From 708729bef81e73636e5cf68423a1e9136ec4ba96 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miguel=20Madrid-Menc=C3=ADa?=
 <miguel.madrid.mencia@gmail.com>
Date: Mon, 7 Jun 2021 23:34:22 +0200
Subject: [PATCH] Define lpad/rpad in terms of textwidth (#39044)

Fix #38256, per triage consensus there
---
 NEWS.md              |  1 +
 base/strings/util.jl | 16 ++++++++++------
 test/strings/util.jl |  5 +++++
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/NEWS.md b/NEWS.md
index c6a41f44e00c9..cc488312bbc70 100644
--- a/NEWS.md
+++ b/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
diff --git a/base/strings/util.jl b/base/strings/util.jl
index 9bc043513deed..411961d8221e7 100644
--- a/base/strings/util.jl
+++ b/base/strings/util.jl
@@ -327,7 +327,7 @@ 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
@@ -335,6 +335,8 @@ string is returned. Pad with spaces by default.
 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
@@ -355,7 +357,7 @@ 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
@@ -363,6 +365,8 @@ string is returned. Pad with spaces by default.
 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
diff --git a/test/strings/util.jl b/test/strings/util.jl
index e8ea3b643fcda..b0b5a0c36b8ef 100644
--- a/test/strings/util.jl
+++ b/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