From 62e91172ca5ca82662f31acb78ec2b526da8c453 Mon Sep 17 00:00:00 2001
From: Oscar Dowson <o.dowson@gmail.com>
Date: Mon, 16 Feb 2026 12:56:30 +1300
Subject: [PATCH] Soft-deprecate POI.ParameterDual and POI.ParameterValue

---
 docs/src/index.md             |  7 ++++---
 docs/src/reference.md         | 10 ----------
 src/duals.jl                  | 27 ++++++++-------------------
 test/test_JuMP.jl             |  6 ++++--
 test/test_MathOptInterface.jl |  5 ++++-
 5 files changed, 20 insertions(+), 35 deletions(-)

diff --git a/docs/src/index.md b/docs/src/index.md
index bbf3d486..aa74a98c 100644
--- a/docs/src/index.md
+++ b/docs/src/index.md
@@ -215,7 +215,7 @@ choose the approach which works best for your model.
 
 In some applications you may need the dual of a parameter. The dual can be
 computed only if the parameter appears additively in the problem. Query the dual
-assocaited with the parameter using [`ParameterDual`](@ref):
+associated with the parameter as follows:
 ```@repl
 using JuMP, HiGHS
 import ParametricOptInterface as POI
@@ -226,10 +226,11 @@ set_silent(model)
 @constraint(model, x + p >= 3);
 @objective(model, Min, 2x);
 optimize!(model)
-get_attribute(p, POI.ParameterDual())
+dual(VariableInSetRef(p))
 ```
 
-Note how the dual is the same as the `reduced_cost` of an equivalent fixed variable:
+Note how the dual is the same as the `reduced_cost` of an equivalent fixed
+variable:
 ```@repl
 using JuMP, HiGHS
 model = Model(HiGHS.Optimizer);
diff --git a/docs/src/reference.md b/docs/src/reference.md
index 42864d89..02cb56ef 100644
--- a/docs/src/reference.md
+++ b/docs/src/reference.md
@@ -21,13 +21,3 @@ Optimizer
 ```@docs
 ConstraintsInterpretation
 ```
-
-## `ParameterDual`
-```@docs
-ParameterDual
-```
-
-## `ParameterValue`
-```@docs
-ParameterValue
-```
diff --git a/src/duals.jl b/src/duals.jl
index 0f871da8..b01633df 100644
--- a/src/duals.jl
+++ b/src/duals.jl
@@ -139,32 +139,21 @@ function MOI.get(
     ::ParameterDual,
     v::MOI.VariableIndex,
 ) where {T}
-    if !_is_additive(
-        model,
-        MOI.ConstraintIndex{MOI.VariableIndex,MOI.Parameter{T}}(v.value),
-    )
-        error("Cannot compute the dual of a multiplicative parameter")
-    end
-    return model.dual_value_of_parameters[p_val(v)]
+    ci = MOI.ConstraintIndex{MOI.VariableIndex,MOI.Parameter{T}}(v.value)
+    return MOI.get(model, MOI.ConstraintDual(), ci)
 end
 
 function MOI.get(
     model::Optimizer{T},
-    ::MOI.ConstraintDual,
+    attr::MOI.ConstraintDual,
     cp::MOI.ConstraintIndex{MOI.VariableIndex,MOI.Parameter{T}},
 ) where {T}
     if !model.evaluate_duals
-        throw(
-            MOI.GetAttributeNotAllowed(
-                MOI.ConstraintDual(),
-                "$(MOI.ConstraintDual()) not available when " *
-                "evaluate_duals is set to false. " *
-                "Create an optimizer such as POI.Optimizer(HiGHS.Optimizer(); evaluate_duals = true) to enable this feature.",
-            ),
-        )
-    end
-    if !_is_additive(model, cp)
-        error("Cannot compute the dual of a multiplicative parameter")
+        msg = "$attr not available when evaluate_duals is set to false. Create an optimizer such as `POI.Optimizer(HiGHS.Optimizer(); evaluate_duals = true)` to enable this feature."
+        throw(MOI.GetAttributeNotAllowed(attr, msg))
+    elseif !_is_additive(model, cp)
+        msg = "Cannot compute the dual of a multiplicative parameter"
+        throw(MOI.GetAttributeNotAllowed(attr, msg))
     end
     return model.dual_value_of_parameters[p_val(cp)]
 end
diff --git a/test/test_JuMP.jl b/test/test_JuMP.jl
index a44cbb44..8c3591b9 100644
--- a/test/test_JuMP.jl
+++ b/test/test_JuMP.jl
@@ -553,9 +553,11 @@ function test_jump_dual_multiplicative_fail()
     @constraint(model, cons, x * p >= 3)
     @objective(model, Min, 2x)
     optimize!(model)
-    @test_throws ErrorException(
+    err = MOI.GetAttributeNotAllowed(
+        MOI.ConstraintDual(),
         "Cannot compute the dual of a multiplicative parameter",
-    ) MOI.get(model, POI.ParameterDual(), p)
+    )
+    @test_throws err MOI.get(model, POI.ParameterDual(), p)
     return
 end
 
diff --git a/test/test_MathOptInterface.jl b/test/test_MathOptInterface.jl
index 268e1b5f..b043de7c 100644
--- a/test/test_MathOptInterface.jl
+++ b/test/test_MathOptInterface.jl
@@ -2450,7 +2450,10 @@ function test_multiplicative_dual_error()
     p, pc = MOI.add_constrained_variable(model, MOI.Parameter(1.0))
     f = 1.0 * x * p
     ci = MOI.add_constraint(model, f, MOI.EqualTo{Float64}(0.0))
-    @test_throws ErrorException MOI.get(model, MOI.ConstraintDual(), pc)
+    @test_throws(
+        MOI.GetAttributeNotAllowed,
+        MOI.get(model, MOI.ConstraintDual(), pc),
+    )
     return
 end