Merge pull request JuliaLang#19445 from ScottPJones/spj/fixcmp

Fix and improve cmp() on AbstractString

base/strings/basic.jl

@@ -139,15 +139,17 @@ function cmp(a::AbstractString, b::AbstractString)
  end
  i = start(a)
  j = start(b)
- while !done(a,i) && !done(b,i)
+ while !done(a,i)
+ if done(b,j)
+ return +1
+ end
  c, i = next(a,i)
  d, j = next(b,j)
  if c != d
  return c < d ? -1 : +1
  end
  end
- done(a,i) && !done(b,j) ? -1 :
- !done(a,i) && done(b,j) ? +1 : 0
+ done(b,j) ? 0 : -1
 end
 
 ==(a::AbstractString, b::AbstractString) = cmp(a,b) == 0

test/strings/basic.jl

@@ -440,3 +440,23 @@ for s in ("Hello", "Σ", "こんにちは", "😊😁")
  @test next(s, endof(s))[2] > endof(s.data)
  @test nextind(s, endof(s)) > endof(s.data)
 end
+
+# Test cmp with AbstractStrings that don't index the same as UTF-8, which would include
+# (LegacyString.)UTF16String and (LegacyString.)UTF32String, among others.
+
+type CharStr <: AbstractString
+ chars::Vector{Char}
+ CharStr(x) = new(collect(x))
+end
+Base.start(x::CharStr) = start(x.chars)
+Base.next(x::CharStr, i::Int) = next(x.chars, i)
+Base.done(x::CharStr, i::Int) = done(x.chars, i)
+Base.endof(x::CharStr) = endof(x.chars)
+
+# Simple case, with just ANSI Latin 1 characters
+@test "áB" != CharStr("áá") # returns false with bug
+@test cmp("áB", CharStr("áá")) == -1 # returns 0 with bug
+
+# Case with Unicode characters
+@test cmp("\U1f596\U1f596", CharStr("\U1f596")) == 1 # Gives BoundsError with bug
+@test cmp(CharStr("\U1f596"), "\U1f596\U1f596") == -1