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feat(cli): DO NOT MERGE cdk synth --watch re-synthesizes on file changes - #1851

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worktree-synth-watch-flag
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feat(cli): DO NOT MERGE cdk synth --watch re-synthesizes on file changes#1851
iankhou wants to merge 1 commit into
mainfrom
worktree-synth-watch-flag

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@iankhou

@iankhou iankhou commented Aug 19, 2026

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Do not merge. Waiting on consolidation of CLI and Toolkit Lib synth implementations, which are still separate now.

Description

Adds a --watch flag to cdk synth, allowing developers to synth on file changes.

Very similar to cdk validate --watch (which also synths on file changes, but 1. returns the validation report, 2. performs online validation by default)

CLI synth and Toolkit synth do not currently follow the same code path, but implement the same behavior (migration needed).

  • toolkit-lib: new public Toolkit.watchSynth() and WatchSynthOptions, built on the existing generic _watch loop (chokidar, change batching, error resilience, dispose/waitForEnd). The body of Toolkit.synth is extracted into a private _synth(assembly, options) so both can share it, matching the existing validate/_validate split.

  • CLI: new watch option on the synth command, regenerated parser files, and a CdkToolkit.synthWatch() that requires the cdk.json "watch" key (WatchConfigMissing otherwise) and passes an uncached assembly source so every iteration re-synthesizes.

Testing

Unit tests
Integ tests pending

Checklist

  • This change contains a major version upgrade for a dependency and I confirm all breaking changes are addressed
    • Release notes for the new version:

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

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Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

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@iankhou
iankhou deployed to no-approval August 19, 2026 15:08 — with GitHub Actions Active
@aws-cdk-automation
aws-cdk-automation requested a review from a team August 19, 2026 15:08
@iankhou
iankhou deployed to no-approval August 25, 2026 18:12 — with GitHub Actions Active
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2 participants