[New Global] Forbid defining new variables with !global

Closes #600

Author: nex3

lib/src/deprecation.dart

@@ -15,7 +15,7 @@ enum Deprecation {
   // DO NOT EDIT. This section was generated from the language repo.
   // See tool/grind/generate_deprecations.dart for details.
   //
-  // Checksum: d1c9c01ca8d2b69e39b7371d774c9c86349efdef
+  // Checksum: 0be67f32391e119205f8e98cd15fa8e7382b6dd2
 
   /// Deprecation for passing a string directly to meta.call().
   callString('call-string',
@@ -40,6 +40,7 @@ enum Deprecation {
   /// Deprecation for declaring new variables with !global.
   newGlobal('new-global',
       deprecatedIn: '1.17.2',
+      obsoleteIn: '2.0.0',
       description: 'Declaring new variables with !global.'),
 
   /// Deprecation for using color module functions in place of plain CSS functions.

lib/src/visitor/async_evaluate.dart

@@ -2574,21 +2574,10 @@ final class _EvaluateVisitor
     }
 
     if (node.isGlobal && !_environment.globalVariableExists(node.name)) {
-      _warn(
-        _environment.atRoot
-            ? "As of Dart Sass 2.0.0, !global assignments won't be able to "
-                "declare new variables.\n"
-                "\n"
-                "Since this assignment is at the root of the stylesheet, the "
-                "!global flag is\n"
-                "unnecessary and can safely be removed."
-            : "As of Dart Sass 2.0.0, !global assignments won't be able to "
-                "declare new variables.\n"
-                "\n"
-                "Recommendation: add `${node.originalName}: null` at the "
-                "stylesheet root.",
+      throw SassRuntimeException(
+        '!global assignments may not declare new variables.',
         node.span,
-        Deprecation.newGlobal,
+        _stackTrace(node.span),
       );
     }
 

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: b6119944111590722f1b578e1d2338f7d3d9b9a2
+// Checksum: faf491d48ccd341abf6a301773bfce08af22b113
 //
 // ignore_for_file: unused_import
 
@@ -2579,21 +2579,10 @@ final class _EvaluateVisitor
     }
 
     if (node.isGlobal && !_environment.globalVariableExists(node.name)) {
-      _warn(
-        _environment.atRoot
-            ? "As of Dart Sass 2.0.0, !global assignments won't be able to "
-                "declare new variables.\n"
-                "\n"
-                "Since this assignment is at the root of the stylesheet, the "
-                "!global flag is\n"
-                "unnecessary and can safely be removed."
-            : "As of Dart Sass 2.0.0, !global assignments won't be able to "
-                "declare new variables.\n"
-                "\n"
-                "Recommendation: add `${node.originalName}: null` at the "
-                "stylesheet root.",
+      throw SassRuntimeException(
+        '!global assignments may not declare new variables.',
         node.span,
-        Deprecation.newGlobal,
+        _stackTrace(node.span),
       );
     }
 

test/deprecations_test.dart

@@ -15,11 +15,6 @@ void main() {
     _expectDeprecation("a { b: call(random)}", Deprecation.callString);
   });
 
-  // Deprecated in 1.17.2
-  test("newGlobal is violated by declaring a new variable with !global", () {
-    _expectDeprecation(r"a {$foo: bar !global;}", Deprecation.newGlobal);
-  });
-
   // Deprecated in 1.23.0
   group("colorModuleCompat is violated by", () {
     var color = "@use 'sass:color'; a { b: color";