Debugging Kotlin program using VSCode

2 min readJun 25, 2020

TL;DR

Install fwcd.kotlin extension.

Summary

Many sites demostrate how to code and run Kotlin programs using vscode, without showing how to debug it.

I want to share what I tried and got worked, if someone else face the same situation. (I tried on Mac, but the concept is common for Windows PC.)

Background

I know IntelliJ IDEA is the best IDE for kotlin. But it is memory consuming and have different key bindings to VSCode. I wrote frontend(react) using VSCode and wrote backend(kotlin) using IntelliJ IDEA. I found the switching cost is high between the two IDEs. So I tried to write kotlin also in VSCode.

Prerequisites

VSCode
Java

Procedures

1. Install kotlin and gradle

% brew install kotlin
% brew install gradle

2. create a kotlin sample app

% mkdir kt-sample-app
% cd kt-sample-app
% gradle init --type=kotlin-application
# Select all default choices is OK
 
# Have a try is everything is ok
% ./gradlew buildBUILD SUCCESSFUL in 3s
8 actionable tasks: 8 executed

3. Install VSCode extensions

% mkdir -p .vscode
% vi .vscode/extensions.json----- Input contents as below -----
{
    "recommendations": [
        "fwcd.kotlin",
        "vscjava.vscode-java-pack"
    ]
}# Launch vscode
% code .

Select “Install All” to the dialog showed, which will install the 2 extensions wrote above.

Open App.kt file, and you will see “syntax highlight”, “auto compleletion” working.

4. Settings to build and debug

% vi .vscode/tasks.json----- Input the content below -----{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "build",
            "type": "shell",
            "command": "./gradlew build -x test",
            "problemMatcher": [],
            "group": {
                "kind": "build",
                "isDefault": true
            }
        },
        {
            "label": "run",
            "type": "shell",
            "command": "./gradlew run",
            "problemMatcher": []
        },
        {
            "label": "test",
            "type": "shell",
            "command": "./gradlew test",
            "problemMatcher": []}
    ]
}

In vscode menu, Terminal -> Run Task… You can execute gradlew’s build / run / test tasks.

Finally the debug settings:

% vi .vscode/launch.json----- Input content below -----{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "kotlin",
            "request": "launch",
            "name": "Kotlin Launch",
            "projectRoot": "${workspaceFolder}/app",
            "mainClass": "kt/sample/app/AppKt",
            "preLaunchTask": "build"
        }
    ]
}

Set some breakpoint, debug the program by vscode’s Debug tab -> Run button.

See a working repo:

https://github.com/thunderz99/kt-sample-app