Improve inference in chebyshev_clenshaw (#498)

* improve inference in chebyshev_clenshaw

* bump version to v0.8.39

* don't dev ApproxFunBaseTest on v1.9

* Test for empty vector

* use points in domain

* Test for BigInt coeffs

Author: jishnub

.github/workflows/downstream.yml

@@ -58,7 +58,11 @@ jobs:
           try
             # force it to use this PR's version of the package
             Pkg.develop(PackageSpec(path="."))  # resolver may fail with main deps
-            Pkg.develop(PackageSpec(path="ApproxFunBaseTest"))
+            # the following may fail because of https://github.com/JuliaLang/Pkg.jl/issues/3327
+            # currently, we only test on older versions that don't use Pkg extensions
+            if VERSION < v"1.9"
+              Pkg.develop(PackageSpec(path="ApproxFunBaseTest"))
+            end
             Pkg.update()
             Pkg.test(; coverage = true)  # resolver may fail with test time deps
           catch err

Project.toml

@@ -1,6 +1,6 @@
 name = "ApproxFunBase"
 uuid = "fbd15aa5-315a-5a7d-a8a4-24992e37be05"
-version = "0.8.38"
+version = "0.8.39"
 
 [deps]
 AbstractFFTs = "621f4979-c628-5d54-868e-fcf4e3e8185c"

src/LinearAlgebra/clenshaw.jl

@@ -219,9 +219,9 @@ sineshaw(c::AbstractVector,θ::AbstractMatrix) = promote_type(eltype(c),eltype(
 function chebyshev_clenshaw(c::AbstractVector, x)
     N,T = length(c),promote_type(eltype(c),typeof(x))
     if N == 0
-        return zero(x)
+        return zero(float(x) * oneunit(eltype(c)))
     elseif N == 1 # avoid issues with NaN x
-        return first(c)*one(x)
+        return first(c) * oneunit(float(x))
     end
 
     x = 2x

test/runtests.jl

@@ -1,10 +1,11 @@
 using ApproxFunBase
-using ApproxFunBase: ∞
+using ApproxFunBase: chebyshev_clenshaw
 using Aqua
 using BandedMatrices
 using BlockArrays
 using BlockBandedMatrices
 using DomainSets
+using DualNumbers
 using FillArrays
 using InfiniteArrays
 using Infinities
@@ -732,4 +733,19 @@ end
 @time include("ETDRK4Test.jl")
 include("show.jl")
 
+@testset "chebyshev_clenshaw" begin
+    @test @inferred(chebyshev_clenshaw(Int[], 1)) == 0
+    @test @inferred(chebyshev_clenshaw(Int[], Dual(0,1))) == Dual(0,0)
+    @test @inferred(chebyshev_clenshaw(Int[], Dual(2,1))) == Dual(0,0)
+    @test @inferred(chebyshev_clenshaw(Float64[], 1)) == 0
+    @test @inferred(chebyshev_clenshaw(Float64[], 1.0)) == 0
+    @test @inferred(chebyshev_clenshaw(Int[1], 1)) == 1
+    @test @inferred(chebyshev_clenshaw([1,2], 1)) == 3
+    @test @inferred(chebyshev_clenshaw([1,2], Dual(0,1))) == Dual(1,2)
+    @test @inferred(chebyshev_clenshaw([1,2], Dual(1,1))) == Dual(3,2)
+    @test @inferred(chebyshev_clenshaw([1,2], Dual(2,1))) == Dual(5,2)
+
+    @test @inferred(chebyshev_clenshaw(BigInt[1], 1)) == 1
+end
+
 include("PolynomialSpacesTests.jl")