Only emit each warning once per source location

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.33.1
+
+* Don't emit the same warning in the same location multiple times.
+
 ## 1.33.0
 
 * Deprecate the use of `/` for division. The new `math.div()` function should be

lib/src/visitor/async_evaluate.dart

@@ -148,6 +148,13 @@ class _EvaluateVisitor
   /// The logger to use to print warnings.
   final Logger _logger;
 
+  /// A set of message/location pairs for warnings that have been emitted via
+  /// [_warn].
+  ///
+  /// We only want to emit one warning per location, to avoid blowing up users'
+  /// consoles with redundant warnings.
+  final _warningsEmitted = <Tuple2<String, SourceSpan>>{};
+
   /// Whether to track source map information.
   final bool _sourceMap;
 
@@ -1936,7 +1943,7 @@ class _EvaluateVisitor
     }
 
     if (node.isGlobal && !_environment.globalVariableExists(node.name)) {
-      _logger.warn(
+      _warn(
           _environment.atRoot
               ? "As of Dart Sass 2.0.0, !global assignments won't be able to\n"
                   "declare new variables. Since this assignment is at the root "
@@ -1946,8 +1953,7 @@ class _EvaluateVisitor
                   "declare new variables. Consider adding "
                   "`${node.originalName}: null` at the root of the\n"
                   "stylesheet.",
-          span: node.span,
-          trace: _stackTrace(node.span),
+          node.span,
           deprecation: true);
     }
 
@@ -1987,9 +1993,13 @@ class _EvaluateVisitor
   Future<Value?> visitWarnRule(WarnRule node) async {
     var value =
         await _addExceptionSpanAsync(node, () => node.expression.accept(this));
-    _logger.warn(
-        value is SassString ? value.text : _serialize(value, node.expression),
-        trace: _stackTrace(node.span));
+    var message =
+        value is SassString ? value.text : _serialize(value, node.expression);
+
+    // Don't use [_warn] because we don't want to pass the span to the logger.
+    if (_warningsEmitted.add(Tuple2(message, node.span))) {
+      _warn(message, node.span);
+    }
     return null;
   }
 
@@ -3087,9 +3097,11 @@ class _EvaluateVisitor
   }
 
   /// Emits a warning with the given [message] about the given [span].
-  void _warn(String message, FileSpan span, {bool deprecation = false}) =>
-      _logger.warn(message,
-          span: span, trace: _stackTrace(span), deprecation: deprecation);
+  void _warn(String message, FileSpan span, {bool deprecation = false}) {
+    if (!_warningsEmitted.add(Tuple2(message, span))) return;
+    _logger.warn(message,
+        span: span, trace: _stackTrace(span), deprecation: deprecation);
+  }
 
   /// Returns a [SassRuntimeException] with the given [message].
   ///

lib/src/visitor/evaluate.dart

@@ -5,7 +5,7 @@
 // DO NOT EDIT. This file was generated from async_evaluate.dart.
 // See tool/grind/synchronize.dart for details.
 //
-// Checksum: 1fc6b9e6018eba3ac520464abb56e686f4cb9886
+// Checksum: 75235f66937f2acdfb9d433bd25f821c63d5ff53
 //
 // ignore_for_file: unused_import
 
@@ -156,6 +156,13 @@ class _EvaluateVisitor
   /// The logger to use to print warnings.
   final Logger _logger;
 
+  /// A set of message/location pairs for warnings that have been emitted via
+  /// [_warn].
+  ///
+  /// We only want to emit one warning per location, to avoid blowing up users'
+  /// consoles with redundant warnings.
+  final _warningsEmitted = <Tuple2<String, SourceSpan>>{};
+
   /// Whether to track source map information.
   final bool _sourceMap;
 
@@ -1928,7 +1935,7 @@ class _EvaluateVisitor
     }
 
     if (node.isGlobal && !_environment.globalVariableExists(node.name)) {
-      _logger.warn(
+      _warn(
           _environment.atRoot
               ? "As of Dart Sass 2.0.0, !global assignments won't be able to\n"
                   "declare new variables. Since this assignment is at the root "
@@ -1938,8 +1945,7 @@ class _EvaluateVisitor
                   "declare new variables. Consider adding "
                   "`${node.originalName}: null` at the root of the\n"
                   "stylesheet.",
-          span: node.span,
-          trace: _stackTrace(node.span),
+          node.span,
           deprecation: true);
     }
 
@@ -1977,9 +1983,13 @@ class _EvaluateVisitor
 
   Value? visitWarnRule(WarnRule node) {
     var value = _addExceptionSpan(node, () => node.expression.accept(this));
-    _logger.warn(
-        value is SassString ? value.text : _serialize(value, node.expression),
-        trace: _stackTrace(node.span));
+    var message =
+        value is SassString ? value.text : _serialize(value, node.expression);
+
+    // Don't use [_warn] because we don't want to pass the span to the logger.
+    if (_warningsEmitted.add(Tuple2(message, node.span))) {
+      _warn(message, node.span);
+    }
     return null;
   }
 
@@ -3058,9 +3068,11 @@ class _EvaluateVisitor
   }
 
   /// Emits a warning with the given [message] about the given [span].
-  void _warn(String message, FileSpan span, {bool deprecation = false}) =>
-      _logger.warn(message,
-          span: span, trace: _stackTrace(span), deprecation: deprecation);
+  void _warn(String message, FileSpan span, {bool deprecation = false}) {
+    if (!_warningsEmitted.add(Tuple2(message, span))) return;
+    _logger.warn(message,
+        span: span, trace: _stackTrace(span), deprecation: deprecation);
+  }
 
   /// Returns a [SassRuntimeException] with the given [message].
   ///

test/dart_api/logger_test.dart

@@ -4,6 +4,8 @@
 
 @TestOn('vm')
 
+import 'dart:async';
+
 import 'package:test/test.dart';
 import 'package:source_span/source_span.dart';
 import 'package:stack_trace/stack_trace.dart';
@@ -29,6 +31,32 @@ void main() {
       }));
     });
 
+    test("passes multiple messages with different locations to the logger", () {
+      var controller = StreamController<String>();
+      compileString('''
+        @mixin foo {@warn heck}
+        @include foo;
+        @warn heck;
+      ''',
+          logger: _TestLogger.withWarn((message,
+                  {span, trace, deprecation = false}) =>
+              controller.add(message)));
+
+      expect(controller.stream, emitsInOrder(["heck", "heck"]));
+    });
+
+    test("only passes a message with a single location to the logger once", () {
+      var count = 0;
+      compileString(r'''
+        @for $i from 1 to 5 {
+          @warn heck;
+        }
+      ''',
+          logger: _TestLogger.withWarn(
+              (message, {span, trace, deprecation = false}) => count++));
+      expect(count, equals(1));
+    });
+
     test("stringifies the argument", () {
       var mustBeCalled = expectAsync0(() {});
       compileString('@warn #abc', logger: