Newline in string prop treated differently if in curly braces

[timephy]

Describe the bug

Given any child component taking a prop text: string.

<Component text={"A\nB"}></Component>
<Component text="A\nB"></Component>

results in:

A B
A\nB

To me this is very unexcepted. It broke my layout that depended on a \n.

I can see that syntax highlighting marks \n as "special" when in curly braces, so I could have noticed it.

However, the linting warning Unexpected mustache interpolation with a string literal value.eslint[svelte/no-useless-mustaches](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-useless-mustaches/) lead me to remove the curly braces.

Reproduction

https://svelte.dev/playground/a709bcd1203b4664ab2188c4434b8099?version=5.23.2#H4sIAAAAAAAAE3WRzWrDMBCEX2VZemjBxHdjG9Le8wLdHhRnHQTySkibJsb43Yv6ExMnvc5-M9pZTShmYKxwx2dnhcEKJI1WjhCiD6CRjfIBDrbvObKoG8H2mepO0Y2wj6bjhAX21nHC6n1CHUMOzAIWf_HbEDbpk51mbW8SP9I7L8qiCSusUxdt0JaElNQOwUeFNz8ELywKffQDEG7Kq_SbQkhSl4tZ6sWkfNFmItwSySvh3NaLvb0nr-ANhwXmKVYaTzwX_9Rdr3Vb-sH0vjo4I8eGUBPh9xk6L0lhyq_P0MBT_p_0_LLuG9ofpC7DatmP-QundUBE7gEAAA==

Logs

System Info

playground

Severity

annoyance

[timephy]

I needed to add this to my eslint config to get rid of the error.

            "svelte/no-useless-mustaches": [
                "error",
                {
                    ignoreIncludesComment: true,
                    ignoreStringEscape: true,
                },
            ],

But shouldn't that be the default behaviour?

[brunnerh]

The overall behavior is expected, without {}, this is just a plain HTML attribute. \n has no meaning in HTML.

This is a failure of the ESLint rule; if the string uses escape sequences this is arguably not a "useless mustache". There are of course ways to encode special characters in HTML but this is usually more verbose (involving entities like 
 - there appears to be a bug here).