Merge remote-tracking branch 'pr/1559'

Author: gnprice

lib/model/content.dart

@@ -460,6 +460,28 @@ class KatexVlistRowNode extends ContentNode {
   }
 }
 
+class KatexNegativeMarginNode extends KatexNode {
+  const KatexNegativeMarginNode({
+    required this.leftOffsetEm,
+    required this.nodes,
+    super.debugHtmlNode,
+  }) : assert(leftOffsetEm < 0);
+
+  final double leftOffsetEm;
+  final List<KatexNode> nodes;
+
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+    super.debugFillProperties(properties);
+    properties.add(DoubleProperty('leftOffsetEm', leftOffsetEm));
+  }
+
+  @override
+  List<DiagnosticsNode> debugDescribeChildren() {
+    return nodes.map((node) => node.toDiagnosticsNode()).toList();
+  }
+}
+
 class MathBlockNode extends MathNode implements BlockContentNode {
   const MathBlockNode({
     super.debugHtmlNode,

lib/model/katex.dart

@@ -1,3 +1,4 @@
+import 'package:collection/collection.dart';
 import 'package:csslib/parser.dart' as css_parser;
 import 'package:csslib/visitor.dart' as css_visitor;
 import 'package:flutter/foundation.dart';
@@ -167,16 +168,42 @@ class _KatexParser {
   }
 
   List<KatexNode> _parseChildSpans(List<dom.Node> nodes) {
-    return List.unmodifiable(nodes.map((node) {
-      if (node case dom.Element(localName: 'span')) {
-        return _parseSpan(node);
-      } else {
+    var resultSpans = QueueList<KatexNode>();
+    for (final node in nodes.reversed) {
+      if (node is! dom.Element || node.localName != 'span') {
         throw _KatexHtmlParseError(
           node is dom.Element
             ? 'unsupported html node: ${node.localName}'
             : 'unsupported html node');
       }
-    }));
+
+      final span = _parseSpan(node);
+
+      if (span is KatexSpanNode) {
+        final marginRightEm = span.styles.marginRightEm;
+        if (marginRightEm != null && marginRightEm.isNegative) {
+          final previousSpans = resultSpans;
+          resultSpans = QueueList<KatexNode>();
+          resultSpans.addFirst(KatexNegativeMarginNode(
+            leftOffsetEm: marginRightEm,
+            nodes: previousSpans));
+        }
+      }
+
+      resultSpans.addFirst(span);
+
+      if (span is KatexSpanNode) {
+        final marginLeftEm = span.styles.marginLeftEm;
+        if (marginLeftEm != null && marginLeftEm.isNegative) {
+          final previousSpans = resultSpans;
+          resultSpans = QueueList<KatexNode>();
+          resultSpans.addFirst(KatexNegativeMarginNode(
+            leftOffsetEm: marginLeftEm,
+            nodes: previousSpans));
+        }
+      }
+    }
+    return resultSpans;
   }
 
   static final _resetSizeClassRegExp = RegExp(r'^reset-size(\d\d?)$');
@@ -266,13 +293,31 @@ class _KatexParser {
                 final pstrutStyles = _parseSpanInlineStyles(pstrutSpan)!;
                 final pstrutHeight = pstrutStyles.heightEm ?? 0;
 
+                KatexSpanNode innerSpanNode = KatexSpanNode(
+                  styles: styles,
+                  text: null,
+                  nodes: _parseChildSpans(otherSpans));
+
+                final marginRightEm = styles.marginRightEm;
+                final marginLeftEm = styles.marginLeftEm;
+                if (marginRightEm != null && marginRightEm.isNegative) {
+                  throw _KatexHtmlParseError();
+                }
+                if (marginLeftEm != null && marginLeftEm.isNegative) {
+                  innerSpanNode = KatexSpanNode(
+                    styles: KatexSpanStyles(),
+                    text: null,
+                    nodes: [
+                      KatexNegativeMarginNode(
+                        leftOffsetEm: marginLeftEm,
+                        nodes: [innerSpanNode]),
+                    ]);
+                }
+
                 rows.add(KatexVlistRowNode(
                   verticalOffsetEm: topEm + pstrutHeight,
                   debugHtmlNode: kDebugMode ? innerSpan : null,
-                  node: KatexSpanNode(
-                    styles: styles,
-                    text: null,
-                    nodes: _parseChildSpans(otherSpans))));
+                  node: innerSpanNode));
               } else {
                 throw _KatexHtmlParseError();
               }
@@ -605,17 +650,11 @@ class _KatexParser {
 
               case 'margin-right':
                 marginRightEm = _getEm(expression);
-                if (marginRightEm != null) {
-                  if (marginRightEm < 0) throw _KatexHtmlParseError();
-                  continue;
-                }
+                if (marginRightEm != null) continue;
 
               case 'margin-left':
                 marginLeftEm = _getEm(expression);
-                if (marginLeftEm != null) {
-                  if (marginLeftEm < 0) throw _KatexHtmlParseError();
-                  continue;
-                }
+                if (marginLeftEm != null) continue;
             }
 
             // TODO handle more CSS properties

lib/widgets/content.dart

@@ -22,6 +22,7 @@ import 'code_block.dart';
 import 'dialog.dart';
 import 'icons.dart';
 import 'inset_shadow.dart';
+import 'katex.dart';
 import 'lightbox.dart';
 import 'message_list.dart';
 import 'poll.dart';
@@ -884,6 +885,7 @@ class _KatexNodeList extends StatelessWidget {
               KatexSpanNode() => _KatexSpan(e),
               KatexStrutNode() => _KatexStrut(e),
               KatexVlistNode() => _KatexVlist(e),
+              KatexNegativeMarginNode() => _KatexNegativeMargin(e),
             }));
       }))));
   }
@@ -957,23 +959,21 @@ class _KatexSpan extends StatelessWidget {
     }
 
     final marginRight = switch (styles.marginRightEm) {
-      double marginRightEm => marginRightEm * em,
-      null => null,
+      double marginRightEm when marginRightEm >= 0 => marginRightEm * em,
+      _ => null,
     };
     final marginLeft = switch (styles.marginLeftEm) {
-      double marginLeftEm => marginLeftEm * em,
-      null => null,
+      double marginLeftEm when marginLeftEm >= 0 => marginLeftEm * em,
+      _ => null,
     };
 
     EdgeInsets? margin;
     if (marginRight != null || marginLeft != null) {
       margin = EdgeInsets.zero;
       if (marginRight != null) {
-        assert(marginRight >= 0);
         margin += EdgeInsets.only(right: marginRight);
       }
       if (marginLeft != null) {
-        assert(marginLeft >= 0);
         margin += EdgeInsets.only(left: marginLeft);
       }
     }
@@ -1031,6 +1031,21 @@ class _KatexVlist extends StatelessWidget {
   }
 }
 
+class _KatexNegativeMargin extends StatelessWidget {
+  const _KatexNegativeMargin(this.node);
+
+  final KatexNegativeMarginNode node;
+
+  @override
+  Widget build(BuildContext context) {
+    final em = DefaultTextStyle.of(context).style.fontSize!;
+
+    return NegativeLeftOffset(
+      leftOffset: node.leftOffsetEm * em,
+      child: _KatexNodeList(nodes: node.nodes));
+  }
+}
+
 class WebsitePreview extends StatelessWidget {
   const WebsitePreview({super.key, required this.node});