Missing output directives error when executing Android build.gradle.kts

[pueffl]

I' trying to setup protobuf for Android, but I get "> protoc: stdout: . stderr: Missing output directives." I think that is just a configuration issue, but the message is not very helpful and I'm stuck at the moment. The gradle code looks as follows:

import com.eight.build.*
import com.google.protobuf.gradle.*

plugins {
    `android-base-lib`
}

apply(plugin = "com.google.protobuf")

dependencies {
...
    implementation("com.google.protobuf:protobuf-lite:3.0.0")
...
}

protobuf {
    generatedFilesBaseDir = "$projectDir/src/generated"
    protoc {
        artifact = "com.google.protobuf:protoc:3.15.8"
    }
    plugins {
        id("javalite") {
            artifact = "com.google.protobuf:protoc-gen-javalite:3.0.0"
        }
    }
    generateProtoTasks {
        ofSourceSet("main").forEach {
            it.plugins {
                id("java") {
                    option("lite")
                }
            }
        }
    }
}

[voidzcy]

If you are using protobuf version before 3.8, protoc-gen-javalite is provided as a protoc plugin. So you need to configure the "javalite" plugin for GenerateProtoTask:

protobuf {
    ...

    protoc {
        artifact = "com.google.protobuf:protoc:3.0.0"
    }
    plugins {
        id("javalite") {
            artifact = "com.google.protobuf:protoc-gen-javalite:3.0.0"
        }
    }
    generateProtoTasks {
        ofSourceSet("main").forEach {
            task.builtins {
               remove java  // you probably do not need full java
            }
            it.plugins {
                id("javalite") { }
            }
        }
    }
}

If you are using protobuf 3.8+ (as 3.15.8 is used in your buildscript), the lite runtime is built into protoc's Java codegen. So you need to configure the "java" builtin for GenerateProtoTask:

protobuf {
    ...

    protoc {
        artifact = "com.google.protobuf:protoc:3.15.8"
    }
    generateProtoTasks {
        ofSourceSet("main").forEach {
            it.builtins {
                id("java") {
                  option("lite")
                }
            }
        }
    }
}

You can see details in Default outputs section of README for Android projects.

[pueffl]

You where right that there was a mixup with some artefacts, but unfortunately, correcting that doesn't change a thing:

apply(plugin = "com.google.protobuf")

dependencies {
    implementation("com.google.protobuf:protobuf-javalite:3.15.8")
}

protobuf {

    protoc {
        artifact = "com.google.protobuf:protoc:3.15.8"
    }
    generateProtoTasks {
        ofSourceSet("main").forEach {
            it.builtins {
                id("java") {
                    option("lite")
                }
            }
        }
    }
}

Same error:
Execution failed for task ':preferences_app:generateDebugProto'.

protoc: stdout: . stderr: Missing output directives.

[voidzcy]

I forgot to mention the difference for Android builds...

In Android projects the minimum compilation unit is variant (compared to sourceSet in normal Java projects), so proto generation tasks are associated with each variant.

protobuf {
    ...

    generateProtoTasks {
        // You probably just want to configure for all variants. Although we provide 
        // `ofFlavor()`/`ofBuildType()`/`ofVariant()`/`ofNonTest()`/etc API, in most
        // cases users do not have customized per buildType/flavor configurations (it
        // tends to be very use-case specific).
        all().forEach {
            it.builtins {
                id("java") {
                    option("lite")
                }
            }
        }
    }
}

[guness]

For Android developers who uses full version of protobuf, but not lite, this is the solution that works for me:

generateProtoTasks {
    all().forEach { task ->
        task.builtins {
            id("java") {
                java { }
            }
        }
    }
}