Add SolutionLimit attribute

docs/src/manual/models.md

@@ -101,3 +101,4 @@ The following attributes are available:
  * [`SolveTimeSec`](@ref)
  * [`TimeLimitSec`](@ref)
  * [`ObjectiveLimit`](@ref)
+ * [`SolutionLimit`](@ref)

docs/src/reference/models.md

@@ -78,6 +78,7 @@ SolverVersion
 Silent
 TimeLimitSec
 ObjectiveLimit
+SolutionLimit
 RawOptimizerAttribute
 NumberOfThreads
 RawSolver

docs/src/tutorials/implementing.md

@@ -334,6 +334,7 @@ method for each attribute.
 | [`Silent`](@ref)       | Yes           | Yes           | Yes                |
 | [`TimeLimitSec`](@ref) | Yes           | Yes           | Yes                |
 | [`ObjectiveLimit`](@ref) | Yes         | Yes           | Yes                |
+| [`SolutionLimit`](@ref) | Yes          | Yes           | Yes                |
 | [`RawOptimizerAttribute`](@ref) | Yes  | Yes           | Yes                |
 | [`NumberOfThreads`](@ref) | Yes        | Yes           | Yes                |
 | [`AbsoluteGapTolerance`](@ref) | Yes   | Yes           | Yes                |

src/Test/test_attribute.jl

@@ -216,6 +216,32 @@ function setup_test(
     return
 end
 
+function test_attribute_SolutionLimit(model::MOI.AbstractOptimizer, ::Config)
+    @requires MOI.supports(model, MOI.SolutionLimit())
+    # Get the current value to restore it at the end of the test
+    value = MOI.get(model, MOI.SolutionLimit())
+    MOI.set(model, MOI.SolutionLimit(), 3)
+    @test MOI.get(model, MOI.SolutionLimit()) == 3
+    MOI.set(model, MOI.SolutionLimit(), nothing)
+    @test MOI.get(model, MOI.SolutionLimit()) === nothing
+    MOI.set(model, MOI.SolutionLimit(), 1)
+    @test MOI.get(model, MOI.SolutionLimit()) == 1
+    MOI.set(model, MOI.SolutionLimit(), value)
+    _test_attribute_value_type(model, MOI.SolutionLimit())
+    return
+end
+
+test_attribute_SolutionLimit(::MOI.ModelLike, ::Config) = nothing
+
+function setup_test(
+    ::typeof(test_attribute_SolutionLimit),
+    model::MOIU.MockOptimizer,
+    ::Config,
+)
+    MOI.set(model, MOI.SolutionLimit(), nothing)
+    return
+end
+
 """
     test_attribute_AbsoluteGapTolerance(model::MOI.AbstractOptimizer, config::Config)
 

src/attributes.jl

@@ -867,6 +867,35 @@ the [`TerminationStatus`](@ref) should be `OBJECTIVE_LIMIT`.
 """
 struct ObjectiveLimit <: AbstractOptimizerAttribute end
 
+"""
+    SolutionLimit()
+
+An optimizer attribute for setting a limit on the number of available feasible
+solutions.
+
+## Default values
+
+The provided limit must be a `Union{Nothing,Int}`.
+
+When `set` to `nothing`, the limit reverts to the solver's default.
+
+The default value is `nothing`.
+
+## Termination criteria
+
+The solver may stop when the [`ResultCount`](@ref) is larger than or equal to
+the `SolutionLimit`. If stopped because of this attribute, the
+[`TerminationStatus`](@ref) must be `SOLUTION_LIMIT`.
+
+## Solution quality
+
+The quality of the available solutions is solver-dependent. The set of resulting
+solutions is not guaranteed to contain an optimal solution.
+"""
+struct SolutionLimit <: AbstractOptimizerAttribute end
+
+attribute_value_type(::SolutionLimit) = Union{Nothing,Int}
+
 """
     RawOptimizerAttribute(name::String)