Fix for reverse search, fixes #39401, fixes #40244(#41203)

Author: Moelf

base/strings/search.jl

@@ -459,7 +459,7 @@ function _rsearchindex(s::AbstractVector{<:Union{Int8,UInt8}}, t::AbstractVector
     n = length(t)
     m = length(s)
     k = Int(_k) - sentinel
-    k < 1 && throw(BoundsError(s, _k))
+    k < 0 && throw(BoundsError(s, _k))
 
     if n == 0
         return 0 <= k <= m ? max(k, 1) : sentinel

test/strings/search.jl

@@ -97,6 +97,8 @@ for str in [astr]
     @test findprev('l', str, 2) == nothing
     @test findlast(',', str) == 6
     @test findprev(',', str, 5) == nothing
+    @test findlast(str, "") == nothing
+    @test findlast(str^2, str) == nothing
     @test findlast('\n', str) == 14
 end
 

test/strings/util.jl

@@ -163,6 +163,7 @@ end
     @test split("", "") == rsplit("", "") == [""]
     @test split("abc", "") == rsplit("abc", "") == ["a","b","c"]
     @test rsplit("abc", "", limit=2) == ["ab","c"]
+    @test rsplit("", "//") == [""]
     @test split("abc", "", limit=2) == ["a","bc"]
 
     @test split("", r"") == [""]