Avoid ignored directive errors in disabled regions (#78158)

Author: jjonescz

src/Compilers/CSharp/Portable/Parser/DirectiveParser.cs

@@ -695,19 +695,22 @@ private DirectiveTriviaSyntax ParseShebangDirective(SyntaxToken hash, SyntaxToke
 
         private DirectiveTriviaSyntax ParseIgnoredDirective(SyntaxToken hash, SyntaxToken colon, bool isActive, bool isFollowingToken)
         {
-            if (!lexer.Options.FileBasedProgram)
+            if (isActive)
             {
-                colon = this.AddError(colon, ErrorCode.ERR_PPIgnoredNeedsFileBasedProgram);
-            }
+                if (!lexer.Options.FileBasedProgram)
+                {
+                    colon = this.AddError(colon, ErrorCode.ERR_PPIgnoredNeedsFileBasedProgram);
+                }
 
-            if (isFollowingToken)
-            {
-                colon = this.AddError(colon, ErrorCode.ERR_PPIgnoredFollowsToken);
-            }
+                if (isFollowingToken)
+                {
+                    colon = this.AddError(colon, ErrorCode.ERR_PPIgnoredFollowsToken);
+                }
 
-            if (_context.SeenAnyIfDirectives)
-            {
-                colon = this.AddError(colon, ErrorCode.ERR_PPIgnoredFollowsIf);
+                if (_context.SeenAnyIfDirectives)
+                {
+                    colon = this.AddError(colon, ErrorCode.ERR_PPIgnoredFollowsIf);
+                }
             }
 
             SyntaxToken endOfDirective = this.lexer.LexEndOfDirectiveWithOptionalContent(out SyntaxToken content);

src/Compilers/CSharp/Test/Syntax/Parsing/IgnoredDirectiveParsingTests.cs

@@ -287,7 +287,7 @@ public void AfterToken()
         EOF();
     }
 
-    [Fact]
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/78157")]
     public void AfterIf()
     {
         var source = """
@@ -299,7 +299,7 @@ public void AfterIf()
             """;
 
         VerifyTrivia();
-        UsingTree(source, TestOptions.Regular.WithFeature(FeatureName),
+        UsingTree(source, TestOptions.Regular.WithFeature(FeatureName).WithPreprocessorSymbols("X"),
             // (3,2): error CS9283: '#:' directives cannot be after '#if' directive
             // #:y
             Diagnostic(ErrorCode.ERR_PPIgnoredFollowsIf, ":").WithLocation(3, 2),
@@ -366,6 +366,71 @@ public void AfterIf()
             }
         }
         EOF();
+
+        UsingTree(source, TestOptions.Regular.WithFeature(FeatureName),
+            // (5,2): error CS9299: '#:' directives cannot be after '#if' directive
+            // #:z
+            Diagnostic(ErrorCode.ERR_PPIgnoredFollowsIf, ":").WithLocation(5, 2));
+
+        N(SyntaxKind.CompilationUnit);
+        {
+            N(SyntaxKind.EndOfFileToken);
+            {
+                L(SyntaxKind.IgnoredDirectiveTrivia);
+                {
+                    N(SyntaxKind.HashToken);
+                    N(SyntaxKind.ColonToken);
+                    N(SyntaxKind.StringLiteralToken, "x");
+                    N(SyntaxKind.EndOfDirectiveToken);
+                    {
+                        T(SyntaxKind.EndOfLineTrivia, "\n");
+                    }
+                }
+                L(SyntaxKind.IfDirectiveTrivia);
+                {
+                    N(SyntaxKind.HashToken);
+                    N(SyntaxKind.IfKeyword);
+                    {
+                        T(SyntaxKind.WhitespaceTrivia, " ");
+                    }
+                    N(SyntaxKind.IdentifierName);
+                    {
+                        N(SyntaxKind.IdentifierToken, "X");
+                    }
+                    N(SyntaxKind.EndOfDirectiveToken);
+                    {
+                        T(SyntaxKind.EndOfLineTrivia, "\n");
+                    }
+                }
+                L(SyntaxKind.IgnoredDirectiveTrivia);
+                {
+                    N(SyntaxKind.HashToken);
+                    N(SyntaxKind.ColonToken);
+                    N(SyntaxKind.StringLiteralToken, "y");
+                    N(SyntaxKind.EndOfDirectiveToken);
+                    {
+                        T(SyntaxKind.EndOfLineTrivia, "\n");
+                    }
+                }
+                L(SyntaxKind.EndIfDirectiveTrivia);
+                {
+                    N(SyntaxKind.HashToken);
+                    N(SyntaxKind.EndIfKeyword);
+                    N(SyntaxKind.EndOfDirectiveToken);
+                    {
+                        T(SyntaxKind.EndOfLineTrivia, "\n");
+                    }
+                }
+                L(SyntaxKind.IgnoredDirectiveTrivia);
+                {
+                    N(SyntaxKind.HashToken);
+                    N(SyntaxKind.ColonToken);
+                    N(SyntaxKind.StringLiteralToken, "z");
+                    N(SyntaxKind.EndOfDirectiveToken);
+                }
+            }
+        }
+        EOF();
     }
 
     [Fact]