Make sure all source spans use interpolation maps

lib/src/interpolation_map.dart

@@ -44,11 +44,14 @@ final class InterpolationMap {
 
   /// Maps [error]'s span in the string generated from this interpolation to its
   /// original source.
+  ///
+  /// Returns [error] if its span is null, or if it's already been mapped.
   FormatException mapException(SourceSpanFormatException error) {
     var target = error.span;
     if (target == null) return error;
 
     if (_interpolation.contents.isEmpty) {
+      if (_isMapped(target)) return error;
       return SourceSpanFormatException(
         error.message,
         _interpolation.span,
@@ -57,6 +60,8 @@ final class InterpolationMap {
     }
 
     var source = mapSpan(target);
+    if (identical(source, target)) return error;
+
     var startIndex = _indexInContents(target.start);
     var endIndex = _indexInContents(target.end);
 
@@ -79,24 +84,36 @@ final class InterpolationMap {
 
   /// Maps a span in the string generated from this interpolation to its
   /// original source.
-  FileSpan mapSpan(SourceSpan target) => switch ((
-        _mapLocation(target.start),
-        _mapLocation(target.end),
-      )) {
-        (FileSpan start, FileSpan end) => start.expand(end),
-        (FileSpan start, FileLocation end) => _interpolation.span.file.span(
-            _expandInterpolationSpanLeft(start.start),
-            end.offset,
-          ),
-        (FileLocation start, FileSpan end) => _interpolation.span.file.span(
-            start.offset,
-            _expandInterpolationSpanRight(end.end),
-          ),
-        (FileLocation start, FileLocation end) => _interpolation.span.file.span(
-            start.offset,
-            end.offset,
-          ),
-        _ => throw '[BUG] Unreachable',
+  ///
+  /// Returns [target] as-is if it's already been mapped.
+  FileSpan mapSpan(SourceSpan target) {
+    if (_isMapped(target)) return target as FileSpan;
+
+    return switch ((
+      _mapLocation(target.start),
+      _mapLocation(target.end),
+    )) {
+      (FileSpan start, FileSpan end) => start.expand(end),
+      (FileSpan start, FileLocation end) => _interpolation.span.file.span(
+          _expandInterpolationSpanLeft(start.start),
+          end.offset,
+        ),
+      (FileLocation start, FileSpan end) => _interpolation.span.file.span(
+          start.offset,
+          _expandInterpolationSpanRight(end.end),
+        ),
+      (FileLocation start, FileLocation end) => _interpolation.span.file.span(
+          start.offset,
+          end.offset,
+        ),
+      _ => throw '[BUG] Unreachable',
+    };
+  }
+
+  /// Returns whether [span] has already been mapped by this mapper.
+  bool _isMapped(SourceSpan span) => switch (span) {
+        FileSpan(:var file) => identical(file, _interpolation.span.file),
+        _ => false,
       };
 
   /// Maps a location in the string generated from this interpolation to its

lib/src/parse/css.dart

@@ -46,7 +46,7 @@ class CssParser extends ScssParser {
     super.silentComment();
     error(
       "Silent comments aren't allowed in plain CSS.",
-      scanner.spanFrom(start),
+      spanFrom(start),
     );
   }
 
@@ -86,7 +86,7 @@ class CssParser extends ScssParser {
   /// Throws an error for a forbidden at-rule.
   Never _forbiddenAtRule(LineScannerState start) {
     almostAnyValue();
-    error("This at-rule isn't allowed in plain CSS.", scanner.spanFrom(start));
+    error("This at-rule isn't allowed in plain CSS.", spanFrom(start));
   }
 
   /// Consumes a plain-CSS `@import` rule that disallows interpolation.
@@ -128,8 +128,8 @@ class CssParser extends ScssParser {
     var modifiers = tryImportModifiers();
     expectStatementSeparator("@import rule");
     return ImportRule([
-      StaticImport(url, scanner.spanFrom(urlStart), modifiers: modifiers),
-    ], scanner.spanFrom(start));
+      StaticImport(url, spanFrom(urlStart), modifiers: modifiers),
+    ], spanFrom(start));
   }
 
   ParenthesizedExpression parentheses() {
@@ -140,7 +140,7 @@ class CssParser extends ScssParser {
     _whitespace();
     var expression = expressionUntilComma();
     scanner.expectChar($rparen);
-    return ParenthesizedExpression(expression, scanner.spanFrom(start));
+    return ParenthesizedExpression(expression, spanFrom(start));
   }
 
   Expression identifierLike() {
@@ -179,14 +179,14 @@ class CssParser extends ScssParser {
     if (_disallowedFunctionNames.contains(plain)) {
       error(
         "This function isn't allowed in plain CSS.",
-        scanner.spanFrom(start),
+        spanFrom(start),
       );
     }
 
     return FunctionExpression(
       plain,
-      ArgumentList(arguments, const {}, scanner.spanFrom(beforeArguments)),
-      scanner.spanFrom(start),
+      ArgumentList(arguments, const {}, spanFrom(beforeArguments)),
+      spanFrom(start),
     );
   }
 

lib/src/parse/parser.dart

@@ -669,8 +669,18 @@ class Parser {
   /// Like [scanner.spanFrom], but passes the span through [_interpolationMap]
   /// if it's available.
   @protected
-  FileSpan spanFrom(LineScannerState state) {
-    var span = scanner.spanFrom(state);
+  FileSpan spanFrom(LineScannerState start, [LineScannerState? end]) {
+    var span = scanner.spanFrom(start, end);
+    return _interpolationMap == null
+        ? span
+        : LazyFileSpan(() => _interpolationMap.mapSpan(span));
+  }
+
+  /// Like [scanner.spanFromPosition], but passes the span through
+  /// [_interpolationMap] if it's available.
+  @protected
+  FileSpan spanFromPosition(int start, [int? end]) {
+    var span = scanner.spanFromPosition(start, end);
     return _interpolationMap == null
         ? span
         : LazyFileSpan(() => _interpolationMap.mapSpan(span));
@@ -728,7 +738,10 @@ class Parser {
         var map = _interpolationMap;
         if (map == null) rethrow;
 
-        throwWithTrace(map.mapException(error), error, stackTrace);
+        var mapped = map.mapException(error);
+        if (identical(mapped, error)) rethrow;
+
+        throwWithTrace(mapped, error, stackTrace);
       }
     } on MultiSourceSpanFormatException catch (error, stackTrace) {
       var span = error.span as FileSpan;

lib/src/parse/sass.dart

@@ -50,7 +50,7 @@ class SassParser extends StylesheetParser {
     } while (buffer.trailingString.trimRight().endsWith(',') &&
         scanCharIf((char) => char.isNewline));
 
-    return buffer.interpolation(scanner.spanFrom(start));
+    return buffer.interpolation(spanFrom(start));
   }
 
   void expectStatementSeparator([String? name]) {
@@ -97,7 +97,7 @@ class SassParser extends StylesheetParser {
       next = scanner.peekChar();
     }
     var url = scanner.substring(start.position);
-    var span = scanner.spanFrom(start);
+    var span = spanFrom(start);
 
     if (isPlainImportUrl(url)) {
       // Serialize [url] as a Sass string because [StaticImport] expects it to
@@ -218,7 +218,7 @@ class SassParser extends StylesheetParser {
 
     return lastSilentComment = SilentComment(
       buffer.toString(),
-      scanner.spanFrom(start),
+      spanFrom(start),
     );
   }
 
@@ -269,7 +269,7 @@ class SassParser extends StylesheetParser {
             if (scanner.peekChar(1) == $slash) {
               buffer.writeCharCode(scanner.readChar());
               buffer.writeCharCode(scanner.readChar());
-              var span = scanner.spanFrom(start);
+              var span = spanFrom(start);
               whitespace(consumeNewlines: false);
 
