proper diagonal in copytri! (fix #30055)

stdlib/LinearAlgebra/src/matmul.jl

@@ -340,6 +340,11 @@ function copytri!(A::AbstractMatrix, uplo::AbstractChar, conjugate::Bool=false)
     else
         throw(ArgumentError("uplo argument must be 'U' (upper) or 'L' (lower), got $uplo"))
     end
+    if conjugate
+        for i = 1:n
+            A[i,i] = adjoint(A[i,i])
+        end
+    end
     A
 end
 

stdlib/LinearAlgebra/src/symmetric.jl

@@ -236,14 +236,14 @@ similar(A::Union{Symmetric,Hermitian}, ::Type{T}, dims::Dims{N}) where {T,N} = s
 function Matrix(A::Symmetric)
     B = copytri!(convert(Matrix, copy(A.data)), A.uplo)
     for i = 1:size(A, 1)
-        B[i,i] = symmetric(B[i,i], sym_uplo(A.uplo))::symmetric_type(eltype(A.data))
+        B[i,i] = symmetric(A[i,i], sym_uplo(A.uplo))::symmetric_type(eltype(A.data))
     end
     return B
 end
 function Matrix(A::Hermitian)
     B = copytri!(convert(Matrix, copy(A.data)), A.uplo, true)
     for i = 1:size(A, 1)
-        B[i,i] = hermitian(B[i,i], sym_uplo(A.uplo))::hermitian_type(eltype(A.data))
+        B[i,i] = hermitian(A[i,i], sym_uplo(A.uplo))::hermitian_type(eltype(A.data))
     end
     return B
 end

stdlib/LinearAlgebra/test/matmul.jl

@@ -301,6 +301,13 @@ end
 
 @test_throws ArgumentError LinearAlgebra.copytri!(Matrix{Float64}(undef,10,10),'Z')
 
+@testset "Issue 30055" begin
+    A = UpperTriangular([1+im 2+im 3+im; 4+im 5+im 6+im; 7+im 9+im 0])'
+    @test copy(A) == A # copy uses copytri!
+    A = LowerTriangular([1+im 2+im 3+im; 4+im 5+im 6+im; 7+im 9+im 0])'
+    @test copy(A) == A # copy uses copytri!
+end
+
 @testset "gemv! and gemm_wrapper for $elty" for elty in [Float32,Float64,ComplexF64,ComplexF32]
     A10x10, x10, x11 = Array{elty}.(undef, ((10,10), 10, 11))
     @test_throws DimensionMismatch LinearAlgebra.gemv!(x10,'N',A10x10,x11)