Auto merge of #26447 - jdm:white-space-2020, r=nox

Layout 2020: Implement basic white-space: pre support

With these changes `<pre>` and `<br>` preserve spaces and force line breaks appropriately.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #26440
- [x] There are tests for these changes

components/layout_2020/flow/construct.rs

@@ -20,6 +20,7 @@ use rayon_croissant::ParallelIteratorExt;
 use servo_arc::Arc;
 use std::borrow::Cow;
 use std::convert::{TryFrom, TryInto};
+use style::computed_values::white_space::T as WhiteSpace;
 use style::properties::longhands::list_style_position::computed_value::T as ListStylePosition;
 use style::properties::ComputedValues;
 use style::selector_parser::PseudoElement;
@@ -293,8 +294,15 @@ where
     }
 
     fn handle_text(&mut self, info: &NodeAndStyleInfo<Node>, input: Cow<'dom, str>) {
-        let (leading_whitespace, mut input) = self.handle_leading_whitespace(&input);
+        // Skip any leading whitespace as dictated by the node's style.
-        if leading_whitespace || !input.is_empty() {
+        let white_space = info.style.get_inherited_text().white_space;
+        let (preserved_leading_whitespace, mut input) =
+            self.handle_leading_whitespace(&input, white_space);
+
+        if !preserved_leading_whitespace && input.is_empty() {
+            return;
+        }
+
         // This text node should be pushed either to the next ongoing
         // inline level box with the parent style of that inline level box
         // that will be ended, or directly to the ongoing inline formatting
@@ -320,23 +328,53 @@ where
                 output = new_text_run_contents.as_mut().unwrap();
             }
 
-                if leading_whitespace {
+            if preserved_leading_whitespace {
                 output.push(' ')
             }
-                loop {
+
-                    if let Some(i) = input.bytes().position(|b| b.is_ascii_whitespace()) {
+            match (
+                white_space.preserve_spaces(),
+                white_space.preserve_newlines(),
+            ) {
+                // All whitespace is significant, so we don't need to transform
+                // the input at all.
+                (true, true) => {
+                    output.push_str(input);
+                },
+
+                // There are no cases in CSS where where need to preserve spaces
+                // but not newlines.
+                (true, false) => unreachable!(),
+
+                // Spaces are not significant, but newlines might be. We need
+                // to collapse non-significant whitespace as appropriate.
+                (false, preserve_newlines) => loop {
+                    // If there are any spaces that need preserving, split the string
+                    // that precedes them, collapse them into a single whitespace,
+                    // then process the remainder of the string independently.
+                    if let Some(i) = input
+                        .bytes()
+                        .position(|b| b.is_ascii_whitespace() && (!preserve_newlines || b != b'\n'))
+                    {
                         let (non_whitespace, rest) = input.split_at(i);
                         output.push_str(non_whitespace);
                         output.push(' ');
-                        if let Some(i) = rest.bytes().position(|b| !b.is_ascii_whitespace()) {
+
+                        // Find the first byte that is either significant whitespace or
+                        // non-whitespace to continue processing it.
+                        if let Some(i) = rest.bytes().position(|b| {
+                            !b.is_ascii_whitespace() || (preserve_newlines && b == b'\n')
+                        }) {
                             input = &rest[i..];
                         } else {
                             break;
                         }
                     } else {
+                        // No whitespace found, so no transformation is required.
                         output.push_str(input);
                         break;
                     }
+                },
             }
         }
 
@@ -349,7 +387,6 @@ where
         }
     }
 }
-}
 
 impl<'dom, Node> BlockContainerBuilder<'dom, '_, Node>
 where
@@ -359,10 +396,14 @@ where
     ///
     /// * Whether this text run has preserved (non-collapsible) leading whitespace
     /// * The contents starting at the first non-whitespace character (or the empty string)
-    fn handle_leading_whitespace<'text>(&mut self, text: &'text str) -> (bool, &'text str) {
+    fn handle_leading_whitespace<'text>(
+        &mut self,
+        text: &'text str,
+        white_space: WhiteSpace,
+    ) -> (bool, &'text str) {
         // FIXME: this is only an approximation of
         // https://drafts.csswg.org/css2/text.html#white-space-model
-        if !text.starts_with(|c: char| c.is_ascii_whitespace()) {
+        if !text.starts_with(|c: char| c.is_ascii_whitespace()) || white_space.preserve_spaces() {
             return (false, text);
         }
 

