Accept 'false' instead of just empty arity and add 0 arity test

Author: nagilson

src/Cli/dotnet/Commands/Tool/Install/ToolInstallCommandParser.cs

@@ -51,7 +51,7 @@ internal static class ToolInstallCommandParser
     public static readonly Option<bool> CreateManifestIfNeededOption = new("--create-manifest-if-needed")
     {
         Description = CliCommandStrings.CreateManifestIfNeededOptionDescription,
-        Arity = ArgumentArity.Zero,
+        Arity = ArgumentArity.ZeroOrOne,
         DefaultValueFactory = _ => true,
     };
 

test/dotnet.Tests/CommandTests/Tool/Install/ToolInstallLocalCommandTests.cs

@@ -127,13 +127,33 @@ public void WhenRunWithPackageIdItShouldSaveToCacheAndAddToManifestFile()
             AssertDefaultInstallSuccess();
         }
 
+        [Fact]
+        public void GivenCreateManifestIfNeededWithoutArgumentTheDefaultIsTrueForLegacyBehavior()
+        {
+            _fileSystem.File.Delete(_manifestFilePath);
+            ParseResult parseResult =
+            Parser.Instance.Parse(
+               $"dotnet tool install {_packageIdA.ToString()} --create-manifest-if-needed");
+
+            var toolInstallLocalCommand = new ToolInstallLocalCommand(
+                parseResult,
+                _packageIdA,
+                _toolPackageDownloaderMock,
+                _toolManifestFinder,
+                _toolManifestEditor,
+                _localToolsResolverCache,
+                _reporter);
+
+            toolInstallLocalCommand.Execute().Should().Be(0);
+        }
+
         [Fact]
         public void GivenNoManifestFileItShouldThrowAndContainNoManifestGuide()
         {
             _fileSystem.File.Delete(_manifestFilePath);
             ParseResult parseResult =
             Parser.Instance.Parse(
-               $"dotnet tool install {_packageIdA.ToString()} --create-manifest-if-needed=false");
+               $"dotnet tool install {_packageIdA.ToString()} --create-manifest-if-needed false");
 
             var toolInstallLocalCommand = new ToolInstallLocalCommand(
                 parseResult,