How to fix this bazel project for kotlin? - kotlin

Question

I want to be able to use bazel to organize a simple kotlin project.
I am using the templates as listed in rules_kotlin (https://github.com/bazelbuild/rules_kotlin)
This is my BUILD file
load("#io_bazel_rules_kotlin//kotlin:kotlin.bzl", "kt_jvm_library")
kt_jvm_library(
name = "redis-tools",
srcs = glob(["*.kt"]),
deps = [],
)
This is my WORKSPACE file
load("#bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
rules_kotlin_version = "legacy-1.3.0"
rules_kotlin_sha = "4fd769fb0db5d3c6240df8a9500515775101964eebdf85a3f9f0511130885fde"
http_archive(
name = "io_bazel_rules_kotlin",
urls = ["https://github.com/bazelbuild/rules_kotlin/archive/%s.zip" % rules_kotlin_version],
type = "zip",
strip_prefix = "rules_kotlin-%s" % rules_kotlin_version,
sha256 = rules_kotlin_sha,
)
load("#io_bazel_rules_kotlin//kotlin:kotlin.bzl", "kotlin_repositories", "kt_register_toolchains")
kotlin_repositories() # if you want the default. Otherwise see custom kotlinc distribution below
kt_register_toolchains() # to use the default toolchain, otherwise see toolchains below
My kotlin file main.kt:
import java.util.Scanner
fun main(args: Array<String>) {
// Creates a reader instance which takes
// input from standard input - keyboard
val reader = Scanner(System.`in`)
print("Enter a number: ")
// nextInt() reads the next integer from the keyboard
var integer:Int = reader.nextInt()
// println() prints the following line to the output screen
println("You entered: $integer")
}
I use a very simple file to test my setup.
Without bazel, I can do these to build: kotlinc main.kt -include-runtime -d test.jar
then run it with java -jar test.jar
When I use bazel build ., bazel creates a few folders. I tried to run java -jar bazel-out/darwin-fastbuild/bin/redis-tools.jar but it failed.
$ java -jar bazel-out/darwin-fastbuild/bin/redis-tools.jar
no main manifest attribute, in bazel-out/darwin-fastbuild/bin/redis-tools.jar
Did I miss a target? How can I run the main.tk from the bazel output?

Answer 1

The jar you are trying to run is missing a manifest file which declares its main class.
For executing a binary, Bazel uses a shell script wrapper which includes the required jvm flags and its run-time dependencies.
Notice that you are using kt_jvm_library. This rule builds a shared dependency without the wrapper. To include a wrapper you should use the kt_jvm_binary rule. Then you can specify the main class by setting the main_class attribute.
Notice that you can use the bazel run :redis-tools to run the jar (use -s to see which script Bazel excuted)
You can also use bazel build :redis-tools_deploy.jar to build a "fat-jar" which will include the manifest.