[Bridges] Fix deletion corner cases

src/Bridges/Constraint/bridges/functionize.jl

@@ -132,8 +132,17 @@ function MOI.delete(
     new_func = MOI.Utilities.eachscalar(func)[idx]
     set = MOI.get(model, MOI.ConstraintSet(), bridge.constraint)
     new_set = MOI.update_dimension(set, MOI.dimension(set) - 1)
-    MOI.delete(model, bridge.constraint)
+    # If we first do `MOI.delete` and then `MOI.add_constraint`,
+    # there might be an issue of `MOI.delete` ends up deleting a
+    # bridged variables.
+    # Indeed, in that case,
+    # `_delete_variables_in_vector_of_variables_constraint` might
+    # then try to get `get` `ConstraintFunction` for this bridge
+    # which will fail since the `bridge.constraint` is invalid.
+    # We avoid this issue by calling `add_constraint` first.
+    old_constraint = bridge.constraint
     bridge.constraint = MOI.add_constraint(model, new_func, new_set)
+    MOI.delete(model, old_constraint)
     return
 end
 

src/Bridges/Variable/map.jl

@@ -550,7 +550,9 @@ That is, the variable indices bridged by this bridge or the bridges that
 created it will not be unbridged in [`unbridged_function`](@ref).
 """
 function call_in_context(map::Map, bridge_index::Int64, f::Function)
-    if iszero(bridge_index)
+    # This is a shortcut that is used in particular in the common case where
+    # no variable bridge is used.
+    if iszero(bridge_index) && iszero(map.current_context)
         return f()
     end
     previous_context = map.current_context

test/Bridges/lazy_bridge_optimizer.jl

@@ -2110,6 +2110,21 @@ function test_objective_conversion_cost(T = Float64)
     return
 end
 
+function test_delete_index_in_vector(T::Type = Float64)
+    model = MOI.instantiate(StandardSDPAModel{T}; with_bridge_type = T)
+    x = MOI.add_variables(model, 4)
+    c = MOI.add_constraint(model, x, MOI.Nonpositives(4))
+    @test MOI.is_valid(model, c)
+    MOI.delete(model, x[3])
+    @test MOI.is_valid(model, c)
+    @test MOI.is_valid(model, x[1])
+    @test MOI.is_valid(model, x[2])
+    @test !MOI.is_valid(model, x[3])
+    @test MOI.is_valid(model, x[4])
+    @test MOI.get(model, MOI.ConstraintFunction(), c).variables == x[[1, 2, 4]]
+    return
+end
+
 end  # module
 
 TestBridgesLazyBridgeOptimizer.runtests()