[tannevaled]

Problem

In a 400px <h1> (20px), <span style="white-space:nowrap">A rather long heading that would wrap over two lines otherwise</span> still wrapped: h1 52px tall, span on two lines. white-space:nowrap on the h1 itself gave one line.

Spec read

• CSS Text 3 §3: white-space applies to all elements and is inherited.
• CSS Text 3 §5.5 (Line Breaking Details): a soft wrap opportunity at the boundary between two characters is controlled by the white-space property on their nearest common ancestor. One created by a character that disappears at the break (a space) is controlled by the box directly containing that character.

Root cause

Only the block container's white-space reached line breaking: blockOrInlineContents computed a single nowrap flag (layout/layout.go:518). Every inter-word space was a wrap opportunity (glueRun glued only items with SpaceBefore == 0), whatever the inline ancestors said.

Change

• InlineItem.NoWrapBefore, set after collection by markNoWrap when the nearest common ancestor of an item and the previous one has white-space: nowrap or pre.
• glueRun keeps such items in one run and counts the space between them. forceOne places a whole nowrap run that is wider than the line as one overflowing piece, instead of one word per line.
• Boundaries around the span still wrap: the span moves to the next line as a whole.
• Approximation: the space-at-the-boundary case uses the common ancestor rather than the space's own box. That only differs for a nowrap span ending in a space.

Checked

• pre on an inline span already did not wrap: its preserved spaces are not break points. Covered by the test.
• pre-wrap and pre-line are parsed as pre (css/parse.go:789), so a block with them never wraps. That is wrong: both should wrap. break-spaces is not parsed at all. Not fixed here; reported.

Tests

• TestInlineWhiteSpaceNowrap (RenderHTML + script measuring h1/span heights): nowrap span → one line, and a break before a nowrap span (52,26). Failed on main (52,52 / 52,52). Controls: nowrap on the block, pre span, normal span.
• TestInlineNowrapSpan (layout unit): an overflowing nowrap run stays whole. layout coverage 100.0%.

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