Add CallbackNodeStatus attribute (#1199)

* Add CallbackNodeStatus attribute

* Add docs and tests

Author: odow

docs/src/apireference.md

@@ -140,10 +140,6 @@ Silent
 TimeLimitSec
 RawParameter
 NumberOfThreads
-AbstractCallback
-LazyConstraintCallback
-HeuristicCallback
-UserCutCallback
 ```
 
 List of attributes useful for optimizers
@@ -168,6 +164,17 @@ PrimalStatus
 DualStatus
 ```
 
+Attributes relating to solver callbacks:
+
+```@docs
+AbstractCallback
+LazyConstraintCallback
+HeuristicCallback
+UserCutCallback
+CallbackNodeStatus
+CallbackNodeStatusCode
+CallbackVariablePrimal
+```
 ### Termination Status
 
 The `TerminationStatus` attribute indicates why the optimizer stopped executing.
@@ -258,7 +265,6 @@ Calls to `get` and `set` should include as an argument a single `VariableIndex`
 VariableName
 VariablePrimalStart
 VariablePrimal
-CallbackVariablePrimal
 ```
 
 ### Constraints

src/attributes.jl

@@ -534,6 +534,41 @@ function Base.showerror(io::IO, err::InvalidCallbackUsage)
     print(io, "InvalidCallbackUsage: Cannot submit $(err.submittable) inside a $(err.callback).")
 end
 
+"""
+    CallbackNodeStatusCode
+
+An Enum of possible return values from calling [`get`](@ref) with
+[`CallbackNodeStatus`](@ref).
+
+Possible values are:
+
+* CALLBACK_NODE_STATUS_INTEGER: the primal solution available from
+  [`CallbackVariablePrimal`](@ref) is integer feasible.
+* CALLBACK_NODE_STATUS_FRACTIONAL: the primal solution available from
+  [`CallbackVariablePrimal`](@ref) is integer infeasible.
+* CALLBACK_NODE_STATUS_UNKNOWN: the primal solution available from
+  [`CallbackVariablePrimal`](@ref) might be integer feasible or infeasible.
+"""
+@enum(
+    CallbackNodeStatusCode,
+    CALLBACK_NODE_STATUS_INTEGER,
+    CALLBACK_NODE_STATUS_FRACTIONAL,
+    CALLBACK_NODE_STATUS_UNKNOWN,
+)
+
+"""
+    CallbackNodeStatus(callback_data)
+
+An optimizer attribute describing the (in)feasibility of the primal solution
+available from [`CallbackVariablePrimal`](@ref) during a callback identified by
+`callback_data`.
+
+Returns a [`CallbackNodeStatusCode`](@ref) Enum.
+"""
+struct CallbackNodeStatus{CallbackDataType} <: AbstractOptimizerAttribute
+    callback_data::CallbackDataType
+end
+is_set_by_optimize(::CallbackNodeStatus) = true
 
 ## Optimizer attributes
 

test/attributes.jl

@@ -3,6 +3,7 @@
         @test MOI.is_set_by_optimize(MOI.TerminationStatus())
         @test !MOI.is_set_by_optimize(MOI.ConstraintSet())
         @test !MOI.is_set_by_optimize(MOI.ObjectiveSense())
+        @test MOI.is_set_by_optimize(MOI.CallbackNodeStatus(1))
     end
     @testset "is_copyable" begin
         @test !MOI.is_copyable(MOI.TerminationStatus())