Generating build/debug assets should not overwrite existing launch and tasks

[bwateratmsft]

Currently when generating build/debug assets for .NET Core projects, anything in launch.json and tasks.json will be overwritten. This can cause data loss and user confusion. Instead, the relevant launch and tasks should be added if missing, and if already present, prompted for overwriting.

The vscode-docker extension does this by checking the name of the launch/task. If another launch/task of the same name we're about to create exists, we will prompt if they want to overwrite.

[bwateratmsft]

Here's an example scenario for why this is a problem.

1. User creates a .NET Core app, and opens in VSCode
2. User hits F5 without clicking the "Add required assets..." to set up for .NET Core
3. In the "Select environment" pick, user selects the Docker launch configuration, which depends on .NET Core build
4. The Docker extension will abort the debugging attempt and indicate that the user must add Docker support / debug assets. Adding these cannot be done automatically as it requires several inputs.
5. The user adds these assets for Docker debugging. The user hits F5 on the Docker launch profile.
   1. For whatever reason, VSCode does not warn or error if a task's dependsOn doesn't exist (in this case, the .NET Core build task).
6. Debugging fails, as the project was never built.

Eventually, suppose they figure out they need to add the .NET Core assets. Upon doing so, the Docker launch and tasks are now overwritten. They can be added back via "Docker: Initialize for debugging" command, but this causes needless confusion and possible data loss.

[ucheNkadiCode]

The Docker Tools Team would like to bump this thread and request a fix for the ".NET Generate Assets for Build and Debug" command.

For our .NET customers (our 2nd highest user category), this bug negatively affects our ability to scaffold single dockerfiles and compose files for .NET projects. Also if a user has already created a docker launch configuration, this bug undoes the users work because it wipes their launch configurations when the command is run rather than appending to the file.

When our users try to scaffold a dockerfile or compose file by running the command "Docker: Add Docker Files to Workspace" without having the proper .NET tasks and launch config, we fail the command with a message that says to run ".NET Generate Assets for Build and Debug". Ideally, we want the ability to automatically run the .NET debug assets command in the background before completing our scaffolding command when a user isn't correctly configured because this would be a better user experience. However, due to this command's nature of wiping a user's launch configuration and tasks.json rather than appending to the file or overwriting an identically named config, our team is refraining from doing so or we would risk wiping our own docker launch configurations that the user may have just set up.

This issue has affected 1646 of our users about 3983 times in the just the past 60 days.

This is a blocking issue for our team - vscode-docker#1423