`gum input` doubles prompt output

[amancevice]

Describe the bug
Since v0.15+, gum input doubles the prompt when executed

To Reproduce
Steps to reproduce the behavior:

cat <<-DOCKERFILE | docker build --tag gum - && docker run --rm -it gum input
FROM alpine
WORKDIR /gum
ADD https://github.com/charmbracelet/gum/releases/download/v0.16.0/gum_0.16.0_aarch64.apk .
RUN apk add --allow-untrusted gum_0.16.0_aarch64.apk
ENTRYPOINT ["gum"]
DOCKERFILE

Expected behavior
The prompt should only appear once, as it does in gum v0.14.x

Screenshots

Desktop (please complete the following information):

• OS: macOS / alpine linux
• Browser N/A
• Version v0.16.0

[deepankermishra]

I am also seeing this behaviour.

[sebastianhuus]

Also seeing this on MacOS Sonoma with Gum 0.16.2

Interesting note: This is only present in the MacOS Terminal app. I do not see the same issue in VS Code's integrated terminal.

MacOS Terminal:

VS Code terminal:

[sebastianhuus]

I believe I fixed it!

I don't know Go, so I had Gemini CLI & Claude Code analyze the bug. They both independently identified that the issue is in the Bubbles library, specifically in the placeholderView function in textinput/textinput.go.

The Problem:
The function creates a rune slice with size m.Width+1 on line 708. During the initial render when m.Width is 0, this creates a slice of length 1, which truncates the placeholder to just the first character. On subsequent renders when the width is properly calculated, the full placeholder displays correctly.

The Fix:
I changed line 708 from:

p := make([]rune, m.Width+1)

to:

p := make([]rune, max(len(m.Placeholder), m.Width+1))

And updated the early return condition on line 716 to check len(m.Placeholder) instead of len(p).

This ensures the slice is always large enough to hold the entire placeholder text, eliminating the two-phase rendering bug.

Here is how it looks with normal Gum installed with Homebrew:

Here's how it looks when I build Gum with my modified Bubbles:

[amancevice]

thanks, @sebastianhuus! have you opened a PR in bubbles?

[sebastianhuus]

thanks, @sebastianhuus! have you opened a PR in bubbles?

Yes awaiting review from a maintainer.

charmbracelet/bubbles#816