RFC: Make empty ranges compare equal

NEWS.md

@@ -9,6 +9,7 @@ New language features
 Language changes
 ----------------
 
+* Empty ranges now compare equal, regardless of their startpoint and step ([#32348]).
 
 Multi-threading changes
 -----------------------

base/range.jl

@@ -714,18 +714,20 @@ show(io::IO, r::UnitRange) = print(io, repr(first(r)), ':', repr(last(r)))
 show(io::IO, r::OneTo) = print(io, "Base.OneTo(", r.stop, ")")
 
 ==(r::T, s::T) where {T<:AbstractRange} =
-    (first(r) == first(s)) & (step(r) == step(s)) & (last(r) == last(s))
+    (isempty(r) & isempty(s)) | ((first(r) == first(s)) & (step(r) == step(s)) & (last(r) == last(s)))
 ==(r::OrdinalRange, s::OrdinalRange) =
-    (first(r) == first(s)) & (step(r) == step(s)) & (last(r) == last(s))
+    (isempty(r) & isempty(s)) | ((first(r) == first(s)) & (step(r) == step(s)) & (last(r) == last(s)))
 ==(r::T, s::T) where {T<:Union{StepRangeLen,LinRange}} =
-    (first(r) == first(s)) & (length(r) == length(s)) & (last(r) == last(s))
+    (isempty(r) & isempty(s)) | ((first(r) == first(s)) & (length(r) == length(s)) & (last(r) == last(s)))
 ==(r::Union{StepRange{T},StepRangeLen{T,T}}, s::Union{StepRange{T},StepRangeLen{T,T}}) where {T} =
-    (first(r) == first(s)) & (last(r) == last(s)) & (step(r) == step(s))
+    (isempty(r) & isempty(s)) | ((first(r) == first(s)) & (step(r) == step(s)) & (last(r) == last(s)))
 
 function ==(r::AbstractRange, s::AbstractRange)
     lr = length(r)
     if lr != length(s)
         return false
+    elseif iszero(lr)
+        return true
     end
     yr, ys = iterate(r), iterate(s)
     while yr !== nothing

base/strings/util.jl

@@ -324,8 +324,8 @@ end
 function _split(str::AbstractString, splitter, limit::Integer, keepempty::Bool, strs::Array)
     i = 1 # firstindex(str)
     n = lastindex(str)
-    r = something(findfirst(splitter,str), 0)
-    if r != 0:-1
+    r = findfirst(splitter,str)
+    if !isnothing(r)
         j, k = first(r), nextind(str,last(r))
         while 0 < j <= n && length(strs) != limit-1
             if i < k
@@ -335,8 +335,8 @@ function _split(str::AbstractString, splitter, limit::Integer, keepempty::Bool,
                 i = k
             end
             (k <= j) && (k = nextind(str,j))
-            r = something(findnext(splitter,str,k), 0)
-            r == 0:-1 && break
+            r = findnext(splitter,str,k)
+            isnothing(r) && break
             j, k = first(r), nextind(str,last(r))
         end
     end

stdlib/Dates/test/ranges.jl

@@ -7,6 +7,11 @@ using Dates
 
 using InteractiveUtils: subtypes
 
+# Compare ranges by comparing their `first` and `last` elements and their `length`. This
+# returns `false` if empty ranges have different startpoints.
+==ᵣ(r::AbstractRange, s::AbstractRange) =
+    (first(r) == first(s)) & (length(r) == length(s)) & (last(r) == last(s))
+
 let
     for T in (Dates.Date, Dates.DateTime)
         f1 = T(2014); l1 = T(2013, 12, 31)
@@ -35,7 +40,7 @@ let
                 @test first(reverse(dr)) < f1
                 @test last(reverse(dr)) >= f1
                 @test issorted(dr)
-                @test sortperm(dr) == 1:1:0
+                @test sortperm(dr) ==ᵣ 1:1:0
                 @test !(f1 in dr)
                 @test !(l1 in dr)
                 @test !(f1 - pos_step in dr)
@@ -93,7 +98,7 @@ let
                 @test first(reverse(dr)) > l1
                 @test last(reverse(dr)) <= l1
                 @test issorted(dr)
-                @test sortperm(dr) == 1:1:0
+                @test sortperm(dr) ==ᵣ 1:1:0
                 @test !(l1 in dr)
                 @test !(l1 in dr)
                 @test !(l1 - neg_step in dr)
@@ -153,7 +158,7 @@ let
                     @test first(reverse(dr)) < f1
                     @test last(reverse(dr)) >= f1
                     @test issorted(dr)
-                    @test sortperm(dr) == 1:1:0
+                    @test sortperm(dr) ==ᵣ 1:1:0
                     @test !(f1 in dr)
                     @test !(l1 in dr)
                     @test !(f1 - pos_step in dr)
@@ -211,7 +216,7 @@ let
                     @test first(reverse(dr)) > l1
                     @test last(reverse(dr)) <= l1
                     @test issorted(dr)
-                    @test sortperm(dr) == 1:1:0
+                    @test sortperm(dr) ==ᵣ 1:1:0
                     @test !(l1 in dr)
                     @test !(l1 in dr)
                     @test !(l1 - neg_step in dr)

