Why does Gradle build my module in Release mode when the app is in Debug

Question

I'm making a new Android project, with the standard 'app' module, as well as a library project (let's call it 'custom_lib'). In the app's build.gradle file, I link the module as such :

dependencies {     compile project(':custom_lib') } 

When I trigger the build process (Menu Build > Make Project), I get the following output in the Gradle console

Executing tasks: [clean, :app:compileDebugSources, :custom_lib:compileDebugSources]  Configuration on demand is an incubating feature. :app:clean :custom_lib:clean :app:preBuild :app:preDebugBuild :app:checkDebugManifest :app:preReleaseBuild :custom_lib:compileLint :custom_lib:copyReleaseLint UP-TO-DATE :custom_lib:mergeReleaseProguardFiles UP-TO-DATE :custom_lib:preBuild :custom_lib:preReleaseBuild :custom_lib:checkReleaseManifest :custom_lib:prepareReleaseDependencies :custom_lib:compileReleaseAidl :custom_lib:compileReleaseRenderscript :custom_lib:generateReleaseBuildConfig :custom_lib:generateReleaseAssets UP-TO-DATE :custom_lib:mergeReleaseAssets :custom_lib:generateReleaseResValues UP-TO-DATE :custom_lib:generateReleaseResources :custom_lib:packageReleaseResources :custom_lib:processReleaseManifest :custom_lib:processReleaseResources :custom_lib:generateReleaseSources :custom_lib:compileReleaseJava :custom_lib:processReleaseJavaRes UP-TO-DATE :custom_lib:packageReleaseJar :custom_lib:compileReleaseNdk :custom_lib:packageReleaseJniLibs UP-TO-DATE :custom_lib:packageReleaseLocalJar UP-TO-DATE :custom_lib:packageReleaseRenderscript UP-TO-DATE :custom_lib:bundleRelease :app:prepareComAndroidSupportAppcompatV72102Library :app:prepareComAndroidSupportSupportV42102Library :app:prepareTestDoubleBuildCustom_libUnspecifiedLibrary :app:prepareDebugDependencies :app:compileDebugAidl :app:compileDebugRenderscript :app:generateDebugBuildConfig :app:generateDebugAssets UP-TO-DATE :app:mergeDebugAssets :app:generateDebugResValues UP-TO-DATE :app:generateDebugResources :app:mergeDebugResources :app:processDebugManifest :app:processDebugResources :app:generateDebugSources :app:compileDebugJava :app:compileDebugNdk :app:compileDebugSources :custom_lib:preDebugBuild :custom_lib:checkDebugManifest :custom_lib:prepareDebugDependencies :custom_lib:compileDebugAidl :custom_lib:compileDebugRenderscript :custom_lib:generateDebugBuildConfig :custom_lib:generateDebugAssets UP-TO-DATE :custom_lib:mergeDebugAssets :custom_lib:generateDebugResValues UP-TO-DATE :custom_lib:generateDebugResources :custom_lib:packageDebugResources :custom_lib:processDebugManifest :custom_lib:processDebugResources :custom_lib:generateDebugSources :custom_lib:compileDebugJava :custom_lib:compileDebugNdk :custom_lib:compileDebugSources  BUILD SUCCESSFUL  Total time: 2.184 secs 

What puzzles me is that the build mechanism triggers a Debug build (as the first line says), but almost immediately, Gradle uses the task :app:preReleaseBuild which make my custom_lib module to be built with the Release configuration.

And then, after the app is fully built, Gradle compiles my module with the Debug configuration.

So my questions are :

• Why is it doing this double build which seems incoherent ?
• How can I make sure that the library is built with debug configuration when I launch a Debug build process ?

EDIT :

app/build.gradle :

apply plugin: 'com.android.application'  android {     compileSdkVersion 21     buildToolsVersion "21.1.1"      defaultConfig {         applicationId "com.deezer.testdoublebuild"         minSdkVersion 8         targetSdkVersion 21         versionCode 1         versionName "1.0"     }      compileOptions {         sourceCompatibility JavaVersion.VERSION_1_7         targetCompatibility JavaVersion.VERSION_1_7     }     buildTypes {         debug{             debuggable true         }         release {             debuggable false             minifyEnabled false         }     } }  dependencies {     compile project(':custom_lib') } 

custom_lib/build.gradle :

apply plugin: 'com.android.library'  android {     compileSdkVersion 21     buildToolsVersion "21.1.1"      defaultConfig {         applicationId "com.deezer.mylibrary"         minSdkVersion 8         targetSdkVersion 21         versionCode 1         versionName "1.0"     }      compileOptions {         sourceCompatibility JavaVersion.VERSION_1_7         targetCompatibility JavaVersion.VERSION_1_7     }     buildTypes {         release {             minifyEnabled false             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'         }     } }  dependencies { } 

Note : I'm using Android Studio 1.0 RC 1 / Gradle 2.2, and reproduced this issue by creating a new project from scratch, add an empty Android Library module, and "voila"

Answer 1

Put this in your app dependencies:

dependencies {     debugCompile project(path: ':custom_lib', configuration: "debug")     releaseCompile project(path: ':custom_lib', configuration: "release") } 

and in your library's build.gradle add:

android {      defaultConfig {         defaultPublishConfig 'release'         publishNonDefault true     }  } 

Then the library will be built in the same mode as the app. Contrary to previous revisions of this answer, I've confirmed a flavor is not required on the library (this may be due to Gradle or Android plugin versions - I'm using Gradle 2.14 and Android plugin 2.1.0 and did not require it).

Edit: You may have trouble if you don't clean/rebuild after modifying the gradle files, as outlined in this answer here.