fix(format/html): keep at most 1 empty line between elements

crates/biome_html_formatter/src/html/lists/element_list.rs

@@ -6,8 +6,7 @@ use crate::{
     comments::HtmlComments,
     prelude::*,
     utils::children::{
-        html_split_children, is_meaningful_html_text, HtmlChild, HtmlChildrenIterator,
-        HtmlRawSpace, HtmlSpace,
+        html_split_children, is_meaningful_html_text, HtmlChild, HtmlChildrenIterator, HtmlSpace,
     },
 };
 use biome_formatter::{best_fitting, prelude::*, CstFormatContext};
@@ -106,7 +105,6 @@ impl FormatHtmlElementList {
 
         while let Some(child) = children_iter.next() {
             let mut child_breaks = false;
-
             match &child {
                 // A single word: Both `a` and `b` are a word in `a b` because they're separated by HTML Whitespace.
                 HtmlChild::Word(word) => {
@@ -148,34 +146,7 @@ impl FormatHtmlElementList {
                 // * Whitespace before an opening tag: `a <div>`
                 HtmlChild::Whitespace => {
                     flat.write(&HtmlSpace, f);
-
-                    // ```javascript
-                    // <div>a
-                    // {' '}</div>
-                    // ```
-                    let is_after_line_break =
-                        last.as_ref().map_or(false, |last| last.is_any_line());
-
-                    // `<div>aaa </div>` or `<div> </div>`
-                    let is_trailing_or_only_whitespace = children_iter.peek().is_none();
-
-                    if is_trailing_or_only_whitespace || is_after_line_break {
-                        multiline.write_separator(&HtmlRawSpace, f);
-                    }
-                    // Leading whitespace. Only possible if used together with a expression child
-                    //
-                    // ```
-                    // <div>
-                    //
-                    //   {' '}
-                    //   <b />
-                    // </div>
-                    // ```
-                    else if last.is_none() {
-                        multiline.write_with_separator(&HtmlRawSpace, &hard_line_break(), f);
-                    } else {
-                        multiline.write_separator(&HtmlSpace, f);
-                    }
+                    multiline.write_separator(&soft_line_break_or_space(), f);
                 }
 
                 // A new line between some JSX text and an element
@@ -245,30 +216,7 @@ impl FormatHtmlElementList {
                 // An empty line between some JSX text and an element
                 HtmlChild::EmptyLine => {
                     child_breaks = true;
-
-                    // Additional empty lines are not preserved when any of
-                    // the children are a meaningful text node.
-                    //
-                    // <>
-                    //   <div>First</div>
-                    //
-                    //   <div>Second</div>
-                    //
-                    //   Third
-                    // </>
-                    //
-                    // Becomes:
-                    //
-                    // <>
-                    //   <div>First</div>
-                    //   <div>Second</div>
-                    //   Third
-                    // </>
-                    if children_meta.meaningful_text {
-                        multiline.write_separator(&hard_line_break(), f);
-                    } else {
-                        multiline.write_separator(&empty_line(), f);
-                    }
+                    multiline.write_separator(&empty_line(), f);
                 }
 
                 // Any child that isn't text

crates/biome_html_formatter/src/utils/children.rs

@@ -119,6 +119,7 @@ pub(crate) enum HtmlChild {
 }
 
 impl HtmlChild {
+    #[expect(dead_code)]
     pub(crate) const fn is_any_line(&self) -> bool {
         matches!(self, HtmlChild::EmptyLine | HtmlChild::Newline)
     }
@@ -170,6 +171,7 @@ where
 {
     let mut builder = HtmlSplitChildrenBuilder::new();
 
+    let mut prev_was_content = false;
     for child in children {
         match child {
             AnyHtmlElement::HtmlContent(text) => {
@@ -181,17 +183,18 @@ where
 
                 // Text starting with a whitespace
                 if let Some((_, HtmlTextChunk::Whitespace(_whitespace))) = chunks.peek() {
-                    match chunks.next() {
-                        Some((_, HtmlTextChunk::Whitespace(whitespace))) => {
-                            if whitespace.contains('\n') {
+                    // SAFETY: We just checked this above.
+                    match chunks.next().unwrap() {
+                        (_, HtmlTextChunk::Whitespace(whitespace)) => {
+                            if whitespace.contains('\n') && !prev_was_content {
                                 if chunks.peek().is_none() {
                                     // A text only consisting of whitespace that also contains a new line isn't considered meaningful text.
                                     // It can be entirely removed from the content without changing the semantics.
                                     let newlines =
                                         whitespace.chars().filter(|c| *c == '\n').count();
 
