Existing output file should be deleted/overwritten (#2886)

The CLI currently uses `File.OpenWrite(path)` (added in #2677) to create an output stream for the resulting swagger document. This does not delete the existing contents, but instead starts writing from position 0, causing issues if the output is smaller than the previous file content.

Changed to `File.Create(path)` to make sure any previous content is discarded.

src/Swashbuckle.AspNetCore.Cli/Program.cs

@@ -101,7 +101,7 @@ public static int Main(string[] args)
                         ? Path.Combine(Directory.GetCurrentDirectory(), arg1)
                         : null;
 
-                    using (Stream stream = outputPath != null ? File.OpenWrite(outputPath) : Console.OpenStandardOutput())
+                    using (Stream stream = outputPath != null ? File.Create(outputPath) : Console.OpenStandardOutput())
                     using (var streamWriter = new FormattingStreamWriter(stream, CultureInfo.InvariantCulture))
                     {
                         IOpenApiWriter writer;

test/Swashbuckle.AspNetCore.Cli.Test/ToolTests.cs

@@ -28,6 +28,28 @@ public void Can_Generate_Swagger_Json()
             Assert.True(productsPath.TryGetProperty("post", out _));
         }
 
+        [Fact(Skip = "Disabled because it makes CI unstable")]
+        public void Overwrites_Existing_File()
+        {
+            using var temporaryDirectory = new TemporaryDirectory();
+            var path = Path.Combine(temporaryDirectory.Path, "swagger.json");
+
+            var dummyContent = new string('x', 100_000);
+            File.WriteAllText(path, dummyContent);
+
+            var args = new string[] { "tofile", "--output", path, Path.Combine(Directory.GetCurrentDirectory(), "Basic.dll"), "v1" };
+            Assert.Equal(0, Program.Main(args));
+
+            var readContent = File.ReadAllText(path);
+            Assert.True(readContent.Length < dummyContent.Length);
+            using var document = JsonDocument.Parse(readContent);
+
+            // verify one of the endpoints
+            var paths = document.RootElement.GetProperty("paths");
+            var productsPath = paths.GetProperty("/products");
+            Assert.True(productsPath.TryGetProperty("post", out _));
+        }
+
         [Fact]
         public void CustomDocumentSerializer_Writes_Custom_V2_Document()
         {