Add support for --if-present to NpmRunScript settings and tests

src/Cake.Npm.Tests/RunScript/NpmScriptRunnerTests.cs

@@ -63,6 +63,38 @@ public void Should_Add_ScriptName_To_Arguments_If_Not_Null()
             Assert.Equal("run-script \"foo bar\"", result.Args);
         }
 
+
+        [Fact]
+        public void Should_Add_IfPresent_If_Specified()
+        {
+            // Given
+            var fixture = new NpmRunScriptFixture();
+            fixture.Settings.ScriptName = "foo bar";
+            fixture.Settings.IfPresent = true;
+
+            // When
+            var result = fixture.Run();
+
+            // Then
+            Assert.Equal("run-script \"foo bar\" --if-present", result.Args);
+        }
+
+        [Fact]
+        public void Should_Add_IfPresent_and_Arguments_If_Specified()
+        {
+            // Given
+            var fixture = new NpmRunScriptFixture();
+            fixture.Settings.ScriptName = "foo bar";
+            fixture.Settings.IfPresent = true;
+            fixture.Settings.Arguments.Add("--foo=bar");
+
+            // When
+            var result = fixture.Run();
+
+            // Then
+            Assert.Equal("run-script \"foo bar\" --if-present -- --foo=bar", result.Args);
+        }
+
         [Fact]
         public void Should_Add_ScriptArguments_To_Arguments_If_Not_Empty()
         {

src/Cake.Npm/RunScript/NpmRunScriptSettings.cs

@@ -26,11 +26,17 @@ public NpmRunScriptSettings()
     /// </summary>
     public string ScriptName { get; set; }
 
+    /// <summary>
+    /// If true, the script will only be executed if it is present in package.json.
+    /// </summary>
+    public bool IfPresent { get; set; }
+
     /// <summary>
     /// Arguments to pass to the target script.
     /// </summary>
     public IList<string> Arguments => _arguments;
 
+
     /// <summary>
     /// Evaluates the settings and writes them to <paramref name="args"/>.
     /// </summary>
@@ -45,6 +51,11 @@ protected override void EvaluateCore(ProcessArgumentBuilder args)
         base.EvaluateCore(args);
 
         args.AppendQuoted(ScriptName);
+
+        if (IfPresent)
+        {
+            args.Append("--if-present");
+        }
 
         if (Arguments.Any())
         {