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layout: Use a consistent definition of "document white space" #44424

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Merged
mrobinson merged 1 commit into from
Apr 28, 2026
Merged

layout: Use a consistent definition of "document white space" #44424

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24 changes: 13 additions & 11 deletions components/layout/construct_modern.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -84,12 +84,14 @@ impl<'dom> ModernContainerJob<'dom> {
.push_text(flex_text_run.text, &flex_text_run.info);
}

let inline_formatting_context = inline_formatting_context_builder.finish(
builder.context,
true, /* has_first_formatted_line */
false, /* is_single_line_text_box */
builder.info.style.to_bidi_level(),
)?;
let inline_formatting_context = inline_formatting_context_builder
.finish(
builder.context,
true, /* has_first_formatted_line */
false, /* is_single_line_text_box */
builder.info.style.to_bidi_level(),
)
.expect("Did not expect document white space only text runs");

let block_formatting_context = BlockFormattingContext::from_block_container(
BlockContainer::InlineFormattingContext(inline_formatting_context),
Expand Down Expand Up @@ -178,14 +180,14 @@ struct ModernContainerTextRun<'dom> {
}

impl ModernContainerTextRun<'_> {
/// <https://drafts.csswg.org/css-text/#white-space>
/// <https://drafts.csswg.org/css-flexbox/#flex-items>:
/// > However, if the entire text sequences contains only document white space characters (i.e.
/// > characters that can be affected by the white-space property) it is instead not rendered
/// > (just as if its text nodes were display:none).
fn is_only_document_white_space(&self) -> bool {
// FIXME: is this the right definition? See
// https://github.com/w3c/csswg-drafts/issues/5146
// https://github.com/w3c/csswg-drafts/issues/5147
self.text
.bytes()
.all(|byte| matches!(byte, b' ' | b'\n' | b'\t'))
.all(|byte| InlineFormattingContextBuilder::is_document_white_space(byte.into()))

@Loirooriol Loirooriol Apr 22, 2026 •
edited
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I have tested Firefox and Chrome, and U+000C doesn't create a flex item:

<!DOCTYPE html>
<div style="display: flex; justify-content: space-between">&#x000c;<span>item</span></div>

But it's not included in is_document_white_space

@mrobinson mrobinson Apr 22, 2026

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I wasn't sure how to test this, so it is good to have confirmation. I've updated the change to include the form feed character (U+00C), which also happens to be WhatWG's definition of ASCII white space and the Rust is_ascii_whitespace function.

}
}

Expand Down
24 changes: 21 additions & 3 deletions components/layout/flow/inline/construct.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,22 @@ pub(crate) struct InlineFormattingContextBuilder {
}

impl InlineFormattingContextBuilder {
/// <https://drafts.csswg.org/css-text/#white-space>:
/// > Except where specified otherwise, white space processing in CSS affects only the document
/// > white space characters: spaces (U+0020), tabs (U+0009), and segment breaks.
///
/// From <https://github.com/w3c/csswg-drafts/issues/5147#issuecomment-637816669>:
/// > HTML clearly treats CR, LF, and CRLF as segment breaks.
///
/// Other browsers also consider the form feed character (0x0c) to be document white space, it
/// seems.
///
/// Taken all together, this is equivalent to the WhatWG Infra Standard's definition of ASCII
/// white space.
pub(crate) fn is_document_white_space(character: char) -> bool {
character.is_ascii_whitespace()
}

pub(crate) fn new(info: &NodeAndStyleInfo, context: &LayoutContext) -> Self {
Self {
// For the purposes of `text-transform: capitalize` the start of the IFC is a word boundary.
Expand Down Expand Up @@ -370,9 +386,9 @@ impl InlineFormattingContextBuilder {

self.is_empty = self.is_empty &&
match white_space_collapse {
WhiteSpaceCollapse::Collapse => character.is_ascii_whitespace(),
WhiteSpaceCollapse::Collapse => Self::is_document_white_space(character),
WhiteSpaceCollapse::PreserveBreaks => {
character.is_ascii_whitespace() && character != '\n'
Self::is_document_white_space(character) && character != '\n'
},
WhiteSpaceCollapse::Preserve | WhiteSpaceCollapse::BreakSpaces => false,
};
Expand Down Expand Up @@ -550,7 +566,9 @@ where
// Don't push non-newline whitespace immediately. Instead wait to push it until we
// know that it isn't followed by a newline. See `push_pending_whitespace_if_needed`
// above.
if character.is_ascii_whitespace() && character != '\n' {
if InlineFormattingContextBuilder::is_document_white_space(character) &&
character != '\n'
{
self.inside_white_space = true;
continue;
}
Expand Down
7 changes: 7 additions & 0 deletions tests/wpt/meta/MANIFEST.json
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Original file line number Diff line number Diff line change
Expand Up @@ -2921,6 +2921,13 @@
]
]
},
"anonymous-flex-item-document-white-space-crash.html": [
"b670a1029ddf7552eaba97a77444815042e222e7",
[
null,
{}
]
],
"button-column-wrap-crash.html": [
"0741735d4e357af037169937229c96209c457ac7",
[
Expand Down
7 changes: 7 additions & 0 deletions tests/wpt/tests/css/css-flexbox/anonymous-flex-item-document-white-space-crash.html
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
<!DOCTYPE html>
<link rel="assert" href="Flex containers that only contain document white space should not cause a crash">
<link rel="help" href="https://github.com/servo/servo/issues/43550">

<div style="display: flex">&#10;&#13;</div>
<div style="display: flex">&#13;</div>
<div style="display: flex">&#12;</div>
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