stdlib/REPL/test/replcompletions.jl

@@ -95,6 +95,11 @@ test_scomplete(s) =  map_completion_text(shell_completions(s,lastindex(s)))
 test_bslashcomplete(s) =  map_completion_text(bslash_completions(s,lastindex(s))[2])
 test_complete_context(s) =  map_completion_text(completions(s,lastindex(s),Main.CompletionFoo))
 
+# Compare ranges by comparing their `first` and `last` elements and their `length`. This
+# returns `false` if empty ranges have different startpoints.
+==ᵣ(r::AbstractRange, s::AbstractRange) =
+    (first(r) == first(s)) & (length(r) == length(s)) & (last(r) == last(s))
+
 let s = ""
     c, r = test_complete(s)
     @test "CompletionFoo" in c
@@ -126,7 +131,7 @@ end
 let s = "Main.CompletionFoo."
     c, r = test_complete(s)
     @test "bar" in c
-    @test r == 20:19
+    @test r ==ᵣ 20:19
     @test s[r] == ""
 end
 
@@ -550,7 +555,12 @@ end
 
 # The return type is of importance, before #8995 it would return nothing
 # which would raise an error in the repl code.
-@test (String[], 0:-1, false) == test_scomplete("\$a")
+let c, r, res
+    c, r, res = test_scomplete("\$a")
+    @test c == String[]
+    @test r ==ᵣ 0:-1
+    @test res === false
+end
 
 if Sys.isunix()
 let s, c, r
@@ -598,7 +608,7 @@ let s, c, r
         s = "/tmp/"
         c,r = test_scomplete(s)
         @test !("tmp/" in c)
-        @test r == 6:5
+        @test r ==ᵣ 6:5
         @test s[r] == ""
     end
 
@@ -615,7 +625,7 @@ let s, c, r
         file = joinpath(path, "repl completions")
         s = "/tmp "
         c,r = test_scomplete(s)
-        @test r == 6:5
+        @test r ==ᵣ 6:5
     end
 
     # Test completing paths with an escaped trailing space
@@ -929,7 +939,7 @@ end
 let s = ""
     c, r = test_complete_context(s)
     @test "bar" in c
-    @test r == 1:0
+    @test r ==ᵣ 1:0
     @test s[r] == ""
 end
 

test/core.jl

@@ -6701,7 +6701,7 @@ function f27597(y)
     return y
 end
 @test f27597([1]) == [1]
-@test f27597([]) == 1:0
+@test f27597([]) === 1:0
 
