Ignore SlackBridgePrimalDualStart for non-Slack bridge (#2365)

Author: blegat

src/Bridges/Objective/bridges/slack.jl

@@ -199,6 +199,15 @@ end
 # Pretend that every model supports, and silently skip in set if unsupported
 MOI.supports_fallback(::MOI.ModelLike, ::SlackBridgePrimalDualStart) = true
 
+function MOI.throw_set_error_fallback(
+    ::MOI.ModelLike,
+    ::SlackBridgePrimalDualStart,
+    ::AbstractBridge,
+    ::Nothing,
+)
+    return # Silently ignore for other bridges
+end
+
 function MOI.set(
     model::MOI.ModelLike,
     ::SlackBridgePrimalDualStart,

test/Bridges/Objective/slack.jl

@@ -514,6 +514,20 @@ function test_deletion_of_variable_in_slacked_objective()
     return
 end
 
+function test_SlackBridgePrimalDualStart_non_slack()
+    inner = MOI.Utilities.MockOptimizer(
+        MOI.Utilities.UniversalFallback(MOI.Utilities.Model{Float64}()),
+    )
+    # Should ignore without erroring
+    MOI.set(inner, MOI.Bridges.Objective.SlackBridgePrimalDualStart(), nothing)
+    model = MOI.Bridges.Objective.Functionize{Float64}(inner)
+    x = MOI.add_variable(model)
+    MOI.set(model, MOI.ObjectiveFunction{typeof(x)}(), x)
+    # Should ignore without erroring
+    MOI.set(model, MOI.Bridges.Objective.SlackBridgePrimalDualStart(), nothing)
+    return
+end
+
 function test_SlackBridgePrimalDualStart()
     inner = MOI.Utilities.MockOptimizer(
         MOI.Utilities.UniversalFallback(MOI.Utilities.Model{Float64}()),