fix(formatter_htmlish): keep SVG text under xml:space="preserve" as written (#28382)

```html
<svg>
  <text x="0" y="10" xml:space="preserve">  a  <tspan>b</tspan>  c</text>
</svg>
```

Preserve these as-is.

crates/oxc_formatter_htmlish/DIVERGENCES.md

@@ -274,6 +274,36 @@ whitespace between them is kept or omitted as written, as between HTML inline el
 Prettier lays out every SVG element but `<svg>` as a block (prettier/prettier#17713, prettier/prettier#10121).
 With `htmlWhitespaceSensitivity: "ignore"` they stay blocks, as HTML inline elements do.
 
+## svg-xml-space-preserve
+
+- Why: semantics (whitespace in an SVG `<text>` under `xml:space="preserve"` renders as written; prettier/prettier#10121)
+- Pin: `tests/fixtures/html/svg-xml-space-preserve.html`
+
+```html
+<!-- input -->
+<svg><text x="0" y="10" xml:space="preserve">  a  <tspan>b</tspan>  c</text></svg>
+
+<!-- ours -->
+<svg>
+  <text x="0" y="10" xml:space="preserve">  a  <tspan>b</tspan>  c</text>
+</svg>
+
+<!-- prettier -->
+<svg>
+  <text x="0" y="10" xml:space="preserve">
+    a
+    <tspan>b</tspan>
+    c
+  </text>
+</svg>
+```
+
+An SVG `<text>` (or an element in one) under `xml:space="preserve"`, on it or an SVG ancestor, keeps its content as written, as a `pre` does.
+Browsers render every space of it, and a line break with its indentation as spaces.
+They differ beyond the element itself: Gecko applies an ancestor's `preserve` and keeps it under a `xml:space="default"`, Blink does neither,
+so any `preserve` above counts.
+Prettier lays the content out as blocks, adding and removing whitespace that renders.
+
 ## dialog-out-of-flow
 
 - Why: semantics (whitespace added on both sides of a `dialog` renders between its inline neighbors)

crates/oxc_formatter_htmlish/src/tree/build.rs

@@ -384,7 +384,7 @@ impl Builder<'_> {
             }
             NodeKind::Element(el) => {
                 self_closing = closes_at_start_tag(node);
-                pre_like = is_pre_like(el);
+                pre_like = is_pre_like(el) || self.preserves_svg_text(id, el);
                 script_like = matches!(el.key, "script" | "style");
             }
             _ => {}
@@ -429,11 +429,31 @@ impl Builder<'_> {
         }
     }
 
+    /// An SVG `<text>`, or an element in one, under `xml:space="preserve"` on it or an SVG ancestor:
+    /// its whitespace renders as written (DIVERGENCES.md#svg-xml-space-preserve).
+    fn preserves_svg_text(&self, id: NodeId, el: &Element<'_>) -> bool {
+        let source = self.tree.source;
+        el.namespace == Namespace::Svg
+            && (el.key == "text" || self.in_svg_text(id))
+            && self.svg_elements(Some(id)).any(|el| {
+                el.attributes.iter().any(|attribute| {
+                    self.tree.attribute_is(attribute.name.slice(source), "xml:space")
+                        && attribute
+                            .value
+                            .is_some_and(|value| value.span.slice(source) == "preserve")
+                })
+            })
+    }
+
     /// Whether an SVG element is inside a `<text>`, whose content lays out as inline text.
     fn in_svg_text(&self, id: NodeId) -> bool {
-        std::iter::successors(self.tree.root[id].parent, |&p| self.tree.root[p].parent)
+        self.svg_elements(self.tree.root[id].parent).any(|el| el.key == "text")
+    }
+
+    /// The SVG elements from `from` up, until one that is not.
+    fn svg_elements(&self, from: Option<NodeId>) -> impl Iterator<Item = &Element<'_>> {
+        std::iter::successors(from, |&p| self.tree.root[p].parent)
             .map_while(|p| self.tree.element(p).filter(|el| el.namespace == Namespace::Svg))
-            .any(|el| el.key == "text")
     }
 
     /// Whether whitespace on one side of the node is significant, before the neighbor's side is combined in:
@@ -495,7 +515,7 @@ impl Builder<'_> {
         leading: bool,
     ) -> bool {
         let t = &self.tree;
-        let (item, parent) = (&t[id], &t[parent_id]);
+        let parent = &t[parent_id];
         let text_or_interpolation = |id: NodeId| t.is_text(id) || t.is_interpolation(id);
         let sensitive =
             if text_or_interpolation(flow_item) && neighbor.is_some_and(text_or_interpolation) {
@@ -507,8 +527,9 @@ impl Builder<'_> {
             } else if let Some(neighbor) = neighbor {
                 self.display_of(neighbor).sides_sensitive()
             } else {
+                // An HTML `pre`'s own edges, not those of all pre-like content
                 !(parent_id == NodeId::DOCUMENT
-                    || item.pre_like
+                    || t.element(id).is_some_and(is_pre_like)
                     || parent.script_like
                     || !parent.display.edges_sensitive())
             };
@@ -619,7 +640,7 @@ fn is_whitespace_text(node: &Node<'_>) -> bool {
     matches!(&node.kind, NodeKind::Text(text) if text.is_whitespace_only())
 }
 
