Android studio manifest merging

Manifest Merging

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With Android Studio and Gradle-based builds, each app can contain manifest files in multiple locations, such as the src/main/ folder for the productFlavor , libraries, Android ARchive (AAR) bundles of Android Library projects, and dependencies. During the build process, manifest merging combines the settings from the various AndroidManifest.xml files included in your app into a single, generated APK manifest file for app packaging and distribution. Manifest settings are merged based on the manifest priority, determined by the manifest’s file location. Building your app merges the manifest elements, attributes, and sub-elements from these manifests for the specified build variant.

Merge Conflict Rules

Merge conflicts occur when merged manifests contain the same manifest element but with a different attribute value that does not resolve based on the default merge conflict rules. Conflict markers and selectors can also define custom merge rules, such as allowing an imported library to have a minSdkVersion higher than the version defined in the other higher priority manifests.

The manifest merge priority determines which manifest settings are retained in merge conflicts, with the settings in higher priority manifest overwriting those in lower priority manifests. The following list details which manifest settings are are the highest priority during the merge process:

• Highest priority: buildType manifest settings
• Higher priority: productFlavor manifest settings
• Medium priority: Manifests in the src/main/ directory of an app project
• Low priority: Dependency and library manifest settings

Manifest merge conflicts are resolved at the XML node and attribute levels based on the following merge rules.

High Priority Element	Low Priority Element	Manifest Merge Result
no attribute	no attribute	no attribute
	attribute set to default	default attribute
	attribute set to non-default	low priority attribute
attribute set to default	no attribute	default attribute
attribute set to non-default		high priority attribute
attribute set to default	attribute set to default	default attribute
attribute set to default	attribute set to non-default	low priority attribute
attribute set to non-default	attribute set to default	high priority attribute
attribute set to non-default	attribute set to non-default	Merge if settings match, otherwise causes conflict error.

Exceptions to the manifest merge rules:

• The uses-feature android:required; and uses-library android:required elements default to true and use an OR merge so that any required feature or library is included in the generated APK.
• If not declared, the elements, minSdkVersion and targetSdkVersion , default to a value of 1. When merge conflicts occur, the value in the higher priority manifest version is used.
• Importing a library with a minSdkVersion value higher than the app’s src/main/ manifest manifest generates an error unless the overrideLibrary conflict marker is used.

Note: If not explicitly declared, the targetSdkVersion defaults to the minSdkVersion value. When no element is present in any manifest or the build.gradle file, the minSdkVersion defaults to 1.

When importing a library with a targetSdkVersion value lower than the app’s src/main/ manifest, the manifest merge process explicitly grants permissions and ensures that the imported library functions properly.

The manifest element only merges with child manifest elements.

The intent-filter element is never changed and is always added to the common parent node in the merged manifest.

Important: After the manifests are merged, the build process overrides the final manifest settings with any settings that are also in the build.gradle file. For more details, see Configuring Gradle Builds.

Merge Conflict Markers and Selectors

Manifest markers and selectors override the default merge rules through specific conflict resolutions. For example, use a conflict marker to merge a library manifest with a higher minSdkVersion value than the higher priority manifest, or to merge manifests with the same activity but different android:theme values.

Merge Conflict Markers

A merge conflict marker is a special attribute in the Android tools namespace that defines a specific merge conflict resolution. Create a conflict marker to avoid a merge conflict error for conflicts not resolved by the default merge rules. Supported merge conflict markers include:

merge Merges attributes when there are no conflicts with the merge rules. The default merge action. replace Replaces attributes in the lower priority manifest with those from the higher priority manifest. strict Sets the merge policy level so that merged elements with same attributes, but different values generate a build failure, unless resolved through the conflict rules. merge-only Allows merge actions for only lower priority attributes. remove Removes the specified lower priority element from the merged manifest. remove-All Removes all lower priority elements of the same node type from the merged manifest.

By default, the manifest merge process applies the merge conflict marker to the node level. All declared manifest attributes default to a strict merging policy.

To set a merge conflict marker, first declare the namespace in the AndroidManifest.xml file. Then, enter the merge conflict marker in the manifest to specify a custom merge conflict action. This example inserts the replace marker to set a replace action to resolve conflicts between the android:icon and android:label manifest elements.

Marker attributes

Conflict markers use tools:node and tools:attr attributes to restrict merge actions at the XML node or attribute level.

The tools:attr markers use only the restrict , remove , and replace merge actions. Multiple tools:attr marker values can be applied to a specific element. For example, use tools:replace=»icon, label, theme» to replace lower priority icon , label , and theme attributes.

Merge conflict marker for imported libraries

The overrideLibrary conflict marker applies to the manifest declaration and is used to import a library even though the library’s values, such as minSdkVersion are set to different values than those in the other higher priority manifests.

Without this marker, library manifest merge conflicts from the values cause the merge process to fail.

This example applies the overrideLibrary conflict marker to resolve the merge conflict between minSdkVersion values in the src/main/ manifest and an imported library manifest.

Note: The default merge process does not allow importing a library with a higher minSdkVersion than the app’s src/main/ manifest unless the overrideLibrary conflict marker is used.

Marker Selectors

Marker selectors limit a merge action to a specific lower priority manifest. For example, a marker selector can be used to remove a permission from only one library, while allowing the same permission from other libraries.

This example uses the tools:node marker to remove the permisionOne attribute, while the tools:selector selector specifies the specific library as com.example.lib1. The permisionOne permission is filtered from only the lib1 library manifests.

Injecting Build Values into a Manifest

Manifest merging can also be configured to use manifest placeholders to inject property values from the build.gradle file into the manifest attributes.

