SAM run/debug: eliminate temporary directory

[justinmk3]

Problem

Toolkit currently always builds and runs from a temporary /tmp/vstck-xx directory. This confuses tooling and may defeat SAM CLI "cache" functionality.

• SAM run/debug: support custom --build-dir instead of temporary dir #1988
• SAM: slow build time when building multiple functions #2024
• (Rancher) SAM debug fails #3413 (comment)

Reason for the temporary directory:

• we wanted to avoid building artifacts into the user's workspace (which then might be accidentally committed)

Related notes:

• A similar but not identical concept is that Toolkit copies the actual template.yaml to a temporary counterpart.
  • YAML Handling Improvements #1159
  • Use existing template for template invoke-targets #990

Proposal

1. what does aws-toolkit-jetbrains do?
2. Switch to building in the user's workspace.
   • auto-add to .git/info/excludes ?
3. in .aws-sam/ directory?
   • Bonus: works better with sam invocations outside of the Toolkit
4. Strategy: instead of "temp dir per execution", change the model to "temp dir per template"?

Alternative:

1. Mostly keep the same logic, but always re-use the same /tmp/vstck-xx directory for the same template.yaml
   • risk: does this complicate the logic that maps the temporary template.yaml from the actual template.yaml ? YAML Handling Improvements #1159

Alternative:

1. are we passing the temporary as --build-dir correctly? Maybe this will avoid needing to remap the paths in the temporary template.yaml YAML Handling Improvements #1159 Use existing template for template invoke-targets #990 ?

[danw-mpl]

This would be amazing. We wait over two minutes every time we invoke a function because the cache is wiped out. Super frustrating when trying to develop.

@justinmk3 Regarding JetBrains, we experience the same problem.

[JadenSimon]

The next release (1.30.0) will include a way to set a directory via a buildDir field in the launch config (under "sam")
Example config:

"type": "aws-sam",
"request": "direct-invoke",
"name": "lambda-go1.x:HelloWorldFunction (go1.x)",
"invokeTarget": {
    "target": "template",
    "templatePath": "${workspaceFolder}/lambda-go1.x/template.yaml",
    "logicalId": "HelloWorldFunction"
},
"lambda": {
    "payload": {},
    "environmentVariables": {},
    "runtime": "go1.x"
},
"sam": {
    "buildDir": "${workspaceFolder}/buildDir"
}

[justinmk3]

#2755 mitigates some issues with the temporary directory by setting the process working directory.