Merge pull request #1386 from JuliaOpt/bl/suppconerror

Add error message for unsupported constraint

src/JuMP.jl

@@ -301,7 +301,16 @@ MOI.isvalid(m::Model, cr::ConstraintRef{Model}) = cr.m === m && MOI.isvalid(m.mo
 Add a constraint `c` to `Model m` and sets its name.
 """
 function addconstraint(m::Model, c::AbstractConstraint, name::String="")
-    cindex = MOI.addconstraint!(m.moibackend, moi_function_and_set(c)...)
+    f, s = moi_function_and_set(c)
+    if !MOI.supportsconstraint(m.moibackend, typeof(f), typeof(s))
+        if m.moibackend isa MOI.Bridges.LazyBridgeOptimizer
+            bridge_message = " and there are no bridges that can reformulate it into supported constraints."
+        else
+            bridge_message = ", try using `bridge_constraints=true` in the `JuMP.Model` constructor if you believe the constraint can be reformulated to constraints supported by the solver."
+        end
+        error("Constraints of type $(typeof(f))-in-$(typeof(s)) are not supported by the solver" * bridge_message)
+    end
+    cindex = MOI.addconstraint!(m.moibackend, f, s)
     cref = ConstraintRef(m, cindex)
     if !isempty(name)
         setname(cref, name)

test/model.jl

@@ -33,13 +33,12 @@ end
         @test model.moibackend isa MOIU.CachingOptimizer
         @test model.moibackend === JuMP.caching_optimizer(model)
         @variable model x
-        @constraint model 0 <= x + 1 <= 1
-        @test_throws ErrorException JuMP.optimize(model)
+        @test_throws ErrorException @constraint model 0 <= x + 1 <= 1
     end
     @testset "No bridge automatically added in Direct mode" begin
         optimizer = MOIU.MockOptimizer(LPModel{Float64}());
         model = Model(backend=optimizer, mode=JuMP.Direct)
         @variable model x
-        @test_throws MethodError @constraint model 0 <= x + 1 <= 1
+        @test_throws ErrorException @constraint model 0 <= x + 1 <= 1
     end
 end