               // For backwards compatibility, allow additional comments after
@@ -290,7 +290,7 @@ class SassParser extends StylesheetParser {
                 }
                 throw MultiSpanSassFormatException(
                   "Unexpected text after end of comment",
-                  scanner.spanFrom(errorStart),
+                  spanFrom(errorStart),
                   "extra text",
                   {span: "comment"},
                 );
@@ -318,7 +318,7 @@ class SassParser extends StylesheetParser {
       _readIndentation();
     }
 
-    return LoudComment(buffer.interpolation(scanner.spanFrom(start)));
+    return LoudComment(buffer.interpolation(spanFrom(start)));
   }
 
   void whitespaceWithoutComments({required bool consumeNewlines}) {

lib/src/parse/scss.dart

@@ -50,7 +50,7 @@ class ScssParser extends StylesheetParser {
               'versions.\n'
               '\n'
               'Recommendation: @else if',
-          span: scanner.spanFrom(beforeAt),
+          span: spanFrom(beforeAt),
         ));
         scanner.position -= 2;
         return true;
@@ -140,13 +140,13 @@ class ScssParser extends StylesheetParser {
     if (plainCss) {
       error(
         "Silent comments aren't allowed in plain CSS.",
-        scanner.spanFrom(start),
+        spanFrom(start),
       );
     }
 
     return lastSilentComment = SilentComment(
       scanner.substring(start.position),
-      scanner.spanFrom(start),
+      spanFrom(start),
     );
   }
 
@@ -172,7 +172,7 @@ class ScssParser extends StylesheetParser {
           if (scanner.peekChar() != $slash) continue loop;
 
           buffer.writeCharCode(scanner.readChar());
-          return LoudComment(buffer.interpolation(scanner.spanFrom(start)));
+          return LoudComment(buffer.interpolation(spanFrom(start)));
 
         case $cr:
           scanner.readChar();

lib/src/parse/selector.dart

@@ -236,7 +236,7 @@ class SelectorParser extends Parser {
         if (_plainCss) {
           error(
             "Placeholder selectors aren't allowed in plain CSS.",
-            scanner.spanFrom(start),
+            spanFrom(start),
           );
         }
         return selector;
@@ -247,7 +247,7 @@ class SelectorParser extends Parser {
         if (!allowParent) {
           error(
             "Parent selectors aren't allowed here.",
-            scanner.spanFrom(start),
+            spanFrom(start),
           );
         }
         return selector;
@@ -316,7 +316,7 @@ class SelectorParser extends Parser {
 
   /// Consumes an attribute selector's operator.
   AttributeOperator _attributeOperator() {
-    var start = scanner.state;
+    var start = scanner.position;
     switch (scanner.readChar()) {
       case $equal:
         return AttributeOperator.equal;
@@ -342,7 +342,7 @@ class SelectorParser extends Parser {
         return AttributeOperator.substring;
 
       default:
-        scanner.error('Expected "]".', position: start.position);
+        scanner.error('Expected "]".', position: start);
     }
   }
 
@@ -486,16 +486,12 @@ class SelectorParser extends Parser {
       return scanner.scanChar($asterisk)
           ? UniversalSelector(spanFrom(start), namespace: "*")
           : TypeSelector(
-              QualifiedName(identifier(), namespace: "*"),
-              spanFrom(start),
-            );
+              QualifiedName(identifier(), namespace: "*"), spanFrom(start));
     } else if (scanner.scanChar($pipe)) {
       return scanner.scanChar($asterisk)
           ? UniversalSelector(spanFrom(start), namespace: "")
           : TypeSelector(
-              QualifiedName(identifier(), namespace: ""),
-              spanFrom(start),
-            );
+              QualifiedName(identifier(), namespace: ""), spanFrom(start));
     }
 
     var nameOrNamespace = identifier();
@@ -505,9 +501,8 @@ class SelectorParser extends Parser {
       return UniversalSelector(spanFrom(start), namespace: nameOrNamespace);
     } else {
       return TypeSelector(
-        QualifiedName(identifier(), namespace: nameOrNamespace),
-        spanFrom(start),
-      );
+          QualifiedName(identifier(), namespace: nameOrNamespace),
+          spanFrom(start));
     }
   }