 # issue #22291
 wrap22291(ind) = (ind...,)

test/ranges.jl

@@ -422,10 +422,10 @@ end
     end
 end
 @testset "indexing range with empty range (#4309)" begin
-    @test (3:6)[5:4] == 7:6
+    @test (3:6)[5:4] === 7:6
     @test_throws BoundsError (3:6)[5:5]
     @test_throws BoundsError (3:6)[5]
-    @test (0:2:10)[7:6] == 12:2:10
+    @test (0:2:10)[7:6] === 12:2:10
     @test_throws BoundsError (0:2:10)[7:7]
 end
 # indexing with negative ranges (#8351)
@@ -765,7 +765,8 @@ end
                        map(Int32,1:3:17), map(Int64,1:3:17), 1:0, 1:-1:0, 17:-3:0,
                        0.0:0.1:1.0, map(Float32,0.0:0.1:1.0),map(Float32,LinRange(0.0, 1.0, 11)),
                        1.0:eps():1.0 .+ 10eps(), 9007199254740990.:1.0:9007199254740994,
-                       range(0, stop=1, length=20), map(Float32, range(0, stop=1, length=20))]
+                       range(0, stop=1, length=20), map(Float32, range(0, stop=1, length=20)),
+                       3:2, 5:-2:7, range(0.0, step=2.0, length=0), 3//2:3//2:0//1, LinRange(2,3,0)]
     for r in Rs
         local r
         ar = Vector(r)
@@ -785,6 +786,7 @@ end
     @test 1:1:10 == 1:10 == 1:10 == Base.OneTo(10) == Base.OneTo(10)
     @test 1:10 != 2:10 != 2:11 != Base.OneTo(11)
     @test Base.OneTo(10) != Base.OneTo(11) != 1:10
+    @test Base.OneTo(0) == 5:4
 end
 # issue #2959
 @test 1.0:1.5 == 1.0:1.0:1.5 == 1.0:1.0
@@ -1477,11 +1479,11 @@ end
         for stops in [-2, 0, 2, 100]
             for lengths in [2, 10, 100]
                 if stops >= starts
-                    @test range(starts, stops, length=lengths) == range(starts, stop=stops, length=lengths)
+                    @test range(starts, stops, length=lengths) === range(starts, stop=stops, length=lengths)
                 end
             end
             for steps in [0.01, 1, 2]
-                @test range(starts, stops, step=steps) == range(starts, stop=stops, step=steps)
+                @test range(starts, stops, step=steps) === range(starts, stop=stops, step=steps)
             end
         end
     end

test/regex.jl

@@ -49,8 +49,8 @@
     # findall:
     @test findall(r"\w+", "foo bar") == [1:3, 5:7]
     @test findall(r"\w+", "foo bar", overlap=true) == [1:3, 2:3, 3:3, 5:7, 6:7, 7:7]
-    @test findall(r"\w*", "foo bar") == [1:3, 4:3, 5:7, 8:7]
-    @test findall(r"\b", "foo bar") == [1:0, 4:3, 5:4, 8:7]
+    @test all(findall(r"\w*", "foo bar") .=== [1:3, 4:3, 5:7, 8:7]) # use === to compare empty ranges
+    @test all(findall(r"\b", "foo bar") .=== [1:0, 4:3, 5:4, 8:7])  # use === to compare empty ranges
 
     # Named subpatterns
     let m = match(r"(?<a>.)(.)(?<b>.)", "xyz")

test/sorting.jl

@@ -35,6 +35,12 @@ let a=[1:10;]
 end
 @test sum(randperm(6)) == 21
 
+# Compare ranges by comparing their `first` and `last` elements and their `length`. This
+# returns `false` if empty ranges have different startpoints, which is relevant for
+# `searchsorted`
+==ᵣ(r::AbstractRange, s::AbstractRange) =
+    (first(r) == first(s)) & (length(r) == length(s)) & (last(r) == last(s))
+
 @testset "searchsorted" begin
     numTypes = [ Int8,  Int16,  Int32,  Int64,  Int128,
                 UInt8, UInt16, UInt32, UInt64, UInt128,
@@ -46,16 +52,16 @@ end
     @test searchsorted(fill(1, 15), 1, 6, 10, Forward) == 6:10
 
     for R in numTypes, T in numTypes
-        @test searchsorted(R[1, 1, 2, 2, 3, 3], T(0)) == 1:0
+        @test searchsorted(R[1, 1, 2, 2, 3, 3], T(0)) === 1:0
         @test searchsorted(R[1, 1, 2, 2, 3, 3], T(1)) == 1:2
         @test searchsorted(R[1, 1, 2, 2, 3, 3], T(2)) == 3:4
-        @test searchsorted(R[1, 1, 2, 2, 3, 3], T(4)) == 7:6
-        @test searchsorted(R[1, 1, 2, 2, 3, 3], 2.5) == 5:4
+        @test searchsorted(R[1, 1, 2, 2, 3, 3], T(4)) === 7:6
+        @test searchsorted(R[1, 1, 2, 2, 3, 3], 2.5) === 5:4
 
