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fix(text): truncate by grapheme cluster, like DisplayWidth measures #314

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fix(text): truncate by grapheme cluster, like DisplayWidth measures #314

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4 changes: 2 additions & 2 deletions go.mod
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ require (
github.com/alecthomas/chroma/v2 v2.27.0
github.com/charmbracelet/glamour v0.10.0
github.com/charmbracelet/lipgloss v1.1.1-0.20250404203927-76690c660834
github.com/charmbracelet/x/ansi v0.8.0
github.com/cli/browser v1.3.0
github.com/cli/safeexec v1.0.1
github.com/cli/shurcooL-graphql v0.0.4
Expand All @@ -17,7 +18,6 @@ require (
github.com/itchyny/gojq v0.12.19
github.com/leaanthony/go-ansi-parser v1.6.1
github.com/mgutz/ansi v0.0.0-20200706080929-d51e80ef957d
github.com/muesli/reflow v0.3.0
github.com/muesli/termenv v0.16.0
github.com/stretchr/testify v1.12.1
github.com/thlib/go-timezone-local v0.0.8
Expand All @@ -35,7 +35,6 @@ require (
github.com/aymanbagabas/go-osc52/v2 v2.0.1 // indirect
github.com/aymerick/douceur v0.2.0 // indirect
github.com/charmbracelet/colorprofile v0.2.3-0.20250311203215-f60798e515dc // indirect
github.com/charmbracelet/x/ansi v0.8.0 // indirect
github.com/charmbracelet/x/cellbuf v0.0.13 // indirect
github.com/charmbracelet/x/exp/slice v0.0.0-20250327172914-2fdc97757edf // indirect
github.com/charmbracelet/x/term v0.2.1 // indirect
Expand All @@ -55,6 +54,7 @@ require (
github.com/microcosm-cc/bluemonday v1.0.27 // indirect
github.com/mitchellh/copystructure v1.2.0 // indirect
github.com/mitchellh/reflectwalk v1.0.2 // indirect
github.com/muesli/reflow v0.3.0 // indirect
github.com/rivo/uniseg v0.4.7 // indirect
github.com/shopspring/decimal v1.4.0 // indirect
github.com/spf13/cast v1.7.0 // indirect
Expand Down
9 changes: 7 additions & 2 deletions pkg/text/text.go
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Expand Up @@ -9,7 +9,7 @@ import (
"unicode"

"github.com/charmbracelet/lipgloss"
"github.com/muesli/reflow/truncate"
"github.com/charmbracelet/x/ansi"
"golang.org/x/text/runes"
"golang.org/x/text/transform"
"golang.org/x/text/unicode/norm"
Expand Down Expand Up @@ -46,7 +46,12 @@ func Truncate(maxWidth int, s string) string {
if maxWidth >= minWidthForEllipsis {
tail = ellipsis
}
r := truncate.StringWithTail(s, uint(maxWidth), tail)
// ansi.Truncate measures in grapheme clusters, the same unit lipgloss.Width
// uses in DisplayWidth above. Measuring the cut with a different width model
// than the one used to decide whether a cut is needed makes the result miss
// the budget: a rune-wise truncator reads an emoji ZWJ sequence as one wide
// character per person in it, so it stops several columns early.
r := ansi.Truncate(s, maxWidth, tail)
if DisplayWidth(r) < maxWidth {
r += " "
}
Expand Down
52 changes: 52 additions & 0 deletions pkg/text/text_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -163,6 +163,24 @@ func TestTruncate(t *testing.T) {
},
want: "\x1b[0;31mé́́é́́é́́é́́é́́é́́é́́é́́...\x1b[0m",
},
{
// A ZWJ sequence occupies two columns however many people are in it,
// so eight of the eleven are still available for the text after it.
name: "Emoji ZWJ sequence",
args: args{
max: 11,
s: "πŸ‘¨β€πŸ‘©β€πŸ‘§β€πŸ‘¦ family names here",
},
want: "πŸ‘¨β€πŸ‘©β€πŸ‘§β€πŸ‘¦ famil...",
},
{
name: "Regional indicator pair",
args: args{
max: 11,
s: "πŸ‡―πŸ‡΅ Japanese README",
},
want: "πŸ‡―πŸ‡΅ Japan...",
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
Expand All @@ -172,6 +190,40 @@ func TestTruncate(t *testing.T) {
}
}

func TestTruncateFillsTheBudget(t *testing.T) {
// Truncate measures with DisplayWidth to decide whether a string is too
// wide, so the result has to be measured the same way: never wider than the
// budget, and never narrower than it once the string really was too long.
// Mixing two width models silently loses columns, which shows up as ragged
// table output for anyone whose text is not ASCII.
corpus := []string{
"hello world, a plain ascii string",
"γƒ†γ‚Ήγƒˆγƒ†γ‚Ήγƒˆγƒ†γ‚Ήγƒˆγƒ†γ‚Ήγƒˆ",
"εΉ«ζ–°θˆ‰ε ±ι•η« ε·₯ε» ζ–°ε’žη·¨θ™Ÿ",
"ν”„λ‘œμ νŠΈ λ‚΄μ˜",
"πŸ’‘πŸ’‘πŸ’‘πŸ’‘πŸ’‘πŸ’‘πŸ’‘πŸ’‘πŸ’‘πŸ’‘πŸ’‘πŸ’‘",
"πŸ‘¨β€πŸ‘©β€πŸ‘§β€πŸ‘¦ family names here",
"πŸ‡―πŸ‡΅ Japanese README",
"πŸ³οΈβ€πŸŒˆ pride flag entry",
"πŸ‘πŸ½ thumbs up with a skin tone",
"❀️ reactions on issues",
"é́́é́́é́́é́́é́́é́́é́́é́́é́́é́́é́́é́́",
"\x1b[0;31mcoloured text that is long\x1b[0m",
}
for _, s := range corpus {
for maxWidth := 1; maxWidth <= 24; maxWidth++ {
got := Truncate(maxWidth, s)
gotWidth := DisplayWidth(got)
assert.LessOrEqual(t, gotWidth, maxWidth,
"Truncate(%d, %q) = %q is wider than the budget", maxWidth, s, got)
if DisplayWidth(s) > maxWidth {
assert.Equal(t, maxWidth, gotWidth,
"Truncate(%d, %q) = %q leaves columns unused", maxWidth, s, got)
}
}
}
}

func TestPadRight(t *testing.T) {
type args struct {
max int
Expand Down