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Merged
ematipico merged 3 commits into from
Apr 20, 2026
Merged

fix(parser): fix crash when parsing Svelte templates #10043

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ae401b1
fix(parser): fix crash when parsing Svelte templates
mujpao Apr 19, 2026
024611a
Add link to issue in changeset
mujpao Apr 19, 2026
3371e25
Enter parser recovery mode
mujpao Apr 20, 2026
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5 changes: 5 additions & 0 deletions .changeset/honest-shirts-wear.md
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---
"@biomejs/biome": patch
---

Fixed [#10003](https://github.com/biomejs/biome/issues/10003): Biome no longer panics when parsing Svelte files containing `{#}`.
26 changes: 22 additions & 4 deletions crates/biome_html_parser/src/syntax/svelte.rs
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Expand Up @@ -32,8 +32,17 @@ pub(crate) fn parse_svelte_hash_block(p: &mut HtmlParser) -> ParsedSyntax {
T![await] => parse_await_block(p, m),
T![snippet] => parse_snippet_block(p, m),
_ => {
m.abandon(p);
Absent
p.error(p.err_builder(
"Expected `if`, `each`, `key`, `await`, or `snippet`",
p.cur_range(),
));

if !p.at(T!['}']) {
let _ = ParseRecoveryTokenSet::new(HTML_BOGUS, token_set![T!['}']]).recover(p);
}

p.expect(T!['}']);
Present(m.complete(p, SVELTE_BOGUS_BLOCK))
}
Comment thread
coderabbitai[bot] marked this conversation as resolved.
}
}
Expand Down Expand Up @@ -826,8 +835,17 @@ pub(crate) fn parse_svelte_at_block(p: &mut HtmlParser) -> ParsedSyntax {
T![render] => parse_render_block(p, m),
T![const] => parse_const_block(p, m),
_ => {
m.abandon(p);
Absent
p.error(p.err_builder(
"Expected `render`, `html`, `const`, or `debug`",
p.cur_range(),
));

if !p.at(T!['}']) {
let _ = ParseRecoveryTokenSet::new(HTML_BOGUS, token_set![T!['}']]).recover(p);
}

p.expect(T!['}']);
Present(m.complete(p, SVELTE_BOGUS_BLOCK))
}
}
}
Expand Down
1 change: 1 addition & 0 deletions crates/biome_html_parser/tests/html_specs/error/svelte/at_block_invalid_block_type.svelte
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@@ -0,0 +1 @@
{@notarealblocktype}
66 changes: 66 additions & 0 deletions ...s/biome_html_parser/tests/html_specs/error/svelte/at_block_invalid_block_type.svelte.snap
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---
source: crates/biome_html_parser/tests/spec_test.rs
expression: snapshot
---

## Input

```svelte
{@notarealblocktype}

```


## AST

```
HtmlRoot {
bom_token: missing (optional),
frontmatter: missing (optional),
directive: missing (optional),
html: HtmlElementList [
SvelteBogusBlock {
items: [
SV_CURLY_AT@0..2 "{@" [] [],
HtmlBogus {
items: [
IDENT@2..19 "notarealblocktype" [] [],
],
},
R_CURLY@19..20 "}" [] [],
],
},
],
eof_token: EOF@20..21 "" [Newline("\n")] [],
}
```

## CST

```
0: HTML_ROOT@0..21
0: (empty)
1: (empty)
2: (empty)
3: HTML_ELEMENT_LIST@0..20
0: SVELTE_BOGUS_BLOCK@0..20
0: SV_CURLY_AT@0..2 "{@" [] []
1: HTML_BOGUS@2..19
0: IDENT@2..19 "notarealblocktype" [] []
2: R_CURLY@19..20 "}" [] []
4: EOF@20..21 "" [Newline("\n")] []

```

## Diagnostics

```
at_block_invalid_block_type.svelte:1:3 parse ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

× Expected `render`, `html`, `const`, or `debug`

> 1 │ {@notarealblocktype}
│ ^^^^^^^^^^^^^^^^^
2 │

```
1 change: 1 addition & 0 deletions crates/biome_html_parser/tests/html_specs/error/svelte/at_block_missing_block_type.svelte
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{@}
59 changes: 59 additions & 0 deletions ...s/biome_html_parser/tests/html_specs/error/svelte/at_block_missing_block_type.svelte.snap
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---
source: crates/biome_html_parser/tests/spec_test.rs
expression: snapshot
---

## Input

```svelte
{@}

```


## AST

```
HtmlRoot {
bom_token: missing (optional),
frontmatter: missing (optional),
directive: missing (optional),
html: HtmlElementList [
SvelteBogusBlock {
items: [
SV_CURLY_AT@0..2 "{@" [] [],
R_CURLY@2..3 "}" [] [],
],
},
],
eof_token: EOF@3..4 "" [Newline("\n")] [],
}
```

## CST

```
0: HTML_ROOT@0..4
0: (empty)
1: (empty)
2: (empty)
3: HTML_ELEMENT_LIST@0..3
0: SVELTE_BOGUS_BLOCK@0..3
0: SV_CURLY_AT@0..2 "{@" [] []
1: R_CURLY@2..3 "}" [] []
4: EOF@3..4 "" [Newline("\n")] []

