in lib/parser.dart [220:260]
SourceMapSpan? spanFor(int line, int column,
{Map<String, SourceFile>? files, String? uri}) {
// TODO: Remove type arg https://github.com/dart-lang/sdk/issues/42227
uri = ArgumentError.checkNotNull<String>(uri, 'uri');
// Find the longest suffix of the uri that matches the sourcemap
// where the suffix starts after a path segment boundary.
// We consider ":" and "/" as path segment boundaries so that
// "package:" uris can be handled with minimal special casing. Having a
// few false positive path segment boundaries is not a significant issue
// as we prefer the longest matching prefix.
// Using package:path `path.split` to find path segment boundaries would
// not generate all of the path segment boundaries we want for "package:"
// urls as "package:package_name" would be one path segment when we want
// "package" and "package_name" to be sepearate path segments.
var onBoundary = true;
var separatorCodeUnits = ['/'.codeUnitAt(0), ':'.codeUnitAt(0)];
for (var i = 0; i < uri.length; ++i) {
if (onBoundary) {
var candidate = uri.substring(i);
var candidateMapping = _mappings[candidate];
if (candidateMapping != null) {
return candidateMapping.spanFor(line, column,
files: files, uri: candidate);
}
}
onBoundary = separatorCodeUnits.contains(uri.codeUnitAt(i));
}
// Note: when there is no source map for an uri, this behaves like an
// identity function, returning the requested location as the result.
// Create a mock offset for the output location. We compute it in terms
// of the input line and column to minimize the chances that two different
// line and column locations are mapped to the same offset.
var offset = line * 1000000 + column;
var location = SourceLocation(offset,
line: line, column: column, sourceUrl: Uri.parse(uri));
return SourceMapSpan(location, location, '');
}