Tighten validation of hvncat implementation (#43940)

base/abstractarray.jl

@@ -2364,6 +2364,24 @@ function _typed_hvncat_dims(::Type{T}, dims::NTuple{N, Int}, row_first::Bool, as
 
     outdims = zeros(Int, N)
 
+    # validate shapes for lowest level of concatenation
+    d = findfirst(>(1), dims)
+    if d !== nothing # all dims are 1
+        nblocks = length(as) ÷ dims[d]
+        for b ∈ 1:nblocks
+            offset = ((b - 1) * dims[d])
+            startelementi = offset + 1
+            for i ∈ offset .+ (2:dims[d])
+                for dd ∈ 1:N
+                    dd == d && continue
+                    if size(as[startelementi], dd) != size(as[i], dd)
+                        throw(ArgumentError("incompatible shape in element $i"))
+                    end
+                end
+            end
+        end
+    end
+
     # discover number of rows or columns
     for i ∈ 1:dims[d1]
         outdims[d1] += cat_size(as[i], d1)

test/abstractarray.jl

@@ -1534,6 +1534,10 @@ using Base: typed_hvncat
     @test Int[] == typed_hvncat(Int, 1) isa Array{Int, 1}
     @test Array{Int, 2}(undef, 0, 0) == typed_hvncat(Int, 2) isa Array{Int, 2}
     @test Array{Int, 3}(undef, 0, 0, 0) == typed_hvncat(Int, 3) isa Array{Int, 3}
+
+    # Issue 43933 - semicolon precedence mistake should produce an error
+    @test_throws ArgumentError [[1 1]; 2 ;; 3 ; [3 4]]
+    @test_throws ArgumentError [[1 ;;; 1]; 2 ;;; 3 ; [3 ;;; 4]]
 end
 
 @testset "keepat!" begin