-        @test searchsorted(1:3, T(0)) == 1:0
+        @test searchsorted(1:3, T(0)) ==ᵣ 1:0
         @test searchsorted(1:3, T(1)) == 1:1
         @test searchsorted(1:3, T(2)) == 2:2
-        @test searchsorted(1:3, T(4)) == 4:3
+        @test searchsorted(1:3, T(4)) ==ᵣ 4:3
 
         @test searchsorted(R[1:10;], T(1), by=(x -> x >= 5)) == 1:4
         @test searchsorted(R[1:10;], T(10), by=(x -> x >= 5)) == 5:10
@@ -67,31 +73,31 @@ end
         rg_r = reverse(rg)
         rgv, rgv_r = [rg;], [rg_r;]
         for i = I
-            @test searchsorted(rg,i) == searchsorted(rgv,i)
-            @test searchsorted(rg_r,i,rev=true) == searchsorted(rgv_r,i,rev=true)
+            @test searchsorted(rg,i) === searchsorted(rgv,i)
+            @test searchsorted(rg_r,i,rev=true) === searchsorted(rgv_r,i,rev=true)
         end
     end
 
     rg = 0.0:0.01:1.0
     for i = 2:101
         @test searchsorted(rg, rg[i]) == i:i
-        @test searchsorted(rg, prevfloat(rg[i])) == i:i-1
-        @test searchsorted(rg, nextfloat(rg[i])) == i+1:i
+        @test searchsorted(rg, prevfloat(rg[i])) === i:i-1
+        @test searchsorted(rg, nextfloat(rg[i])) === i+1:i
     end
 
     rg_r = reverse(rg)
     for i = 1:100
         @test searchsorted(rg_r, rg_r[i], rev=true) == i:i
-        @test searchsorted(rg_r, prevfloat(rg_r[i]), rev=true) == i+1:i
-        @test searchsorted(rg_r, nextfloat(rg_r[i]), rev=true) == i:i-1
+        @test searchsorted(rg_r, prevfloat(rg_r[i]), rev=true) === i+1:i
+        @test searchsorted(rg_r, nextfloat(rg_r[i]), rev=true) === i:i-1
     end
 
     @test searchsorted(1:10, 1, by=(x -> x >= 5)) == searchsorted([1:10;], 1, by=(x -> x >= 5))
     @test searchsorted(1:10, 10, by=(x -> x >= 5)) == searchsorted([1:10;], 10, by=(x -> x >= 5))
 
-    @test searchsorted([], 0) == 1:0
-    @test searchsorted([1,2,3], 0) == 1:0
-    @test searchsorted([1,2,3], 4) == 4:3
+    @test searchsorted([], 0) === 1:0
+    @test searchsorted([1,2,3], 0) === 1:0
+    @test searchsorted([1,2,3], 4) === 4:3
 
     @testset "issue 8866" begin
         @test searchsortedfirst(500:1.0:600, -1.0e20) == 1

test/strings/search.jl

@@ -247,7 +247,7 @@ end
 for i = 1:lastindex(u8str)
     @test findnext("", u8str, i) == i:i-1
 end
-@test findfirst("", "") == 1:0
+@test findfirst("", "") === 1:0
 
 # string backward search with a zero-char string
 for i = 1:lastindex(astr)
@@ -256,7 +256,7 @@ end
 for i = 1:lastindex(u8str)
     @test findprev("", u8str, i) == i:i-1
 end
-@test findlast("", "") == 1:0
+@test findlast("", "") === 1:0
 
 # string forward search with a zero-char regex
 for i = 1:lastindex(astr)
@@ -377,7 +377,7 @@ s_18109 = "fooα🐨βcd3"
 @testset "findall" begin
     @test findall("fooo", "foo") == UnitRange{Int}[]
     @test findall("ing", "Spinning laughing dancing") == [6:8, 15:17, 23:25]
-    @test findall("", "foo") == [1:0, 2:1, 3:2, 4:3]
+    @test all(findall("", "foo") .=== [1:0, 2:1, 3:2, 4:3]) # use === to compare empty ranges
     @test findall("αβ", "blαh blαβ blαββy") == findall("αβ", "blαh blαβ blαββy", overlap=true) == [9:11, 16:18]
     @test findall("aa", "aaaaaa") == [1:2, 3:4, 5:6]
     @test findall("aa", "aaaaaa", overlap=true) == [1:2, 2:3, 3:4, 4:5, 5:6]