This is not working as I expect based on the prior information in this issue. I have created a brand new dart project, a simple cli app. For my launch config, I first tried this:

        {
            "name": "toolTest",
            "request": "launch",
            "type": "dart",
            "program": "bin/main.dart",
            "customTool": "echo",
        }

Output:
--enable-asserts --enable-vm-service=0 --pause_isolates_on_start=true --no-serve-devtools --write-service-info=file:///var/folders/h0/y0mhxm317slfr5k149cfxvfr0000gn/T/dart-vm-service-7630.json -DSILENT_OBSERVATORY=true bin/main.dart

So far so good. I then tried to see if I could remove args:

        {
            "name": "toolTest",
            "request": "launch",
            "type": "dart",
            "program": "bin/main.dart",
            "customTool": "echo",
            "customToolReplacesArgs": 2,
        }

Output:
--enable-asserts --enable-vm-service=0 --pause_isolates_on_start=true --no-serve-devtools --write-service-info=file:///var/folders/h0/y0mhxm317slfr5k149cfxvfr0000gn/T/dart-vm-service-6a28.json -DSILENT_OBSERVATORY=true bin/main.dart

Hmm, that's odd. Nothing got removed. Maybe it need tool args to replace them?

        {
            "name": "toolTest",
            "request": "launch",
            "type": "dart",
            "program": "bin/main.dart",
            "customTool": "echo",
            "customToolReplacesArgs": 2,
            "toolArgs": [
                "test",
                "arg"
            ]
        }

Output:
test arg --enable-asserts --enable-vm-service=0 --pause_isolates_on_start=true --no-serve-devtools --write-service-info=file:///var/folders/h0/y0mhxm317slfr5k149cfxvfr0000gn/T/dart-vm-service-6280.json -DSILENT_OBSERVATORY=true bin/main.dart

So it appears that "echo" replaces "dart" as the tool but customToolReplacesArgs maybe does nothing?

        {
            "name": "toolTest",
            "request": "launch",
            "type": "dart",
            "program": "bin/main.dart",
            "customTool": "echo",
            "toolArgs": [
                "test",
                "arg"
            ]
        }

Output:
test arg --enable-asserts --enable-vm-service=0 --pause_isolates_on_start=true --no-serve-devtools --write-service-info=file:///var/folders/h0/y0mhxm317slfr5k149cfxvfr0000gn/T/dart-vm-service-19d2.json -DSILENT_OBSERVATORY=true bin/main.dart

Same thing. How do I get the arg replacement to work?

Additionally, if I try this with a flutter project, it completely ignores "customTool" and continues running as normal even though I'm using the exact same launch config. How does the extension determine whether it's a flutter project or not and why does it ignore the customTool arg?

Originally posted by @point-source in #3656 (comment)