allow nchar to be geater than string length in first/last without thr…

…owing an error

base/strings/basic.jl

@@ -595,7 +595,7 @@ end
 """
     first(str::AbstractString, nchar::Integer)
 
-Get a string consisting of the first `nchar` characters of `str`.
+Get a string consisting of at most the first `nchar` characters of `str`.
 
 ```jldoctest
 julia> first("∀ϵ≠0: ϵ²>0", 0)
@@ -606,19 +606,24 @@ julia> first("∀ϵ≠0: ϵ²>0", 1)
 
 julia> first("∀ϵ≠0: ϵ²>0", 3)
 "∀ϵ≠"
+
+julia> first("1234", 10)
+"1234"
 ```
 """
 function first(str::AbstractString, nchar::Integer)
+    s = start(s)
     if 0 <= nchar <= 1
-        return str[1:nchar]
+        return str[s:(s-1+nchar)]
     end
-    str[1:nextind(str, 1, nchar-1)]
+    idx = min(endof(str), nextind(str, s, nchar-1))
+    str[s:idx]
 end
 
 """
     last(str::AbstractString, nchar::Integer)
 
-Get a string consisting of the last `nchar` characters of `str`.
+Get a string consisting of at most the last `nchar` characters of `str`.
 
 ```jldoctest
 julia> last("∀ϵ≠0: ϵ²>0", 0)
@@ -629,14 +634,18 @@ julia> last("∀ϵ≠0: ϵ²>0", 1)
 
 julia> last("∀ϵ≠0: ϵ²>0", 3)
 "²>0"
+
+julia> last("1234", 10)
+"1234"
 ```
 """
 function last(str::AbstractString, nchar::Integer)
     e = endof(str)
     if 0 <= nchar <= 1
         return str[(e-nchar+1):e]
     end
-    str[prevind(str, e, nchar-1):e]
+    idx = max(start(str), prevind(str, e, nchar-1))
+    str[idx:e]
 end
 
 # reverse-order iteration for strings and indices thereof

test/strings/basic.jl

@@ -645,15 +645,15 @@ end
     @test first(s, 3) == "∀ϵ≠"
     @test first(s, 4) == "∀ϵ≠0"
     @test first(s, length(s)) == s
-    @test_throws BoundsError first(s, length(s)+1)
+    @test first(s, length(s)+1) == s
     @test_throws ArgumentError last(s, -1)
     @test last(s, 0) == ""
     @test last(s, 1) == "0"
     @test last(s, 2) == ">0"
     @test last(s, 3) == "²>0"
     @test last(s, 4) == "ϵ²>0"
     @test last(s, length(s)) == s
-    @test_throws BoundsError last(s, length(s)+1)
+    @test last(s, length(s)+1) == s
 end
 
 @testset "invalid code point" begin