# Locking dependency versions

version 8.1

Use of dynamic dependency versions (e.g. `1.+` or `[1.0,2.0)`) makes builds non-deterministic. This causes builds to break without any obvious change, and worse, can be caused by a transitive dependency that the build author has no control over.

To achieve reproducible builds, it is necessary to lock versions of dependencies and transitive dependencies such that a build with the same inputs will always resolve the same module versions. This is called dependency locking.

It enables, amongst others, the following scenarios:

- Companies dealing with multi repositories no longer need to rely on `-SNAPSHOT` or changing dependencies, which sometimes result in cascading failures when a dependency introduces a bug or incompatibility. Now dependencies can be declared against major or minor version range, enabling to test with the latest versions on CI while leveraging locking for stable developer builds.

- Teams that want to always use the latest of their dependencies can use dynamic versions, locking their dependencies only for releases. The release tag will contain the lock states, allowing that build to be fully reproducible when bug fixes need to be developed.

Combined with publishing resolved versions, you can also replace the declared dynamic version part at publication time. Consumers will instead see the versions that your release resolved.

Locking is enabled per dependency configuration. Once enabled, you must create an initial lock state. It will cause Gradle to verify that resolution results do not change, resulting in the same selected dependencies even if newer versions are produced. Modifications to your build that would impact the resolved set of dependencies will cause it to fail. This makes sure that changes, either in published dependencies or build definitions, do not alter resolution without adapting the lock state.

| Dependency locking makes sense only with dynamic versions. It will have no impact on changing versions (like `-SNAPSHOT`) whose coordinates remain the same, though the content may change. Gradle will even emit a warning when persisting lock state and changing dependencies are present in the resolution result.

## Enabling locking on configurations

Locking of a configuration happens through the ResolutionStrategy:

Example 1. Locking a specific configuration
build.gradle.kts

    configurations {
        compileClasspath {
            resolutionStrategy.activateDependencyLocking()
        }
    }

build.gradle

    configurations {
        compileClasspath {
            resolutionStrategy.activateDependencyLocking()
        }
    }

| Only configurations that can be resolved will have lock state attached to them. Applying locking on non resolvable-configurations is simply a no-op.

Or the following, as a way to lock all configurations:

Example 2. Locking all configurations
build.gradle.kts

    dependencyLocking {
        lockAllConfigurations()
    }

build.gradle

    dependencyLocking {
        lockAllConfigurations()
    }

| The above will lock all project configurations, but not the buildscript ones.

You can also disable locking on a specific configuration. This can be useful if a plugin configured locking on all configurations but you happen to add one that should not be locked.

Example 3. Unlocking a specific configuration
build.gradle.kts

    configurations.compileClasspath {
        resolutionStrategy.deactivateDependencyLocking()
    }

build.gradle

    configurations {
        compileClasspath {
            resolutionStrategy.deactivateDependencyLocking()
        }
    }

### Locking buildscript classpath configuration

If you apply plugins to your build, you may want to leverage dependency locking there as well. In order to lock the `classpath` configuration used for script plugins, do the following:

Example 4. Locking buildscript classpath configuration
build.gradle.kts

    buildscript {
        configurations.classpath {
            resolutionStrategy.activateDependencyLocking()
        }
    }

build.gradle

    buildscript {
        configurations.classpath {
            resolutionStrategy.activateDependencyLocking()
        }
    }

## Generating and updating dependency locks

In order to generate or update lock state, you specify the `--write-locks` command line argument in addition to the normal tasks that would trigger configurations to be resolved. This will cause the creation of lock state for each resolved configuration in that build execution. Note that if lock state existed previously, it is overwritten.

| Gradle will not write lock state to disk if the build fails. This prevents persisting possibly invalid state.

### Lock all configurations in one build execution

When locking multiple configurations, you may want to lock them all at once, during a single build execution.

For this, you have two options:

- Run `gradle dependencies --write-locks`. This will effectively lock all resolvable configurations that have locking enabled. Note that in a multi project setup, `dependencies` only is executed on one project, the root one in this case.