Manifest placeholders use the syntax $ for attribute values, where name is the injected build.gradle property. The build.gradle file uses the manifestPlaceholders property to define the placeholder values.

Note: Unresolved placeholder names in apps cause build failures. Unresolved placeholder names in libraries generate warnings and need to be resolved when importing the library into an app.

This example shows the manifest placeholder $ used to inject the build.gradle applicationId property value in to android:name attribute value.

Note: Android Studio provides a default $ placeholder for the build.gradle applicationId value that is not shown in the build file.

Gradle build file:

Merged manifest value:

The manifest placeholder syntax and build file manifestPlaceholders property can be used to inject other manifest values. For properties other than the applicationId , the manifestPlaceholders property is explicitly declared in the build.gradle file. This example shows the manifest placeholder for injecting activityLabel values.

Gradle build file:

Placeholder in the manifest file:

Note: The placeholder value supports partial value injection, for example android:authority=»com.acme.$.foo» .

Manifest Merging Across Product Flavor Groups

When using the GroupableProductFlavor property, the manifest merge priority of any manifests in the product flavor groups follows the order in which the product flavor groups are listed in the build file. The manifest merge process creates a single merged manifest for the product flavor groups based on the configured build variant.

For example, if a build variant references the product flavors x86 , mdpi , 21 , and paid from the respective product flavor groups ABI , Density , API , and Prod , listed in this order in the build.gradle file, then the manifest merge process merges the manifests in this priority order, which follows how the product flavors are listed in the build file.

To illustrate this example, the following table shows how the product flavors are listed for each product flavor group. This combination of product flavors and groups defines the build variant.

Product Flavor Group	Product Flavor
ABI	x86
density	mdpi
API	22
prod	paid

Manifest merge order:

• prod-paid AndroidManifest.xml (lowest priority) merges into API-22 AndroidManifest.xml
• API-22 AndroidManifest.xml merges into density-mpi AndroidManifest.xml
• density-mpi AndroidManifest.xml merges into ABI-x86 AndroidManifest.xml (highest priority)

Implicit Permissions

Importing a library that targets an Android runtime with implicitly granted permissions may automatically add the permissions to the resulting merged manifest. For example, if an application with a targetSdkVersion of 16 imports a library with a targetSdkVersion of 2, Android Studio adds the WRITE_EXTERNAL_STORAGE permission to ensure permission compatibility across the SDK versions.

Note: More recent Android releases replace implicit permissions with permission declarations.

This table lists the importing library versions and the declared permissions.

Importing this library version	Declares this permission in the manifest
targetSdkVersion WRITE_EXTERNAL_STORAGE
targetSdkVersion WRITE_EXTERNAL_STORAGE , READ_PHONE_STATE
Declared WRITE_EXTERNAL_STORAGE	READ_EXTERNAL_STORAGE
targetSdkVersion READ_CONTACTS permission	READ_CALL_LOG
targetSdkVersion WRITE_CONTACTS permission	WRITE_CALL_LOG

Handling Manifest Merge Build Errors

During the build process, the manifest merge process stores a record of each merge transaction in the manifest-merger-

-report.txt file in the module build/outputs/logs folder. A different log file is generated for each of the module’s build variants.

When a manifest merge build error occurs, the merge process records the error message describing the merge conflict in the log file. For example, the android:screenOrientation merge conflict between the following manifests causes a build error.

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Android Manifest file merging

Each element in a manifest file can be identified by its element type (e.g. activity, intent-filter) and an optional key value. Some elements like “activity” must have a key since there can be multiple present in a single AndroidManifest.xml. Other elements like “application” do not require a key since there can be only one.

The element type and key value pair represent the identity of a manifest element.

The merging activity is always between two identically typed elements, one coming from a higher priority manifest file, one coming from a lower priority manifest file. Each merging activity has a default behavior that will be described subsequently. Also each default merging activity on the node or on a specific attribute can potentially be overridden by including tools specific markers.

The merging process will also record all decisions taken along the way for each node, described in the «Logging» section.

Elements and Attributes merging process

Implicit declarations

A number of attributes can have default values (defined in the online docs as defaults). When a higher priority element does not define an attribute which has a default value of X, if a lower priority element defines that very attribute with the same value X, it will still be added to the merged element (with value X of course) since it represents a clear choice from the library to not consider this value as the default value but the right value for the feature (in case the default ever changes).

Most attributes with default values will be ignored by the manifest merger if a lower priority attribute defines a value; it will be merged since there is no conflict between a default value and an attribute set to any value. The attribute will be set to that set value in the resulting merged element.

However, there are a few exceptions listed below:

Defaults to true. Merging with other attributes will use a OR merging policy since if any library requires the feature, the resulting application will require the feature.

Same as uses-feature:required.

The higher priority document’s version will be used but importing a library with a more recent version will generate an error.

Same as uses-sdk:minSdkVersion

Same as uses-sdk:minSdkVersion

Automatic upgrades

When importing a library with a lower target SDK than the project’s, it may be necessary to explicitly grant permissions (and perhaps make other changes) for the library to function properly in the later runtime. This will be performed automatically by the manifest merger.

Placeholder support

When an attribute value contains a placeholder (see format below), the manifest merger will swap this placeholder value with an injected value. Injected values are specified in the build.gradle.

The syntax for placeholder values is $ since @ is reserved for links. After the last file merging occurred, and before the resulting merged android manifest file is written out, all values with a placeholder will be swapped with injected values. A build breakage will be generated if a variable name is unknown.

The placeholder string can have a prefix and/or a suffix allowing to partially replace the value.

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