiseType),

src/variables.jl

@@ -372,6 +372,25 @@
     getdescription(x) != ""
 end
 
+## Label =================================================================
+struct VariableLabel end
+Symbolics.option_to_metadata_type(::Val{:label}) = VariableLabel
+
+getlabel(x::Num) = getlabel(Symbolics.unwrap(x))
+
+"""
+    getlabel(x)
+
+Return labels attached to variables `x`. If no label is attached, an empty string is returned.
+"""
+function getlabel(x)
+    p = Symbolics.getparent(x, nothing)
+    p === nothing || (x = p)
+    Symbolics.getmetadata(x, VariableLabel, "")
+end
+
+haslabel(x) = (getlabel(x) != "")
+
 ## binary variables =================================================================
 struct VariableBinary end
 Symbolics.option_to_metadata_type(::Val{:binary}) = VariableBinary

test/model_parsing.jl

@@ -274,13 +274,15 @@ end
 @testset "Metadata in variables" begin
     metadata = Dict(:description => "Variable to test metadata in the Model.structure",
         :input => true, :bounds => (-1, 1), :connection_type => :Flow, :integer => true,
-        :binary => false, :tunable => false, :disturbance => true, :dist => Normal(1, 1))
+        :binary => false, :tunable => false, :disturbance => true, :dist => Normal(1, 1),
+        :label => "MockVariable")
 
     @connector MockMeta begin
         m(t),
         [description = "Variable to test metadata in the Model.structure",
-            input = true, bounds = (-1, 1), connect = Flow, integer = true,
-            binary = false, tunable = false, disturbance = true, dist = Normal(1, 1)]
+            label = "MockVariable", input = true, bounds = (-1, 1), connect = Flow,
+            integer = true, binary = false, tunable = false, disturbance = true,
+            dist = Normal(1, 1)]
     end
 
     for (k, v) in metadata

test/test_variable_metadata.jl

@@ -84,6 +84,15 @@ sp = Set(p)
 @test getdescription(u) == ""
 @test !hasdescription(u)
 
+## Labels
+@variables l [label = "Label"]
+@test getlabel(l) == "Label"
+@test haslabel(l)
+
+@variables l
+@test getlabel(l) == ""
+@test !haslabel(l)
+
 @parameters t
 @variables u(t) [description = "A short description of u"]
 @parameters p [description = "A description of p"]