- Declare a custom task that resolves all configurations. This does not work for Android projects.

Example 5. Resolving all configurations
build.gradle.kts

    tasks.register("resolveAndLockAll") {
        notCompatibleWithConfigurationCache("Filters configurations at execution time")
        doFirst {
            require(gradle.startParameter.isWriteDependencyLocks)
        }
        doLast {
            configurations.filter {
                // Add any custom filtering on the configurations to be resolved
                it.isCanBeResolved
            }.forEach { it.resolve() }
        }
    }

build.gradle

    tasks.register('resolveAndLockAll') {
        notCompatibleWithConfigurationCache("Filters configurations at execution time")
        doFirst {
            assert gradle.startParameter.writeDependencyLocks
        }
        doLast {
            configurations.findAll {
                // Add any custom filtering on the configurations to be resolved
                it.canBeResolved
            }.each { it.resolve() }
        }
    }

That second option, with proper selection of configurations, can be the only option in the native world, where not all configurations can be resolved on a single platform.

## Lock state location and format

Lock state will be preserved in a file located at the root of the project or subproject directory. Each file is named `gradle.lockfile`. The one exception to this rule is for the lock file for the buildscript itself. In that case the file will be named `buildscript-gradle.lockfile`.

The lockfile will have the following content:

gradle.lockfile

    # This is a Gradle generated file for dependency locking.
    # Manual edits can break the build and are not advised.
    # This file is expected to be part of source control.
    org.springframework:spring-beans:5.0.5.RELEASE=compileClasspath, runtimeClasspath
    org.springframework:spring-core:5.0.5.RELEASE=compileClasspath, runtimeClasspath
    org.springframework:spring-jcl:5.0.5.RELEASE=compileClasspath, runtimeClasspath
    empty=annotationProcessor

- Each line still represents a single dependency in the `group:artifact:version` notation

- It then lists all configurations that contain the given dependency

- Module and configurations are ordered alphabetically, to ease diffs

- The last line of the file lists all empty configurations, that is configurations known to have no dependencies

which matches the following dependency declaration:

Example 6. Dynamic dependency declaration
build.gradle.kts

    configurations {
        compileClasspath {
            resolutionStrategy.activateDependencyLocking()
        }
        runtimeClasspath {
            resolutionStrategy.activateDependencyLocking()
        }
        annotationProcessor {
            resolutionStrategy.activateDependencyLocking()
        }
    }

    dependencies {
        implementation("org.springframework:spring-beans:[5.0,6.0)")
    }

build.gradle

    configurations {
        compileClasspath {
            resolutionStrategy.activateDependencyLocking()
        }
        runtimeClasspath {
            resolutionStrategy.activateDependencyLocking()
        }
        annotationProcessor {
            resolutionStrategy.activateDependencyLocking()
        }
    }

    dependencies {
        implementation 'org.springframework:spring-beans:[5.0,6.0)'
    }

### Migrating from the lockfile per configuration format

If your project uses the legacy lock file format of a file per locked configuration, follow these instructions to migrate to the new format:

- Follow the documentation for writing or updating dependency lock state.

- Upon writing the single lock file per project, Gradle will also delete all lock files per configuration for which the state was transferred.

| Migration can be done one configuration at a time. Gradle will keep sourcing the lock state from the per configuration files as long as there is no information for that configuration in the single lock file.

### Configuring the per project lock file name and location

When using the single lock file per project, you can configure its name and location. The main reason for providing this is to enable having a file name that is determined by some project properties, effectively allowing a single project to store different lock state for different execution contexts. One trivial example in the JVM ecosystem is the Scala version that is often found in artifact coordinates.

Example 7. Changing the lock file name
build.gradle.kts

    val scalaVersion = "2.12"
    dependencyLocking {
        lockFile.set(file("$projectDir/locking/gradle-${scalaVersion}.lockfile"))
    }

build.gradle

    def scalaVersion = "2.12"
    dependencyLocking {
        lockFile = file("$projectDir/locking/gradle-${scalaVersion}.lockfile")
    }

## Running a build with lock state present

The moment a build needs to resolve a configuration that has locking enabled and it finds a matching lock state, it will use it to verify that the given configuration still resolves the same versions.