components/layout_2020/flow/inline.rs

@@ -756,13 +756,21 @@ impl TextRun {
             let mut glyphs = vec![];
             let mut advance_width = Length::zero();
             let mut last_break_opportunity = None;
+            let mut force_line_break = false;
+            // Fit as many glyphs within a single line as possible.
             loop {
                 let next = runs.next();
+                // If there are no more text runs we still need to check if the last
+                // run was a forced line break
                 if next
                     .as_ref()
                     .map_or(true, |run| run.glyph_store.is_whitespace())
                 {
+                    // If this run exceeds the bounds of the containing block, then
+                    // we need to attempt to break the line.
                     if advance_width > ifc.containing_block.inline_size - ifc.inline_position {
+                        // Reset the text run iterator to the last whitespace if possible,
+                        // to attempt to re-layout the most recent glyphs on a new line.
                         if let Some((len, width, iter)) = last_break_opportunity.take() {
                             glyphs.truncate(len);
                             advance_width = width;
@@ -774,10 +782,24 @@ impl TextRun {
                 if let Some(run) = next {
                     if run.glyph_store.is_whitespace() {
                         last_break_opportunity = Some((glyphs.len(), advance_width, runs.clone()));
+                        // If this whitespace ends with a newline, we need to check if
+                        // it's meaningful within the current style. If so, we force
+                        // a line break immediately.
+                        let last_byte = self.text.as_bytes().get(run.range.end().to_usize() - 1);
+                        if last_byte == Some(&b'\n') &&
+                            self.parent_style
+                                .get_inherited_text()
+                                .white_space
+                                .preserve_newlines()
+                        {
+                            force_line_break = true;
+                            break;
+                        }
                     }
                     glyphs.push(run.glyph_store.clone());
                     advance_width += Length::from(run.glyph_store.total_advance());
                 } else {
+                    // No more runs, so we can end the line.
                     break;
                 }
             }
@@ -812,7 +834,8 @@ impl TextRun {
                     glyphs,
                     text_decoration_line: ifc.current_nesting_level.text_decoration_line,
                 }));
-            if runs.as_slice().is_empty() {
+            // If this line is being broken because of a trailing newline, we can't ignore it.
+            if runs.as_slice().is_empty() && !force_line_break {
                 break;
             } else {
                 // New line

components/style/properties/longhands/inherited_text.mako.rs

@@ -186,7 +186,6 @@ ${helpers.predefined_type(
     name="white-space"
     values="normal pre nowrap pre-wrap pre-line"
     engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
     extra_gecko_values="break-spaces -moz-pre-space"
     gecko_enum_prefix="StyleWhiteSpace"
     needs_conversion="True"

tests/wpt/metadata-layout-2020/css/CSS2/abspos/hypothetical-inline-alone-on-second-line.html.ini

@@ -1,2 +0,0 @@
-[hypothetical-inline-alone-on-second-line.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/colors/color-applies-to-008.xht.ini

@@ -1,2 +0,0 @@
-[color-applies-to-008.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/colors/color-applies-to-015.xht.ini

@@ -1,2 +0,0 @@
-[color-applies-to-015.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/css1/c562-white-sp-000.xht.ini

@@ -1,2 +0,0 @@
-[c562-white-sp-000.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/floats-clear/float-003.xht.ini

@@ -1,2 +0,0 @@
-[float-003.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/floats/float-no-content-beside-001.html.ini

@@ -0,0 +1,2 @@
+[float-no-content-beside-001.html]
+  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/floats/floats-placement-vertical-004.xht.ini

@@ -0,0 +1,2 @@
+[floats-placement-vertical-004.xht]
+  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/generated-content/content-171.xht.ini

@@ -1,2 +0,0 @@
-[content-171.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/generated-content/content-173.xht.ini

@@ -0,0 +1,2 @@
+[content-173.xht]
+  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/generated-content/content-newline-001.xht.ini

@@ -1,2 +0,0 @@
-[content-newline-001.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/generated-content/content-white-space-002.xht.ini

@@ -0,0 +1,2 @@
+[content-white-space-002.xht]
+  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/margin-padding-clear/padding-percentage-inherit-001.xht.ini

@@ -1,2 +0,0 @@
-[padding-percentage-inherit-001.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/normal-flow/block-replaced-width-006.xht.ini

@@ -1,2 +0,0 @@
-[block-replaced-width-006.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/normal-flow/inline-replaced-width-001.xht.ini

@@ -1,2 +0,0 @@
-[inline-replaced-width-001.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/normal-flow/inline-replaced-width-006.xht.ini

@@ -1,2 +0,0 @@
-[inline-replaced-width-006.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/normal-flow/inlines-016.xht.ini

@@ -1,2 +0,0 @@
-[inlines-016.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/positioning/absolute-non-replaced-height-008.xht.ini

@@ -1,2 +0,0 @@
-[absolute-non-replaced-height-008.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/positioning/position-static-001.xht.ini

@@ -1,2 +0,0 @@
-[position-static-001.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/tables/table-anonymous-objects-009.xht.ini

@@ -0,0 +1,2 @@
+[table-anonymous-objects-009.xht]
+  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/tables/table-anonymous-objects-010.xht.ini

@@ -0,0 +1,2 @@
+[table-anonymous-objects-010.xht]
+  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/text/white-space-004.xht.ini

@@ -1,2 +0,0 @@
-[white-space-004.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/text/white-space-applies-to-003.xht.ini

@@ -1,2 +0,0 @@
-[white-space-applies-to-003.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/text/white-space-processing-013.xht.ini

@@ -1,2 +0,0 @@
-[white-space-processing-013.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/text/white-space-processing-016.xht.ini

@@ -1,2 +0,0 @@
-[white-space-processing-016.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/text/white-space-processing-017.xht.ini

