[Bridges] fix bug in QuadToSOCBridge getting ConstraintPrimal (#2240)

Author: odow

src/Bridges/Constraint/bridges/quad_to_soc.jl

@@ -229,8 +229,8 @@ end
 function MOI.get(
     model::MOI.ModelLike,
     attr::Union{MOI.ConstraintPrimal,MOI.ConstraintPrimalStart},
-    bridge::QuadtoSOCBridge,
-)
+    bridge::QuadtoSOCBridge{T},
+) where {T}
     # The constraint primal is x'Qx/2 + a'x
     # If `less_than` then `Q = U'U` and we have the value of
     # `Ux` and `-a'x + ub`, so we get it with
@@ -242,7 +242,7 @@ function MOI.get(
     if soc === nothing
         return nothing
     end
-    output = sum(soc[i]^2 for i in 3:bridge.dimension)
+    output = sum(soc[i]^2 for i in 3:bridge.dimension; init = zero(T))
     output /= 2
     output -= soc[1] * soc[2]
     if !bridge.less_than

test/Bridges/Constraint/quad_to_soc.jl

@@ -325,6 +325,21 @@ function test_deletion_of_variable_in_bridged_slacked_objective()
     return
 end
 
+function test_constraint_primal_no_quad_terms()
+    inner = MOI.Utilities.UniversalFallback(MOI.Utilities.Model{Float64}())
+    model = MOI.Bridges.Constraint.QuadtoSOC{Float64}(inner)
+    x = MOI.add_variable(model)
+    f = MOI.ScalarQuadraticFunction(
+        MOI.ScalarQuadraticTerm{Float64}[],
+        [MOI.ScalarAffineTerm(1.0, x)],
+        0.0,
+    )
+    c = MOI.add_constraint(model, f, MOI.LessThan(1.0))
+    MOI.set(model, MOI.ConstraintPrimalStart(), c, 1.0)
+    @test MOI.get(model, MOI.ConstraintPrimalStart(), c) == 1.0
+    return
+end
+
 end  # module
 
 TestConstraintQuadToSOC.runtests()