Use absolute URIs in stack trace in embedded protocol

lib/src/embedded/compilation_dispatcher.dart

@@ -15,6 +15,7 @@ import 'package:sass/sass.dart' as sass;
 import 'package:sass/src/importer/node_package.dart' as npi;
 
 import '../logger.dart';
+import '../util/trace.dart';
 import '../value/function.dart';
 import '../value/mixin.dart';
 import 'embedded_sass.pb.dart';
@@ -241,14 +242,14 @@ final class CompilationDispatcher {
         ..loadedUrls.addAll(result.loadedUrls.map((url) => url.toString()));
     } on sass.SassException catch (error) {
       var formatted = withGlyphs(
-        () => error.toString(color: request.alertColor),
+        () => error.toString(color: request.alertColor, prettyUri: false),
         ascii: request.alertAscii,
       );
       return OutboundMessage_CompileResponse()
         ..failure = (OutboundMessage_CompileResponse_CompileFailure()
           ..message = error.message
           ..span = protofySpan(error.span)
-          ..stackTrace = error.trace.toString()
+          ..stackTrace = error.trace.printString(prettyUri: false)
           ..formatted = formatted)
         ..loadedUrls.addAll(error.loadedUrls.map((url) => url.toString()));
     }

lib/src/embedded/logger.dart

@@ -2,13 +2,12 @@
 // MIT-style license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
 
-import 'package:path/path.dart' as p;
 import 'package:source_span/source_span.dart';
 import 'package:stack_trace/stack_trace.dart';
 
 import '../deprecation.dart';
 import '../logger.dart';
-import '../util/nullable.dart';
+import '../util/trace.dart';
 import '../utils.dart';
 import 'compilation_dispatcher.dart';
 import 'embedded_sass.pb.dart' hide SourceSpan;
@@ -35,7 +34,9 @@ final class EmbeddedLogger extends LoggerWithDeprecationType {
         ..type = LogEventType.DEBUG
         ..message = message
         ..span = protofySpan(span)
-        ..formatted = (span.start.sourceUrl.andThen(p.prettyUri) ?? '-') +
+        ..formatted = (span.start.sourceUrl == null
+                ? '-'
+                : span.start.sourceUrl.toString()) +
             ':${span.start.line + 1} ' +
             (_color ? '\u001b[1mDebug\u001b[0m' : 'DEBUG') +
             ': $message\n',
@@ -70,7 +71,8 @@ final class EmbeddedLogger extends LoggerWithDeprecationType {
         buffer.writeln(' on ${span.message("\n" + message, color: _color)}');
       }
       if (trace != null) {
-        buffer.writeln(indent(trace.toString().trimRight(), 4));
+        buffer.writeln(
+            indent(trace.printString(prettyUri: false).trimRight(), 4));
       }
       return buffer.toString();
     }, ascii: _ascii);
@@ -82,7 +84,7 @@ final class EmbeddedLogger extends LoggerWithDeprecationType {
       ..message = message
       ..formatted = formatted;
     if (span != null) event.span = protofySpan(span);
-    if (trace != null) event.stackTrace = trace.toString();
+    if (trace != null) event.stackTrace = trace.printString(prettyUri: false);
     if (deprecation != null) event.deprecationType = deprecation.id;
     _dispatcher.sendLog(event);
   }

lib/src/exception.dart

@@ -9,6 +9,7 @@ import 'package:stack_trace/stack_trace.dart';
 import 'package:term_glyph/term_glyph.dart' as term_glyph;
 
 import 'util/nullable.dart';
+import 'util/trace.dart';
 import 'utils.dart';
 import 'value.dart';
 
@@ -53,12 +54,12 @@ class SassException extends SourceSpanException {
   SassException withLoadedUrls(Iterable<Uri> loadedUrls) =>
       SassException(message, span, loadedUrls);
 
-  String toString({Object? color}) {
+  String toString({Object? color, bool prettyUri = true}) {
     var buffer = StringBuffer()
       ..writeln("Error: $message")
       ..write(span.highlight(color: color));
 
-    for (var frame in trace.toString().split("\n")) {
+    for (var frame in trace.printString(prettyUri: prettyUri).split("\n")) {
       if (frame.isEmpty) continue;
       buffer.writeln();
       buffer.write("  $frame");
@@ -158,7 +159,8 @@ class MultiSpanSassException extends SassException
         loadedUrls,
       );
 
-  String toString({Object? color, String? secondaryColor}) {
+  String toString(
+      {Object? color, String? secondaryColor, bool prettyUri = true}) {
     var useColor = false;
     String? primaryColor;
     if (color is String) {
@@ -180,7 +182,7 @@ class MultiSpanSassException extends SassException
         )
         .andThen(buffer.write);
 
-    for (var frame in trace.toString().split("\n")) {
+    for (var frame in trace.printString(prettyUri: prettyUri).split("\n")) {
       if (frame.isEmpty) continue;
       buffer.writeln();
       buffer.write("  $frame");

lib/src/util/trace.dart

@@ -0,0 +1,47 @@
+// Copyright 2026 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:math' as math;
+
+import 'package:stack_trace/stack_trace.dart';
+
+/// Extensions for printing Trace
+extension TraceExtensions on Trace {
+  /// Returns a human-readable representation of this trace.
+  ///
+  /// This will not use `path.prettyUri()` when [prettyUri] is false.
+  String printString({bool prettyUri = true}) {
+    if (prettyUri) return toString();
+
+    // Figure out the longest path so we know how much to pad.
+    var longest =
+        frames.map((frame) => frame._location.length).fold(0, math.max);
+
+    // Print out the stack trace nicely formatted.
+    return frames.map((frame) {
+      if (frame is UnparsedFrame) return '$frame\n';
+      return '${frame._location.padRight(longest)}  ${frame.member}\n';
+    }).join();
+  }
+}
+
+/// Extensions for printing Frame
+extension FrameExtensions on Frame {
+  /// Returns a human-friendly description of the library that this stack frame
+  /// comes from.
+  ///
+  /// This will usually be the string form of [uri]. Absolute URIs will not be
+  /// converted to relative URIs. Data URIs will be truncated.
+  String get _library {
+    if (uri.scheme == 'data') return 'data:...';
+    return uri.toString();
+  }
+
+  /// A human-friendly description of the code location.
+  String get _location {
+    if (line == null) return _library;
+    if (column == null) return '$_library $line';
+    return '$_library $line:$column';
+  }
+}

test/embedded/protocol_test.dart

@@ -604,7 +604,8 @@ void main() {
         var failure = await getCompileFailure(process);
         expect(p.fromUri(failure.span.url), equalsPath(path));
         expect(failure.stackTrace, endsWith(" 1:7  root stylesheet\n"));
-        expect(failure.stackTrace.split(" ").first, equalsPath(path));
+        expect(
+            p.fromUri(failure.stackTrace.split(" ").first), equalsPath(path));
         await process.close();
       });
     });