add find(first|last|next|prev) methods that return nothing (#513)

* fix for find(first|last|next|prev) returning nothing rather than 0:-1

* Do not use isempty

README.md

@@ -353,7 +353,8 @@ Currently, the `@compat` macro supports the following syntaxes:
   sometimes combined with `equalto` or `occursin` ([#24673]).
 
 * `Compat.findfirst`, `Compat.findnext`, `Compat.findlast` and `Compat.findprev`,
-  return `nothing` when no match is found (rather than `0`) as on Julia 0.7 ([#24673]).
+  return `nothing` when no match is found (rather than `0` or `0:-1`)
+  as on Julia 0.7 ([#24673], [#26149]).
 
 * `findin(a, b)` is now `findall(occursin(b), a)` ([#24673]).
 
@@ -586,4 +587,5 @@ includes this fix. Find the minimum version from there.
 [#25990]: https://github.com/JuliaLang/julia/issues/25990
 [#26069]: https://github.com/JuliaLang/julia/issues/26069
 [#26089]: https://github.com/JuliaLang/julia/issues/26089
+[#26149]: https://github.com/JuliaLang/julia/issues/26149
 [#26156]: https://github.com/JuliaLang/julia/issues/26156

src/Compat.jl

@@ -1498,6 +1498,7 @@ else
     export occursin
 
     zero2nothing(x::Integer) = x == 0 ? nothing : x
+    zero2nothing(x::AbstractUnitRange{<:Integer}) = x == 0:-1 ? nothing : x
     zero2nothing(x) = x
 
     findnext(xs...) = zero2nothing(Base.findnext(xs...))

test/runtests.jl

@@ -1378,18 +1378,19 @@ for (f1, f2, i) in ((Compat.findfirst, Compat.findnext, 1),
         @test f2(occursin(chars), "bx", i) == f1(occursin(chars), "bx") == nothing
     end
 end
-for (f1, f2, i) in ((findfirst, findnext, 1),
-                    (findlast, findprev, 2),
-                    (Compat.findfirst, Compat.findnext, 1),
-                    (Compat.findlast, Compat.findprev, 2))
-    @test f2("a", "ba", i) == f1("a", "ba") == 2:2
-    @test f2("z", "ba", i) == f1("z", "ba") == 0:-1
-end
-for (f1, f2, i) in ((findfirst, findnext, 1),
-                    (Compat.findfirst, Compat.findnext, 1))
-    @test f2(r"a", "ba", 1) == f1(r"a", "ba") == 2:2
-    @test f2(r"z", "ba", 1) == f1(r"z", "ba") == 0:-1
-end
+@test findnext("a", "ba", 1) == findfirst("a", "ba") == 2:2
+@test findnext("z", "ba", 1) == findfirst("z", "ba") == (VERSION < v"0.7.0-DEV.4480" ? (0:-1) : nothing)
+@test findprev("a", "ba", 2) == findlast("a", "ba") == 2:2
+@test findprev("z", "ba", 2) == findlast("z", "ba") == (VERSION < v"0.7.0-DEV.4480" ? (0:-1) : nothing)
+@test Compat.findnext("a", "ba", 1) == Compat.findfirst("a", "ba") == 2:2
+@test Compat.findnext("z", "ba", 1) == Compat.findfirst("z", "ba") == nothing
+@test Compat.findprev("a", "ba", 2) == Compat.findlast("a", "ba") == 2:2
+@test Compat.findprev("z", "ba", 2) == Compat.findlast("z", "ba") == nothing
+
+@test findnext(r"a", "ba", 1) == findfirst(r"a", "ba") == 2:2
+@test findnext(r"z", "ba", 1) == findfirst(r"z", "ba") == (VERSION < v"0.7.0-DEV.4480" ? (0:-1) : nothing)
+@test Compat.findnext(r"a", "ba", 1) == Compat.findfirst(r"a", "ba") == 2:2
+@test Compat.findnext(r"z", "ba", 1) == Compat.findfirst(r"z", "ba") == nothing
 
 @test Compat.findfirst(equalto(UInt8(0)), IOBuffer(UInt8[1, 0])) == 2
 @test Compat.findfirst(equalto(UInt8(9)), IOBuffer(UInt8[1, 0])) == nothing