Unnecessary space added for non-rendered `{#if}` block

[bdpartridge]

Describe the bug

An unnecessary space is included in the HTML output of elements that include an {#if} block that is not rendered.

Reproduction

https://svelte.dev/playground/hello-world?version=5.25.6#H4sIAAAAAAAAE5WRsU7DMBCGX-VkGFopSvaQVnToxsiGGVznolh1HMu-0qIoKw_AI_Ik2EkpjdoiMfr3_f99d9cxIxpkOVsfyAnwVkgEURE6UBVsdCu3LGGV0uhZ_tIxerexOgpBP3pX1qb-DTVFbSM8XtNlawgNhRhWeOmUpSU3nFRjW0fwpMwWKtc2wFmaxdfRydkDN0X26zCFHYwrA3jGrDwoI_WuxBL2NRqgGk8jxF_TEjg0JTos8xhQDD1rh9WCs5rI-jzL8CAaqzGVbcPZcj2-QIfKYqBappHGnoM81yFy7DAhukrxT4IYiM4I_SdK2C6FQpaT22Gf3LjS2VKnZ5p-3LiTRoIuoiYnJlhAJbTHBGStdBlG64N0b11r_Wx-cTYx-vshrnscN3Gyzub9oN-Fbf006L8-PrtMVX2MEheDvoaXUHqvTMnygaT_BuckIsrPAgAA

Logs

System Info

System:
  OS: macOS 15.3.2
  CPU: (12) arm64 Apple M2 Pro
  Memory: 2.44 GB / 32.00 GB
  Shell: 5.9 - /bin/zsh
Binaries:
  Node: 20.14.0 - ~/projects/fwd/.gradle/nodejs/node-v20.14.0-darwin-arm64/bin/node
  npm: 10.7.0 - ~/projects/fwd/.gradle/nodejs/node-v20.14.0-darwin-arm64/bin/npm
  pnpm: 9.1.4 - ~/projects/fwd/.gradle/pnpm/pnpm-v9.1.4/bin/pnpm
Browsers:
  Chrome: 134.0.6998.166
  Edge: 134.0.3124.95
  Safari: 18.3.1
npmPackages:
  svelte: 5.22.5 => 5.22.5

Severity

annoyance

[brunnerh]

See e.g.:

• Extra spaces are added when rending markup #15655

[bdpartridge]

@brunnerh Looks like the relevant bit from the migration docs is this:

Whitespace between nodes is collapsed to one whitespace

That makes sense, but I'm surprised that logic applies to an {#if} block when it's not rendered. Should a node that's not in the DOM count as a node? Happy to close this issue if that's the case, but it might be worth clarifying this behavior somewhere in the docs at least.

[brunnerh]

Should a node that's not in the DOM count as a node?

Maybe not, though it looks like it currently does and changing it probably is not an option without a major version.

Regarding documentation, it would be nice to have a section on whitespace handling somewhere at the end of the basic markup section, especially since currently it only seems to be mentioned in the migration guide.