```

## Diagnostics

```
at_block_missing_block_type.svelte:1:3 parse ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

× Expected `render`, `html`, `const`, or `debug`

> 1 │ {@}
│ ^
2 │

```
1 change: 1 addition & 0 deletions ...parser/tests/html_specs/error/svelte/at_block_missing_block_type_and_closing_brace.svelte
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{@
57 changes: 57 additions & 0 deletions ...r/tests/html_specs/error/svelte/at_block_missing_block_type_and_closing_brace.svelte.snap
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@@ -0,0 +1,57 @@
---
source: crates/biome_html_parser/tests/spec_test.rs
expression: snapshot
---

## Input

```svelte
{@

```


## AST

```
HtmlRoot {
bom_token: missing (optional),
frontmatter: missing (optional),
directive: missing (optional),
html: HtmlElementList [
SvelteBogusBlock {
items: [
SV_CURLY_AT@0..2 "{@" [] [],
],
},
],
eof_token: EOF@2..3 "" [Newline("\n")] [],
}
```

## CST

```
0: HTML_ROOT@0..3
0: (empty)
1: (empty)
2: (empty)
3: HTML_ELEMENT_LIST@0..2
0: SVELTE_BOGUS_BLOCK@0..2
0: SV_CURLY_AT@0..2 "{@" [] []
4: EOF@2..3 "" [Newline("\n")] []

```

## Diagnostics

```
at_block_missing_block_type_and_closing_brace.svelte:2:1 parse ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

× Expected `render`, `html`, `const`, or `debug`

1 │ {@
> 2 │
│

```
1 change: 1 addition & 0 deletions crates/biome_html_parser/tests/html_specs/error/svelte/template_invalid_block_type.svelte
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@@ -0,0 +1 @@
{#notarealblocktype}
64 changes: 64 additions & 0 deletions ...s/biome_html_parser/tests/html_specs/error/svelte/template_invalid_block_type.svelte.snap
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---
source: crates/biome_html_parser/tests/spec_test.rs
expression: snapshot
---

## Input

```svelte
{#notarealblocktype}
```


## AST

```
HtmlRoot {
bom_token: missing (optional),
frontmatter: missing (optional),
directive: missing (optional),
html: HtmlElementList [
SvelteBogusBlock {
items: [
SV_CURLY_HASH@0..2 "{#" [] [],
HtmlBogus {
items: [
IDENT@2..19 "notarealblocktype" [] [],
],
},
R_CURLY@19..20 "}" [] [],
],
},
],
eof_token: EOF@20..20 "" [] [],
}
```

## CST

```
0: HTML_ROOT@0..20
0: (empty)
1: (empty)
2: (empty)
3: HTML_ELEMENT_LIST@0..20
0: SVELTE_BOGUS_BLOCK@0..20
0: SV_CURLY_HASH@0..2 "{#" [] []
1: HTML_BOGUS@2..19
0: IDENT@2..19 "notarealblocktype" [] []
2: R_CURLY@19..20 "}" [] []
4: EOF@20..20 "" [] []

```

## Diagnostics

```
template_invalid_block_type.svelte:1:3 parse ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

× Expected `if`, `each`, `key`, `await`, or `snippet`

> 1 │ {#notarealblocktype}
│ ^^^^^^^^^^^^^^^^^

```
1 change: 1 addition & 0 deletions crates/biome_html_parser/tests/html_specs/error/svelte/template_missing_block_type.svelte
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@@ -0,0 +1 @@
{#}
59 changes: 59 additions & 0 deletions ...s/biome_html_parser/tests/html_specs/error/svelte/template_missing_block_type.svelte.snap
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---
source: crates/biome_html_parser/tests/spec_test.rs
expression: snapshot
---

## Input

```svelte
{#}

```


## AST

```
HtmlRoot {
bom_token: missing (optional),
frontmatter: missing (optional),
directive: missing (optional),
html: HtmlElementList [
SvelteBogusBlock {
items: [
SV_CURLY_HASH@0..2 "{#" [] [],
R_CURLY@2..3 "}" [] [],
],
},
],
eof_token: EOF@3..4 "" [Newline("\n")] [],
}
```

## CST

```
0: HTML_ROOT@0..4
0: (empty)
1: (empty)
2: (empty)
3: HTML_ELEMENT_LIST@0..3
0: SVELTE_BOGUS_BLOCK@0..3
0: SV_CURLY_HASH@0..2 "{#" [] []
1: R_CURLY@2..3 "}" [] []
4: EOF@3..4 "" [Newline("\n")] []

```

## Diagnostics

```
template_missing_block_type.svelte:1:3 parse ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

× Expected `if`, `each`, `key`, `await`, or `snippet`

> 1 │ {#}
│ ^
2 │

```
1 change: 1 addition & 0 deletions ...parser/tests/html_specs/error/svelte/template_missing_block_type_and_closing_brace.svelte
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{#
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