Update formatter to not write newlines if content is empty (PowerShell#11193)

Author: SteveL-MSFT

src/System.Management.Automation/FormatAndOutput/common/ComplexWriter.cs

@@ -49,14 +49,24 @@ internal void WriteObject(List<FormatValue> formatValueList)
             // we always start with no indentation
             _indentationManager.Clear();
 
+            bool hasContent = false;
             foreach (FormatEntry fe in formatValueList)
             {
-                // operate on each directive inside the list,
-                // carrying the indentation from invocation to invocation
-                GenerateFormatEntryDisplay(fe, 0);
+                if (fe.formatValueList.Count > 0)
+                {
+                    hasContent = true;
+
+                    // operate on each directive inside the list,
+                    // carrying the indentation from invocation to invocation
+                    GenerateFormatEntryDisplay(fe, 0);
+                }
             }
+
             // make sure that, if we have pending text in the buffer it gets flushed
-            WriteToScreen();
+            if (hasContent)
+            {
+                WriteToScreen();
+            }
         }
 
         /// <summary>

src/System.Management.Automation/FormatAndOutput/common/FormatViewGenerator_Complex.cs

@@ -281,11 +281,10 @@ private void ExecuteFormatTokenList(TraversalInfo level,
                     // do the formatting and we will be done
                     if (cpt.control == null || cpt.control is FieldControlBody)
                     {
-                        // Since it is a leaf node we just consider it an empty string and go
-                        // on with formatting
                         if (val == null)
                         {
-                            val = string.Empty;
+                            // Since it is a leaf node we just ignore it
+                            return;
                         }
 
                         FieldFormattingDirective fieldFormattingDirective = null;
@@ -780,4 +779,3 @@ private List<FormatValue> AddIndentationLevel(List<FormatValue> formatValueList)
         private int _enumerationLimit;
     }
 }
-

test/powershell/Modules/Microsoft.PowerShell.Utility/Format-Custom.Tests.ps1

@@ -438,3 +438,69 @@ SelectScriptBlock
         $ps.Streams.Error | Should -BeNullOrEmpty
     }
 }
+
+Describe "Custom formatting returning nothing" -Tags "CI" {
+  BeforeAll {
+      $formatFilePath = Join-Path $TestDrive 'UpdateFormatDataTests.format.ps1xml'
+      $xmlContent = @'
+      <Configuration>
+      <ViewDefinitions>
+          <View>
+              <Name>Test</Name>
+              <ViewSelectedBy>
+                  <TypeName>MyTestObject</TypeName>
+              </ViewSelectedBy>
+              <CustomControl>
+                  <CustomEntries>
+                      <CustomEntry>
+                          <CustomItem>
+                              <ExpressionBinding>
+                                  <ScriptBlock>
+                                    $null
+                                  </ScriptBlock>
+                              </ExpressionBinding>
+                          </CustomItem>
+                      </CustomEntry>
+                  </CustomEntries>
+              </CustomControl>
+          </View>
+      </ViewDefinitions>
+  </Configuration>
+'@
+
+      Set-Content -Path $formatFilePath -Value $xmlContent
+      $ps = [powershell]::Create()
+      $iss = [initialsessionstate]::CreateDefault2()
+      $iss.Formats.Add($formatFilePath)
+      $rs = [runspacefactory]::CreateRunspace($iss)
+      $rs.Open()
+      $ps.Runspace = $rs
+  }
+
+  AfterAll {
+      $rs.Dispose()
+      $ps.Dispose()
+  }
+
+  It 'Newlines are not written if nothing is returned by custom format' {
+      $script = {
+          [PSCustomObject]@{
+              PSTypeName = 'MyTestObject'
+              Name = 'testing'
+          }
+      }
+
+      $null = $ps.AddScript($script).AddCommand('Out-String')
+      $ps.Streams.Error.Clear()
+
+      # one newline for start, one for grouping, and one for end
+      $expectedOutput = @'
+
+
+
+'@ -replace '\r?\n', "^"
+
+      $ps.Invoke() -replace '\r?\n', "^" | Should -BeExactly $expectedOutput
+      $ps.Streams.Error | Should -BeNullOrEmpty
+  }
+}