Now Enum values definition have space-insensitive syntax (#2690)

Fix to support whitespace after the `=` and before the value expression.

src/System.Management.Automation/engine/parser/Parser.cs

@@ -4311,23 +4311,33 @@ namespace System.Management.Automation.Language
 
             IScriptExtent endExtent = enumeratorName.Extent;
             ExpressionAst initialValueAst = null;
-            var assignToken = PeekToken();
             var missingInitializer = false;
-            if (assignToken.Kind == TokenKind.Equals)
+            var oldTokenizerMode = _tokenizer.Mode;
+            Token assignToken = null;
+            try
             {
-                SkipToken();
-                initialValueAst = ExpressionRule();
-                if (initialValueAst == null)
+                SetTokenizerMode(TokenizerMode.Expression);
+                assignToken = PeekToken();
+                if (assignToken.Kind == TokenKind.Equals)
                 {
-                    ReportError(After(assignToken), () => ParserStrings.ExpectedValueExpression, assignToken.Kind.Text());
-                    endExtent = assignToken.Extent;
-                    missingInitializer = true;
-                }
-                else
-                {
-                    endExtent = initialValueAst.Extent;
+                    SkipToken();
+                    initialValueAst = ExpressionRule();
+                    if (initialValueAst == null)
+                    {
+                        ReportError(After(assignToken), () => ParserStrings.ExpectedValueExpression, assignToken.Kind.Text());
+                        endExtent = assignToken.Extent;
+                        missingInitializer = true;
+                    }
+                    else
+                    {
+                        endExtent = initialValueAst.Extent;
+                    }
                 }
             }
+            finally
+            {
+                SetTokenizerMode(oldTokenizerMode);
+            }
 
             Token terminatorToken = PeekToken();
             if (terminatorToken.Kind != TokenKind.NewLine && terminatorToken.Kind != TokenKind.Semi && terminatorToken.Kind != TokenKind.RCurly)

test/powershell/Language/Classes/scripting.enums.tests.ps1

@@ -3,7 +3,6 @@
 #
 
 Describe 'enums' -Tags "CI" {
-
     Context 'basic enums' {
         enum E1
         {
@@ -62,9 +61,10 @@ Describe 'enums' -Tags "CI" {
             e0 = [E6]::e0 + 2
         }
 
+        # Don't add space after 'e0 ='! Fix #2543
         enum E6
         {
-            e0 = 38
+            e0 =38
         }
 
         It 'E4 has correct value' { [E4]::e0 | Should Be ([E4]42) }