@@ -1,2 +0,0 @@
-[white-space-processing-017.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/text/white-space-processing-018.xht.ini

@@ -1,2 +0,0 @@
-[white-space-processing-018.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/text/white-space-processing-046.xht.ini

@@ -1,2 +0,0 @@
-[white-space-processing-046.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/text/white-space-processing-047.xht.ini

@@ -1,2 +0,0 @@
-[white-space-processing-047.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/text/white-space-processing-052.xht.ini

@@ -1,2 +0,0 @@
-[white-space-processing-052.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/visuren/anonymous-boxes-001b.xht.ini

@@ -1,2 +0,0 @@
-[anonymous-boxes-001b.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-backgrounds/background-size-027.html.ini

@@ -1,2 +0,0 @@
-[background-size-027.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-backgrounds/background-size-028.html.ini

@@ -1,2 +0,0 @@
-[background-size-028.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-backgrounds/background-size-030.html.ini

@@ -1,2 +0,0 @@
-[background-size-030.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-backgrounds/background-size-031.html.ini

@@ -1,2 +0,0 @@
-[background-size-031.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-flexbox/anonymous-flex-item-004.html.ini

@@ -0,0 +1,2 @@
+[anonymous-flex-item-004.html]
+  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-flexbox/anonymous-flex-item-005.html.ini

@@ -0,0 +1,2 @@
+[anonymous-flex-item-005.html]
+  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-flexbox/anonymous-flex-item-006.html.ini

@@ -0,0 +1,2 @@
+[anonymous-flex-item-006.html]
+  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-text-decor/text-decoration-subelements-001.html.ini

@@ -1,2 +0,0 @@
-[text-decoration-subelements-001.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/cssom/serialize-values.html.ini

@@ -23,15 +23,9 @@
   [page-break-before: always]
     expected: FAIL
 
-  [white-space: inherit]
-    expected: FAIL
-
   [page-break-after: inherit]
     expected: FAIL
 
-  [white-space: nowrap]
-    expected: FAIL
-
   [page-break-before: left]
     expected: FAIL
 
@@ -215,9 +209,6 @@
   [display: table-cell]
     expected: FAIL
 
-  [white-space: pre]
-    expected: FAIL
-
   [text-indent: 5%]
     expected: FAIL
 
@@ -257,9 +248,6 @@
   [clear: both]
     expected: FAIL
 
-  [white-space: pre-wrap]
-    expected: FAIL
-
   [outline-width: 0px]
     expected: FAIL
 
@@ -326,9 +314,6 @@
   [vertical-align: 1px]
     expected: FAIL
 
-  [white-space: pre-line]
-    expected: FAIL
-
   [display: table-column]
     expected: FAIL
 
@@ -386,9 +371,6 @@
   [float: none]
     expected: FAIL
 
-  [white-space: normal]
-    expected: FAIL
-
   [list-style-type: lower-roman]
     expected: FAIL
 

tests/wpt/mozilla/meta-layout-2020/css/br.html.ini

@@ -1,2 +0,0 @@
-[br.html]
-  expected: FAIL

tests/wpt/mozilla/meta-layout-2020/css/input_whitespace.html.ini

@@ -1,2 +0,0 @@
-[input_whitespace.html]
-  expected: FAIL

tests/wpt/mozilla/meta-layout-2020/css/line_breaking_whitespace_collapse_a.html.ini

@@ -1,2 +0,0 @@
-[line_breaking_whitespace_collapse_a.html]
-  expected: FAIL

tests/wpt/mozilla/meta-layout-2020/css/many_brs_a.html.ini

@@ -1,2 +0,0 @@
-[many_brs_a.html]
-  expected: FAIL

tests/wpt/mozilla/meta-layout-2020/css/white-space-pre-line.htm.ini

@@ -0,0 +1,2 @@
+[white-space-pre-line.htm]
+  expected: FAIL

tests/wpt/mozilla/meta-layout-2020/css/white_space_intrinsic_sizes_a.html.ini

@@ -1,2 +0,0 @@
-[white_space_intrinsic_sizes_a.html]
-  expected: FAIL

tests/wpt/mozilla/meta-layout-2020/css/whitespace_pre.html.ini

@@ -1,2 +0,0 @@
-[whitespace_pre.html]
-  expected: FAIL

tests/wpt/mozilla/meta-layout-2020/css/word-break-keep-all-005.htm.ini

@@ -1,2 +0,0 @@
-[word-break-keep-all-005.htm]
-  expected: FAIL

tests/wpt/mozilla/meta-layout-2020/css/word-break-keep-all-006.htm.ini

@@ -1,2 +0,0 @@
-[word-break-keep-all-006.htm]
-  expected: FAIL

tests/wpt/mozilla/meta-layout-2020/css/word-break-keep-all-007.htm.ini

@@ -1,2 +0,0 @@
-[word-break-keep-all-007.htm]
-  expected: FAIL

tests/wpt/mozilla/meta-layout-2020/mozilla/hit_test_multiple_sc.html.ini

@@ -0,0 +1,4 @@
+[hit_test_multiple_sc.html]
+  [Hit testing works for following stacking contexts]
+    expected: FAIL
+