-/// CSS `white-space: pre*`.
+/// An HTML element whose default style is `white-space: pre*`.
 fn is_pre_like(el: &Element<'_>) -> bool {
     el.namespace != Namespace::Svg
         && matches!(el.key, "pre" | "textarea" | "listing" | "plaintext" | "xmp")

crates/oxc_formatter_htmlish/src/tree/mod.rs

@@ -38,7 +38,8 @@ pub struct Facts {
     /// No children and no end tag: the start tag closes the node (Prettier's `isSelfClosing`).
     /// Text-like nodes count too.
     pub self_closing: bool,
-    /// CSS `white-space: pre*`: `pre`, `textarea`, `listing`, `plaintext`, `xmp`, outside SVG.
+    /// CSS `white-space: pre*`: `pre`, `textarea`, `listing`, `plaintext`, `xmp`, outside SVG;
+    /// an SVG `<text>`, or an element in one, under `xml:space="preserve"` (DIVERGENCES.md#svg-xml-space-preserve).
     /// Children keep their whitespace and indentation.
     pub pre_like: bool,
     /// `script` / `style`: children keep their whitespace.
@@ -46,7 +47,7 @@ pub struct Facts {
     /// The deepest last descendant is text-like, or the node itself is
     /// (an interpolation ends in its text).
     pub ends_in_text_like: bool,
-    /// The node is a `pre` without an end tag, or ends in one through its last children without end tags:
+    /// The node is pre-like without an end tag, or ends in one through its last children without end tags:
     /// what follows it up to the end tag that closes them is `pre` content.
     pub ends_in_pre: bool,
     /// A CDATA section, or a text that merged one: its sections are never re-wrapped.

crates/oxc_formatter_htmlish/tests/fixtures/html/svg-xml-space-preserve.html

@@ -0,0 +1,5 @@
+<svg><text x="0" y="10" xml:space="preserve">  a  <tspan>b</tspan>  c</text></svg>
+<svg xml:space="preserve"><g><text x="0" y="10">  a
+    b  </text></g></svg>
+<svg><text x="0" y="10">  a  <tspan xml:space="preserve">  b  </tspan>  c</text></svg>
+<svg><text x="0">a<tspan> <tspan xml:space="preserve">b</tspan></tspan> c</text></svg>

crates/oxc_formatter_htmlish/tests/fixtures/html/svg-xml-space-preserve.html.snap

@@ -0,0 +1,54 @@
+---
+source: crates/oxc_formatter_htmlish/tests/fixtures/mod.rs
+---
+==================== Input ====================
+<svg><text x="0" y="10" xml:space="preserve">  a  <tspan>b</tspan>  c</text></svg>
+<svg xml:space="preserve"><g><text x="0" y="10">  a
+    b  </text></g></svg>
+<svg><text x="0" y="10">  a  <tspan xml:space="preserve">  b  </tspan>  c</text></svg>
+<svg><text x="0">a<tspan> <tspan xml:space="preserve">b</tspan></tspan> c</text></svg>
+
+==================== Output ====================
+------------------
+{ printWidth: 80 }
+------------------
+<svg>
+  <text x="0" y="10" xml:space="preserve">  a  <tspan>b</tspan>  c</text>
+</svg>
+<svg xml:space="preserve">
+  <g>
+    <text x="0" y="10"
+>  a
+    b  </text>
+  </g>
+</svg>
+<svg>
+  <text x="0" y="10">a <tspan xml:space="preserve">  b  </tspan> c</text>
+</svg>
+<svg>
+  <text x="0">
+    a<tspan> <tspan xml:space="preserve">b</tspan></tspan> c
+  </text>
+</svg>
+
+-------------------
+{ printWidth: 100 }
+-------------------
+<svg><text x="0" y="10" xml:space="preserve">  a  <tspan>b</tspan>  c</text></svg>
+<svg xml:space="preserve">
+  <g>
+    <text x="0" y="10"
+>  a
+    b  </text>
+  </g>
+</svg>
+<svg>
+  <text x="0" y="10">a <tspan xml:space="preserve">  b  </tspan> c</text>
+</svg>
+<svg>
+  <text x="0">
+    a<tspan> <tspan xml:space="preserve">b</tspan></tspan> c
+  </text>
+</svg>
+
+===================== End =====================