Fix error in constructor

Project.toml

@@ -1,6 +1,6 @@
 name = "PooledArrays"
 uuid = "2dfb63ee-cc39-5dd5-95bd-886bf059d720"
-version = "1.4.1"
+version = "1.4.2"
 
 [deps]
 DataAPI = "9a962f9c-6df0-11e9-0e5d-c546b8b5ee8a"
@@ -12,6 +12,7 @@ julia = "1"
 
 [extras]
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+OffsetArrays = "6fe1bfb0-de20-5000-8ca7-80f57d26f881"
 
 [targets]
-test = ["Test"]
+test = ["OffsetArrays", "Test"]

src/PooledArrays.jl

@@ -114,20 +114,25 @@ function _label(xs::AbstractArray,
                ) where {T, I<:Integer}
 
     @inbounds for i in start:length(xs)
-        x = xs[i]
-        lbl = get(invpool, x, zero(I))
-        if lbl !== zero(I)
-            labels[i] = lbl
+        idx = i + firstindex(xs) - 1
+        if !isassigned(xs, idx)
+            labels[i] = zero(I)
         else
-            if nlabels == typemax(I)
-                I2 = _widen(I)
-                return _label(xs, T, I2, i, convert(Vector{I2}, labels),
-                              convert(Dict{T, I2}, invpool), pool, nlabels)
+            x = xs[idx]
+            lbl = get(invpool, x, zero(I))
+            if lbl !== zero(I)
+                labels[i] = lbl
+            else
+                if nlabels == typemax(I)
+                    I2 = _widen(I)
+                    return _label(xs, T, I2, i, convert(Vector{I2}, labels),
+                                convert(Dict{T, I2}, invpool), pool, nlabels)
+                end
+                nlabels += 1
+                labels[i] = nlabels
+                invpool[x] = nlabels
+                push!(pool, x)
             end
-            nlabels += 1
-            labels[i] = nlabels
-            invpool[x] = nlabels
-            push!(pool, x)
         end
     end
     labels, invpool, pool

test/runtests.jl

@@ -1,4 +1,4 @@
-using Test
+using Test, OffsetArrays
 using PooledArrays
 using DataAPI: refarray, refvalue, refpool, invrefpool
 using PooledArrays: refcount
@@ -601,3 +601,21 @@ end
     @test popfirst!(x) == "1"
     @test x == ["2"]
 end
+
+@testset "constructor corner cases" begin
+    x = Vector{Any}(undef, 3)
+    y = PooledArray(x)
+    @test y isa PooledArray{Any}
+    @test all(iszero, y.refs)
+    @test isempty(y.pool)
+    @test isempty(y.invpool)
+
+    x[2] = "a"
+    for v in (x, OffsetVector(x, -5))
+        y = PooledArray(v)
+        @test y isa PooledArray{Any}
+        @test y.refs == [0, 1, 0]
+        @test y.pool == ["a"]
+        @test y.invpool == Dict("a" => 1)
+    end
+end