cli: Action text flashes while the spinner is active

[jsteinich]

Expected Behavior

The text stays static while the spinner is spinning

Actual Behavior

The text (synthesizing, processing, etc) flashes while the spinner is animating

Steps to Reproduce

1. Run any action that uses the spinner in the cli
2. Observe its behavior

Versions

language: typescript
cdktn-cli: 0.24.0-pre.91
node: v22.22.2
cdktn: 0.24.0-pre.91
cdktf: null
constructs: 10.6.0
jsii: null
terraform: 1.14.3
arch: x64
os: win32 10.0.26200

Migration Context

Not sure / don't remember

Upstream cdktf Issue

No response

Providers

No response

Gist

No response

Possible Solutions

No response

Workarounds

No response

Anything Else?

I checked both powershell and command prompt and observed the same behavior. I have not checked linux / mac.

References

No response

Help Wanted

• I'm interested in contributing a fix myself

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[so0k]

We tried to reproduce this on macOS to answer whether it's Windows-specific. Full cross-cutting triage of all three CLI issues is in #361 — the #359-relevant part:

Not Windows-specific in code. Zero process.platform / win32 hits in tty-stream.ts or project-runner.ts — the same ANSI bytes are emitted on every OS.

Reproduced on macOS: mechanism yes, visible symptom no. We captured raw ANSI byte streams from a real macOS pty (script -q, so isTTY===true actually engaged) and confirmed a full erase-and-rewrite of the entire bar — spinner glyph and static label together — roughly every 80ms, plus two more full repaints per log line during deploy. What we did not do is watch a rendered Terminal.app/iTerm2 window, so we can't claim a human-perceptible flash here. Please read that as a code-level finding, not a visual one.

Likely cause — three uncoordinated repaint triggers, none debounced:

• packages/cdktn-cli/src/bin/cmds/helper/tty-stream.ts:155 — paintBar() always rewrites glyph + label; never updates the glyph in place.
• packages/cdktn-cli/src/bin/cmds/helper/tty-stream.ts:181 — startSpinner()'s unthrottled 80ms setInterval does eraseBar() + paintBar() every tick even when the label hasn't changed.
• packages/cdktn-cli/src/bin/cmds/helper/tty-stream.ts:86 — appendLog() does its own erase + repaint per line.
• packages/cdktn-cli/src/bin/cmds/helper/project-runner.ts:113-116 — fires opts.onLog?.(event) and then unconditionally fireStatus(runningStatus(project)), so every log line causes two full repaints back-to-back on top of the spinner's cadence.

Why Windows looks worse is plausibly the terminal, not the CLI: legacy consoles (conhost hosting cmd/powershell — what you tested) redraw synchronously per write without compositor double-buffering, whereas macOS/GPU-composited terminals tend to coalesce bursts into one vsync'd frame. That's reasoning from documentation, not measurement — we had no Windows host.

Severity: cosmetic, TTY-only — StreamRenderer skips the bar entirely when this.tty is false, so CI logs are unaffected.

Being straight about one thing: of the three, this is the only genuine 0.24 regression. tty-stream.ts arrived in a6aff7e6c (#264, the Ink + React removal) and has never shipped in a stable tag. We also did not A/B against 0.23's Ink renderer, so we can't say whether flicker got worse, better, or merely different.

A fix would be two independent changes: update only the spinner glyph in place when the label is unchanged, and stop the redundant fireStatus refire per log line (or debounce it so a repaint only happens when the bar text actually changes).