Resolve all method ambiguities in LinearAlgebra (#28749)

* Add a test to check method ambiguities

* Use StridedMatrix to avoid method ambiguity; fixes #27405

* Avoid method ambiguity in promote_leaf_eltypes

This change is only for making Test.detect_ambiguities and shouldn't
introduce any change in working code (unless it depends on MethodError).

Before this change, we have:

julia> LinearAlgebra.promote_leaf_eltypes(())
ERROR: MethodError: LinearAlgebra.promote_leaf_eltypes(::Tuple{}) is ambiguous. Candidates:

With this change, we have:

julia> LinearAlgebra.promote_leaf_eltypes(())
Bool

(cherry picked from commit 4498d27)

Author: tkf

stdlib/LinearAlgebra/src/diagonal.jl

@@ -277,9 +277,9 @@ mul!(out::AbstractVector, A::Diagonal, in::AbstractVector) = out .= A.diag .* in
 mul!(out::AbstractVector, A::Adjoint{<:Any,<:Diagonal}, in::AbstractVector) = out .= adjoint.(A.parent.diag) .* in
 mul!(out::AbstractVector, A::Transpose{<:Any,<:Diagonal}, in::AbstractVector) = out .= transpose.(A.parent.diag) .* in
 
-mul!(out::AbstractMatrix, A::Diagonal, in::AbstractMatrix) = out .= A.diag .* in
-mul!(out::AbstractMatrix, A::Adjoint{<:Any,<:Diagonal}, in::AbstractMatrix) = out .= adjoint.(A.parent.diag) .* in
-mul!(out::AbstractMatrix, A::Transpose{<:Any,<:Diagonal}, in::AbstractMatrix) = out .= transpose.(A.parent.diag) .* in
+mul!(out::AbstractMatrix, A::Diagonal, in::StridedMatrix) = out .= A.diag .* in
+mul!(out::AbstractMatrix, A::Adjoint{<:Any,<:Diagonal}, in::StridedMatrix) = out .= adjoint.(A.parent.diag) .* in
+mul!(out::AbstractMatrix, A::Transpose{<:Any,<:Diagonal}, in::StridedMatrix) = out .= transpose.(A.parent.diag) .* in
 
 # ambiguities with Symmetric/Hermitian
 # RealHermSymComplex[Sym]/[Herm] only include Number; invariant to [c]transpose

stdlib/LinearAlgebra/src/generic.jl

@@ -1324,8 +1324,8 @@ julia> promote_leaf_eltypes(a)
 Complex{Float64}
 ```
 """
-promote_leaf_eltypes(x::Union{AbstractArray{T},Tuple{Vararg{T}}}) where {T<:Number} = T
-promote_leaf_eltypes(x::Union{AbstractArray{T},Tuple{Vararg{T}}}) where {T<:NumberArray} = eltype(T)
+promote_leaf_eltypes(x::Union{AbstractArray{T},Tuple{T,Vararg{T}}}) where {T<:Number} = T
+promote_leaf_eltypes(x::Union{AbstractArray{T},Tuple{T,Vararg{T}}}) where {T<:NumberArray} = eltype(T)
 promote_leaf_eltypes(x::T) where {T} = T
 promote_leaf_eltypes(x::Union{AbstractArray,Tuple}) = mapreduce(promote_leaf_eltypes, promote_type, x; init=Bool)
 

stdlib/LinearAlgebra/test/matmul.jl

@@ -445,4 +445,8 @@ end
     @test Xv1'*Xv3' ≈ XcXc
 end
 
+@testset "method ambiguity" begin
+    @test detect_ambiguities(LinearAlgebra, Base; imported=true, recursive=true) == []
+end
+
 end # module TestMatmul