Define lpad/rpad in terms of textwidth (JuliaLang#39044)

Fix JuliaLang#38256, per triage consensus there

NEWS.md

@@ -100,6 +100,7 @@ Standard library changes
 * `keys(::RegexMatch)` is now defined to return the capture's keys, by name if named, or by index if not ([#37299]).
 * `keys(::Generator)` is now defined to return the iterator's keys ([#34678])
 * `RegexMatch` now iterate to give their captures. ([#34355]).
+* `lpad/rpad` are now defined in terms of `textwidth` ([#39044])
 * `Test.@test` now accepts `broken` and `skip` boolean keyword arguments, which
  mimic `Test.@test_broken` and `Test.@test_skip` behavior, but allows skipping
  tests failing only under certain conditions. For example

base/strings/util.jl

@@ -327,14 +327,16 @@ strip(f, s::AbstractString) = lstrip(f, rstrip(f, s))
  lpad(s, n::Integer, p::Union{AbstractChar,AbstractString}=' ') -> String
 
 Stringify `s` and pad the resulting string on the left with `p` to make it `n`
-characters (code points) long. If `s` is already `n` characters long, an equal
+characters (in [`textwidth`](@ref)) long. If `s` is already `n` characters long, an equal
 string is returned. Pad with spaces by default.
 
 # Examples
 ```jldoctest
 julia> lpad("March", 10)
 " March"
 ```
+!!! compat "Julia 1.7"
+ In Julia 1.7, this function was changed to use `textwidth` rather than a raw character (codepoint) count.
 """
 lpad(s, n::Integer, p::Union{AbstractChar,AbstractString}=' ') = lpad(string(s)::AbstractString, n, string(p))
 
@@ -344,9 +346,9 @@ function lpad(
  p::Union{AbstractChar,AbstractString}=' ',
 ) :: String
  n = Int(n)::Int
- m = signed(n) - Int(length(s))::Int
+ m = signed(n) - Int(textwidth(s))::Int
  m ≤ 0 && return string(s)
- l = length(p)
+ l = textwidth(p)
  q, r = divrem(m, l)
  r == 0 ? string(p^q, s) : string(p^q, first(p, r), s)
 end
@@ -355,14 +357,16 @@ end
  rpad(s, n::Integer, p::Union{AbstractChar,AbstractString}=' ') -> String
 
 Stringify `s` and pad the resulting string on the right with `p` to make it `n`
-characters (code points) long. If `s` is already `n` characters long, an equal
+characters (in [`textwidth`](@ref)) long. If `s` is already `n` characters long, an equal
 string is returned. Pad with spaces by default.
 
 # Examples
 ```jldoctest
 julia> rpad("March", 20)
 "March "
 ```
+!!! compat "Julia 1.7"
+ In Julia 1.7, this function was changed to use `textwidth` rather than a raw character (codepoint) count.
 """
 rpad(s, n::Integer, p::Union{AbstractChar,AbstractString}=' ') = rpad(string(s)::AbstractString, n, string(p))
 
@@ -372,9 +376,9 @@ function rpad(
  p::Union{AbstractChar,AbstractString}=' ',
 ) :: String
  n = Int(n)::Int
- m = signed(n) - Int(length(s))::Int
+ m = signed(n) - Int(textwidth(s))::Int
  m ≤ 0 && return string(s)
- l = length(p)
+ l = textwidth(p)
  q, r = divrem(m, l)
  r == 0 ? string(s, p^q) : string(s, p^q, first(p, r))
 end

test/strings/util.jl

@@ -44,6 +44,11 @@
  # Issue #32160 (unsigned underflow in lpad/rpad)
  @test lpad("xx", UInt(1), " ") == "xx"
  @test rpad("xx", UInt(1), " ") == "xx"
+ # Issue #38256 (lpad/rpad defined in terms of textwidth)
+ @test lpad("⟨k|H₁|k̃⟩", 12) |> textwidth == 12
+ @test rpad("⟨k|H₁|k̃⟩", 12) |> textwidth == 12
+ @test lpad("⟨k|H₁|k⟩", 12) |> textwidth == 12
+ @test rpad("⟨k|H₁|k⟩", 12) |> textwidth == 12
 end
 
 # string manipulation