Don't add extra newlines to StyleRule.selector (#2853)

This was causing a crash when mapping errors in the selector back to
the original text.

Closes #2848

Author: nex3

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## 1.104.1-dev
 
+* Fix a bug in which an invalid selector at the end of an indented syntax
+  stylesheet would cause the parser to crash instead of emitting a useful error
+  message.
+
 ### Command Line Interface
 
 * Many-to-many compilations no longer compile any files that appear in the

lib/src/parse/sass.dart

@@ -46,11 +46,15 @@ class SassParser(super.contents, {super.url, super.parseSelectors})
     var start = scanner.state;
 
     var buffer = InterpolationBuffer();
-    do {
+    while (true) {
       buffer.addInterpolation(almostAnyValue(omitComments: true));
-      buffer.writeCharCode($lf);
-    } while (buffer.trailingString.trimRight().endsWith(',') &&
-        scanCharIf((char) => char.isNewline));
+      if (buffer.trailingString.trimRight().endsWith(',') &&
+          scanCharIf((char) => char.isNewline)) {
+        buffer.writeCharCode($lf);
+      } else {
+        break;
+      }
+    }
 
     return buffer.interpolation(spanFrom(start));
   }

lib/src/parse/stylesheet.dart

@@ -540,7 +540,17 @@ abstract class StylesheetParser(
         buffer.addInterpolation(interpolation);
         interpolation = buffer.interpolation(spanFrom(start));
       }
-      if (interpolation.contents.isEmpty) scanner.error('expected "}".');
+      if (interpolation.contents.isEmpty) {
+        var unknown = _interpolatedDeclarationValue(
+          allowEmpty: true,
+          allowOpenBrace: false,
+        );
+        if (unknown.contents.isEmpty) {
+          scanner.error('expected end of rule.');
+        } else {
+          error('unrecognized syntax', unknown.span);
+        }
+      }
 
       return _withStyleRuleChildren(
         interpolation,

pkg/sass-parser/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 0.4.55-dev
 
-* No user-visible changes.
+* Omit an extra newline that was being added to the end of `Rule.selector` in
+  the indented syntax.
 
 ## 0.4.54
 

pkg/sass_api/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 17.10.1-dev
 
-* No user-visible changes.
+* Omit an extra newline that was being added to the end of `StyleRule.selector`
+  in the indented syntax.
 
 ## 17.10.0