From 9fe6bddce5e341fef32914f31bb7a31ec566e1f4 Mon Sep 17 00:00:00 2001
From: kimikage <kimikage.ceo@gmail.com>
Date: Sun, 27 Sep 2026 23:06:12 +0900
Subject: [PATCH] Support for non-concrete types in
 `promote_rule(::Type{<:FixedPoint}, ::Type{<:FixedPoint})`

---
 src/FixedPointNumbers.jl |  9 +++++----
 test/traits.jl           | 12 +++++++++++-
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/src/FixedPointNumbers.jl b/src/FixedPointNumbers.jl
index fb99dc7e..dad2ff1c 100644
--- a/src/FixedPointNumbers.jl
+++ b/src/FixedPointNumbers.jl
@@ -49,7 +49,8 @@ reinterpret(::Type{X}, x::T) where {T <: Integer, X <: FixedPoint{T}} = X(x, 0)
 
 # static parameters
 nbitsfrac(::Type{X}) where {T, f, X <: FixedPoint{T,f}} = f
-rawtype(::Type{X}) where {T, X <: FixedPoint{T}} = T
+rawtype(::Type{X}) where {T <: Integer, X <: FixedPoint{T}} = T
+rawtype(::Type{<:FixedPoint}) = Union{} # Don't care the constraints for `T`
 
 # traits based on static parameters
 signbits(::Type{X}) where {T, X <: FixedPoint{T}} = T <: Unsigned ? 0 : 1
@@ -539,15 +540,15 @@ promote_rule(::Type{X}, ::Type{Tr}) where {X <: FixedPoint, Tr <: Rational} = Tr
 promote_rule(::Type{X}, ::Type{Ti}) where {X <: FixedPoint, Ti <: Integer} = floattype(X)
 
 function promote_rule(::Type{X1}, ::Type{X2}) where {X1 <: FixedPoint, X2 <: FixedPoint}
-    (isconcretetype(X1) && isconcretetype(X2)) || return Union{}
     X1w, X2w = wrapper(X1), wrapper(X2)
     if X1w !== X2w
-        # X1w <: X2w && return X2w # for non-concrete types
-        # X2w <: X1w && return X1w # for non-concrete types
+        X1w <: X2w && return X2w
+        X2w <: X1w && return X1w
         return promote_type(floattype(X1), floattype(X2))
     end
     X = X1w
     T1, T2 = rawtype(X1), rawtype(X2)
+    isconcretetype(T1) && isconcretetype(T2) || return X{promote_type(T1, T2)}
     f1, f2 = nbitsfrac(X1), nbitsfrac(X2)
     f = max(f1, f2) # ensure we have enough precision
     Tp = promote_type(T1, T2)
diff --git a/test/traits.jl b/test/traits.jl
index c248b4c0..63d5646c 100644
--- a/test/traits.jl
+++ b/test/traits.jl
@@ -1,5 +1,5 @@
 using FixedPointNumbers, Test
-using FixedPointNumbers: bitwidth
+using FixedPointNumbers: bitwidth, rawtype
 
 struct MyReal <: Real end
 
@@ -18,3 +18,13 @@ struct MyReal <: Real end
 
     @test_skip(@test_throws MethodError floattype(MyReal))   # TODO: eliminate `@test_skipped` when depwarn is eliminated. See #177.
 end
+
+@testset "rawtype" begin
+    @test rawtype(FixedPoint) === Union{}
+    @test rawtype(Normed) === Union{}
+    @test rawtype(Fixed) === Union{}
+    @test rawtype(Normed{<:Unsigned}) === Union{}
+    @test rawtype(Fixed{Union{Int8, Int16}}) === Union{Int8, Int16}
+    @test rawtype(N0f8) === UInt8
+    @test rawtype(Q0f7) === Int8
+end