From b185f65ad5b58dceaf0bd2d6dbcee45ef2d87d65 Mon Sep 17 00:00:00 2001
From: Jukka Aho <ahojukka5@gmail.com>
Date: Sat, 9 May 2026 18:32:52 +0300
Subject: [PATCH] feat(quadrature): integrate basis degree into quadrature
 selection

Add `basis_quadrature_order` and an `integration_points(topology, basis)` overload
so assembly can match Gauss rules to `Lagrange{P}` / `Serendipity{P}` instead of
inferring order only from topology node counts.

- Delegate rule choice to `default_quadrature(T, ord)` with `ord` from the basis.
---
 src/quadrature/integration_basis.jl | 33 +++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 src/quadrature/integration_basis.jl

diff --git a/src/quadrature/integration_basis.jl b/src/quadrature/integration_basis.jl
new file mode 100644
index 0000000..536c6cb
--- /dev/null
+++ b/src/quadrature/integration_basis.jl
@@ -0,0 +1,33 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE.md
+
+"""
+    basis_quadrature_order(basis::AbstractBasis) -> Int
+
+Polynomial order passed to [`default_quadrature(::Type{<:AbstractTopology}, ::Int)`](@ref)
+when building [`integration_points(topology, basis)`](@ref).
+
+Extensible: add methods for new [`AbstractBasis`](@ref) subtypes used in assembly caches.
+Patch/tensor-product bases used in IGA (B-spline/NURBS on a parameter cell) should
+implement this hook so quadrature matches the quadrature rule degree of the weak form,
+analogous to [`Lagrange`](@ref) / [`Serendipity`](@ref).
+"""
+basis_quadrature_order(::Lagrange{P}) where {P} = P
+basis_quadrature_order(::Serendipity{P}) where {P} = P
+
+"""
+    integration_points(topology::AbstractTopology, basis::AbstractBasis)
+
+Like [`integration_points(topology)`](@ref), but selects [`default_quadrature`](@ref)
+from **`basis`** via [`basis_quadrature_order`](@ref) instead of inferring order only
+from [`nnodes`](@ref). Use this when the mesh topology node count does not reflect
+the polynomial degree of the active basis (or to force a consistent rule with
+[`create_element_cache`](@ref)).
+"""
+function integration_points(topology::T, basis::AbstractBasis) where {T<:AbstractTopology}
+    ord = basis_quadrature_order(basis)
+    rule = default_quadrature(T, ord)
+    quad_topo = _quadrature_topology_type(T)
+    quad_points = get_quadrature_points(quad_topo, rule)
+    return Tuple(quad_points)
+end