A successful build indicates that the same dependencies are used as stored in the lock state, regardless if new versions matching the dynamic selector have been produced.

The complete validation is as follows:

- Existing entries in the lock state must be matched in the build

  - A version mismatch or missing resolved module causes a build failure

- Resolution result must not contain extra dependencies compared to the lock state

### Fine tuning dependency locking behaviour with lock mode

While the default lock mode behaves as described above, two other modes are available:

Strict mode

  In this mode, in addition to the validations above, dependency locking will fail if a configuration marked as locked does not have lock state associated with it.

Lenient mode

  In this mode, dependency locking will still pin dynamic versions but otherwise changes to the dependency resolution are no longer errors.

The lock mode can be controlled from the `dependencyLocking` block as shown below:

Example 8. Setting the lock mode
build.gradle.kts

    dependencyLocking {
        lockMode.set(LockMode.STRICT)
    }

build.gradle

    dependencyLocking {
        lockMode = LockMode.STRICT
    }

## Selectively updating lock state entries

In order to update only specific modules of a configuration, you can use the `--update-locks` command line flag. It takes a comma (`,`) separated list of module notations. In this mode, the existing lock state is still used as input to resolution, filtering out the modules targeted by the update.

    ❯ gradle classes --update-locks org.apache.commons:commons-lang3,org.slf4j:slf4j-api

Wildcards, indicated with `*`, can be used in the group or module name. They can be the only character or appear at the end of the group or module respectively. The following wildcard notation examples are valid:

- `org.apache.commons:*`: will let all modules belonging to group `org.apache.commons` update

- `*:guava`: will let all modules named `guava`, whatever their group, update

- `org.springframework.spring*:spring*`: will let all modules having their group starting with `org.springframework.spring` and name starting with `spring` update

| The resolution may cause other module versions to update, as dictated by the Gradle resolution rules.

## Disabling dependency locking

1. Make sure that the configuration for which you no longer want locking is not configured with locking.

2. Next time you update the save lock state, Gradle will automatically clean up all stale lock state from it.

Gradle needs to resolve a configuration, no longer marked as locked, to detect that associated lock state can be dropped.

## Ignoring specific dependencies from the lock state

Dependency locking can be used in cases where reproducibility is not the main goal. As a build author, you may want to have different frequency of dependency version updates, based on their origin for example. In that case, it might be convenient to ignore some dependencies because you always want to use the latest version for those. An example is the internal dependencies in an organization which should always use the latest version as opposed to third party dependencies which have a different upgrade cycle.

| This feature can break reproducibility and should be used with caution. There are scenarios that are better served with leveraging different lock modes or using different names for lock files.

You can configure ignored dependencies in the `dependencyLocking` project extension:

Example 9. Ignoring dependencies for the lock state
build.gradle.kts

    dependencyLocking {
        ignoredDependencies.add("com.example:*")
    }

build.gradle

    dependencyLocking {
        ignoredDependencies.add('com.example:*')
    }

The notation is a `<group>:<name>` dependency notation, where `*` can be used as a trailing wildcard. See the description on updating lock files for more details. Note that the value `*:*` is not accepted as it is equivalent to disabling locking.

Ignoring dependencies will have the following effects:

- An ignored dependency applies to all locked configurations. The setting is project scoped.

- Ignoring a dependency does not mean lock state ignores its transitive dependencies.

- There is no validation that an ignored dependency is present in any configuration resolution.

- If the dependency is present in lock state, loading it will filter out the dependency.

- If the dependency is present in the resolution result, it will be ignored when validating that resolution matches the lock state.

- Finally, if the dependency is present in the resolution result and the lock state is persisted, it will be absent from the written lock state.

## Locking limitations

- Locking cannot yet be applied to source dependencies.

## Nebula locking plugin

This feature is inspired by the Nebula Gradle dependency lock plugin.