-                                    // Keep up to one blank line between tags/expressions and text.
-                                    // ```javascript
+                                    // Keep up to one blank line between tags.
+                                    // ```html
                                     // <div>
                                     //
                                     //   <MyElement />
@@ -236,9 +239,44 @@ where
                         }
                     }
                 }
+                prev_was_content = true;
             }
             child => {
+                let text = child.to_string();
+                let mut chunks = HtmlSplitChunksIterator::new(&text).peekable();
+
+                // Text starting with a whitespace
+                if let Some((_, HtmlTextChunk::Whitespace(_whitespace))) = chunks.peek() {
+                    // SAFETY: We just checked this above.
+                    match chunks.next().unwrap() {
+                        (_, HtmlTextChunk::Whitespace(whitespace)) => {
+                            if whitespace.contains('\n') {
+                                // A text only consisting of whitespace that also contains a new line isn't considered meaningful text.
+                                // It can be entirely removed from the content without changing the semantics.
+                                let newlines = whitespace.chars().filter(|c| *c == '\n').count();
+
+                                // Keep up to one blank line between tags.
+                                // ```html
+                                // <div>
+                                //
+                                //   <MyElement />
+                                // </div>
+                                // ```
+                                if newlines > 1 {
+                                    builder.entry(HtmlChild::EmptyLine);
+                                } else {
+                                    builder.entry(HtmlChild::Newline);
+                                }
+                            } else {
+                                builder.entry(HtmlChild::Whitespace)
+                            }
+                        }
+                        _ => unreachable!(),
+                    }
+                }
+
                 builder.entry(HtmlChild::NonText(child));
+                prev_was_content = false;
             }
         }
     }

crates/biome_html_formatter/tests/specs/html/elements/spacing/case0.html

@@ -0,0 +1,6 @@
+text
+
+
+
+
+<div>foo</div>

crates/biome_html_formatter/tests/specs/html/elements/spacing/case0.html.snap

@@ -0,0 +1,36 @@
+---
+source: crates/biome_formatter_test/src/snapshot_builder.rs
+info: elements/spacing/case0.html
+---
+# Input
+
+```html
+text
+
+
+
+
+<div>foo</div>
+
+```
+
+
+=============================
+
+# Outputs
+
+## Output 1
+
+-----
+Indent style: Tab
+Indent width: 2
+Line ending: LF
+Line width: 80
+Attribute Position: Auto
+-----
+
+```html
+text
+
+<div>foo</div>
+```

crates/biome_html_formatter/tests/specs/html/elements/spacing/case1.html

@@ -0,0 +1,8 @@
+<div>
+  <div>foo</div>
+
+  text
+
+  <div>foo</div>
+</div>
+

crates/biome_html_formatter/tests/specs/html/elements/spacing/case1.html.snap

@@ -0,0 +1,41 @@
+---
+source: crates/biome_formatter_test/src/snapshot_builder.rs
+info: elements/spacing/case1.html
+---
+# Input
+
+```html
+<div>
+  <div>foo</div>
+
+  text
+
+  <div>foo</div>
+</div>
+
+
+```
+
+
+=============================
+
+# Outputs
+
+## Output 1
+
+-----
+Indent style: Tab
+Indent width: 2
+Line ending: LF
+Line width: 80
+Attribute Position: Auto
+-----
+
+```html
+<div>
+	<div>foo</div>
+	text
+
+	<div>foo</div>
+</div>
+```

crates/biome_html_formatter/tests/specs/html/elements/spacing/case2.html

@@ -0,0 +1,6 @@
+text
+
+
+
+
+<div>foo</div>

crates/biome_html_formatter/tests/specs/html/elements/spacing/case2.html.snap

@@ -0,0 +1,36 @@
+---
+source: crates/biome_formatter_test/src/snapshot_builder.rs
+info: elements/spacing/case2.html
+---
+# Input
+
+```html
+text
+
+
+
+
+<div>foo</div>
+
+```
+
+
+=============================
+
+# Outputs
+
+## Output 1
+
+-----
+Indent style: Tab
+Indent width: 2
+Line ending: LF
+Line width: 80
+Attribute Position: Auto
+-----
+
+```html
+text
+
+<div>foo</div>
+```

crates/biome_html_formatter/tests/specs/html/elements/spacing/case3.html

@@ -0,0 +1,6 @@
+<!-- foo -->
+<!-- foo -->
+
+
+
+test

crates/biome_html_formatter/tests/specs/html/elements/spacing/case3.html.snap

@@ -0,0 +1,43 @@
+---
+source: crates/biome_formatter_test/src/snapshot_builder.rs
+info: elements/spacing/case3.html
+---
+# Input
+
+```html
+<!-- foo -->
+<!-- foo -->
+
+
+
+test
+
+```
+
+
+=============================
+
+# Outputs
+
+## Output 1
+
+-----
+Indent style: Tab
+Indent width: 2
+Line ending: LF
+Line width: 80
+Attribute Position: Auto
+-----
+
+```html
+<!-- foo -->
+<!-- foo -->
+test
+```
+
+
+
+## Unimplemented nodes/tokens
+
+"<!-- foo -->" => 0..12
+"<!-- foo -->\n" => 13..26

crates/biome_html_formatter/tests/specs/html/elements/spacing/case4.html

@@ -0,0 +1,3 @@
+foo
+
+bar

crates/biome_html_formatter/tests/specs/html/elements/spacing/case4.html.snap

@@ -0,0 +1,31 @@
+---
+source: crates/biome_formatter_test/src/snapshot_builder.rs
+info: elements/spacing/case4.html
+---
+# Input
+
+```html
+foo
+
+bar
+
+```
+
+
+=============================
+
+# Outputs
+
+## Output 1
+
+-----
+Indent style: Tab
+Indent width: 2
+Line ending: LF
+Line width: 80
+Attribute Position: Auto
+-----
+
+```html
+foo bar
+```