Ensure whitespace-only if branches still execute assign side effects (#923)

* Initial plan

* Fix if whitespace-only branch skipping assign execution

Co-authored-by: sebastienros <1165805+sebastienros@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: sebastienros <1165805+sebastienros@users.noreply.github.com>

Author: Copilot

Fluid.Tests/IfStatementTests.cs

@@ -210,6 +210,48 @@ public async Task IfProcessAwaitedAndElse(bool async)
 
             Assert.Equal("c", sw.ToString());
         }
+
+        [Fact]
+        public async Task IfExecutesAssignInElseBranchWhenWhitespaceOrCommentOnly()
+        {
+            var e = new IfStatement(
+                BooleanExpression(false, async: false),
+                TEXT("a"),
+                new ElseStatement(new List<Statement>
+                {
+                    new AssignStatement("x", new LiteralExpression(new StringValue("value")))
+                })
+            );
+
+            var context = new TemplateContext();
+
+            await e.WriteToAsync(new StringWriter(), HtmlEncoder.Default, context);
+
+            Assert.Equal("value", context.GetValue("x").ToStringValue());
+        }
+
+        [Fact]
+        public async Task IfExecutesAssignInElseIfBranchWhenWhitespaceOrCommentOnly()
+        {
+            var e = new IfStatement(
+                BooleanExpression(false, async: false),
+                TEXT("a"),
+                null,
+                new List<ElseIfStatement>
+                {
+                    new ElseIfStatement(BooleanExpression(true, async: false), new List<Statement>
+                    {
+                        new AssignStatement("x", new LiteralExpression(new StringValue("value")))
+                    })
+                }
+            );
+
+            var context = new TemplateContext();
+
+            await e.WriteToAsync(new StringWriter(), HtmlEncoder.Default, context);
+
+            Assert.Equal("value", context.GetValue("x").ToStringValue());
+        }
     }
 
     sealed class AwaitedExpression : Expression

Fluid/Ast/IfStatement.cs

@@ -127,11 +127,6 @@ public override ValueTask<Completion> WriteToAsync(IFluidOutput output, TextEnco
 
                         if (elseIfConditionTask.Result.ToBooleanValue())
                         {
-                            if (elseIf.IsWhitespaceOrCommentOnly)
-                            {
-                                return Statement.NormalCompletion;
-                            }
-
                             var writeTask = elseIf.WriteToAsync(output, encoder, context);
                             if (!writeTask.IsCompletedSuccessfully)
                             {
@@ -144,11 +139,6 @@ public override ValueTask<Completion> WriteToAsync(IFluidOutput output, TextEnco
 
                     if (Else != null)
                     {
-                        if (Else.IsWhitespaceOrCommentOnly)
-                        {
-                            return Statement.NormalCompletion;
-                        }
-
                         return Else.WriteToAsync(output, encoder, context);
                     }
                 }
@@ -244,4 +234,4 @@ private async ValueTask<Completion> AwaitedElseBranch(
 
         protected internal override Statement Accept(AstVisitor visitor) => visitor.VisitIfStatement(this);
     }
-}
+}